Friday, November 17, 2006

RICKETTSIA, CHLAMYDIA, MYCOPLASMA

A lecture








Table of Contents

* Educational Objectives
* Rickettsia
* Chlamydia
* Mycoplasma and L-Forms
* Summary

EducationalObjectives
General
1. To introduce the rickettsia, chlamydia and mycoplasma as distinct groups of degenerate bacteria.

2. To differentiate the rickettsia, chlamydia and mycoplasma on the basis of cell structure, metabolism, genetic
characteristics, pathogenicity, routes of disease transmission and methods of diagnosis.

Specific educational objectives (terms and concepts upon which you will be tested)

1. To define the following terms and concepts:

* ATP generation by mycoplasma
* Animal reservoirs of rickettsia
* Arthropod vectors of rickettsia
* Castaneda stain
* Chlamydia
* Cold agglutinins
* Evidence for endotoxin production by rickettsia
* Frei test
* Giemsa stain
* L-form
* Latency of infection
* Macchiavello stain
* Mycoplasma
* Obligate parasitism
* Physiologic basis of obligate parasitism
* Pleuropneumonia-like organism (PPLO)
* Pleuropneumonia organism (PPO)
* Protochlamydia
* Rickettsia
* T-stains Weil-Felix reaction

2. To define the etiology of these human diseases:

* Bacillary angiomatosis
* Chlamydial bronchitis/sinusitis/pneumonia
* Ehrlichiosis
* Inclusion conjunctivitis
* Lymphogranuloma venereum
* Ornithosis
* Primary atypical pneumonia
* Psittacosis
* Q fever
* Rickettsialpox
* Rocky Mountain spotted fever
* Trachoma
* Typhus

Rickettsia
General Features

The rickettsia are bacteria which are obligate intracellular parasites. They are considered a separate group of bacteria because they have the common feature of being spread by arthropod vectors (lice, fleas, mites and ticks). The cells are extremely small (0.25 u in diameter) rod-shaped, coccoid and often pleomorphic microorganisms which have typical bacterial cell walls, no flagella, are gram-negative and multiply via binary fission only inside host cells. They occur singly, in pairs, or in strands. Most species are found only in the cytoplasm of host cells, but those which cause spotted fevers multiply in nuclei as well as in cytoplasm. In the laboratory, they may be cultivated in living tissues such as embryonated chicken eggs or vertebrate cell cultures.

The family Rickettsiaceae is taxonomically divided into three genera:

1. Rickettsia (11 species)--obligate intracellular parasites which do not multiply within vacuoles and do not
parasitize white blood cells.

2. Ehrlichia (2 species) - obligate intracellular parasites which do not multiply within vacuoles but do parasitize
white blood cells.

3. Coxiella (1 species)--obligate intracellular parasite which grows preferentially in vacuoles of host cells.

4. Baartonella (3 species)--intracellular parasite which attacks the red blood cell.

Structure

The structure of the typical rickettsia is very similar to that of Gram-negative bacteria. The typical envelope consists of three major layers: an innermost cytoplasmic membrane, a thin electron dense rigid cell wall and an outer layer. The outer layer resembles typical membranes in its chemical composition and its trilaminar appearance. The cell wall is chemically similar to that of Gram-negative bacteria in that it contains diaminopimelic acid and lacks teichoic acid. Intracytoplasmic invaginations of the plasma membrane (mesosomes) and ribosomes are also seen. There are no discrete nuclear structures.

Metabolism

In dilute buffered salt solutions, isolated rickettsia are unstable, losing both metabolic activity and infectivity for animal cells. If, however, the medium is enriched with potassium, serum albumin and sucrose, the isolated organisms can survive for many hours. If ATP is added to the solution, the organisms metabolize and consume oxygen. The basis for the obligate parasitism of these cells is that they require the rich cytoplasm to stabilize an unusually permeable cell membrane.

The rickettsia have many of the metabolic capabilities of bacteria, but require an exogenous supply of cofactors to express these capabilities. The response to exogenous cofactors implies an unusually permeable cytoplasmic membrane.

Growth and Multiplication

Rickettsia normally multiply by transverse binary fission. Under poor nutritional conditions, the rickettsia cease dividing and grow into long filamentous forms, which subsequently undergo rapid and multiple division into the typical short rod forms when fresh nutrient is added. Immediately after division, the rickettsia engage in extensive movements through the cytoplasm of the cell. C. burnetii differs from other rickettsia in that it is enclosed in a persistent vacuole during growth and division. Six to ten daughter cells will form within a host cell before the cell ruptures and releases them.

Pathogenicity

In their arthropod vectors, the rickettsia multiply in the epithelium of the intestinal tract; they are excreted in the feces, but occasionally gain access to the arthropods salivary glands. They are transmitted to man, via the arthropod saliva, through a bite. In their mammalian host, they are found principally in the endothelium of the small blood vessels, particularly in those of the brain, skin and heart. Hyperplasia of endothelial cells and localized thrombus formation lead to obstruction of blood flow, with escape of RBC's into the surrounding tissue. Inflammatory cells also accumulate about affected segments of blood vessels. This angiitis appears to account for some of the more prominent clinical manifestations, such as petechial rash, stupor and terminal shock. Death is ascribed to damage of endothelial cells, resulting in leakage of plasma, decrease in blood volume, and shock.

It is assumed that the observed clinical manifestations of a rickettsial infection are due to production of an endotoxin, although this endotoxin is quite different in physiological effects from that produced by members of the Enterobacteriaceae. This is inferred, although the toxin has not been isolated, from these facts:

1. IV-injected rickettsia cause rapid death in experimental animals.

2. UV-irradiation of rickettsia diminished their infectivity without reducing toxicity.

3. The use of anti-rickettsial drugs does not prevent rapid death in experimental animals.

4. Antiserum specific for cell wall antigens of the rickettsia prevents the toxic effect.

Laboratory Diagnosis

Presumptive laboratory diagnosis is based on the finding of rickettsial-like organisms in tissue or blood. Although the organisms are gram-negative, they only weakly take the counter stain, safranin. Therefore, special staining procedures are used. Infected tissue may be stained with:

1. Macchiavello stain--organisms are bright red against the blue background of the tissue.

2. Castaneda stain--blue organisms against a red background.

3. Giemsa stain--bluish purple organisms.

Confirmative diagnosis is based on a serological reaction (Weil-Felix reaction) in which the titer of the agglutinins in the patient's serum against the Proteus strains OX-19, OX-2 and OX-K are determined. These Proteus strains have no etiological role in rickettsial infections, but appear to share antigens in common with certain rickettsia. These antigens are alkali stable polysaccharide haptens which are distinct from the group-specific and type-specific antigens. In interpreting the results, it must be kept in mind that Proteus infections are fairly common (especially in the urinary tract) and that they, too, may evoke antibodies to the Proteus-OX strains. This test is usually positive seven days after the initial infection. A more specific complement fixation test is available but does not show positive results until 14 days into the infection. The indirectfluorescentantibodytest is also useful for the detection of IgM and IgG antibodies against rickettsia. In fact, this is the diagnostic test of choice for ehrlichiosis.

Diseases

The rickettsial diseases of man are usually broken down according to the arthropod vector as seen in table below.



DISEASE

CAUSAL AGENT

ANIMAL RESERVOIR

WEIL-FELIX RESPONSE
1. Louse-borne
European epidemic typhus Rickettsia prowazekii ------------------------------------------- OX-19
Brill's disease Rickettsia prowazekii ------------------------------------------- Negative
Trench fever Bartonella quintana ------------------------------------------- Negative
2. Flea-borne
Endemic murine typhus Rickettsia typhi Wild rodents OX-19
Cat scratch
fever/Bacilliary angiomatosis Bartonella henselae Domestic cat Unknown
3. Mite-borne
Scrub typhus Orientia (Rickettsia) tsutsugamushi Wild rodents OX-K
Rickettsialpox Rickettsia akari House mice Negative
4. Tick-borne
Rocky Mountain Spotted
Fever Rickettsia rickettsii Dog, rodents OX-19, OX-2
North Asian tick typhus Rickettsia siberica Wild rodents OX-19, OX-2
Fievre boutonneuse Rickettsia conorii Dog, rodents OX-19, OX-2
Queensland tick typhus Rickettsia australis Marsupials, rodents OX-19, OX-2
Q-fever Coxiella burnetii Cattle, sheep, goats Negative
Spotted fever Rickettsia rhipicephali Dogs Unknown
Ehrlichiosis Ehrlichia canis Dogs Negative
Ehrlichiosis Ehrlichia chaffeensis Dogs Negative
5. Fly-borne
Oroyo fever/Verruga peruana Bartonella bacilliformis Unknown


Chemotherapy

The drugs of choice for the treatment of rickettsial diseases are chloramphenicol and tetracycline. Each of these is highly toxic, especially in children, and must be used with care. The sulfonamides stimulate rickettsial growth and thus are contraindicated in the treatment of these diseases.

Chlamydia

General Characteristics

The chlamydia, which are incorrectly called the PLT viruses or Bedsonia or basophilic viruses, are bacteria which are obligate intracellular parasites of higher animals (mammals and birds). The members of this group share a unique development cycle, a common morphology and a common family antigen. They are not transmitted by arthropods. These organisms are termed basophilic because they take up the Giemsa stain (i.e., they stain blue). They are gram-negative, non-motile and multiply in the cytoplasm of the host cell. These organisms generally parasitize epithelial cells. The methods used to study them are, in the main, those of the virologist rather than the bacteriologist. Furthermore, the clinical features, pathogenesis, pathology and epidemiology of chlamydial infections are similar to those of viral infections.

Taxonomy

The chlamydia fall into two main ecological groups. In the first group, are the agents causing trachoma, inclusion conjunctivitis, and lymphogranuloma venereum, which seem to infect man only. In the second group, are those agents transmitted to man as zoonotic infections. About 100 species of birds are naturally infected with chlamydia. This includes 71 species of parrots as well as finches, pigeons, chickens, ducks, turkeys and seabirds. The chlamydia are thought to have evolved in the following way:
Gram-negative cocci
Facultative intracellular parasites of mammals

Protochlamydiae
Gram-negative cocci
Obligate intracellular parasites
Host range restricted to rodents
Restricted virulence (compact inclusions)
Folates synthesized (sulfonamide susceptible)
Glycogen synthesized and deposited in inclusions

Subgroup A Subgroup B


Mammalian parasites Primarily bird parasites

Compact inclusions Diffuse inclusions

Glycogen synthesized Glycogen not synthesized

Folates synthesized Folates not synthesized

Sensitive to D-cycloserine Resistant to D-cycloserine

Restricted host range Broadening of host range

Chlamydia trachomatis Chlamydia psittaci

Seven strains which are probably Ten strains which are probably
distinct species distinct species


Chlamydia pneumoniae
Only one serotype has been identified

Morphology and Structure

The chlamydial cell is roughly spherical and measures between 0.3 and 1.0 u in diameter, according to the stage of development. Both the small and the large cell types contain complete cell walls which are similar to the cell walls of gram-negative bacteria.

Under the cell wall lies a separate cytoplasmic membrane made up of large amounts of lipid. The DNA occurs as an irregular mass in the cytoplasm. There is no nuclear membrane. Ribosomes can be seen throughout the cytoplasm. The cells contain no capsule or flagella.

Metabolism

There are no detectable flavoproteins or cytochromes. It appears that the basis of the obligate intracellular parasitism is due to a lack of ATP-generating ability and the need to obtain ATP from the host cell. The cells can synthesize DNA, RNA and protein.

Growth and multiplication

Chlamydia pass through a series of developmental forms while multiplying by binary fission. This is termed the "developmental cycle." Two morphologically different developmental forms with a continuous gradation of intermediates between them can be recognized. One is a small cell about 0.3 u in diameter, with an electron-dense nucleoid. The other is a large cell, 0.5 to 1.0 u in diameter without a dense center.

There appears to be no significant difference in morphology or developmental cycle among the various chlamydia, and a single generalized description applies to all. The development cycle may be regarded as an orderly alternation of the small and large cell type. It is initiated by the highly infectious small cell which is taken into the host cell by phagocytosis. The engulfed small cell retains its morphological integrity in vacuoles bound by membrane derived from the surface of the host cell, and there is no eclipse (period in which the parasite loses the infectious ability). Instead, without loss of individuality, the small cell is reorganized into a large cell which is the vegetative multiplying form of these organisms. Then, still within the membrane-bound vacuole, the large cell grows in size and multiplies by repeated binary fission. The developmental cycle is completed by the reorganization of most of the large cells into small ones which are then available for infection of new host cells. The time required for completion of a cycle varies from 24-48 hours, depending on the particular host/parasite system involved.
Chlamydial Development Cycle





Characteristics of the elementary and reticulate bodies of Chlamydia can be found in the table below.


ELEMENTARY BODY (EB)

RETICULATE BODY (RB)
Size 0.3 um

Size 0.5 - 1.0 um
RNA:DNA content = 1.1

RNA:DNA content = 3.1
Infectious

Not infectious
Adapted for extracellular survival

Adapted for intracellular growth
Hemagglutinin present

Hemagglutinin absent
Induces endocytosis

Does not induce endocytosis
Metabolically inactive

Metabolically active

Pathogenicity

Subgroup A organisms primarily infect the mucous membranes of the eye or the genitourinary tract of humans. Subgroup B organisms, although primarily parasites of birds, can be transmitted to man where they cause a lung infection.

The mechanism by which chlamydia cause disease or injure cells is unknown. Chlamydial infections of mucous membranes cause damage to tissues deep in the epithelial layer; for example, in trachoma, scarring of the tarsal plate occurs frequently. There is some evidence that a toxin is produced.

Laboratory Diagnosis

Laboratory diagnosis is made by one or more of the following:

1. Isolation of the organism from infected tissue. The tissue is inoculated into the yolk sac of seven-day chick embryos
or in McCoy human cells.

2. Characteristic cytoplasmic inclusion bodies infected cells.

3. Serological diagnosis:

a. Microimmunofluorescent tests in tears of patients with eye infections for the presence of anti-chlamydia
antibody. In neonatal conjunctivitis and early trachoma, direct immunofluorescence of conjunctive cells with
fluorescein - conjugated monoclonal antibody is sensitive and specific.

b. Delayed-type skin reaction (type IV hypersensitivity) to killed organisms in genitourinary infections (Frei test).

c. Rising titer of antibody against the chlamydial family antigen in lung infecitons. This accomplished with the
complement fixation test or the fluorescent antibody test.

Treatment

Chlamydia exhibit low pathogenicity except in a compromised host. The chlamydial diseases are relatively easy to treat, but present two problems.

1. Latency of infection--infections may remain latent or sub-clinical
for years.

2. Susceptibility of compromised host to reinfection--the compromised host usually remains compromised
because of genetic and/or environmental factors and becomes reinfected.

3. Minimal symptomology

Chlamydia trachomatis - doxycycline or azithromycin
Chlamydia pneumonia - doxycycline or azithromycin or erythromycin
Chlamydia psittaci - doxycycline or erythromycin

Diseases

The chlamydial diseases include:


DISEASE CAUSUAL AGENT HOST
Subgroup A (person-to-person transmition)
Trachoma Chlamydia trachomatis Man
Inclusion conjunctivitis Chlamydia trachomatis Fowl, Man
Urethritis Chlamydia trachomatis Man
Cervicitis Chlamydia trachomatis Man
Ophthalmia neonatorum Chlamydia trachomatis Man
Myocarditis Chlamydia trachomatis Man
Lymphogranuloma venereum Chlamydia trachomatis Man
Atherosclerosis Chlamydia trachomatis Man
Neonatal Pneumonia Chlamydia trachomatis Man
-------------------------------------------------------------- -------------------------------------------------------------------------------- ------------------------------------------------
Subgroup B (mostly bird-to-human
(transmition)
Bronchitis/pneumonia/sinusitis Chlamydia pneumoniae Man
Atherosclerosis Chlamydia pneumoniae Man
Meningopneumonitis Chlamydia psittaci Birds --> Man
Hepatic and renal dysfunction Chlamydia psttaci Birds --> Man
Conjunctivitis Chlamydia psttaci Birds --> Man
Abortion Chlamydia psttaci Birds --> Man
Endocarditis Chlamydia psttaci Birds --> Man

Chlamydia has on its surface, a peptide that resembles one in heart myosin. The peptide, when displayed by antigen-presenting cells, can trigger T-cells that attack both Chlamydia and heart cells, thus causing heart muscle inflammation (myocarditis). This autoimmune reaction also plays a role in the formation of the artery-clogging plaques of atherosclerosis.
Mycoplasma and L-Forms

General Characteristics

The mycoplasmas are essentially bacteria lacking a rigid cell wall during their entire life cycle, although they are also much smaller than bacteria. The first organism of this type was associated with pleuropneumonia of cattle, and was originally called the pleuropneumonia organism (PPO). Since that time, a number of organisms with similar morphological characteristics and cultural properties have been isolated. These are commonly referred to as pleuropneumonia-like organisms or PPLO. A certain group of mycoplasmas produce extremely tiny colonies on agar plates, and are called the T-strains.

Some bacteria readily give rise spontaneously to variants that can replicate in the form of small filterable protoplasmic elements with defective or absent cell walls. These organisms, called L-forms, can also be formed by many species when cell wall synthesis is impaired by antibiotic treatment or high salt concentration. These organisms differ from mycoplasma in that they contain a rigid cell wall, at least at one stage of their life cycle and contain no sterols in their cytoplasmic membrane.

These organisms are the smallest known free-living organisms. Because of the absence of cell walls, they do not stain with the Gram stain, and they are more pleomorphic and plastic than eubacteria. With Giemsa stain, they appear as tiny pleomorphic cocci, short rods, short spirals, and sometimes as hollow ring forms. Their diameter ranges from 0.15 u to 0.30 u.

Most mycoplasmas require a rich medium containing a sterol and serum proteins for growth. Despite the lack of a cell wall, they do not require a medium of very high osmotic pressure. On solid media, they form minute, transparent colonies. When viewed under low-power magnification, the colony looks like a fried egg. The different strains vary in their growth rate and may take from two days to several weeks to form a colony.

Structure

The cell is enclosed by a limiting membrane which is more similar to that of animal cells than that of bacterial cells because of sterols present in the membrane. The cytoplasm contains ribosomes, but lacks mesosomes. There is no nuclear membrane. In some strains, amorphous material on the outer surface of the membrane suggests the existence of a capsule.

Metabolism

The parasitic mycoplasmas have truncated respiratory systems, lacking quinones and cytochromes. Another indication for the simplicity of the electron transport chain is the finding that the reduced nicotinamide adenine dinucleotide (NADH) oxidase activity is cytoplasmic. Complex electron transport chains are usually membrane bound, since they depend on the spatial organization of their components. Ruling out oxidative phosphorylation as an ATP-generating system leaves only two proven ways of ATP generation, both based on substrate level phosphorylation. The major source for ATP is the arginine dihydrolase pathway.
arginine deaminase
Arginine + H2O ----------------------------> citrulline + NH3
ornithine carbamoyltransferase
Citrulline+inorganic orthophosphate-------------------------------------------->ornithine+carbamoylPO

carbamate kinase
Carbamoyl PO4 + ADP --------------------------> ATP + CO2 + NH3

Another mechanism for ATP generation is:

phosphate acetyltransferase
Acetyl CoA + inorganic orthophosphate -----------------------------------------> acetyl PO4 + CoA

acetate kinase
Acetyl PO4+ ADP ------------------------------------> Acetate + ATP

Acetyl CoA is produced by oxidative decarboxylation of pyruvate.

A few species derive their energy from the degradation of glucose or the hydrolysis of urea. All species synthesize DNA, RNA, lipids and proteins. However, it is not known if they can synthesize amino acids. Those species that require sterols incorporate these sterols (mainly cholesterol) into the cell membrane up to concentrations of 65%.

Multiplication

In the absence of a rigid cell wall, the pattern of replication is quite different from that of typical bacteria, whose division starts with the formation of a well-defined septum. Though the mechanism of division in mycoplasmas is controversial, sequential microscopic observation suggests that new elementary particles arise by fragmentation of filamentous cells containing several discrete DNA components.

Pathogenesis

M. pneumoniae is an extracellular pathogen that adheres to the respiratory epithelium by a specialized terminal protein attachment factor. This adherence protein interacts specifically with neuraminic acid residues on the epithelial cell surface. Ciliastasis occurs following attachment and then destruction of the superficial layer of epithelial cells. Destruction is due to release of hydrogen peroxide and superoxide anion.

Diseases

The human diseases caused by mycoplasmas are shown in the table below.


DISEASE OR SYMPTOM AGENT HOST
Primary atypical pneumonia Mycoplasma pneumoniae Man
Non-gonococcal urethritis (NGU) Mycoplasma genitalium Man
NGU Ureaplasma urealyticum Man
Stillbirth Mycoplasma hominis Man
Spontaneous abortion Mycoplasma hominis Man
Infertility Mycoplasma hominis Man

Laboratory Diagnosis

The laboratory diagnosis of mycoplasma infection can be accomplished by:

1. Culturing the organism from sputum, mucous membrane swabbings or other specimens by direct inoculation into
liquid or solid media containing serum, yeast extract and penicillin to inhibit contaminating bacteria. Colonies will
become detectable in one to three weeks. They stain intensely with neutral red or tetrazolium or methylene blue.
The organism can be presumptively identified by its hemabsorption or B-hemolysis of guinea pig red blood cells. It
is conclusively identified by staining its colonies with homologous fluorescein-labelled antibody.

2. Quantitation of the patient antibody response to mycoplasma by complement fixation tests on acute and
convalescent serum. Cold agglutinins to human O erythrocytes may also be measured.

Chemotherapy

Primary atypical pneumonia is usually selflimiting and does not require antibiotic treatment. However, if antibiotics are needed, the drug of choice is one of the macrolide antibiotics:

Azithromycin
Clarithromycin
Dirithromycin
Erythromycin

Urogenital diseases may be treated with:

Metronidazole (except during the first trimester of pregnancy)
Clindamycin

Summary

1. The rickettsia are extremely small gram-negative rod-shaped, coccoid or pleomorphic bacteria with limited
metabolic capabilities.

2. The Family Rickettsiaceae contains three genera: Rickettsia, Ehrlichia, and Coxiella.

3. All of the members of the Family Rickettsiaceae are obligate intracellular parasites due to a highly permeable
cytoplasmic membrane.

4. Confirmative diagnosis of rickettsial diseases is accomplished via the Weil-Felix test, a complement fixation test
and/or an indirect fluorescent antibody test.

5. The drugs of choice for the treatment of rickettsial diseases are chloramphenicol and tetracycline.

6. Louse-borne rickettsial diseases include European epidemic typhus, and Brill's disease. Man is the sole reservoir for
louse-borne diseases.

7. The only flea-borne rickettsial disease is endemic murine typhus.

8. Mite-borne rickettsial diseases include scrub typhus and rickettsialpox.

9. Tick-borne rickettsial diseases include Rocky Mountain spotted fever, North Asian tick typhus, Fievre boutonneuse,
Queensland tick typhus, Q fever, spotted fever and ehrlichiosis.

10. The major target tissue of the rickettsia is vascular endothelium.

11. The chlamydia are extremely small, gram-negative, coccal-shaped, obligate intracellular parasites with limited
metabolic capability which are classified as bacteria.

12. The chlamydia lack flavoproteins and cytochromes.

13. Chlamydia undergo a unique developmental cycle which is an alternation in size between the small elementary
body and the relatively large reticulate body.

14. The elementary body is relatively metabolically inactive, adapted for extracellular survival and is the infectious
unit.

15. The reticulate body is metabolically active, adapted for intracellular growth and is not infectious.

16. The major target tissue of the chlamydia is mucous membranes.

17. Serological diagnosis of chlamydial diseases is via a fluorescent antibody test, complement fixation test or a
delayed type hypersensitivity test (Frei test) for lymphogranuloma venereum.

18. Chlamydial diseases include trachoma, inclusion conjunctivitis, lymphogranuloma venereum, bronchitis,
pneumonia, sinusitis and meningopneumonitis, hepatic and renal dysfunction, abortion and endocarditis.

19. The mycoplasma are extremely small free-living bacteria which lack a cell wall and cytochromes.

20. Mycoplasma can be cultured on agar media but colonies take up to three weeks to develop.

21. Serological identification of mycoplasma disease relies upon the quantitation of cold agglutinins to human O
erythrocytes or a complement fixation test or serum inhibition of mycoplasma growth.

22. Human diseases of mycoplasma etiology are primary atypical pneumonia, non-gonococcal urethritis, stillbirth,
spontaneous abortion and infertility.

Frei's test

Associated persons:
Wilhelm Siegmund Frei

Description:
Skin test developed in 1925 for venereal lymphogranuloma inguinale using Frei’s antigen. Today mostly replaced by electromicroscopy. Demonstration of the trigger mechanism. See also Durand-Nicolas-Favre disease (the fifth venereal disease).

Se also Kveim’s test under Morten Ansgar Kveim, Norwegian pathologist, 1892-1966

Wednesday, November 15, 2006

Definition of the Couinaud Segments

Couinaud Liver Segments

The Couinaud classification divides the liver into 8 independent segments each of which has its own vascular inflow, outflow, and biliary drainage. Because of this division into self-contained units, each can be resected without damaging those remaining. For the liver to remain viable, resections must proceed along the vessels that define the peripheries of these segments. In general, this means resection lines parallel the hepatic veins while preserving the portal veins, bile ducts, and hepatic arteries that provide vascular inflow and biliary drainage through the center of the segment. [Gazelle]

Resecting only specific liver segments is especially useful in patients with hepatocellular carcinoma. Fifty to 75% of these patients have underlying liver cirrhosis and poor liver reserve. The surgical challenge in these patients is to resect enough liver to allow complete tumor resection while retaining all possible non-tumorous liver to prevent further loss of liver function. In support of the benefit of resections along segmental boundaries, MacIntosh has reported an operative mortality of 0-16% with segment based resections compared to mortalities of 20-60% in patients receiving traditional lobectomies or non-segment based wedge resections. [MacIntosh].

Liver Vessels Related to Surface Contours

liver mip

Fig 4-1 MIP views of vessels related to surface contours
with the gallbladder, ivc, and falciform ligament labeled.
MPEG Movie (323K)
The 3-dimensional Maximum Intensity Projections (MIP) shown above outline the vessels in white while showing the liver parenchyma in grey. This allows us to "see through" the parenchyma and relate surface contours to the underlying vessels. These MIP views show the portal vein entering the liver hilum. The additional components of the portal triad, the hepatic artery and bile ducts, are below the resolution of the scan. The portal veins (along with the hepatic artery and the bile duct) project into the center of the Couinaud segments. In most cases, the vascular outflow for each segment is provided by the 3 hepatic veins at its periphery, however accessory hepatic veins are common.

Plane of the Right Hepatic Vein

RHV mipRHV ssd

Fig 4-2 MIP view of the liver (left panel) showing plane of right hepatic vein as it courses to the IVC. Shaded-Surface projection (right panel) showing, how the plane of the right hepatic vein provides the vertical division of the right liver lobe into anterior and posterior segment groups.
MPEG Movie (236K)
The intersegmental plane defined by the right hepatic vein subdivides the right lobe of the liver into anterior (V and VIII) and posterior (VI and VII) divisions. Note that the right lateral border of the liver contour is formed by segments VIII (superiorly) and V (inferiorly) as the liver viewed in situ. Segments VI and VII lie posterior to VIII and V respectively. Shown above are a maximum intensity projection and surface projection of the liver indicating the location and significance of the right hepatic vein plane. Both projections are rotated 30 degrees to illustrate the positions of segments VI and VII which actually lie posterior to V and VIII and not lateral to them as as they often appear in the literature. As will be explained later, the anterior and posterior divisions are further subdivided by a plane defined by the right portal vein. [VanLeeuwen, Makuuchi, Masselot, Nakamura].

Plane of the Middle Hepatic Vein

MHV mipRHV mip

Fig 4-3 MIP and shaded surface views showing that the course of the middle hepatic vein falls roughly along a palne extending from the gallbladder fossa and the IVC. This plane divides the right hepatic lobe from the left hepatic lobe.
MPEG Movie (234K)
In both the traditional and the Couinaud classifications, the plane defined by the middle hepatic vein subdivides the liver into the true right and left lobes. A standard right or left lobectomy requires division along the plane of the middle hepatic vein. Segments IVa and IVb lie to the left of the plane while segments V and VIII lie to the right with VIII being superior to V. In the movie, the gallbladder is slightly brighter than the rest of the plane. Because the plane of the middle hepatic vein usually intersects the gallbladder fossa, Cantlie's line (the projection on the liver surface of a plane between the gallbladder and IVC) is generally a valid line of division between the right and left lobes. However, it is the vasculature that determines the true boundary.

Plane of the Umbilical Fissure

umbilical plane mipRHV mip

Fig 4-4 MIP and shaded-surface views showing that the plane of the umbilical fissure divides the left lobe into medial and lateral portions which need to be further divided to qualify as independent Couinaud segments.
MPEG Movie (234K)
The umbilical plane divides the left lobe of the liver into medial (segment IV) and lateral (segments II and III) divisions. This division is the only vertically oriented plane of division that is not defined by the hepatic veins. It can be defined on the surface of the liver by its associated landmarks. It extends from the umbilical fissure anteriorly through the ligamentum venosum along the lateral aspect of the caudate lobe. Structures within the plane of the umbilical fissure include the falciform ligament, ligamentum venosum, and the ligamentum teres. The ligamentum venosum and the ligamentum teres are remnants of the ductus venosus and umbilical vein respectively [Schneck].

Plane of the Left Hepatic Vein

LHV mipLHV mip

Fig 4-5 MIP and shaded-surface views showing that the plane of the left hepatic vein subdivides the lateral portion of the left hepatic lobe.
MPEG Movie (234K)
The significance of the left hepatic vein plane is somewhat controversial [Gazelle]. Some authors have shown it to coincide with the umbilical fissure [Soyer]. In reality the left hepatic vein courses to the lateral to the umbilical fissure. Some authors have claimed that the true division between segments II and III is formed by the transverse plane of the left portal vein [Pagani, Soyer, Gupta, and Nelson]. Most investigators feel that the plane defined by the left hepatic vein is a true intersegmental boundary and is not the same as the plane of the umbilical fissure [Lafortune, Gazelle, Bismuth, Mukai, Lunderquist, and Ger]. Here we define the plane of the left hepatic vein as the boundary between segments II and III. In actual practice, when a lesion occurs within the lateral segment of the left lobe, both Couinaud segments II and III are usually removed based on the plane formed by the umbilical fissure (left lateral segmentectomy). Note that because the plane of the left hepatic vein is oblique, it forms a division between segments III anteriorly and segment II posteriorly.

Plane of the Portal Vein

portal vein plane mipRHV mip

Fig 4-6 MIP and shaded surface views showing the plane of the main intrahepatic portal vein. Note, this plane (arrow on surface view) is roughly horizontal but in some cases may be angled as shown in the in the MIP dataset. The dotted line indicates how this plane is sometimes used to divide segment IV into superior (IVa) and inferior (IVb) divisions.
MPEG Movie (237K)
In Couinaud nomenclature, the plane defined by the right branch of the portal vein divides the anterior and posterior divisions of the right liver superiorly and inferiorly, thus dividing the right lobe into 4 segments (V-VIII). The medial segment of the left lobe can also be divided into two segments by the plane of the portal vein (IVa and IVb)[Bismuth]. While the portal vein plane has often been portrayed as transverse [Soyer], it may be oblique since the left branch runs superiorly and the right branch runs inferiorly. In addition to forming an oblque transverse plane between segments, the left and right portal veins branch superiorly and inferiorly to project into the center of each segment.

Segment 1: The Caudate Lobe

Segment 1 (caudate lobe)
Fig 4-7 Posterior shaded surface view of the liver magnified to show the relation of the caudate with the IVC medially and the fissure for the ligamentum venosum laterally.
The most unique of the Couinaud segments is segment I which corresponds to the caudate lobe (also known as the Spigel lobe). It is located on the posterior surface of the liver adjacent to segment IV. Its medial and lateral boundaries are defined by the IVC and ligamentum venosum respectively.

Segment I is different than the other segments in that its portal inflow is derived from the left and right branches of the portal vein, and it often has its own short hepatic veins connecting directly to the IVC. The vessels of the caudate lobe are rarely seen on CT because they are small. Because of the extensive crossing of vessels and its position relative to the porta hepatis and IVC, segment I is not often resected. However, several examples exist in the literature [Lerut, Yamamoto].

Couinaud Segments: the Complete Picture

Axial mip of the liver
Fig 4-8 Definition of the segments is shown with maximum intensity projections from an inferior view of the entire 3D data set much as seen on the standard CT scan except that the "see through" nature of 3D data allows us to see the courses of the portal and hepatic veins in one view.
In the projections of the entire 3D data set below, you are looking through the entire liver, and the course of the portal and hepatic veins are seen in a single view (left panel). The right panel maps the peripheries of the Couinaud segments with dotted lines. Note that the portal branches supply the middle of the segments while the hepatic veins drain the periphery of the segments. Note also that segments I, II, VI, and VII are mostly posterior and hidden from the surgeon's view in the operating room. Before surgical resection, focal liver lesions must be defined in relation to the deep vessels and the segmental anatomy. This is easily, and quickly accomplished using intraoperative ultrasound. (See next section).

RHV mip

Surface Projection Movie of the 8 Segments

Fig 4-9 Surface Projection of the liver
showing the 8 Liver Segments as defined by the underlying vascular planes. Note that the plane of the portal vein subdivides segment IV into two parts (IVa and IVb).
MPEG Movie (323K)
Anterior and Posterior view of 8 segments

Fig 4-10a Anterior and posterior view of liver showing 3-dimensional reconstructions of helical CT scan data in shaded surface projections which have been segmented according to the Couinaud classification.
Superior and Inferiof view of the 8 segments
Fig 4-10b Shaded-Surface 3D reconstructions of the liver segments viewed in the transverse plane at the level of the rostral part of the liver and inferiorly from the caudal surface.
The Couinaud segments and their corresponding traditional nomenclature are summarized above. The corresponding images of the liver surface are for visualization of the relative positions of the segments. It is important to note that the view marked "anterior" is actually rotated about 30 degrees to the patients left so that the posterior segments of the right lobe (VI/VII) can be seen. In an AP view, usually only the anterior segments (V and VIII) of the right lobe are seen since they form the lateral border of the liver contour in a true frontal view.
I) caudate/Spigel lobe
II) left posterolateral segment
III) left anterolateral segment
IVa) left superomedial segment
IVb) left inferomedial segment
V) right anteroinferior segment
VI) right posteroinferior segment
VII) right posterosuperior segment
VIII) right anterosuperior segment

Tuesday, November 07, 2006

Paget’s disease of the nipple

# What is Paget’s disease of the nipple?

Paget’s disease of the nipple, also called Paget’s disease of the breast, is an uncommon type of cancer that forms in or around the nipple (1, 2, 3). More than 95 percent of people with Paget’s disease of the nipple also have underlying breast cancer; however, Paget’s disease of the nipple accounts for less than 5 percent of all breast cancers (1). For instance, of the 211,240 new cases of breast cancer projected to be diagnosed in 2005, fewer than 11,000 will also involve Paget’s disease of the nipple (4).

Most patients diagnosed with Paget’s disease of the nipple are over age 50, but rare cases have been diagnosed in patients in their 20s (1). The average age at diagnosis is 62 for women and 69 for men. The disease is rare among both women and men.

Paget’s disease of the nipple was named after Sir James Paget, a scientist who noted an association between changes in the appearance of the nipple and underlying breast cancer (1, 5). There are several other unrelated diseases named after Paget, including Paget’s disease of the bone and Paget’s disease of the vulva; this fact sheet discusses only Paget’s disease of the nipple.

# What are the possible causes of Paget’s disease of the nipple?

Scientists do not know exactly what causes Paget’s disease of the nipple, but two major theories have been suggested for how it develops (1, 2). One theory proposes that cancer cells, called Paget cells, break off from a tumor inside the breast and move through the milk ducts to the surface of the nipple, resulting in Paget’s disease of the nipple. This theory is supported by the fact that more than 97 percent of patients with Paget’s disease also have underlying invasive breast cancer or ductal carcinoma in situ (DCIS) (1). DCIS, also called intraductal carcinoma, is a condition in which abnormal cells are present only in the lining of the milk ducts in the breast, and have not invaded surrounding tissue or spread to the lymph nodes. DCIS sometimes becomes invasive breast cancer. Invasive breast cancer is cancer that has spread outside the duct into the breast tissue, and possibly into the lymph nodes under the arm or into other parts of the body.

The other theory suggests that skin cells of the nipple spontaneously become Paget cells. This theory is supported by the rare cases of Paget’s disease in which there is no underlying breast cancer, and the cases in which the underlying breast cancer is found to be a separate tumor from the Paget’s disease (1).

# What are the symptoms of Paget’s disease of the nipple?

Symptoms of early Paget’s disease of the nipple include redness and mild scaling and flaking of the nipple skin (1). Early symptoms may cause only mild irritation and may not be enough to prompt a visit to the doctor (3). Improvement in the skin can occur spontaneously, but this should not be taken as a sign that the disease has disappeared. More advanced disease may show more serious destruction of the skin (1). At this stage, the symptoms may include tingling, itching, increased sensitivity, burning, and pain. There may also be discharge from the nipple, and the nipple can appear flattened against the breast (1, 2).

In approximately half of patients with Paget’s disease of the nipple, a lump or mass in the breast can be felt during physical examination (1). In most cases, Paget’s disease of the nipple is initially confined to the nipple, later spreading to the areola or other regions of the breast (1, 2). The areola is the circular area of darker skin that surrounds the nipple. Paget’s disease of the nipple can also be found only on the areola, where it may resemble eczema, a noncancerous itchy red rash (1). Although rare, Paget’s disease of the nipple can occur in both breasts (2).

# How is Paget’s disease of the nipple diagnosed?

If a health care provider suspects Paget’s disease of the nipple, a biopsy of the nipple skin is performed (1, 2, 3). In a biopsy, the doctor removes a small sample of tissue. A pathologist examines the tissue under a microscope to see if Paget cells are present. The pathologist may use a technique called immunohistochemistry (staining tissues to identify specific cells) to differentiate Paget cells from other cell types (1). A sample of nipple discharge may also be examined under a microscope for the presence of Paget cells (3).

Because most people with Paget’s disease of the nipple also have underlying breast cancer, physical examination and mammography (x-ray of the breast) are used to make a complete diagnosis.

# How is Paget’s disease of the nipple treated?

Surgery is the most common treatment for Paget’s disease of the nipple (1, 2, 5). The specific treatment often depends on the characteristics of the underlying breast cancer.

A modified radical mastectomy may be recommended when invasive cancer or extensive DCIS has been diagnosed (5). In this operation, the surgeon removes the breast, the lining over the chest muscles, and some of the lymph nodes under the arm. In cases where underlying breast cancer is not invasive, the surgeon may perform a simple mastectomy to remove only the breast and the lining over the chest muscles (2, 5).

Alternatively, patients whose disease is confined to the nipple and the surrounding area may undergo breast-conserving surgery or lumpectomy followed by radiation therapy (1, 2, 5). During breast-conserving surgery, the surgeon removes the nipple, areola, and the entire portion of the breast believed to contain the cancer. In most cases, radiation therapy is also used to help prevent recurrence (return of the cancer).

During surgery, particularly modified radical mastectomy, the doctor may perform an axillary node dissection to remove the lymph nodes under the arm (1, 5). The lymph nodes are then examined to see if the cancer has spread to them. In some cases, a sentinel lymph node biopsy may be performed to remove only one or a few lymph nodes. (For more information about sentinel lymph node biopsies, please see National Cancer Institute Fact Sheet 7.44, Sentinel Lymph Node Biopsy: Questions and Answers, at http://www.cancer.gov/cancertopics/factsheet/Therapy/sentinel-node-biopsy on the Internet.)

Adjuvant treatment (treatment that is given in addition to surgery to prevent the cancer from coming back) may be part of the treatment plan, depending on the type of cancer and whether cancer cells have spread to the lymph nodes. Radiation treatment is a common adjuvant therapy for Paget’s disease of the nipple following breast-conserving surgery. Adjuvant treatment with anticancer drugs or hormone therapies may also be recommended, depending on the extent of the disease and prognostic factors (estimated chance of recovery from the disease or chance that the disease will recur).

# Are clinical trials (research studies) available? Where can people get more information about clinical trials?

Yes. The NCI is currently sponsoring many clinical trials for all types of breast cancer. These studies are designed to find new treatments and better ways to use current treatments. As new and improved treatments are found for breast cancer, the treatment options for Paget’s disease of the nipple will also improve (2, 5).

People interested in taking part in a clinical trial should talk with their doctor. Information about clinical trials is available from the NCI’s Cancer Information Service (CIS) (see below) at 1–800–4–CANCER and in the NCI booklet Taking Part in Clinical Trials: What Cancer Patients Need To Know, which can be found at http://www.cancer.gov/publications on the Internet. This booklet describes how research studies are carried out and explains their possible benefits and risks. Further information about clinical trials is available at http://www.cancer.gov/clinicaltrials on the NCI’s Web site. The Web site offers detailed information about specific ongoing studies by linking to PDQ®, the NCI’s cancer information database. The CIS also provides information from PDQ.

Thyroid


1. Rules for Classification

The classification applies only to carcinomas. There should be microscopic confirmation of the disease and division of cases by histological type.

The following are the procedures for assessing T, N, and M categories:

T categories. Physical examination, endoscopy, and imaging
N categories. Physical examination and imaging
M categories. Physical examination and imaging

2. Regional Lymph Nodes

The regional lymph nodes are the cervical and upper/superior mediastinal nodes

Clinical Classification

3.1. T - Primary Tumour
TX. Primary tumour cannot be assessed
T0. No evidence of primary tumour
T1. Tumour 2 cm or less in greatest dimension, limited to the thyroid
T2. Tumour more than 2 cm but not more than 4 cm in greatest dimension, limited to the thyroid
T3. Tumour more than 4 cm in greatest dimension, limited to the thyroid or any tumour with minimal extrathyroid extension (e.g. extension to sternothyroid muscle or perithyroid soft tissues)
T4a. Tumour extends beyond the thyroid capsule and invades any of the following: subcutaneous soft tissues, larynx trachea, oesophagus, recurrent laryngeal nerve
T4b. Tumour invades prevertebral fascia, mediastinal vessels, or encases carotid artery
T4a* (anaplastic carcinoma only). Tumour (any size) limited to the thyroid~
T4b* (anaplastic carcinoma only). Tumour (any size) extends beyond the thyroid capsule±

Notes:
Multifocal tumours of all histological types should be designated (m) (the largest determines the classification), e.g., T2(m).
*All anaplastic/undifferentiated thyroid carcinomas are considered T4.
~Intrathyroidal anaplastic carcinoma-considered surgically resectable.
±Extrathyroidal anaplastic carcinoma-considered surgically unresectable.

3.2. N - Regional Lymph Nodes
NX. Regional lymph nodes cannot be assessed
N0. No regional lymph node metastasis
N1. Regional lymph node metastasis
N1a. Metastasis in Level VI (pretracheal and paratracheal, including prelaryngeal and Delphian lymph nodes)
N1b. Metastasis in other unilateral, bilateral or contralateral cervical or upper/superior mediastinal lymph nodes

3.3. M - Distant Metastasis
MX. Distant metastasis cannot be assessed
M0. No distant metastasis
M1. Distant metastasis

4. pTNM Pathological Classification

The pT, pN, and pM categories correspond to the T, N, and M categories.

pN0. Histological examination of a selective neck dissection specimen will ordinarily include 6 or more lymph nodes. If the lymph nodes are negative, but the number ordinarily examined is not met, classify as pN0.

5. Histopathologic Types

The four major histopathologic types are:
  • Papillary carcinoma (including those with follicular foci)
  • Follicular carcinoma (including so-called Hürthle cell carcinoma)
  • Medullary carcinoma
  • Anaplastic/undifferentiated carcinoma

6. Stage Grouping

Separate stage groupings are recommended for papillary and follicular, medullary, and anaplastic/undifferentiated carcinomas:

Papillary or Follicular
Under 45 years
Stage I
Any T
Any N
M0
Stage II
Any T
Any N
M1
Papillary or Follicular 45 years and older and Medullary
Stage I
T1
N0
M0
Stage II
T2
N0
M0
Stage III
T3
N0
M0

T1. T2. T3
N1a
M0
Stage IVA
T1. T2. T3
N1b
M0

T4a
N0. N1
M0
Stage IVB
T4b
Any N
M0
Stage IVC
Any T
Any N
M1
Anaplastic/ Undifferentiated (all cases are stage IV)
Stage IVA
T4a
Any N
M0
Stage IVB
T4b
Any N
M0
Stage IVC
Any T
Any N
M1


7. Summary

Thyroid Gland

Papillary, follicular and medullary carcinoma
T1
≤2 cm intrathyroidal
T2
>2 to 4 cm intrathyroidal
T3
>4 cm or minimal extension
T4a
Subcutaneous, larynx trachea, oesophagus, recurrent laryngeal nerve
T4b
Prevertebral fascia, mediastinal vessels, carotid artery

Anaplastic/undifferentiated carcinoma
T4a
Tumour limited to thyroid
T4b
Tumour beyond thyroid capsule

All types
N1a
Level VI
N1b
Other regional

The staging of colon cancer

Staging

Staging is a method of evaluating the progress of the cancer in a patient. That is, it looks at the tumor and the extent to which it has spread to other parts of the body. Once doctors know how far along the cancer is, they can decide on the best course of treatment.

The staging of colon cancer is relatively straightforward. Originally there was the Duke's classification system, which placed patients into one of three categories (Stages A, B,C). This system was subsequently modified by Astler-Coller to include a fourth stage (Stage D); Gunderson & Sosin subsequently modified it again in 1978. More recently, the American Joint Committee on Cancer (AJCC) has introduced the TNM staging system, which places patients into one of four stages (Stage I-IV). Listed below are the Duke and TNM staging systems (they are the most often used).


Modified Duke Staging System

Modified Duke A The tumor penetrates into the mucosa of the bowel wall but no further.

Modified Duke B B1: tumor penetrates into, but not through the muscularis propria (the muscular layer) of the bowel wall.

B2: tumor penetrates into and through the muscularis propria of the bowel wall.

Modified Duke C C1: tumor penetrates into, but not through the muscularis propria of the bowel wall; there is pathologic evidence of colon cancer in the lymph nodes.

C2: tumor penetrates into and through the muscularis propria of the bowel wall; there is pathologic evidence of colon cancer in the lymph nodes.

Modified Duke D The tumor, which has spread beyond the confines of the lymph nodes (to organs such as the liver, lung or bone).

TNM Staging System (Tumor, Node, Metastisis)

Tumor
T1: Tumor invades submucosa.
T2: Tumor invades muscularis propria.
T3: Tumor invades through the muscularis propria into the subserosa, or into the pericolic or perirectal tissues.
T4: Tumor directly invades other organs or structures, and/or perforates.

Node

N0: No regional lymph node metastasis.
N1: Metastasis in 1 to 3 regional lymph nodes.
N2: Metastasis in 4 or more regional lymph nodes.

Metastasis
M0: No distant metastasis.
M1: Distant metastasis present.

Stage Groupings

Stage I: T1 N0 M0; T2 N0 M0
Cancer has begun to spread, but is still in the inner lining.

Stage II: T3 N0 M0; T4 N0 M0
Cancer has spread to other organs near the colon or rectum. It has not reached lymph nodes.

Stage III: any T, N1-2, M0
Cancer has spread to lymph nodes, but has not been carried to distant parts of the body

Stage IV: any T, any N, M1
Cancer has been carried through the lymph system to distant parts of the body. This is known as metastasis. The most likely organs to experience metastasis from colorectal cancer are the lungs and liver.

Monday, November 06, 2006

Clinical Case Studies




Cardiovascular system

Dermatology

Emergency Medicine

Endocrinology

Gastroenterology

Hematology

Neurology

Orthopedics

Pediatrics

GENERAL

Dentistry and Oral Health

Eye, ENT (Ear-Nose-Throat) and Respiratory System

Gynecology & Obstetrics

Immunology

Infectious and Parasitic Diseases

Oncology

Pathology & Histopathology

Radiology, Nuclear Medicine, Imaging & Ultrasonography

Surgery/Anesthesiology

Urogenital



Start Page

Cardiovascular system
Cases in Cardiothoracic Imaging , and some Congenital Heart Disease cases - Yale Univ./School of Medicine (US)
A collection of Cases-of-the-Month [subscription required] from the American College of Cardiology
The JHess Collection - UCSD (US)
Case(s) of the Month - American Society of Nuclear Cardiology
ECG Rounds - MDChoice.com
Clinical Cases from the files of West Suburban Cardiologists, Chicago (US)
CT Learning Cases from the Internet Stroke Center
Mystery Cases from the CardioThoracic Surgery Network
Surgery Grand Rounds - Univ of Arizona HSC (US)
Some Case studies in Valvular Diseases - Howard Gilman Institute (US)
Case Studies - UMass Medical School and The American Stroke Association
EKG Case Studies - McGill University (CA)
Case studies from Interventional and Vascular Medicine Forum [free registration required]
(Three) Interesting Clinical Case Studies Involving Secondary Causes of Hypertension [JA Diamond] - Mt Sinai J of Medicine, Oct 2002
Images and cases in Vascular Disease - Vascular Web
A cyanotic baby ... [E Fontenot] - Univ of Utah (US)

Dermatology
Global Dermatology Grand Rounds
Educational Cases in Dermatology - Austin & Repatriation Medical Centre/Dermatology
Some Cases in Dermatology [A Sleiman] - Univ of Beirut (LB)
Dermatology: case-of-the-month - Washington Univ, School of Med., Dermatology (US)
Cases in Dermatopathology [scroll down a bit; WS Weems]
The Dermatology Photo Library at Dermnet.com
A collection of Cases in Dermatopathology [in French] - Club de Dermatopathologie
Archived Clinical Cases at Virtual Grand Rounds in Dermatology
Diagnosis at a glance - Emergency Medicine [journal]
Case studies in Wound Healing (Proxiderm) - Progressive Surgical Products, N.Y. (US)

Emergency Medicine
Radiology Cases in Pediatric Emergency Medicine and Neonatology [Yamamoto et al.] - Univ of Hawaii (US)
Pediatrics Grand Rounds - Univ of Arizona HSC (US)
Emergency Cases - Rhode Island Hospital
Emergency Teaching Cases - Erstat.com
Some Case presentations in Emergency Medicine - Univ of Virginia/HealthSystem (US)
Cases in Emergency Medicine and ECG Rounds - MDChoice.com

Endocrinology
Case Studies in Endocrinology - Tulane Univ. (US)
Dr. Carrington's CPC cases [requires Internet Explorer] - Virginia Commonwealth Univ./Endocrine Pathol. Lab.
The Diabetic Foot: Complications [Learch and Gentili]
A few cases in Endocrinology - DigiDoc (CA)
Some Sample case cases in Endocrinology - Endocrine Fellos Foundation
A couple of Case studies in Endocrinology at Core Endocrine Lab., Penn State Univ. (US)

Gastroenterology
Cases in Gastroenterology - Baylor College of Medicine
Open for Discussion - Canandian Association of Gastroenterology
Case studies - MUSC/Digestive Disease Center (US)
The first, out of five (see left margin/Study Set list), Study Sets of Gastrointestinal Biopsy Cases - AFIP
Some Case studies in Gastrointestinal Disorders - Univ of Minnesota (US)

Hematology
Instructional Cases in Hematology - McMaster Univ., Ontario (CA)
Teaching Cases in Hematology - American Soc of Hematology
Case Studies in Hematography - Univ of Minnesota (US)
Hematology cases - Univ of Washington, WA (US)
Anemia Quiz Studies , and the Answers - Queens Univ./Hematol-Oncol (CA)
Imagerie en Hematologie [in French] - Univ of Rennes (FR)
Lymphedema Case Studies - Peninsula Medical, Inc.
CellAtlas .com [free registration]
A few Clinical Case Studies - Atlas of Hematology, Gdansk (PL)

Neurology
Grand Rounds from the Massachusetts Gen Hosp./Neurosurgical Service (US)
Neurosurgery Grand Rounds - Louisiana State Univ. (US)
A collection of Cases of the Month - Brain Pathology/Int'l Soc Neuropathology
Case studies in Neuropathology - Univ of Medical Sciences, Poznan (PL)
Case summaries in Clinical Neurology - Univ of Utah (US)
Neuropathology cases - McGill Univ. (CA)
Some Neuropathology Biopsy Cases - Univ of N. Carolina/Chapel Hill (US)
A Case Workbook in Medical Neuroanatomy - Univ of New England (US)
The JHess Collection - UCSD (US)
Interesting Cases in Neuroradiology - Univ of California/SF (US)
Cases in Neuroradiology - (Univ of) Iowa Neuroradiology Library (US)
A list of Neuroradiology Teaching File Cases - University of Colorado (US)
A Case-of-the-Month collection from Baylor College of Medicine (US)
Multiple Choice Questions (in Neuropathology) [K Hegedus] - Univ of Debrecen/Neurology (HU)
A collection of Interactive Case in Neurology - Univ of Utah (US)
Case discussions from the Neuro Rounds at Medi-Fax (CA)
Pathway Quizzes in Neuroanatomy - Knowledge Weavers, Utah (US)
Cases in Neurology/Neurosurgery from Johns Hopkins, via Medscape [free registration required]
Cases in Electrodiagnostic Medicine [D Dumitru]
A Clinical Case Study Guide for CNS [D Oliver] - Univ of Connecticut HC (US)
Clinical Cases in Neuroscience - Indiana University (US)

Orthopedics
Case studies from WorldOrtho.com
The Case archive at American Academy of Physical Medicine and Rehabilitation
Upper/Lower Extremity Cases - Univ of Washington, Seattle (US)
Discussions of Interesting Spine Cases - Spine-Surgery
Upper and Lower Extremity Cases [G Schmale] from the School of Medicine, Univ of Washington (US)
Interesting MRI Cases (shoulder, knee) [J Hunter] - Univ of Washington/Dept of Radiology
Clinical Cases in Gait Analysis [C Kirtley]
Clinical Case Presentations from Alfred I duPont Institute
Case examples in Orthopedic Surgery - International Center for Limb Lengthening, Sinai Hosp. (US)
Select the hand you want to diagnose - Loyola Univ. Medical Center (US)
Interesting orthopedic ultrasound and teaching file cases - Hospital for Special Surgery, N.Y. (US)
Cases in Rheumatology - American College of Rheumatology
A collection of Illustrated Case Studies in Rheumatology - MedNet HELLAS (GR)
Some Patient Cases from Orthospine
Clinical Case descriptions [M Saleh] - (UK)
Orthopaedic Pathology Cases [presentations + discussions] - Univ of Florida (US)
A collection of Teaching Cases in Nuclear Medicine - Harvard Med School/JPNM, including Bone Scintigraphy Cases [Parker and Holman] and some interesting images/cases

Pediatrics
PediatricEducation.org [D and M D'Alessandro] - Univ of Iowa (US)
Radiology Cases in Pediatric Emergency Medicine and Neonatology [Yamamoto et al.] - Univ of Hawaii (US)
Case based Pediatrics for Medical Students and Residents - Univ of Hawaii, JA Burns School of Medicine
Case-of-the-Month collection at PedsEducation.org
Case studies for download - Bright Futures Center
Case studies from the Interactive Pathology Laboratory, IPLAB
Pediatric Grand Rounds at the Medical Center, Univ of Nebraska (US)
Some teaching files with Cases in Paeditric Radiology - CUHK (HK)
Grand Rounds Online - Dept of Pediatrics, Univ of Florida (US)
Cases in Pediatric Pathology - Swiss Pediatric Pathology Group (CH)
The Virtual Pediatric Patients [D'Allesandro and Takle] and some case presentations in Pediatric Thoracic Medicine - Virtual Pediatric Hospital
Cases in Pediatric Cardiology - Univ of Kansas Med Center (US)
Grand Rounds - Video Presentations [QuickTime files; restricted access] - Univ of Wisconsin (US)
What's Your Diagnosis? - Pediatric Surgery Update
A collection of Case studies in Pediatrics - MedNet, HELLAS (GR)
Genetics Case Studies - Telegenetics
A collection of Case studies in Cytogenetics - Univ of Wisconsin (US)
A Pediatric Picture Atlas for Parents - Rainbow Pediatrics

GENERAL
Medical Simulations - Interactive Case Studies - InterMed Press
A sorted collection of Cases, with images , - from MDChoice.com
An interdisciplinary collection of Clinical Cases - The Virtual Health Care Team/Univ of Missouri (US)
Articles Menu of Grand Rounds [journal, free access] - e-MED Ltd. (UK)
Case Studies from IPLAB.net
Online Case Studies and Clinical Quizzes from the American Acad of Family Physicians
Medical Grand Rounds - PPT presentations from the Gardiner Library, John Hunter Hospital, NSW (AU)
Clinical Grand Rounds from the NIH Clinical Center (US)
Imaging Cases of the Week - Doctor T
An example of a Case report in Family Medicine - KECK School of Medicine of USC (US)
Cases in Family Medicine [Undergraduate Medical Educ.] - Penn State Univ. (US)
Case Studies in Medicine [links] - Case Studies in Science, State Univ of N.Y. Buffalo (US)
A collection of Case Studies - by Subject [compiled by Fung and Sawh]
A set of Medicine Case Discussions from LUMEN, Loyola Univ. (US)
Medicine Grand Rounds - Univ of Arizona HSC (US)
Make Your Diagnosis , and Casos Clinicos [partly in Portuguese, partly in English] - MedStudents (BR)
Various Clinical Cases (use Clinical Cases pull-down menu at top of page) [Lima and Coico] - Sophie Davis School/City Univ of New York (US)
Cases from eMedicine
A collection of Case Studies from Athena Diagnostics Lab.
A little Short Case Database from MedWeb, Univ of Birmingham (UK)
Clinical Decision Cases [interactive CME] - The Cleveland Clinic (US)
Interactive Case Studies - MedCases Inc.
Clinical Riddler from Walter Reed Army Medical Center (US)
MedicalRounds.com [multimedia medical education]
Medical Grand Rounds Webcasts , archived events - Univ of Miami, Dept of Medicine (US)
A Collection of Illustrated Case studies from MedNet, HELLAS (GR)
Some E-learning modules [free, but only for professionals] from Medcyclopaedia, GE Medical Systems
Grand Rounds Archive blogs - undisclosed
Case studies: set I , set II , and set III [graduate med educ.; AJ Chandrasekhar] - Loyola Univ Medical Center (US)
Virtual Grand Rounds/Lectures [multimedia] - Drexel Univ., College of Medicine (US)
A collection of Clinical Center Grand Rounds [multimedia] - NIH Video Casting (US)
Case Histories in Human Physiology [Van Wynsberghe and Cooley] - Univ of Wisconsin (US)
Medicine Grand Rounds/Lectures [multimedia] - Univ of Arizona (US)
Case Health: Health Success Stories

Dentistry and Oral Health
Web Cases from the Univ. of Iowa/College of Dentistry (US)
A collection of Oral Pathology Case Reviews - Univ of Oklahoma/Dentistry (US)
Les cas cliniques from Journal de Periodontologie et d'Implantologie Orale
Cases i Oral Pathology - UCSF (US)
Clinical Cases [in Spanish and/or English; C Boveda, and others]
Clinical Cases in Oral & Maxillofacial Pathology - Armed Forces Institute of Pathology (US)
Self-Evaluation cases/images in Dental Diagnostics - USC (US)
Some Case reviews in Endodontics - Virginia Commonwealth Univ./School of Dentistry
A Case of the Month collection - Univ of Washington/School of Dentistry (US)
Case studies in Dental Hygiene [M Bower] - Monroe Community College (US)
Real-Life Cases in Dental Hygiene [AM Nieves]
Clinical Cases [KA Galil] - School of Dentistry, Univ of W Ontario (CA)
Clinical Cases in Orthodontics [CB Pereira] - (BR)

Eye, ENT (Ear-Nose-Throat) and Respiratory System
Clinical Cases in Ophthalmology , and a collection of Knowledge Reviews - DJO/Harvard (US)
Digital Grand Rounds - SECO Int'l
RED (recognizing eye diseases) Atlas
Refractive Surgery Grand Rounds - Refractive Source
Ophthalmology Case index - EYERounds.org
Case of the Week collection at The New England Eye Center (US)
Case index at EyeRounds, Univ of Iowa (US)
Case reports from Massachusetts Eye and Ear Infirmary (US)
A Collection of Cases from the Pediatric and Adult Strabismus Resource, McGill Univ. (CA)
Case-of-the-Month - Univ of Wisconsin-Madison/Dept Ophthalmology and Vision Sci (US)
Virtual Eye Clinic [A Field] - American Acad of Optometry/British Chapter
Test your diagnostic skills - Eye Casualty, Oxford (UK)
Cases in Clinical Grand Rounds - EyeUpdate.com
Short Cases in Pediatric Ophthalmology [Thompson et al.; sample chapter of book] - fleshandbones
Cases in Neuro-Ophthalmology - SH Wray, Univ of Utah (US)
Some Case Reviews from Digital Reference of Ophthalmology/ES Harkness Eye Institute
Unusual cases in Retinal Ophthalmology [ed. KB Freund] - Vitreous-Retina-Macula Consultants, N.Y. (US)
Young woman with a red irritated eye and A 54 year-old man needs reading glasses - School of Optometry, Indiana Univ. (US)
Case histories in Voice Medicine [JP Thomas]
Grand Rounds at Univ of Texas/Dept of Otolaryngology (US)
Grand Rounds Archive at the Bobby R Alford Dept. of Otorhinolaryngology and Communicative Science/Baylor College (US)
Grand Rounds Archive: Pediatric Otolaryngology - Bobby R Alford Dept. of Otorhinolaryngology-Head and Neck Surgery
Clinical Otolaryngology OnLine - ENTLink (US)
Some interactive Otitis Media case studies developed by the Univ. of Colorado - American Acad of Pediatrics
A set of Pulmonary Cases - LUMEN, Loyola Univ. (US)
Case studies in Chest Disease Pathology - Univ of California/SF (US)
Case studies in Pulmonary and Critical Care Medicine - Univ of N Carolina at Chapel Hill (US)
Pediatric Upper Airway Case Studies [Santer and d'Alessandro] - Virtual Hosp., Iowa (US)
Some Case Studies in Pulmonary, Renal, and Acid-Base Disorders - Tulane Univ. (US)
Case List of Chest Diseases - Korean Society of Thoracic Radiology (KR)
Some Thoracic Radiology Teaching Files [D Dyer] - UCHSC (US)

Gynecology & Obstetrics
A collection of Case-based Modules from Women's Health/Univ of Washington (US)
Some Problem/Case Based Learning Sessions at LUMEN, Loyola Univ. (US)
A collection of Colposcopy Case Studies - ASCCP (US)
Some Case presentations, with questions - Univ of Utah/Reproductive Endocrinology and Infertility (US)

Immunology
Case studies from the book Essentials of Clinical Immunology [Chapel et al.]

Infectious and Parasitic Diseases
Archived Grand Rounds from Johns Hopkins/Infectious Diseases (US)
Case Studies in Fungal Infections - Fungal Infections Virtual Grand Rounds
Some Clinical (quiz) presentations and a collection of Microbiology Cases [Duckworth et al.] from Univ. of Florida/Medical Microbiology and Infectious Diseases (US)
Four Clinical Case presentations & discussions [J Heritage] - Univ of Leeds/Microbiology (UK)
Monthly Case Studies in Parasitology - CDC/DPDx (US)
Quiz-of -the-month collection 2001 , 2002 , 2003 , and 2004 - PARA-SITE Online
A set of Infectious disease cases, with images - US Armed Forces IDS
Clinical Cases in Microbiology, Mycology, Virology, ... [Lima and Coico] - Sophie Davis School/City Univ of N.Y. (US)
What's Your Diagnosis? [free registration required] - Infectious Diseases in Children

Oncology
A collection of Cancer Training Modules (including case studies) - SEER (US)
A few Case Studies related to Brain Tumors - McGill Univ. (CA)
Links to Breast Imaging Case Studies - via Imaginis
Breast Cancer Case Studies - Breast Cancer Institute, NSW (AU)
8 MRI Case Studies - Wake Forest Univ.
Case Studies from the Interactive Pathology Laboratory, IPLAB
Testicular and Extragonadal Germ Cell Tumor Case Studies [links] - Testicular Cancer Resource Center

Pathology & Histopathology
An Online Case Database , a case-of-the-month collection in Anatomic Pathology and in Clinical Pathology - Univ of Pittsburgh/Dept. of Pathology (US)
Clinical Pathology Cases presented at the Clinico-Pathological Conference/Johns Hopkins Univ. (US)
Pathology Case Studies - Univ of Virginia (US)
Case studies - IPLAB.net
Pathology Case-of-the-Month collection - Univ of Oklahoma (US)
Case Studies in Pathology [MW Braun] - Indiana University/School of Medicine (US)
What went wrong? - CAP (US)
Surgical Pathology Cases from Walter Reed Army Med C. (US)
Cases/Images in Histopathology - SUNY Downstate Med C./Pathology (US)
Some clickable Demo case modules from Robbins Pathologic Basis of Disease
A Pathology Case of the Month from West Virginia Univ./Pathology
A collection of Pathology Cases-of-the-Week - WebPath, Florida State Univ. (US)
Pathology Case Studies [requires Internet Explorer] - Upstate Medical Univ./Pathol, N.Y. (US)
Case in Surgical Pathology (using diagnostic electron microscopy) - Society for Ultrastructural Pathology
Forum Cases in Surgical Pathology and Cytology - TelePathology Consultants (US)
Twenty histological samples for examination - Gateway Community College (US)
Cases in Paleopathology - Virginia Commonwealth Univ. (US)

Radiology, Nuclear Medicine, Imaging & Ultrasonography
Cases by Anatomical Area and by Title from Brigham Radiology/Harvard (US)
Radiology Teaching Files [links ; M D'Alessandro] - Univ of Iowa (US)
Cases of the Month , 2001 - 1995, from SPL/Brigham and Women's Hosp. (US)
Clinical Cases in Radiology - CERF, via Univ. de Rennes (FR)
Cases - by diagnosis - Scottish Radiological Society (UK)
Unknown Cases, with Answers - Radiology Museum, S Bank Univ. (UK)
Cases of the Day, 2001 , and 2005 from the American Roentgen Ray Society
Most interesting cases at The Pediatric Radiology Platform (DE)
Search for Peer-reviewed Teaching Cases at the European Association of Radiology/E-Learning Initiative
Clinical Cases from the Boca Radiology Group, FL (US)
Neuroradiology Teaching Files: by diagnosis - Univ of Cincinnati (US)
A Case-of-the-Month Collection from the Hong Kong College of Radiology (HK)
Some Interesting Cases in Radiology - Wayne State University (US)
A collection of Case-of-the-Week items - Creighton Univ./Radiology (US)
Case studies at Imaging for Idiots (UK)
Radiology Teaching File: Quick Cases from Univ of Washington (US)
A list of Musculoskeletal Radiology Teaching File Collections on the Internet - Soc of Skeletal Radiology
An Interesting Case Archive at Dartmouth-Hitchcock
Radiology cases [AC Downie] from The Scottish Radiological Society
PET Case of the Month - Franklin Square Hospital Center
A collection of Neat Cases [P Cooperberg] - Univ of British Columbia/Radiology (CA)
Women's Diagnostic Imaging Teaching Files - UHRAD.com
Breast Ultrasound Teaching Files (unknown cases + diagnoses) - Univ of Colorado HSC (US)
Radiology cases - USUHS/MedPix (US)
Radiology Grand Rounds [video clips] - SUNY Downstate Medical Center (US)
Clinical Case CT Studies and Digital X-ray Studies - GE Healthcare
Best Cases from AFIP - Radiology Society of North America
Radiology (CME) Cases [subscription access] - RadiologyGraphics, RSNA (US)
CT Case Studies in self-quiz format [uses RealAudio] - CT-is-us
Cases in Neuroradiology - (Univ of) Iowa Neuroradiology Library (US)
Unknown Cases of the Week - Nuclear Medicine, Loyola Univ. (US)
Some MRI Cases from Medicine Australia
Interesting MRI Cases (shoulder, knee) [J Hunter] - Univ of Washington/Dept of Radiology
Case-of-the-Month Cases in Radiology, and Study Cases in Chest Radiology [Hayashi et al.] - Nagasaki Univ. Hospital (JP)
A set of Links to Radiology Case Collections - Martindale's Health Science Guide
Nuclear Medicine Cases by Study Type and Diagnosis - Mallinckrodt Inst of Radiology, Washington Univ.

Surgery/Anesthesiology
Some Case presentations at Trauma.Org
Trauma Cases , and some Sudden Death scenarios [registration required] - Liverpool Hospital/Trauma (AU)
Discussions around some Cases in Spinal Surgery - GICD
Cases in Neurology/Neurosurgery from Johns Hopkins, via Medscape [free registration required]
Surgery Cases for Small Group Discussion - LUMEN, Loyola Univ. (US)
500 Cases Anesthesiology Oral Board Review - Rashad Net University
Mystery Cases from the CardioThoracic Surgery Network
Clinical Tutorials - Surgical-Tutor (UK)
Some Case Studies in Wound Healing - Wound Care Information Network
Clinical Cases in Wound Healing (using Proxiderm) from Progressive Surgical Products, N.Y. (US)

Urogenital
Links to Teaching Cases in Urology - Loyola Univ. Health System/Dept of Urology (US)
A collection of Clinical Cases by Patient History from ProstateHealth.org
Testicular and Extragonadal Germ Cell Tumor Case Studies [links] - Testicular Cancer Resource Center