The macroscopic basis for microscopic pathology

THE MACROSCOPIC BASIS FOR MICROSCOPIC PATHOLOGY
or
(Why We See What We See at Autopsy)

Paul C. Stromberg DVM, PhD
Diplomate, American College of Veterinary Pathologists

Department of Veterinary Biosciences
Ohio State University

The descriptive attributes of gross lesions observed at post mortem examination may provide information about the type of pathologic process, cause, parts ofthe organ or tissue affected or involved and pathogenesis. As pathologists we can learn to read these lesions like “hieroglyphics” interpret their meaning and by putting strings of lesion attributes together with the patient signalment and history, arrive at a presumptive but often accurate diagnosis. A carefully prepared postmortem examination with accurate description of the lesions can be avaluable adjunct to the histopathologic examination if for no other reason than histopathology examines such a tiny fraction of the patient. By establishing some guidelines for the significance of the observed gross lesion attributes and interpreting them in the aggregate, we can often reach logical conclusions about the nature of the pathologic process observed. The long term goal of grosspathology is never to have to do histopathology. Of course this is a receding goal as we always confirm by histopathology what we deduce from the post mortem. But histopathology is relatively expensive (compared to visual observation at postmortem) and takes time.

I. OBJECTIVE

Understand how microscopic lesions produce the macroscopic lesion attributes we see in a variety of organs andtissues and shape the appearance of the lesions we see during the port mortem examination. The approach will be to evaluate different types of lesion attributes in pairs, observing the gross specimen and the sub-gross or microscopic lesion.

INTERPRETATIVE PATHOLOGY OF SPECIFIC ORGANS AND TISSUES

II. LIVER - Dense solid organ normally dark, with symmetrical lobular microscopic architecturedefined by peripheral portal triads and a system of bile ducts. Provides good contrast for pathologic processes causing a light or pale color

1. Multifocal to miliary, well demarcated, random small foci = implies a recent embolic shower. A common pattern in septicemia

a. Beaver with yersiniosis

b. Horse with septicemic salmonellosis

c. Snake with salmonellosis2. Nonrandom well demarcated symmetrical nodules in linear array may indicate a pathologic process which is highlighting the bile ducts

a. Rabbit with hepatic coccidiosis ( Eimeria stediae) - cystic biliary hyperplasia

3. Multifocal poorly demarcated nodules = a process that tends to blend into the surrounding normal tissue or the nodules are composed of altered normaltissue

a. Dog with cirrhosis ~ Porto systemic shunt

b. Cat with chronic hepatitis and nodular regeneration (cirrhosis)
(Also a mast cell tumor in the spleen)

c. Horse with chronic hepatitis, cirrhosis; regenerative nodules contain lipid and bile.

4. Multifocal, random and red - can mask a process causing white foci.

a. Puppy liver withhemorrhage masking necrosis - herpes viral septicemia.

5. Multifocal, well demarcated but random red depressed foci - depressed suggests necrosis; we see the lighter red color over the liver color because of hepatic necrosis or dilation of sinusoids with pooling of blood similar to pigs with Vit E/Se deficiency. Telangiectasis in cats and cattle, dogs with hepatic HSA.

a. Dogwith metatastic HSA in liver.

6. Diffuse pale liver usually means lipidosis. Systemic metabolic disorders usually cause diffuse lipidosis.

a. Cat with hepatic lipidosis

b. Cat with hepatic lipidosis and necrosis with hemorrhage. The depressed red foci = something taken away i.e. necrosis with pooling of blood.

7. Symmetry or organization to the lesion...