Veterinary Pathology

The clinical signs, gross and microscopic appearance, treatment, and follow-up results of 35 dogs with primary ocular melanomas are reviewed. The melanomas are classified as epibulbar or intraocular based on the site of origin. The intraocular tumors are classified as spindle A, spindle B, mixed spindle B and epithelioid, and purely epithelioid based on cytologic criteria. The pathologic findings are matched with the follow-up history in an attempt to determine which features have prognostic significance. The findings are contrasted to those of similar studies of spontaneous ocular melanomas in man.

Pheochromocytomas and ultimobranchial (C-cell) neoplasms were diagnosed at a high frequency in a family of Guernsey bulls. The incidence supported the hypothesis of autosomal dominant inheritance of the neoplasms. These two neoplasms also occur in man as multiple endocrine adenomatosis type 2, which has autosomal dominant inheritance.

Eighteen (3.9%) ovarian hemangiomas were diagnosed in a survey of reproductive disorders in 460 sows from two to eight years of age during a three-year study. Ovarian hemangiomas only were observed in sows aged over 30 months, and no such neoplasms were found in 42 gilts. The incidence of ovarian hemangioma was highest at five to eight years of age. Of the 18 sows with ovarian hemangioma, one was purebred and 17 were crossbred pigs; of these, twelve had farrowed 12 to 15 litters, four had farrowed six lo 11 litters and two had farrowed three litters. All 18 sows with ovarian hemangioma had one or more clinical signs related to reproductive disorders including small litter size, agalactia, fertilization failure, fetal death, silent estrus, anestrus, abortion, and stillbirth. The pathological features of the neoplasms in sows were similar to those described previously in swine and in man. Spontaneous ovarian hemangioma might provide a model for investigation of the etiology and pathogenesis of ovarian hemangioma in man.

The incidence of peliosis hepais-like lesions in two-year-old Charles River-CD Sprague-Dawley rats (Charles River Breeding laboratories, Wilmington, MA) was almost twice as high in males as females. Blood lakes developed from progressive expansion of sinusoids with destruction of the hepatic cell cords. The endothelial processes of the blood lakes had edematous swelling, vesiculation, and denudation. The microvilli of hepatocytes became swollen, blunted, and sloughed where the endothelial processes were disrupted. Subsequently, the hepatocytes were exposed directly to circulating blood cells and had degenerative changes with accumulation of red blood cells in the cytoplasm.

The membrane-bound cysts were observed with the blood lakes and were bounded with atrophic hepatocytes or membranous wall extending to the Disse's space of adjacent hepatocytes. The cysts were filled with proteinaccous fluid, fibrin, and a few red blood cells. The wall of membrane-bound cysts consisted of endothelial processes extending from the endothelial cells of adjacent hepatocytes. The wall appeared to develop from adhesion of endothelial processes surrounding sinusoidal spaces of the hepatocytes following lysis of atrophic hepatocytes.

Immune-mediated hemolytic anemia was diagnosed in two horses on the basis of regenerative anemia, increased erythrocyte fragility in hypotonic saline, auloagglutination, and a positive direct antiglobulin (Coomb's) test. During steroid therapy partial resolution of the anemia was indicated by rising packed cell volume, macrocytosis, and bone marrow erythroid hyperplasia. Using erythrocyte volume distribution histograms (erythrograms), the regenerative response was characterized by analysis of macrocytic and normocytic erythrocyte subpopulations. In both horses, a gradual net increase of about 2 × 10⁶ macrocytes/μl occurred over a four- to five-week period. Over the same interval there was a gradual decrease in the number of normocytes. We suggest that the macrocytes remained large through this period rather than contributing to normocyte population growth. Erythrograms may provide an additional means of evaluating erythrocyte regeneration in horses.

A mononuclear cell leukemia in Sprague-Dawley rats is described in which liver, spleen, and lung involvement was a constant feature. The cell was 16 to 25 μm in diameter with round, oval or indented nucleus, and the cytoplasm contained bright red granules. This is the first report of such a leukemia in Sprague-Dawley rats and a comparison with mononuclear cell leukemia in other strains of laboratory rats is made.

Six foals were inoculated intrabronchially with a suspension of Corynebacterium equi. Six weeks before this challenge, three foals were vaccinated with a C. equi bacterin. Three foals were unvaccinated controls. All foals developed a severe bronchopneumonia in the inoculated lung, indicating that vaccination was not protective. Three foals (two vaccinated, one control) were killed eight to nine days after infection. One control died on day 9 with lesions of disseminated intravascular coagulation. The remaining two foals (one vaccinated, one control) were killed on day 17. C. equi was cultured in large numbers from affected lung and bronchial lymph nodes, and in smaller numbers from unaffected lung. spleen, and liver in all foals. In the 8- to 9-day-old lung lesions, the alveoli were filled with macrophages, neutrophils, and multinucleate giant cells and most contained numerous C. equi. The few foci of alveolar necrosis were associated with groups of bacteria-laden macrophages undergoing degeneration. In the lesions of 17-day duration. there was extensive parenchymal destruction with little fibrous tissue reaction. Lesions common to both groups included hyperplastic bronchiolitis, pulmonary edema, and perivascular lymphocytic cuffs and a pyogranulomatous lymphadenitis in bronchial nodes. One vaccinated foal had a microscopic pyogranulomatous colitis. The lesions in the experimentally infected foals are compared with those in naturally infected foals and discussed in terms of likely pathogenetic mechanisms involved in C. equi pneumonia in foals.

The intragastric inoculation of a suspension of Corynebacterium equi on five consecutive days induced severe ulcerative colitis, typhilitis, and lymphadenitis of colonic and cecal nodes in two ponies necropsied three weeks after infection. No gross lesions were observed in two ponies necropsied ten days after infection. A single inoculum of equivalent size failed to induce gross lesions in four ponies killed at ten or 20 days after infection. Microscopic lesions consistent with early C. equi infection of Peyer's patches were seen in two of the ponies killed ten days after infection. Only one small pulmonary abscess occurred in one foal, suggesting that intestinal lesions are not likely the usual precursor of pulmonary disease in naturally infected foals. The gross and microscopic lesions in the experimentally infected ponies were typical of the intestinal form of naturally occurring C. equi associated disease in foals.

Non-culturable acid-fast bacteria from two spontaneous cases of so-called feline leprosy were transmitted to rats and cats and further passaged in rats or cats. Two to six months after infection, cats developed cutaneous lesions that were indistinguishable from spontaneous cases, including the occurrence of nasal granulomata in one cat. When injected into rats, the mycobacteria caused a generalized mycobacteriosis and the granulomatous reaction was composed chiefly of macrophages without polymorphonuclear granulocytes. Infection of cats with Mycobacterium lepraemurium did not produce any lesions. The feline disease may be a suitable model for the study of human leprosy (Hansen's Disease).

Intraarticular inoculation of Mycoplasma bovis into the joints of six-week-old calves caused severe arthritis in five inoculates and mild arthritis in a sixth. Intraarticular inoculation of killed M. bovis did not cause arthritis.

Arthritic calves had fever, joint swelling, lameness, neutrophilia, and intercurrent pneumonia from which M. bovis could not be recovered.

Gross lesions were massive fibrinosuppurative synovitis and tenosynovitis, erosion of cartilage, and its replacement by polypoid granulation tissue. Histologic lesions were extensive ulceration of synovial membranes, leukocytic infiltration of the suhsynovium, congestion, hyperemia, and thrombosis of the subsynovial vessels. Cartilage erosion was accompanied by chronic osteomyelitis and formation of pannus tissue.

The presence of thrombi and platelet aggregates suggests that the inflammatory process in the synovium may arise from the interaction of M. bovis with the vasculature and the coagulation process of the host.