AFIP Wednesday Slide Conference - No. 21
Febuary 23, 2000

Conference Moderator:
Dr. Peter C. Kennedy, Diplomate, ACVP
University of California at Davis
College of Veterinary Medicine
Davis, California 95616
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Case I - 17145-99 (AFIP 2687067)
Signalment: Canine, schnauzer, female, twelve-year-old.
History: This dog presented with a markedly distended abdomen. A laparotomy was performed. The abdomen was filled with clear amber fluid. The right ovary was enlarged and measured approximately 3.5 - 4 cm in diameter and an ovariohysterectomy was performed. A section of the ovary was submitted for histopathologic examination. Six months following surgical removal, the dog remains clinically normal.
Contributor's Diagnosis and Comments: Ovarian sex-cord stromal cell tumor (luteoma)
These sections of ovarian mass contain dense sheets and nests of round to polyhedral cells with abundant, finely vesiculated eosinophilic cytoplasm. There are broad bands of fibrovascular stroma which separate areas of the mass. In some areas, the mass is disrupted by hemorrhage and edema. Some sections contain a reactive layer of mesothelial cells which are arranged in small papillary projections from the serosal surface. Remnants of normal ovary are present in some sections.
Sex-cord stromal cell tumors, in order of decreasing frequency, are granulosa cell tumor, thecoma, and luteoma. Three distinguishing types of granulosa cell tumors are those that contain Call-Exner bodies, cells which are tall and palisade along basement membranes (Sertoli cell-like), and those which are arranged in a poorly differentiated sarcomatous pattern. Thecoma is a rare tumor found in cows and consists of spindle or star-shaped cells. Luteomas are rare tumors in domestic animals and are generally considered to be benign. Origin of luteal cells in the ovary is theca interna and stratum granulosum.
AFIP Diagnosis: Ovarian interstitial cell tumor (luteoma), schnauzer, canine.
Conference Note: Ovarian tumors are uncommon in all domestic species. There are three categories of primary ovarian tumors: epithelial (papillary adenoma and cystadenoma, papillary adenocarcinoma, and rete adenoma), germ cell (dysgerminoma, teratoma, and embryonal carcinoma) and sex-cord stromal (granulosa cell tumor, thecoma, and interstitial cell tumor (luteoma, lipid cell tumor, steroid cell tumor)).
Sex cord-stromal tumors (most often granulosa cell tumors) are most common in the mare, cow and bitch. They are the most frequent primary ovarian tumor in all domestic animal species, with the possible exception of the dog, which have about equal occurrence of sex cord-stromal tumors and papillary cystadenocarcinomas. In mares, about 80% of ovarian tumors are sex cord-stromal tumors, specifically granulosa cell tumors. Sex cord-stromal tumors are usually unilateral and benign. Although they may occur in young animals, the incidence increases with age. Malignant sex cord-stromal tumors occur most often in cats, less often in dogs and cattle, and rarely in horses. Sex cord-stromal tumors have also been reported in rats, mice, rhesus and squirrel monkeys, domestic fowl, ferrets and pet birds. Sex cord-stromal tumors account for approximately 5% of ovarian neoplasms in humans, with approximately two-thirds occurring in postmenopausal women.
The cell of origin of interstitial cell tumors has not been clearly identified, and may vary between species and between tumors within a species. The most distinctive histomorphological feature is the abundant eosinophilic cytoplasm that contains numerous lipid-type steroid vacuoles. Most of the reported interstitial cell tumors have been hormonally active. Hyperadrenocorticism has been associated with interstitial cell tumors in humans and in one dog.
Contributor: Veterinary Diagnostic Center, Fair Street and East Campus Loop, Lincoln, NE, 68583-0907
1. Jones TC, Hunt RD, King NW: Veterinary Pathology, 6th ed., pp. 1159-1162. Williams & Wilkins, Philadelphia, PA, 1997
2. Kennedy PC, Cullen JM, Edwards JF, Goldschmidt MH, Larsen S, Munson L, Nielsen S: Histological Classification of the Tumors of the Genital System of Domestic Animals. In: World Health Organization, Histological Classification to Tumors of Domestic Animals, ed. Schulman FY, 2nd ed., vol. 4, pp. 24-28. The Armed Forces Institute of Pathology, Washington, DC, 1998
3. Nielsen SW, Kennedy PC: Tumors of the Genital Systems. In: Tumors in Domestic Animals, ed. Moulton JE, 3rd ed., pp. 503-507, University of California Press, 1990
4. Yamini B, VanDenBrink PL, Refsal KR: Ovarian steroid cell tumor resembling luteoma associated with hyperadrenocorticism (Cushing's disease) in a dog. Vet Pathol 34:57-60, 1997
Case II - NADC BK13 (AFIP 2679736)
Signalment: 20-year-old, Morgan-cross quarter horse, gelding, equine.
History: The horse was donated to the Oregon State University's Veterinary Teaching Hospital, Corvallis, OR. Upon presentation, the gelding was in poor body condition and demonstrated severe hind leg ataxia. Body temperature, heart and respiration rates were within normal limits. A clinical diagnosis of equine protozoal myeloencephalitis (EPM) was made. The gelding was injected intramuscularly with 0.2mg/kg dexamethasone s.i.d. for 12 days prior to euthanasia in an attempt to increase the parasite burden.
Gross Pathology: No grossly evident lesions were present.
Laboratory results: Cerebrospinal fluid was positive for Sarcocystis neurona antibodies by western blot examinations as described by Granstrom et al. (J Vet Diagn Invest 1993. 5:88-90)
Contributor's Diagnosis and Comments: Spinal cord (thoracic): Myelitis, lymphohistiocytic, mild, multifocal with protozoan parasites.
Etiology: Neospora caninum
Histologic lesions attributed to protozoal infection were confined to the cerebrum and thoracic spinal cord. The cerebral lesions consisted of multifocal, perivascular, variably-sized granulomas composed of large numbers of epithelioid macrophages containing few protozoa. In the thoracic spinal cord (submitted tissue), there are multifocal areas in the ventral and lateral peripheral white matter with mild to moderate infiltrates of macrophages and fewer lymphocytes around small blood vessels. Variably-sized, non-encysted groups (5 to 50 mm in diameter) of protozoa are often present adjacent to inflammatory foci. The degree of inflammation and numbers of protozoa vary between sections. In some sections containing few groups of protozoa, there is little or no evidence of inflammation.
The protozoa stained by immunohistochemistry with both polyclonal and monoclonal antibodies to Neospora caninum, but not with antibodies to Sarcocystis neurona or Toxoplasma gondii. In addition, ultrastructural features consistent with N. caninum including electron-dense rhoptries were observed. However, a recent report (Marsh et al. 1998) describing a new Neospora species isolated from a horse spinal cord indicates that without close examination of differences in immunoreactive proteins and nucleotides comprising the internal transcribed spacer I region, N. caninum and N. hughesi cannot be distinguished.
It is uncertain at present whether N. caninum or N. hughesi are frequent causative agents of EPM. In the majority of cases of EPM, S. neurona is presumed to be the causative agent. In the present case, the CSF of the horse was positive for S. neurona antibodies by western blot. The etiologic diagnosis was based on the demonstration of Neospora in tissues, as the presence of specific antibodies does not necessarily indicate active disease.
Unusual features in this case, ascribed to the corticosteroid administration, include minimal inflammation, large numbers of intralesional tachyzoites, lack of tissue cysts, and lesions confined to peripheral areas suggesting intrathecal spread of the infection.
AFIP Diagnosis: Spinal cord: Myelitis, nonsuppurative, submeningeal, multifocal, mild to moderate, with multifocal axonal degeneration, myelin sheath swelling, mild meningitis, and protozoal tachyzoites.
Conference Note: Neospora caninum (Phylum Apicomplexa, Family Sarcocystidae) is a protozoan that infects wild and domestic canids (definitive hosts), and ruminants and horses (intermediate hosts). Although Neospora has only recently been associated with equine protozoal myeloencephalitis, it has been proposed as a possibly significant cause of EPM previously misdiagnosed as Sarcocystis neurona. As demonstrated in this case, positive cerebrospinal fluid titers for S. neurona do not confirm active infection. Ultrastructurally, Neospora sp. has many electron-dense rhoptries and may be found within a parasitophorous vacuole. Merozoites of Sarcocystis sp. lack rhoptries and meronts are directly in the host cell cytoplasm. Toxoplasma gondii has few, variably electron-dense rhoptries and is found within a parasitophorous vacuole. Immunohistochemistry, PCR, and/or electron microscopy are necessary for definitive diagnosis.
Contributor: USDA, ARS, National Animal Disease Center, 2300 Dayton Avenue, P0 Box 70, Ames, IA 50010
1. Granstrom DE, Dubey JP, Davis SW, Fayer R, Fox JC, Poonacha KB, Giles RC, Corner PF: Equine protozoal myeloencephalitis: antigen analysis of cultured Sarcocystis neurona merozoites. Vet Diagn Invest 5:88-90, 1993
2. Hamir AN, Tornquist SJ, Gerros TC, Topper MJ, Dubey JP: Neospora caninum-associated equine protozoal myeloencephalitis. Vet Parasitol 79:269-274, 1998
3. Marsh AE, Barr BC, Packham AE, Conrad PA: Description of a new Neospora species (Protozoa: Apicomplexa: Sarcocystidae). J Parasitol 84(5):983-991, 1998
4. McAllister MM, Dubey JP, Lindsay DS, Jolley WR, Wills RA, McGuire AM: Dogs are definitive hosts of Neospora caninum (Rapid Communication). Int J Parasitol 28:1473-1478, 1998
Case III - 97-1130 (AFIP 2595291)
Signalment: 8.5 month gestation crossbred Angus fetus.
History: This bovine fetus was 1 of 2 fetuses that were found dead the same day from a group of heifers in a university herd. Vaccinations against the major abortigenic agents of cattle were current, and husbandry was described as good to excellent. Placenta was presented with the fetus.
Gross Pathology: The animal examined was an approximately 30 kg fetal calf. Necropsy yielded minimal to mild autolysis of the fetus. There were no gross lesions in the fetus or placenta. The lungs were inflated, consistent with the delivery of a live calf.
Laboratory Results:
Bacteriological and mycological procedures yielded only bacterial contaminants from cultures of the placenta, liver, and lung. Virus isolation techniques, performed on spleen, kidney, liver, and lung were negative for all viral agents. Fluorescent antibody techniques were negative for the IBR and BVD viruses and negative for Leptospira species.
Histopathology was performed on 6 mm sections of multiple tissues. In sections of placenta, there was acute to subacute necrotizing placentitis. Necrotic debris at the chorionic villi was admixed with intact and degenerate neutrophils and extracellular protozoal tissue cysts. The cysts were ovoid, measuring 100 x 150 mm, with cyst walls less than 1 mm in thickness. These tissue cysts contained 20-50 basophilic, pyriform to spindled merozoites that were 2-3 mm long. Occasional merozoites formed rosettes that appeared to be within the vascular endothelium. There was focally extensive necrosis of trophoblastic epithelium, most prominent at the tips of the chorionic villi. In the subtrophoblastic stroma, there were small numbers of disseminated neutrophils and mononuclear cells, with multifocal protozoal cysts that were usually located within the cytoplasm of rounded and markedly hypertrophic endothelial cells of the placental stromal blood vessels. There was multifocal necrotizing vasculitis within occasional affected vessels. Endothelial cells were pyknotic and were admixed with neutrophils, cellular debris, and occasional protozoal cysts.
Sections from various other tissues examined included brain, skeletal muscle, myocardium, thymus, liver, lung, and kidney. Protozoal cysts, similar to those located within the placenta, were also located in small to large numbers within arterial and capillary endothelial cells of all organs examined. Focal zones of necrosis were associated with the protozoal cysts in the affected organs.
Contributor's Diagnoses and Comments:
1. Placenta: Placentitis, moderate, multifocal, acute to subacute, necrotizing, with intraendothelial and extracellular protozoal meronts, etiology most consistent with Sarcocystis cruzi (syn., Sarcocystis bovicanis) or other Sarcocystis sp.
2. Placenta; blood vessels: Vasculitis, moderate, multifocal, acute to subacute, necrotizing, with intraendothelial protozoal meronts.
Sarcocystis species are two-host protozoal coccidian parasites of the Phylum Apicomplexa that are considered to be host-specific. The group is characterized by the presence of resistant spore stages and by the production of sexual and asexual stages of the life cycle. Sarcocystis species are frequently named after the intermediate and definitive hosts (eg-S. bovicanis). Numerous species of Sarcocystis have been identified, and most vertebrates appear to be either intermediate hosts or definitive hosts or both for several of these agents. As a general rule, the intermediate hosts are herbivores, with carnivores being the definitive hosts.
The life cycles of many species have been defined. In the case of S. cruzi, oocysts sporulate in the intestine of the dog to form sporocysts that pass with the feces into the external environment. The sporocysts are ingested by cattle and excyst as sporozoites in the intestine. From the bovine intestinal lumen, the sporozoites migrate to arterial vessels and develop into first generation meronts in the endothelial cells. Mature first generation merozoites from the meronts emerge and develop into secondary meronts within capillary endothelial cells. The liberated second generation merozoites emerge and enter mononuclear cells. These merozoites leave the circulation to enter the myofibers of myocardium or skeletal muscle or occasionally neurons to form immature sarcocysts that are not yet infective. The sarcocysts form metrozoites that multiply and eventually develop into bradyzoites, which are the intramuscular stages infectious to carnivores. The life cycle is continued by ingestion of the infected muscle tissue by the definitive carnivore host. Digestion of the sarcocysts in the intestine of the dog liberates tachyzoites that invade the intestinal epithelium and develop directly into macro- and microgametocytes. Gametogony (fertilization) then results in the formation of unsporulated oocysts that sporulate and are then released to the environment as sporocysts.
Although mature sarcocysts that contain bradyzoites are extremely common in the skeletal and myocardial myofibers of cattle, the organisms are seldom identified in the tissues of aborted bovine fetuses in any of the tissue forms. When they occur in the fetus or term calf, the lesions consist of acute to subacute inflammation of brain, hepatic, renal, and other tissues. The large number of tissue cysts that were seen in the placenta and other tissues of this case was considered highly unusual. Diagnosticians at Kansas State University considered that the dam in this case could have been either immunologically naive to Sarcocystis at the time of infection, or may have been immune-compromised by weather, shipping, or the stress of late pregnancy. A detailed history of this individual heifer was unavailable.
The production of occasional rosettes by merozoites in the immature meronts seen in these placental tissues was considered diagnostic for Sarcocystis species. The life cycle of Sarcocystis species is 90 or more days. If immature sarcocysts are present in the intermediate host myofibers, it is assumed that the infection is of a duration of 60 days or longer. As mature sarcocysts were not identified in the fetal or placental tissues of this case, it was assumed that the infection of the dam had occurred less than 60 days previously. Most abortions due to S. cruzi in cattle occur late in gestation, and the calves often live for a short time after parturition, as in this case.
Other protozoal agents that should be considered in the differential diagnosis in late gestation bovine abortions include Neospora sp. and Toxoplasma. Although extremely common as an infectious cause of bovine abortion, Neospora sp. tissue cysts have been reported only in the brain of aborted fetuses, with tachyzoites located in myocardial and skeletal muscle, liver, and brain. Toxoplasma are not thought to be associated with naturally occurring abortions in cattle, but are common agents of abortions in sheep and lesions are usually more necrotizing than Sarcocystis sp. infections.
Further diagnostic tests that could be considered in cases of protozoal abortions would include immunohistochemical testing to identify zoites or tissue cysts of Sarcocystis sp., Toxoplasma, and Neospora sp. Additionally, electron microscopy may be used to differentiate these morphologically similar organisms. Paired serological testing of the serum of the dam has been used to diagnose S. cruzi abortions. Fetal serology for Sarcocystis sp. is unrewarding.
AFIP Diagnosis: Placenta: Placentitis, necrotizing, subacute, diffuse, moderate, with necrotizing vasculitis, and numerous protozoa, etiology consistent with Sarcocystis sp., Angus cross-bred fetus, bovine.
Conference Note: The contributor has provided an excellent summary of this entity.
Contributor: Veterinary Diagnostic Laboratory, Kansas State University, 1800 Denison Avenue, Manhattan, KS 66506-5601
1. Anderson ML, Barr BC, Conrad PA: Protozoal causes of reproductive failure in domestic ruminants. Vet Clin NA: Food Ani Pract 10:449-451, 1994
2. Gardiner CH, Fayer R, Dubey JP: An Atlas of Protozoan Parasites in Animal Tissues. 2nd ed., pp. 41-46, Armed Forces Institute of Pathology, Washington, DC, 1998
3. Kennedy PC, Miller RB: The female genital system. In: Pathology of Domestic Animals, ed. Jubb KVF, Kennedy PC, Palmer N, 4th ed., vol.3, pp. 425-426. Academic Press, San Diego, CA, 1993
4. Stalheim OH: Bovine abortion caused by Sarcocystis. In: Laboratory diagnosis of livestock abortion, ed. Kirkbride CA, 3rd ed., pp. 153-155. Iowa State University Press, Ames, IA, 1990
5. Wouda W, Moen AR, Visser IJR: Bovine fetal neosporosis: a comparison of epizootic and sporadic abortion cases and different age classes with regard to lesion severity and immunohistochemical identification of organisms in brain, heart, and liver. J Vet Diagn Invest 9:180-185, 1997
Case IV - Y-5363 (AFIP 2688416)
Signalment: 13-year-old, female, domestic longhair feline, Felis catus
History: An ovariohysterectomy was performed on the cat for treatment of pyometra. The uterus and ovaries were submitted for histopathology. No additional history was provided.
Case 21-4. Uterus. Extending from the uterine mucosa into the lumen is a multicystic white-tan mass.
Gross Pathology: The formalin-fixed uterus was moderately distended and filled with opaque brown fluid. The uterine horns contained six broad-based to pedunculated endometrial nodules ranging from 0.5 cm to 2 cm in diameter (gross photo of cross-sectioned, formalin-fixed uterus). Nodules were located throughout the uterine horns from near the uterine bifurcation (section on the right) to the tips of the horns (section on the left).
Contributor's Diagnosis and Comments: Cystic endometrial hyperplasia with hyperplastic endometrial polyps, chronic suppurative endometritis, and pyometra with Gram-negative bacilli.
Microscopically, the uterus is characterized by diffuse cystic endometrial hyperplasia with multifocal pedunculated masses of cystic endometrial glands supported by well-vascularized connective tissue stroma. The stroma varies from loose and edematous to dense and collagenous; in some of the masses, smooth muscle is a prominent component of the stroma. The endometrial lamina propria contains numerous plasma cells, lymphocytes, neutrophils, and focal accumulations of hemosiderin-laden macrophages. Purulent exudate in the endometrial glands and lumen of the uterus contains numerous Gram-negative bacilli. Both ovaries from this cat contained multiple follicles and no corpora lutea.
Among domestic species, endometrial hyperplasia (EH) may occur following prolonged estrogen or progesterone influence on the endometrium. Unlike EH in women, EH in domestic animals is not considered a precancerous lesion. Two main events influence the development of endometrial hyperplasia (EH) in dogs and cats. First, the endometrial epithelium is stimulated by estrogen, to produce receptors for progesterone. Second, progesterone from corpora lutea (CL) stimulates growth of endometrial epithelium. Cats are induced-ovulators, but CL in queens may also occur spontaneously. In dogs and cats, hyperplastic endometrial polyps are thought to arise from focal areas of cystic EH. In one study, EH in cats was commonly found in queens 5 years-of-age and older and was not associated with CL; therefore, EH in cats may be due to prolonged estrogenic stimulation. In this same study, there was a positive correlation between endometritis/pyometra and CL. In general, only half of queens with pyometra at surgery or death have CL, and the relationship between EH and pyometra in cats is unclear.
AFIP Diagnosis: Uterus: Cystic endometrial hyperplasia with endometrial polyp and chronic suppurative endometritis.
Conference Note: Cystic endometrial hyperplasia (CEH) in the bitch is associated with increased progesterone from retained corpora lutea following estrogen priming of the endometrium. In women, cows, mares, and ewes, endometrial hyperplasia is associated only with estrogen stimulation, due to cystic follicles, estrogenic plants, or granulosa cell tumors. Investigations of uterine disease in cats by Potter et al, found that retained CL were associated with pyometra and endometritis, but not with endometrial hyperplasia, suggesting that progesterone is not required in the pathogenesis of feline CEH. In a recent study by Perez et al that compared feral cats to colony-reared cats, feral cats had 3 times more ovarian interstitial cells, lower serum estradiol levels and zero incidence of CEH, while domestic cats had an 88% incidence of CEH in cats over 5 years of age and 30% incidence in 2-4 year-old cats. In the cat, ovarian interstitial cells have a histologic appearance that suggests steroid production, and are believed to arise from the theca interna of atretic follicles, but what steroids they secrete remains to be determined. The pathogenesis of feline CEH may be multifactorial and requires further study.
Contributor: Diagnostic Laboratory Service, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS 39762
1. Gelberg HB, McEntee K: Hyperplastic endometrial polyps in the dog and cat. Vet Pathol 21:570-573, 1984
2. Kennedy PC, Miller RB: The female genital system. In: Pathology of Domestic Animals, eds. Jubb KVF, Kennedy PC, Palmer N, 4th ed., Vol. 3, pp. 349-470. Academic Press, Inc., San Diego, CA, 1993
3. Lawler DF, Evans RH, Reimers TJ, Colby ED, Monti KL: Histopathologic features, environmental factors, and serum estrogen, progesterone, and prolactin values associated with ovarian phase and inflammatory uterine disease in cats. Am J Vet Res 52:1747-1753, 1991
4. Perez JF, Conley AJ, Dieter JA, Sanz-Ortega J, Lasley BL: Studies on the origin of ovarian interstitial tissue and the incidence of endometrial hyperplasia in domestic and feral cats. Gen and Comp Endocrin 116:10-20, 1999
5. Potter K, Hancock DH, Gallina AM: Clinical and pathologic features of endometrial hyperplasia, pyometra, and endometritis in cat: 79 cases (1980 1985). J Am Vet Med Assoc 198:1427-1431, 1991
J Scot Estep, DVM
Captain, United States Army
Registry of Veterinary Pathology*
Department of Veterinary Pathology
Armed Forces Institute of Pathology
(202)782-2615; DSN: 662-2615
* The American Veterinary Medical Association and the American College of Veterinary Pathologists are co-sponsors of the Registry of Veterinary Pathology. The C.L. Davis Foundation also provides substantial support for the Registry.
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