AFIP Wednesday Slide Conference - No. 9

28 October 1998
Conference Moderator:
Dr. Keith Harris, Diplomate, ACVP
Product Safety Assessment, Searle
4901 Searle Parkway
Skokie, IL 60077

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Case I - B98-2010 (AFIP 2639018)
Signalment: Adult female B6C3F1 mouse.

History: This mouse was given an intraperitoneal injection with an experimental material and then necropsied 24 hours later.
Gross Pathology: Gross postmortem examination revealed wet, edematous lungs.
Laboratory Results: None.
Contributor's Diagnosis and Comments: Severe acute diffuse bronchiolar necrosis. Etiology: Naphthalene toxicity.
Several toxic agents are known to induce the selective necrosis of Clara cells in rodents. These include 4-ipomeanol, 3-methylindole, and naphthalene (as in this case). Since Clara cells are known to have a high content of cytochrome P-450 enzymes, they are more susceptible to toxicant-induced injury than adjacent ciliated bronchiolar epithelial cells. Mice have a high density of Clara cells in the lower airways and are more sensitive to Clara cell toxicants than rats or hamsters. Note that the lesion in this instance tends to be confined to the lower airways. The dose of naphthalene used in this experiment was 200 mg/kg.
Recently, coumarin (a natural product utilized in the perfume industry as a fragrance enhancer) has been shown to produce selective Clara cell toxicity in the mouse lung. This material has long been recognized as a potent hepatoxicant in rats, but the pulmonary toxicity is just beginning to be understood. The pulmonary toxicity of coumarin may relate to the induction of pulmonary neoplasms as found in the mouse two year bioassay. However, the mechanism for this remains to be determined.
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Case 9-1 . Lung. There are abundant detached and pyknotic epithelial cells and neutrophils within small and medium caliber bronchioles.
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Case 9-1 . Lung. Larger bronchioles retain intact ciliated bronchiolar epithelial cells but scattered foci have bronchiolar epithelial cells with vacuolation, hypereosinophilia, pyknosis, loss of cilia, and detachment (degeneration & necrosis).
AFIP Diagnosis: Lung, bronchiolar epithelium: Degeneration and necrosis, acute, diffuse, B6C3F1 mouse, rodent.
Conference Note: The respiratory system is a major primary target for several classes of toxic compounds including furans, chlorinated hydrocarbons, aromatic hydrocarbons, pyrolizidine alkaloids, paraquat, 3-methylindole, and a host of other chemicals. The lung is exposed to potentially toxic substances both aerogenously and hematogenously (as the lung receives the entire cardiac output from the right ventricle). The primary pulmonary lesion resulting from intoxication with many of these substances, including naphthalene, is bronchiolar epithelial necrosis due to injury of the nonciliated Clara cell population. As noted by the contributor, the Clara cell is a primary target for many toxic substances due to its high content of P-450 isoenzymes; this system metabolically activates many organic compounds resulting in the formation of toxic metabolites.
There are definite species specific and dose-dependent differences in the sensitivity of Clara cells to naphthalene toxicity in the bronchiolar epithelium of the lung and in the olfactory epithelium of the nasal cavity among mice, rats, and hamsters. The species least sensitive to naphthalene-induced Clara cell injury in the lung, the rat, is most sensitive to injury in the nasal cavity. The mouse is most sensitive to pulmonary injury with very low doses of naphthalene, but nasal injury occurs at twice the dose which produces injury in the rat. The hamster is more sensitive than the rat to pulmonary injury, but is less sensitive to nasal injury.
The high degree of anatomical, species, and dose variability in naphthalene metabolism and injury is probably due to the distribution of the various P-450 isoenzymes. The initial and obligate step in naphthalene metabolism is the formation of epoxides and quinones. Studies in mice indicate that one of these metabolites, 1,2-epoxide, is the most toxic metabolite and plays an important role in the cytotoxic actions of naphthalene. The presence of a specific P-450 isoenzyme within Clara cells, Cyp 2F2, is a key factor in determining the rates and stereoselectivity of naphthalene epoxidation. This enzyme is present in mouse but not hamster or rat Clara cells, and may explain the sensitivity of the mouse to naphthalene. This differential susceptibility in Clara cell injury does not occur with most of the organic xenobiotic cytotoxicants. While dose-dependent and species specific differences occur with toxic organic agents, a wide variety of compounds injure bronchiolar Clara cells over a wide range of species.
Contributor: The Procter & Gamble Company, Miami Valley Laboratories, P.O. Box 398707, Cincinnati, OH 45239-8707.
1. Born SL, et al.: Selective Clara cell injury in mouse lung following acute administration of coumarin. Tox Appl Pharmacol, 1998 (in press).
2. Cho M, et al.: Biochemical factors important in Clara cell selective toxicity in the lung. Drug Metabol Rev 27:369-386, 1995.
3. Widdecombe JG, Pack RJ: The Clara cell. Eur J Respir Dis 63:202-220, 1982.
4. Plopper CG, et al.: Relationship of cytochrome P-450 activity to Clara cell cytotoxicity. Histopathologic comparison of the respiratory tract of mice, rats, and hamsters after parenteral administration of naphthalene. J Pharmacol Exp Ther 261:353-363, 1992.
5. Van Winkle LS, et al.: Cellular response in naphthalene-induced Clara cell injury and bronchiolar epithelial repair in mice. Am J Physiol 269:800-818, 1995.
Case II - TAMU1998-1 (AFIP 2641896)

Signalment: Six-year-old, quarter horse stallion.
History: This horse was colicky seven days prior to presentation in the fall. The colic resolved; however, the horse became progressively more lethargic. The owner reported the horse was not urinating. The horse went down in the trailer during transport to the hospital and had to be anesthetized for removal from the trailer and admission to the hospital. The bladder was catheterized and clear urine with dark clots of material presumed to be blood was observed. The animal died under anesthesia.
Gross Pathology: The tongue had bilateral, nearly symmetric ulceration of the ventral tip. The glandular stomach mucosa had numerous, 2-7 mm ulcerations, and two liters of a "coffee ground-like" gastric content were observed in the stomach. Segments of the jejunal mucosa were eroded and reddened. The kidneys protruded prominently into the abdomen, were enlarged 1½ times normal size, and the surfaces bulged when incised. There was mild perirenal edema. Urine was golden brown and did not contain blood clots, in contrast to the catheterized urine sample.

Laboratory Results:
1. Blood Values: PCV: 51.5%; WBC: 39,600 (89% neutrophils); BUN: 220; Creatinine: 31.5; Calcium: 6; Phosphorous: 14.9; Potassium: 7.1; Sodium: 126; CPK: ++++; SGOT: ++++.
2. Catheterized urine: Specific gravity: 1.015; Protein: ++++; Blood: +++.
Contributor's Diagnosis and Comments: Acute tubular nephrosis with tubular epithelial necrosis, interstitial edema and casts of protein and blood.

Etiology: Oak toxicity.
The diagnosis of nephrosis was obvious at necropsy. The horse had been maintained in a box stall with a paddock without access to pasture. The severe tubular changes include both tubular cell necrosis and tubulorrhexis, so that toxins and ischemic acute tubular nephrosis had to be considered. There was no hemolytic anemia, and this horse had no access to pigweed or silver maple trees (unlike in other parts of the country where red maples cause disease, maple toxicity in Texas is caused by the silver maple). There was no history of aminoglycoside administration, and mercury levels were normal. Last year was a banner year for acorns, and many acorns fell into this horse's paddock from oaks overhead. Pieces of acorns were recovered from the stallion's feces.
Although hemoglobinuria is described in some cases of equine oak nephrosis, the mechanism is not understood, and its presence was perplexing in this case. It was hypothesized that the severe necrosis and disruption of the basement membrane and the interstitial inflammation present caused some hemorrhage. Enterocolitis was present in this horse histologically, and has been described in cases of oak toxicity of horses and cattle.
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Case 9-2 . Kidney. Proximal tubule epithelium (right center) is swollen and vacuolated with nuclear pyknosis (degeneration & necrosis). Some distal tubules contain homogenous light pink material (hyaline cast, lower right) and others are filled with hemoglobin casts (left). Some tubular lumens contain an admixture of pink protein, sloughed epithelial cells, and neutrophils. Occassional tubular epithelium has increased basophilia (hyperplasia). The interstitium is expanded by edema and contains low to moderate numbers of lymphocytes and macrophages.
AFIP Diagnosis: Kidney: Tubular degeneration and necrosis (nephrosis), diffuse, with hyaline, granular, and cellular casts, tubular ectasia, tubular regeneration, and diffuse congestion, quarter horse, equine.
Conference Note: Prominent histopathologic findings include degeneration and necrosis of tubular epithelium, sloughing of necrotic tubular epithelial cells, tubular ectasia, and infiltrates of neutrophils. In some tubules, erythrocytes and moderate amounts of a red, granular to globular material, interpreted as protein, are admixed with sloughed tubular epithelial cells. Within the interstitium, there are multifocal areas of hemorrhage and edema. Some tubules are lined by flattened to low cuboidal epithelial cells that have amphophilic to basophilic cytoplasm and large, reactive nuclei, interpreted as tubular regeneration by conference participants.
Oak (Quercus sp.) poisoning has been reported in many regions of the world, and occurs sporadically in individual animals or in minor herd epizootics. More than 60 species of oak have been identified in North America, and all are considered potentially toxic. Tannins and their metabolites are believed to be the toxic components. Their levels are highest in young leaves and the shells of green acorns. Poisoning occurs more commonly in cattle than horses; this may be related to the gastrointestinal anatomy in cattle, which allows ingestion of greater quantities of toxic material at one feeding. Disease outbreaks are often seasonal with bud and leaf poisoning noted in the spring and acorn poisoning prominent in autumn. Young buds are much more palatable than mature leaves, and the levels of tannins become reduced as leaves mature. Poisoning may also occur during periods of drought when normal herbage is not available and animals resort to other sources of food.
While the principal toxins in oak are believed to be the tannins and their metabolites, the exact mechanism of toxicity is incompletely understood. Numerous polyphenols are produced from the metabolism of tannins, the most important of which is probably digallic acid. Digallic acid is converted to gallic acid and pyrogallol, both of which are reducing agents and contribute to toxicosis. Pyrogallol is much more toxic and causes hemorrhagic gastroenteritis, hematuria, subcutaneous hemorrhage, and hemolysis. Tannic acid, pyrogallol, and gallic acid administered to rabbits via stomach tube produce disease similar to that seen in cattle experimentally fed Q. havardii .
Oak toxicity causes signs of alimentary and urinary disease in both cattle and horses. Gastrointestinal signs usually occur early in the course of toxicosis, and animals may be depressed and lethargic and present with anorexia, tenesmus, constipation, and colic. After a few days, constipation is often followed by diarrhea, and fragments of acorns may be present within stools. Urinary dysfunction usually follows intestinal signs, and may include polyuria/polydipsia, dyspnea due to hydrothorax, hemoglobinuria, oliguria, and dependent edema. Mortality rates are often high, with animals surviving acute disease eventually succumbing to progressive renal failure. Gastrointestinal lesions may occur subsequently to renal disease, and uremia and renal failure may have caused the necropsy findings in the stomach, jejunum, and tongue.
The most consistent clinicopathologic findings in oak toxicosis are related to renal disease. Grossly, the kidneys are enlarged, pale, have petechial hemorrhages, and the medulla is congested. There may be perirenal, mesenteric and dependent edema, and fluid accumulation in various body cavities. The most consistent histopathologic finding is renal tubular necrosis, and proximal convoluted tubules often contain proteinaceous casts. Adjacent tubules may be unaffected. The glomeruli are unaffected, and except for congestion, the medulla remains nearly normal. Common serum clinical chemistry findings reflect renal failure and include elevated blood urea nitrogen and creatinine, hypoproteinemia, hypoalbuminemia, hyponatremia, hypochloremia, hyperkalemia, hypocalcemia, and hyperphosphatemia.

Contributor: Department of Veterinary Pathobiology, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843-4467.
1. Anderson GA, et al.: Fatal acorn poisoning in a horse: Pathologic findings and diagnostic considerations. J Am Vet Med Assoc 182:1105-1110, 1983.
2. Duncan CS: Oak leaf poisoning in two horses. Cornell Vet 51:159-162, 1961.
3. Panciera RS: Oak poisoning in cattle. In: Effects of Poisonous Plants on Livestock, Keller RF ed., pp. 499-506, Academic Press, New York, 1978.
4. Schmitz DG: Toxic nephropathy in horses. Compend Cont Ed Pract Vet 10:104-111,1988.
5. Schuh JC, Ross C, Meschter C: Concurrent mercuric blister and dimethyl sulfoxide (DMSO) application as a cause of mercury toxicity in two horses. Eq Vet J 20:68-71, 1988.
6. Tennant B, Dill SG, Glickman LT, et al.: Acute hemolytic anemia, methemoglobinemia and Heinz body formation associated with ingestion of red maple leaves by horses. J Am Vet Med Assoc 179:143-150, 1981.
7. Jones TC, Hunt RD, King NW: Diseases due to extraneous poisons. In: Veterinary Pathology, 6th ed., pp. 704-705, Williams and Wilkins, 1997.
Case III - AP#1946 (AFIP 2420062)
Signalment: Two-year-old, male, New Zealand white rabbit.
History: This rabbit was used as a sperm donor for a reproductive study. Sperm was collected non-invasively with an artificial vagina. The rabbit had hematuria of one day's duration.
Gross Pathology: The right kidney measured 10 x 10 cm with three 1 cm nodules on surface. The bladder was filled with bloody urine. The kidney was hollow on cut section and filled with dark brown fluid. The inner surface of the kidney was necrotic, with approximately 1 cm of viable cortex. The left kidney was normal. No other gross lesions were present.
Case 9-3. Note marked enlargement of right kidney with locally extensive subcapsular hemorrhage and 3 one centimeter tan nodules near the capsular surface. In the cut section, there is diffuse effacement of the cortex by pale white tissue (tumor) and the medulla is hemorrhagic.
Laboratory Results: The results of special stains, lectin histochemistry, and immunohistochemistry are outlined below.
1. Special stains: An un-decalcified section was stained by Alizarin red and von Kossa methods to detect mineralization. With both staining methods, dystrophic calcification was only present within the necrotic debris. All other parts of the tumor were negative.
2. Lectin histochemistry: Ulex europeas agglutinin was heterogeneously positive with a random distribution of staining. Peanut agglutinin staining was spotty, but limited only to tumor cells. Dolichos biflorus and Ricinis communis agglutinins were negative in all areas.
3. Immunohistochemistry: Stains included neuron specific enolase, epithelial membrane antigen, keratins AE1 and AE3, pancytokeratin, vimentin, S-100 and desmin. Desmin, epithelial membrane antigen, and S-100 stains were negative within the tumor. Neuron specific enolase staining was moderately positive, occurring primarily within the center of tumor lobules. All three keratin antibodies demonstrated positive staining in neoplastic cells, with stronger staining in those cells adjacent to necrotic centers. The degree of staining was moderate with pancytokeratin, and minimal to moderate with AE1 and AE3. AE3 staining was slightly darker and more extensive than AE1. Vimentin distribution and degree of vimentin positivity were similar to that of pancytokeratin, except that the surrounding stroma was also moderately stained.
Contributor's Diagnosis and Comments: Carcinoma, renal, NZW rabbit.
Submitted is a section of a neoplastic mass from the right renal area of the affected rabbit. Within the tumor are large areas of coagulative necrosis, cellular debris (some of which is mineralized), and acicular spaces suggestive of cholesterol crystals. Tumor cells are arranged in lobules, sheets, nests and acini, and the cells are often associated with an eosinophilic hyaline matrix resembling osteoid. Round globules of richly eosinophilic material consistent with a secreted protein are present within some acini. The hyaline matrix, which is not anisotropic under polarized light, forms trabeculae next to and between tumor cells and is also present in larger, acellular areas. Islands of neoplastic cells are occasionally surrounded by an eosinophilic fibrillar stroma, which is anisotropic under polarized light. Cell shape varies from columnar, to low cuboidal, to spindled and stellate. The columnar and cuboidal cells appear to align along a basement membrane, while the spindled and stellate cells are more pleomorphic and less differentiated in appearance. Neoplastic cells are moderate in size, with a nuclear to cytoplasmic ratio of 1:3. All tumor nuclei are open-faced with an abundance of euchromatin. Nuclear shapes are round to oval for the columnar and cuboidal populations. In the spindled and stellate cells, nuclei are elongate or irregularly-shaped. The mitotic rate is low at less than 1 per high power field, and nucleoli are variably present, and generally single and small.
The incidence of spontaneous renal neoplasia in animals is quite low. Of pri-mary neoplasms, the percentages of those affecting the kidney are 60, 9.4, 2.3, 1.7 and 0.03, in the pig, horse, cow, dog and rat respectively1, 2. Carcinomas are the most common primary renal tumors of dogs, cattle, and sheep3. In mice, spontaneous renal neoplasms are quite rare except in the case of one inbred mouse strain. BALB/cf/CD strain mice have a 60-70 percent incidence of renal carcinoma4. In rats, nephroblastoma is the most common kidney tumor ob-served. Although spontaneous renal cell carcinomas are rare in rats, there is a high incidence of renal cell carcinomas in rats with the Eker mutation. Heterozygotes for the mutation develop multiple renal cell carcinomas by one year of age.
Renal neoplasms account for 3% of human adult malignancies. The incidence of human renal neoplasia is higher in males, with a ratio of 1.6:16. Human renal cell carcinomas commonly metastasize. The most com-mon metastatic sites are the lungs, bones, lymph nodes, liver, adrenals, and brain7. Renal cell carcinomas commonly affect one pole of the kidney. The lesions usually occur as a single mass. Histologically, the pattern of growth varies from papillary to solid, trabecular, or tubular. The most common cell type is the clear cell, hav-ing a rounded or polygonal shape and abundant clear cytoplasm. Some carcinomas contain granular cells, which have moderately eosinophilic cytoplasm. Other carcinomas grow as spindle-shaped cells resembling mes-enchymal tumors.
In rabbits with renal neoplasia, embryonal nephroma occurs occasionally. An evaluation of rabbit tumors reveals that only uterine adenocarcinomas occur more frequently than embryonal nephromas. Weis-broth reviewed the incidence of neoplasia in rabbits and re-ported 22 cases of embryonal nephroma from 1900-1985, while over the same period 230 uterine adenocarcinomas occurred. Secondary polycythemia associated with nephroblastoma has been re-ported in rabbits. In human Wilm's tumor cases, elevated erythropoietin is commonly demonstrated. However, this has not been shown in the rabbit9. A reproducible model for the human Wilm's tumor was developed by Hard and Fox. A single dose of ethyl-nitrosourea was given intra-peritoneally to rabbits on the 18th day of gestation. When rabbits of the strain IIIVO/J were used, there was a greater than 90% incidence of nephroblastomas in the offspring of treated dams10. In a report by Carlton and Dietz, renal tumors were described in two wild rabbits (Sylvilagus floridanus). One tumor was diagnosed as a hamartoma of urogenital origin. The second tu-mor was diagnosed as a renal adenocarcinoma11.
Renal cell carcinomas have been reported in the laboratory rabbit only once12. The tumor was found in a 2½- year-old female New Zealand white rabbit. The tumor was large and smooth surfaced, and appeared to arise from the cortex of the right kidney. The tumor was firm with soft, red, necrotic areas. A 10 cm cyst containing brownish fluid was pre-sent on one side. No metastases were observed. Cellular morphology varied from low cuboidal to spindle-shaped. Cells were arranged in irregular tubular formations, solid sheets, and nests.
Lectins are carbohydrate binding proteins. Different lectins have a tendency to bind with different sugar moi-eties. In the kidney, the binding sites of various lectins are sometimes specific to certain cells in specific neph-ron segments. However, there are age, developmental, and interspecies differences in the binding patterns of lectins. Therefore, with few exceptions, the results obtained from one species will not be applicable to other species. Holthofer did a comparative study of the lectin binding sites in the kidney of 14 animal species. In normal rabbit kidney, he showed that Ricinus communis (castor bean) and Triticum vulgaris (wheat germ) lectins bound exclusively in proximal renal tubules, whereas soybean and Arachis hypogaea (peanut) lectins bound dis-tal tubules and Dolichos biflorus (horse gram) and Ulex europeus (gorse) lectins bound collecting ducts primarily13. Therefore, the lectin binding pattern in the kidney tumor from this case seems to indicate that the site of origin may have been the distal tubules and collecting duct. However this cannot be confirmed.

Immunohistochemistry is also commonly used to characterize tumors. The keratin positivity in this case serves to confirm that it is an epithelial tumor. However, vimentin, the cytoskeletal protein of mesenchymal cells, was also positive. A similar finding was previously reported in a study by Holthofer et. al. where simultaneous expres-sion of vimentin and cytokeratin occurred in 53% of human renal carcinomas examined14. Although neuron-specific enolase and S-100 protein positivity has been reported in human renal cell carcinomas, both markers were negative in this case15.
The gross and microscopic appearance of the tumor in this report is quite similar to the appearance of the renal cell tumor described by Kaufmann and Quist. Both tumors were large, smooth surfaced and firm, and contained a large fluid-filled cyst. In both cases, cellular morphology varied from low cuboidal to spindled and stellate, and cells were arranged in irregular tubular formations, solid sheets, and nests. Tumor metastases were absent in both animals. The presence of undifferentiated blastema was minimal to absent in both tumors. Finally, the most significant microscopic feature was the conspicuous absence of primitive avascular glomerular formations. The last two points ar-gue against a diagnosis of embryonal nephroma.
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Case 9-3 . Kidney. The tumor capsule is infiltrated by nests, cords, and tubule forming pleomorphic polygonal cells. There are scattered foci of necrosis and occasional mitoses.
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Case 9-3. Kidney. A bright pink amorphous to hyaline material separates tumor cells in many areas. Generally these areas lack silver staining (black), indicating that this material is not collagen or basement membrane.
AFIP Diagnosis: Kidney: Renal cell carcinoma, New Zealand white rabbit, lagomorph.
Conference Note: In humans, renal cell carcinoma occurs most often in older individuals, usually in the sixth or seventh decades of life. The use of tobacco is the most prominent risk factor. Cigarette smokers have twice the incidence of renal cell carcinoma, and pipe and cigar smokers are also more susceptible16. Additional predisposing factors may include obesity (especially in women), hypertension, and exposure to asbestos, heavy metals, and petroleum products.
While most renal carcinomas are sporadic and occur in older people, unusual forms of autosomal dominant cancers may occur, usually in younger individuals. Von Hippel-Lindua (VHL) syndrome is an autosomal dominant disease in which affected individuals develop capillary hemangioblastomas at multiple sites within the central nervous system, including the cerebellum, the retina, and less commonly the brain stem and spinal cord. Patients also have cysts involving the pancreas, liver, and kidneys, and a strong propensity to develop renal cell carcinoma. The VHL gene is implicated in the development of both familial and sporadic clear cell tumors.
Renal cell carcinoma in people tends to produce diverse clinical signs not related to the kidney and is known as one of the great imitators in human medicine. The tumor causes a number of paraneoplastic syndromes attributed to hormone production, including polycythemia, hypercalcemia, hepatic dysfunction, feminization and masculinization, Cushing syndrome, eosinophilia, leukemoid reactions, and amyloidosis. Another characteristic of this tumor in people is its tendency to metastasize widely before the appearance of clinical signs; there is frequently radiologic evidence of metastasis, primarily to the lungs and/or bones, at the time of initial presentation.
Contributor: Center for Comparative Medicine, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030.
1. Baskin GB, De Paoli A: Primary renal neoplasms of the dog. Vet Path 14:591-605, 1977.
2. Hard GC: Tumors of the kidney, renal pelvis and ureter. In: Pathology of Tumors in Laboratory Ani-mals, Tumors of the Rat, vol. 1, pp. 301-344, 2nd ed., Turusov and Mohr ed., IARC Scientific Publica-tions, 1990.
3. Maxie MG: The urinary system. In: Pathology of Domestic Animals, Jubb KVF, Kennedy PC, Palmer N, eds., vol. 2, pp. 518-522, Acad-emic Press, San Diego, CA, 1993.
4. Rabstein LS, Peters RL: Tumors of the kidneys, synovia, exocrine pancreas, and nasal cavity in BALB/cf/Cd mice. J Nat Cancer Inst 51:999-1006, 1973.
5. Eker R, Mossige J, Johannessen JV, Aars H: Hereditary renal adenomas and adenocarcinomas in rats. Diagnostic Histopathology 4:99-110, 1981.
6. Murphy WM, Beckwith JB, Farrow GM: Tumors of the Kidney, Bladder, and Related Urinary Struc-tures. In: Atlas of Tumor Pathology, pp. 92-131, Fascicle 11, 3rd series, Armed Forces Institute of Pathology, Washington DC, 1994.
7. Weisbroth SH: Neoplastic Diseases. In: The Biology of the Laboratory Rabbit, Manning, Ringler, Newcomer, eds., 2nd ed., pp. 259-292, Academic Press, San Diego, CA, 1994.
8. Wardrop KJ, Nakamura J, Giddens WE Jr.: Nephroblastoma with secondary polycythemia in a New Zealand white rabbit. Lab Anim Sci 32:280-282, 1982.
9. Hard GC, Fox, RR: Histologic characterization of renal tumors (nephroblastomas) induced transplacentally in IIIVO/J and WH/J rabbits by N-ethylnitrosourea. Am J Path 113:8-18, 1983.
10. Carlton WW, Dietz JM: Two renal tumors in cottontail rabbits (Sylvilagus floridanus). Vet Pa-th 14:29-35, 1977.
11. Kaufmann AF, Quist KD: Spontaneous renal carcinoma in a New Zealand white rabbit. Lab Anim Care 20:530-531, 1970.
12. Holthöfer H: Lectin binding sites in kidney: A comparative study of 14 animal species. J Histochemistry Cytochemistry 31:531-537, 1983.
13. Holthöfer H, et al.: Cellular origin and differentiation of renal carcinomas: A fluorescence microscopic study with kidney-specific antibodies, antiintermediate filament antibodies, and lectins. Lab Inves 49:317-326, 1983.
14. Kusama K, et al.: Tumor markers in human renal cell carcinoma. Tumor Biology 12:189-197, 1991.
15. Cotran RS, Kumar V, Collins, Robbins SL: The kidney. In: Robbins Pathologic Basis of Disease, 6th ed., pp. 991-994, WB Saunders, Philadelphia, 1999.
Case IV - P98-4500/N (AFIP 2641836)
Signalment: Six-year-old, cross-bred, gelding, equine, Equus caballus.
History: The horse suffered from dysphagia, sweating, intermittent colic, and weakness for a few weeks. Because the onset of clinical signs was insidious, the duration of clinical disease could not be determined with certainty. Physical examination revealed weakness, sweating, dehydration, emaciation, reflux and colonic impaction. The horse stood with an arched back and tucked-up abdomen. No treatment was provided, and the horse was euthanized due to very poor general condition.
Gross Pathology: At necropsy, the horse was emaciated and in very poor condition. The coat in the area of neck and shoulders was bilaterally moist. Internal organs were normal except for the gastrointestinal tract. The stomach contained only minimal amounts of water, and no ingesta was present. The entire large bowel was severely dilated and filled with dry feces. Feces and mucosa were covered by thick, sticky mucus.
Laboratory Results: None.
Contributor's Diagnosis and Comments:
1. Coeliaco-mesenteric ganglion, neurons: Chromatolysis and eosinophilia, diffuse, marked; margination, pyknosis and loss of nuclei, diffuse, marked; vacuolization, multifocal, mild; lipopigment accumulation, diffuse, mild, cross-bred, equine.
2. Coeliaco-mesenteric ganglion: Lymphocytic infiltration, multifocal, minimal.
Lesions are consistent with equine dysautonomia (grass sickness).
Equine dysautonomia (ED) is a profoundly debilitating, almost invariably fatal disease of undetermined etiology that affects equidae in northwestern Europe and South America. The European variant is also known as grass sickness, grass disease and autonomic polyganglionopathy. The South American variant is also known as "mal seco". Similar dysautonomic diseases occur in other species including cats, dogs and hares.
The clinical course of the disease in horses can be acute or chronic. Horses with the acute form of ED usually die within 48 hours after the onset of clinical signs, which are predominated by abdominal pain, gastric reflux, tachycardia, intestinal atony and dysphagia. The chronic form may be insidious in onset, and horses may survive for several weeks. Anorexia leading to progressive weight loss and emaciation, intermittent colic due to colonic impaction, sweating, tremor, weakness and mild dysphagia may occur. In some cases diarrhea is observed.
Gross lesions are variable and non-specific, but may be indicative of gastrointestinal atony. Aspiration pneumonia due to dysphagia may occur. Histologically, the myenteric and submucosal alimentary plexuses and peripheral ganglia are affected by neuronal degeneration. In chronic cases, there may be a numerical decrease of neurons, while the number of non-neuronal cells is increased. Lymphocytic infiltration, as in the submitted case, is a common finding in horses and seems to be unrelated to the development of ED. Neuronal degeneration is not limited to the autonomic plexuses and ganglia, and may also occur in the dorsal root ganglia, the intermediolateral nucleus, and the ventral horns of the spinal cord. Specific brain stem nuclei may be affected including the nucleus (N.) motoricus nervi hypoglossi, N. dorsalis nervi vagi, N. ambiguus, N. vestibularis lateralis, N. occulomotorius, and formatio reticularis.
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Case 9-4 . Ganglion. Multifocally neurons have loss of Nissle substance, with coalescence of the cell cytoplasm as a central homogenous eosinophilic aggregate surrounded by a clear to slightly fibrillar halo zone. Nuclei are karyolytic with poorly defined nuclear outlines. Low to moderate numbers of lymphocytes and macrophages infiltrate these zones of neuronal degeneration.
AFIP Diagnosis: Ganglion: Neuronal degeneration and necrosis, diffuse, with satellite cell proliferation and mild multifocal lymphocytic ganglioneuritis, mixed breed horse, equine.
Conference Note: Conference participants noted several histologic changes affecting neurons including loss of Nissl substance (chromatolysis), swollen nuclei, karyolysis, and hypereosinophilia. Some neurons are pale and contain indistinct or faded nuclei. Occasional neurons contain multiple, peripheral, clear, discreet intracytoplasmic vacuoles that surround a central zone of hypereosinophilia. Axonal swelling with occasional spheroids is present multifocally. There is also a diffuse increase in satellite cells. Nuclear placement and chromatin pattern may be varied depending upon anatomical location of neurons, and participants were cautious in placing emphasis on location and morphology of nuclei.
The nature and distribution of microscopic lesions are very similar in the species which suffer from dysautonomia, and the findings in this case are fairly representative of the condition. The cytoplasm of affected neurons loses the basophilic granularity of Nissl substance and takes on a homogenous, "ground glass", appearance. Initially, neurons are rounded and swollen in the early stages of disease, but eventually become shrunken and irregular with pyknotic and faded nuclei. Progression of the disease leads to neuronal loss and satellite cell proliferation, especially prominent in the cat in which the disease is also known as Key-Gaskell syndrome (KGS).
While the lesions are similar in several species, significant differences in clinical presentation are observed. Horses with ED have increased heart rate and suffer from patchy sweating, while 50% of cats with KGS have bradycardia. Cats and dogs develop dry mucous membranes, while horses drool thick saliva, probably due to the inability to swallow. Cats also have fixed, dilated pupils and greatly reduced lacrimation, while these abnormalities are not present in horses.
The etiology of ED is unknown, although an ingested neurotoxin is suspected. Characteristic autonomic neuronal degeneration was produced in peripheral autonomic ganglia, and spinal cord and brain stem nuclei in several healthy horses following intraperitoneal injection of serum from acute cases of ED, although the experimental recipients did not develop clinical signs of ED. Research thus far supports the hypothesis that ED is caused by a neurotoxin that may gain access to the circulation, and may also injure autonomic neurons through retrograde axonal transport.
The suspected neurotoxin may be ingested, produced during metabolic transformation of an ingested agent, or synthesized by the bacterial flora in the gut. Damage to the neurons in the intestinal myenteric and submucosal plexuses occurs more extensively than at other sites (such as the coeliaco-mesenteric ganglion), and probably reflects the higher concentrations of neurotoxin that are related to the site of absorption. The degeneration and depletion of neurons is most severe in the ileum, and this may be the main site of entry for the toxin. Lesions in autonomic neurons distant to the intestinal tract are less severe, and hypothetically are due to neurotoxin transferred by retrograde axonal flow from the site of absorption. Neurotoxin absorbed into the systemic circulation may also potentially damage neurons which are not protected by the blood-brain barrier. Regardless of the etiopathogenesis, the histologic lesions lead to disordered autonomic innervation of the alimentary tract from the pharynx to the rectum.
Contributor: Department of Veterinary Pathology, Faculty of Veterinary Medicine, Utrecht University, Postbox 80158, 3508 TD Utrecht, The Netherlands.
1. Johnson PJ: Equine dysautonomia. Equine Pract 17:25-32, 1995.
2. Fatzer R, et al.: Sind equine motorische Nervenzell-Degeneration (EMND) und Graskrankheit des Pferdes unterschiedliche Manifestationen der gleichen Grundkrankheit? Pferdeheilk 11:17-29, 1995.
3. Pinsent PJN: Grass sickness of horses (grass disease: equine dysautonomia). Vet Annual 29:169-174, 1989.
4. Pollin MM, Griffiths IR: A review of the primary dysautonomias of domestic animals. J Comp Pathol 106:99-119, 1992.
5. Schulze C, Venner M, Pohlenz J: Chronische Graskrankheit (Equine Dysautonomie) bei einer zweieinhalb-jährigen Isländer-Stute auf einer nordfrisischen Insel. Pferdeheilk 12:345-350, 1997.
6. Jubb KVF, Huxtable CR: The nervous system. In: Pathology of Domestic Animals, Jubb, Kennedy, Palmer eds., 4th ed., vol. 1, pp. 365-366, Academic Press, San Diego, 1993.
Ed Stevens, 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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