History
A 16-year-old 4.24-kg (9.33-lb) spayed female domestic shorthair cat was evaluated at the University of Georgia's Veterinary Teaching Hospital because of vomiting, which had begun 5 days earlier. The owner reported that the cat was vomiting undigested food 2 to 3 times each day, usually 6 to 8 hours following a meal. Additionally, the cat was reportedly urinating in atypical locations around the house and, recently, had not been as active as usual. Clinicopathologic findings obtained by the referring veterinarian 7 months prior were suggestive of chronic renal insufficiency. The cat's vaccination status (FeLV vaccine, rabies virus vaccine, and feline viral rhinotracheitis, calicivirus, and panleukopenia virus vaccine) was reportedly current.
Clinical and Gross Findings
On physical examination, the cat was bright and alert. Thoracic auscultation revealed no abnormalities. On palpation, the cat's abdomen was tense and apparently painful as evidenced by the patient's vocalizations, and the kidneys were small with smooth capsular surfaces. There was mildly prolonged skin tenting. Clinicopathologic analyses revealed moderate azotemia (BUN concentration, 51 mg/dL [reference interval, 10 to 32 mg/dL]; creatinine concentration, 3.8 mg/dL [reference interval, 0.6 to 1.4 mg/dL]). Abdominal ultrasonography revealed small, irregular kidneys and multiple hypoechoic liver nodules. Results of cytologic examination of fine-needle aspirate liver nodule specimens were suggestive of benign cystic lesions. Urinalysis revealed isosthenuria (urine specific gravity, 1.016), with trace protein and numerous bacteria. Escherichia coli was cultured from the urine sample. A definitive cause for the vomiting was not identified. Oral administration of amoxicillin–clavulanic acid and buprenorphine hydrochloride was commenced; the owner was given instructions to return the cat to the hospital if its clinical signs persisted or worsened.
Over the next 2 months, the cat's vomiting persisted and its clinical condition declined with development of inappetence, weight loss, and decreased mobility. The decision was made to euthanize the cat with an overdose injection of pentobarbital-phenytoin solution, and a complete necropsy was performed 24 hours later. Approximately 70% of the stomach was transmurally thickened (wall thickness, ≤ 4 cm) by a tan to white, soft mass that bulged on cut section (Figure 1). The remainder of the gastrointestinal tract was unremarkable. The kidneys were bilaterally shrunken, with the right kidney being smaller than the left kidney. The right kidney had a 1- to 2-mm-diameter capsular indentation. On the right lateral lobe of the liver, there was a 1 × 2 × 2-cm, well-defined, cystic nodule that contained abundant clear fluid. There were no additional notable gross findings.
Photograph of a transmural gastric mass transected along the longitudinal axis of the stomach of a 16-year-old domestic shorthair cat that was evaluated because of vomiting of 5 days’ duration. The mass is tan to white and soft and bulges on cut section.
Citation: Journal of the American Veterinary Medical Association 256, 3; 10.2460/javma.256.3.319
Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page→
Histopathologic Findings
The gastric mass was unencapsulated and infiltrative. The mass was composed of a homogeneous population of round cells that were arranged in sheets and supported by a minimal amount of fine fibrovascular stroma. The round cell neoplasm had extensively effaced the normal gastric architecture. Neoplastic round cells had distinct cell borders, a moderate amount of eosinophilic cytoplasm, and a round to oval and often eccentric nucleus with finely stippled chromatin and an occasional prominent nucleolus. Anisocytosis and anisokaryosis were moderate. The nuclear diameter of neoplastic cells was > 2 times the diameter of erythrocytes. Four mitotic figures were present in 10 representative hpf (400Ă—) with none or 1 mitotic figure in any single field. Neoplastic cells had infiltrated the mesentery multifocally, and the overlying gastric mucosa was diffusely ulcerated. More than 50% of neoplastic cells had strong, cytoplasmic to membranous immunopositivity for CD79a (Figure 2), although immunoreactivity was patchy because of multifocal necrosis and autolysis. There were scattered, CD3-immunopositive round cells throughout the gastric mass. Adjacent sections of the stomach had multiple, deep to midzonal, mucosal, lymphocytic inflammatory nodules with plasma cells.
Photomicrographs of sections of the transmural gastric neoplasm in Figure 1. The mass is composed of sheets of neoplastic lymphocytes, which have effaced the normal gastric architecture and are supported by a fine, fibrovascular stroma. Neoplastic cells have a moderate amount of eosinophilic cytoplasm and a round, occasionally eccentric nucleus (arrow). H&E stain; bar = 10 μm. Inset—More than 50% of the neoplastic cells have moderate, cytoplasmic to membranous immunoreactivity for CD79a. CD79a-specific immunohistochemical stain; bar = 10 μm.
Citation: Journal of the American Veterinary Medical Association 256, 3; 10.2460/javma.256.3.319
The renal cortical architecture was markedly distorted by a dense, interstitial, lymphoplasmacytic infiltrate and fibrous connective tissue, which had frequently entrapped and replaced glomeruli and renal tubules. Intervening cortical tubules were mildly ectatic and lined by attenuated to hypertrophied epithelium. The parathyroid gland was moderately, diffusely hyperplastic and had cells with abundant, frequently vacuolated, eosinophilic cytoplasm. The liver contained multiple, variably sized cysts lined by biliary epithelium. The remaining histopathologic findings were considered incidental in this cat.
Morphologic Diagnosis and Case Summary
Morphologic diagnosis: primary, gastric, transmural, diffuse, large cell-type, B-cell lymphoma and moderate, chronic, multifocal lymphoplasmacytic gastritis; moderate to severe, chronic, lymphoplasmacytic interstitial nephritis; and moderate, chronic, diffuse, parathyroid gland hyperplasia.
Case summary: primary gastric B-cell lymphoma and bilateral chronic kidney disease with parathyroid gland hyperplasia in a 16-year-old cat.
Comments
Histopathologically, the mass in the stomach of the cat of the present report was consistent with a primary, gastric, transmural, diffuse, large cell-type, B-cell lymphoma. The large gastric neoplasm was the most likely explanation for the cat's vomiting and deterioration of its clinical condition, although chronic kidney disease likely contributed to the dehydration, inappropriate urination, and moderate azotemia noted in this case. The presence of parathyroid gland hyperplasia in this cat suggested that there was clinically important renal dysfunction, although histologically there appeared to be adequate renal parenchyma. Multifocal biliary cysts were present in the liver, but these are a common incidental finding in cats.1
Despite a decline in the incidence of FeLV infection in the United States, the incidence of feline lymphoma has actually increased, mainly with regard to gastrointestinal lymphomas.2 The FeLV status of the cat of the present report was unknown, but the cat's vaccination status was reportedly up to date.
The gastrointestinal tract contains the largest population of lymphoid and immune cells in the body and is hence a common location for lymphoma. In a recent study by Moore et al,2 103 of 120 (85.8%) cats with gastrointestinal lymphoma had either mucosal or transmural T-cell lymphoma, whereas 19 of 120 (15.8%) cats had B-cell lymphoma. In that study, 4 cats had concurrent B-cell lymphoma and mucosal T-cell lymphoma, and 2 cats had non–B- and non–T-cell lymphoma.2 Although T-cell lymphomas accounted for most of all gastrointestinal lymphomas in aged cats, these tumors were located in the stomach of only 4 of 120 (3.3%) cats with lymphoma.2 Multiple sites were affected in 9 of 19 (47%) cats with B-cell lymphoma,2 including the stomach and ileocecocolic junction (the latter was not affected in the cat of the present report). The duodenum was only affected in 1 cat, in which extension to the duodenum from the pylorus was noted.2 Gastrointestinal B-cell lymphomas occurred as transmural lesions in 18 of 19 cases, and were not associated with lymphoid follicles in the gastric mucosa, although evidence of B-cell lymphoma could be found in lymphoid follicles adjacent to transmural lesions.2 B-cell lymphomas were associated with lymphoid follicles in the intestine, cecum, and colon of examined specimens.2 Neoplastic B-cells that underwent immunohistochemical analysis expressed CD79a.2 All examined specimens were classified as diffuse, large cell-type, B-cell lymphoma.2 Cats with B-cell lymphoma had a reported median survival time of 3.5 months, whereas cats with mucosal T-cell lymphoma may survive up to 29 months after the time of diagnosis.2
In contrast, Pohlman et al3 identified a predominance of B-cell lymphoma in cats with gastrointestinal lymphoma; among 50 cats, 27 (54%) had B-cell lymphoma. Of the 27 examined B-cell lymphomas in that study,3 20 (74%) were of the large cell type, 3 (11%) were of the small cell type, and 4 (15%) were of the intermediate type. Of the 12 diagnosed gastric tumors, 9 were present only in the stomach; the remaining 3 tumors also involved the small intestine. All gastric lymphomas were of B-cell lineage, and all solitary gastric lymphomas were large cell type.3 In that study,3 there was a strong association between immunophenotype and tumor location within the gastrointestinal tract; the most notable association was for the stomach, with a predominance of diffuse, large cell-type, B-cell lymphoma in this location.3
The cat of the present report had a primary, gastric, transmural, diffuse, large cell-type, B-cell lymphoma, which is a relatively uncommon neoplasm that typically develops as a transmural neoplasm. Primary gastric tumors in cats usually involve CD79a-positive B cells, and most commonly the large cell type (as in this cat). Cats with B-cell lymphoma generally have a poorer prognosis than those with mucosal T-cell lymphoma.
References
1. Adler R, Wilson DW. Biliary cystadenoma of cats. Vet Pathol 1995;32:415–418.
2. Moore PF, Rodriguez-Bertos A, Kass PH. Feline gastrointestinal lymphoma: mucosal architecture, immunophenotype, and molecular clonality. Vet Pathol 2012;49:658–668.
3. Pohlman LM, Higginbotham ML, Welles EG. Immunophenotypic and histologic classification of 50 cases of feline gastrointestinal lymphoma. Vet Pathol 2009;46:259–268.
