Pathomorphology of the renal form of lymphoma in cats

Lymphoma is one of the most common neoplasias in cats, affecting various organs and tissues. Extranodal lymphoma is characterized by local damage to such organs as the nose, eyes, skin, central nervous system, and kidneys. Cats usually have bilateral kidney damage with possible metastatic damage to the liver and lungs. Statistically, the extranodal type of lymphoma, namely the renal form, is found in 7% to 30% of cases, mainly in cats older than five years. Clinical signs of renal lymphoma are non-specific and variable, typical for acute renal failure, and manifest themselves through general exhaustion, polyuria, polydipsia, and renomegaly. In most cases, the prognosis for lymphoma in cats is cautious. The article describes two clinical cases of outbred cats with a primary renal form of lymphoma. In both cases, the cats were clinically diagnosed with acute kidney injury and treated symptomatically. An ultrasound examination of the cats’ kidneys revealed a sharp increase in their volume and increased echogenicity of the cortical layer with a fine-grained and nodular structure. The cytological picture in fine-needle aspirates from the kidneys was characterized by a massive monomorphic population of lymphoblasts, which exceeded erythrocytes by 2–3 times in diameter. The cytoplasm of the lymphoblastic cells was sparse with large round nuclei with dense chromatin. The cells were mostly uninucleate, with atypical mitoses and moderate cellular atypism. Epithelial cells, which were occasionally visualized between large lymphoblastic cells, had broad vacuolated cytoplasm and a large round nucleus. Express tests for feline leukemia virus showed negative results. Both cats died 7 and 10 days after initiation of treatment, respectively. During the autopsy, sharply enlarged and deformed kidneys were recorded, and the border between the cortical and medullary substances was difficult to differentiate. Irregularly shaped, white tumorous formations were visualized in the cortical layer. Diffuse infiltration of the kidneys’ cortical layer with large monomorphic lymphoblastic elements with large hyperchromic nuclei and narrow cytoplasm was noted histologically. Lymphoblastic cells in a state of vacuolar and hydropic dystrophy were located between the proximal and distal tubules. The lumens were filled with protein mass and desquamated epithelium. The capsule of the kidney glomeruli was slightly thickened and the vessel walls were soaked with plasma proteins. Immunohistochemically, intensive expression of the CD79a marker and high expression of the Ki-67 marker were detected in the examined kidney samples, which indicates the development of diffuse B-cell lymphoma with an unfavourable prognosis.