Case 4 - 170825-4

12-year-old, female, spayed domestic longhair cat(Haemorhous mexicanus)

This patient presented for intermittent vomiting and a recent onset of progression to hyporexia and weight loss. One year prior to presentation was diagnosed with diabetes mellitus, which had been managed with insulin. Abdominal ultrasound identified thickened gastric and colonic walls with loss of normal wall layering architecture, multiple small intestinal masses, moderate intraabdominal lymphadenopathy and bilateral chronic renal changes. A fine needle aspirate of the mesenteric lymph nodes and spleen came back as reactive.

Seven small jars of formalin are submitted containing full thickness stomach, duodenum, jejunum, and ileum biopsies as well as gastric and colonic lymph nodes. Samples are bisected and placed in their respective cassettes for processing.

Seven small jars of formalin are submitted containing full thickness stomach, duodenum, jejunum, and ileum biopsies as well as gastric and colonic lymph nodes. Samples are bisected and placed in their respective cassettes for processing.

This slide has four full thickness sections of small intestine, in which the lamina propria, submucosa, and intestinal wall is infiltrated and expanded by a densely cellular, poorly demarcated, unencapsulated neoplastic population of round cells.

The neoplastic population is often concentrated in the deep lamina propria, frequently elevating and distorting the crypts, and also multifocally infiltrates the entire lamina propria extending to the epithelium in vaguely nodular aggregates.

Neoplastic cells are approximately 1.5 to 3 times the diameter of a red blood cell, have indistinct cell borders, and a small to moderate amount of eosinophilic to amphophilic, lacy cytoplasm.

Nuclei are irregularly round to ovoid with finely-stippled chromatin and one variably distinct, central nucleolus.

Anisocytosis and anisokaryosis are moderate to marked, and there are an average of 10 mitotic figures per 400x field.

A dense band of large numbers of small lymphocytes infiltrate the mid-mucosa, and frequently extend into the epithelium (epitheliotropism).

The superficial lamina propria is frequently expanded by clear space (edema) along with moderate numbers of lymphocytes, neutrophils, and fewer plasma cells.

CD20: The population of large lymphocytes have strong, membranous immunoreactivity.

CD3: The intestinal lamina propria population has strong, membranous immunoreactivity and this marker highlights the degree of epitheliotropic T lymphocytes.

Small Intestine: Large B cell lymphoma.

Small Intestine: Epitheliotropic small cell T cell lymphoma (suspected; clonality required for confirmation)

This case was an interesting clash of two populations of neoplastic lymphocytes (B and T). The discussion revolved around the differing patterns of T cell lymphoma in cats and patterns/distributions, which are more indicative of lymphoma versus inflammation in cats. More specifically, T cells are normally epitheliotropic in the intestines to some degree based on normal pathophysiology, however, in cases where epitheliotropism is increased and T cells begin to aggregate within the epithelium, lymphoma must be considered. Additionally, T lymphocytes with epitheliotropism within the crypt epithelium are more suggestive of a potential underlying lymphoma.

Moore PF, Rodriguez-Bertos A, and Kass H. Feline gastrointestinal lymphoma: mucosal architecture, immunophenotype, and molecular clonality. Vet Path. 2012. 49(4):658-668.