The diagnostic relevance of mesenteric lymph node biopsy in small intestinal lymphoma in cats

Abstract

Background: Regional lymph nodes are frequently sampled in cats with suspected intestinal lymphoma; however, their diagnostic value has not been explored.

Objectives: To investigate whether histologic and immunohistochemical analysis of mesenteric lymph nodes correlates with the diagnosis of intestinal lymphoma in cats.

Animals: One hundred 2 client-owned cats diagnosed with intestinal lymphoma.

Methods: Retrospective study. The inclusion criteria required a full-thickness biopsy of the small intestine and concurrent excision of mesenteric lymph nodes. Histologic and immunophenotypic analyses were performed on intestinal biopsies and corresponding lymph nodes. Selected nodal samples diagnosed with reactive lymph nodes underwent clonality testing.

Results: Transmural T-cell lymphomas, encompassing small and large cell types, were predominant (64 cases, 62.7%), with large B-cell lymphomas being more frequently transmural (68.8%) than mucosal (31.2%). Among all lymph nodes examined, 44 (43.1%; 95% CI: 33.9%-52.8%) exhibited neoplastic infiltration. Among cases of small cell lymphoma, 51 out of 72 (70.8%; 95% CI: 59.4%-80.1%) showed no nodal involvement. Clonality results correctly identified 19/30 (63.3%; 95% CI: 45.5%-78.2%) reactive lymph nodes. Concerns were raised regarding clonal identification in the remaining cases and potential misdiagnoses based on phenotypic characteristics.

Conclusion and clinical importance: The study underscores the potential drawbacks of relying solely on mesenteric lymph nodes for diagnosing intestinal lymphomas in cats, particularly small cell subtypes. It emphasizes the importance of full-thickness biopsies for assessing transmural infiltration and recommends caution when utilizing mesenteric lymph nodes for histologic, immunohistochemical and clonality evaluations in mucosal lymphomas. Despite limitations, this research highlights the need for comprehensive diagnostic strategies in cats with intestinal lymphoma.

Keywords: bowel; cat; histology; immunohistochemistry.

FIGURE 1

Full‐thickness duodenal biopsy (A, B) and corresponding mesenteric lymph node (LN; C, D) specimen from a cat diagnosed with mucosal small T‐cell lymphoma (MSTCL) without LN infiltration. 1× magnification. (A) Hematoxylin and eosin (HE) staining showing a monomorphic group of small lymphocytes diffusely invading the mucosa. (B) Anti‐CD3 antibody staining showing diffuse and severe infiltration of neoplastic cells within the mucosa. (C) LN immune stained with anti‐CD3 antibody showing mild hyperplastic paracortex. (D) LN immune stained with anti‐CD20 antibody showing moderate increase in follicle size.

FIGURE 2

Full‐thickness duodenal biopsy (A‐C) and corresponding lymph node (LN; D) specimen from a cat diagnosed with transmural large B‐cell lymphoma (TLBCL) with LN infiltration. (A) Hematoxylin and eosin (HE) staining showing monomorphic large lymphocytes diffusely invading the mucosa, submucosa, and muscular layer. 1× magnification. (B) HE staining revealing the neoplastic infiltrate consisting of large lymphocytes with pleomorphic nuclear morphology. 40× magnification. (C) Anti‐CD20 antibody staining showing diffuse and severe infiltration of neoplastic cells within the mucosa, submucosa, and muscular layer. 1× magnification. (D) Anti‐CD20 antibody staining showing diffuse and severe infiltration of neoplastic cells of the corresponding mesenteric LN. 1× magnification.