Flow Cytometric Analysis of Mediastinal Masses in Cats: A Retrospective Study

Abstract

Mediastinal masses occur in dogs and cats and are often investigated with cytology. However, discrimination between the two most common lesions (thymoma and lymphoma) may be challenging, especially when small/medium lymphocytes represent the prevalent population. The aim of the present study is to describe the flow cytometric aspects of mediastinal masses in cats and to assess the ability of flow cytometry (FC) to differentiate lymphoma from non-lymphomatous lesions. We retrospectively describe FC features of fine needle aspiration cytology from cats with mediastinal masses. Cases were grouped in lymphoma and non-lymphoma based on results of cytology, histopathology, PCR for antigen receptor rearrangement (PARR), clinical presentation, and follow-up. Scatter properties, positivities to CD5, CD4, CD8, CD21, CD18, and their co-expressions were recorded using a multicolour approach. Twenty cats were included, 12 lymphomas and eight non-lymphomatous cases. Forward scatter (FSC) of lymphoid cells was higher in the lymphoma group. Double positive CD4+CD8+ T-cells were the dominant population in eight out of 12 lymphomas, whereas non-lymphomatous lesions showed no dominant lymphoid population in five out of eight cases. Unlike dogs, the high prevalence of CD4+CD8+ lymphomas in cats it makes difficult to differentiate lymphoma from non-lymphomatous lesions using FC alone. FC may add interesting information to refine diagnosis in some cases, but PARR and histopathology remain mandatory to solve differential in case of expansion of small-medium sized double positive lymphoid cells.

Clinical outcome and prognostic factors in dogs with B‐cell chronic lymphocytic leukemia: A retrospective study

“…Nine cases had intermediate‐to‐large‐sized lymphocytes cytologically, but these cases were included because the cells were small‐sized based on flow cytometry. Other groups have highlighted differences in cell size between microscopy and flow cytometry and suggested flow cytometry is more objective for determining size 23‐25 . A few cases had descriptions of atypical chromatin patterns, including smooth, fine, or stippled.…”

“…Other groups have highlighted differences in cell size between microscopy and flow cytometry and suggested flow cytometry is more objective for determining size. [23][24][25] A few cases had descriptions of atypical chromatin patterns, including smooth, fine, or stippled. Moderate numbers of cases were described as having rare cells with a faint nucleolus, but 2 were described as having consistent nucleoli.…”

Successful management of feline CD4⁺ CD8⁺ T-cell mediastinal lymphoma with pericardial effusion

“…In the case of dogs, if the flow cytometry is performed on a mediastinal mass and if the contribution of CD4 + CD8 + double-positive T-cells is more than 10%, it is highly suggestive of thymoma (Lana et al 2006). However, in one study that analysed the immunophenotypes of feline mediastinal masses using flow cytometry, eight of the 12 lymphoma cases (67%) examined were of CD4 + and CD8 + T-cell phenotype (Bernardi et al 2020). Moreover, all the double-positive cases showed a dominant population of small-to medium-sized lymphoid cells (Bernardi et al 2020).…”

Thymic carcinoma and branchial cyst in a cat

“…No other clinical abnormalities were detected. Paraneoplastic syndromes have been reported in feline thymoma, with predominantly exfoliative dermatitis documented, although non‐inflammatory alopecia, polymyositis, myocarditis and myasthenia gravis have also been described 1,19–22 . Comparatively, paraneoplastic syndromes have not been reported in feline thymic lymphoma or thymic carcinoma 1–4,23 .…”

“…The most common diagnoses of feline cranial mediastinal masses are thymoma and thymic lymphoma, which may be cytologically indistinguishable, especially when comprising mainly small to medium lymphocytes 19 . In comparison, mediastinal cysts, fluid filled structures lined by epithelium within the mediastinum, present quite differently.…”