Mesothelial hyperplasia with reactive atypia: Diagnostic pitfalls and role of immunohistochemical studies?a case report

Abstract

The cytomorphologic features of highly reactive mesothelial cells can be difficult to distinguish from malignant cells. We report on an unusual case of mesothelial hyperplasia in a pericardial effusion. The specimen contained bizarre‐shaped cells and large tissue fragments in a patient with a history of lung carcinoma. The atypical cells were negative for CEA and LeuM‐1 and positive for cytokeratins (AE1/3) and HBME‐1. Strong HBME‐1 positivity supported a mesothelial origin of the atypical cells and led to the diagnosis of reactive mesothelium. While HBME‐1 cannot be used as the sole marker to establish an mesothelial origin; its use in a immunohistochemistry panel may be useful in individual cases to distinguish reactive mesothelial cells from carcinoma in effusion cytology. Diagn. Cytopathol. 2000;22:113–116. © 2000 Wiley‐Liss, Inc.

Cytological features of melanoma in exfoliative fluid specimens

“…Reactive mesothelial cells may also exhibit spindle shapes (usually with admixed epithelioid cells), causing difficulties in distinction from spindle cell melanoma 35. When identifiable, the presence of a predominant monolayer arrangement, intercellular “windows”, fine even nuclear chromatin and a gradation of cellular changes from typical benign mesothelial cells to those with reactive features are useful diagnostic features,31 but, in rare cases, the reactive mesothelial cells may contain large nuclei with irregular nuclear membranes, granular hyperchromatic chromatin and prominent nucleoli, mimicking malignancy 33 – 35. Confirmatory immunochemistry (positivity for mesothelial cell markers and negativity for melanocytic markers) is often helpful in arriving at the correct diagnosis 34 – 36…”