Mesothelial Cell Inclusions in Abdominal and Thoracic Lymph Nodes in Association With Recurrent Chylothorax in a Young Man: A Diagnostic Pitfall.

Mesothelial cell inclusions within lymph nodes are rare and may closely mimic metastatic malignant mesothelioma, particularly on cytologic evaluation. We report a 19-year-old man who presented with bilateral chylothorax, mediastinal lymphadenopathy, and extensive venous thrombosis, raising an initial concern for malignancy. Fine-needle aspiration of an inframammary lymph node demonstrated numerous mesothelial cells. Subsequent histopathologic evaluation, immunohistochemistry and fluorescence in situ hybridization confirmed a benign reactive mesothelial proliferation. Recognition of mesothelial cell inclusions, particularly in uncommon nodal locations, is essential to avoid diagnostic error. This report highlights the importance of clinicopathologic correlation and the judicious use of ancillary studies in distinguishing benign mesothelial inclusions from metastatic disease.