Fine-needle aspiration biopsy and intraoperative cytologic smear findings in a case of benign mesothelial-cell inclusions involving a lymph node: case report and review of the literature.

Although first described over a decade ago, the rare entity of mesothelial lymph node inclusions (nonneoplastic mesothelial cells involving lymph node sinuses) is not well-known among pathologists. Unlike most lymph node inclusions such as Müllerian inclusions or nevus cells, which usually occur in the capsule of the lymph node, mesothelial cells involve the lymph node sinus, mimicking metastatic carcinoma or metastatic mesothelioma. The spectrum of histologic findings ranges from a few mesothelial cells, perhaps only detectable by immunohistochemical stains, to a massive distention of the lymph node sinus with abundant mesothelial cells. Mesothelial-cell inclusions in lymph nodes are usually found in mediastinal lymph nodes of patients with pleural and/or pericardial effusions. It is hypothesized that the effusion, due to whatever cause, allows for mesothelial-cell migration into the submesothelial lymphatics and regional lymph nodes. To our knowledge, cytologic findings on aspiration biopsy and intraoperative smear preparations of a lymph node with mesothelial-cell inclusions have never been described. Familiarity with this entity is important in preventing misdiagnosis of malignancy. Copyright 2003 Wiley-Liss, Inc.