Pulmonary epithelioid hemangioendothelioma with prominent signet ring cell features mimicking metastatic adenocarcinoma.

We report the case of a 65-year-old woman who presented with persistent dry cough and was initially treated for pneumonia without much improvement. Computed tomography of the chest showed a 2.5 cm poorly marginated right infrahilar opacity and multiple ill-defined ground glass opacities scattered throughout the lungs. Computed tomography-guided fine needle aspiration of the right infrahilarmass showed malignant epithelioid cells, many of which were strikingly plasmacytoid with a vacuolated cytoplasm suggesting signet ring cells. A diagnosis of adenocarcinoma with signet ring cell features was made and, in view of the clinical history of multiple masses in the lung, metastatic adenocarcinoma from sites such as gastrointestinal or pancreaticobiliary tract was favored. The patient underwent exploratory thoracotomy during which she was found to have multiple, small pulmonary nodules, one of which was sampled for intraoperative examination. Frozen section of the nodule was interpreted as adenocarcinoma with signet ring cell features, probably metastatic in origin. Histopathologic examination of the pulmonary nodules demonstrated fairly well-delineated lesions with an acellular central zone of hyalinized matrix surrounded by a more cellular zone of moderately pleomorphic epithelioid cells, some of which had a peripherally displaced nucleus and vacuolated cytoplasm resembling signet ring cells. The epithelioid cells were positive for vascular markers CD31 and CD34 and, therefore, a diagnosis of epithelioid hemangioendothelioma was confirmed. This case clearly indicates the importance of recognizing the cytomorphologic and histologic spectrum of this entity to avoid misdiagnosing it as either primary or metastatic adenocarcinoma.