Cytology of metastatic thymic well-differentiated neuroendocrine carcinoma (thymic carcinoid) in pleural fluid: report of a case.

Thymic carcinoid tumors (well-differentiated neuroendocrine carcinomas) are uncommon anterior mediastinal neoplasms. These tumors are frequently accompanied by other endocrinopathies as part of a multiple endocrine neoplasia type I syndrome (MEN type I) and by paraneoplastic Cushing's syndrome and have a poor prognosis. We present the case of a 24-year-old man who presented for follow-up of thymic carcinoid with extensive bony metastases. He had recently completed radiotherapy to lesions involving his skull and mandible. An ultrasound-guided left-sided diagnostic and therapeutic thoracentesis was performed yielding 1 l of cloudy yellow fluid. The cytologic fluid preparations consisted of large "cannonballs" and atypical cell groups with salt and pepper nuclear chromatin. A panel of immunohistochemical stains were performed on the cell block material, and the atypical cells were positive for cytokeratin, synaptophysin, and chromogranin, but not for TTF1. These findings were consistent with metastatic well-differentiated neuroendocrine carcinoma (carcinoid tumor). This is the first reported case of a carcinoid tumor manifesting as large, spherical, smoothly contoured cell aggregates ("cannonballs") in a pleural fluid. Despite its rarity, a metastatic carcinoid tumor should be considered when "cannonballs" are found in effusions.