Peripheral spindled carcinoid tumor: a review of its ultrastructure, differential diagnosis, and biologic behavior.

The ultrastructure, differential diagnosis, and biologic behavior of the peripheral pulmonary spindled carcinoid tumor are reviewed. Electron microscopy is useful in distinguishing the spindled carcinoid from a variety of neoplasms with similar histologic features. The spindled morphology is a rare expression of the carcinoid tumor that is almost exclusively confined to the lung periphery. It appears that the spindled carcinoid without atypical features is fully capable of regional lymph node metastases in approximately 20 per cent of the cases.