Carcinoid tumors of the lung: cytologic differential diagnosis in fine-needle aspirates.

Pulmonary carcinoid tumors presenting as peripheral or coin lesions are rare and radiologically may resemble other primary or metastatic neoplasms in the lung. This study consisted of the cytologic evaluation of fine-needle aspirates from five peripheral carcinoid tumors of the lung with particular reference to the differences between the cytologic manifestations of this neoplasm and of small-cell carcinoma and well-differentiated adenocarcinoma. Aspirates of typical carcinoid tumors are characterized by isolated cells and loose aggregates of cells; spindle- and oval-shaped cells of uniform size with scanty, pale eosinophilic cytoplasm; and nuclei with evenly dispersed finely granular chromatin and usually prominent single micronucleoli with occasional macronucleoli. In contrast, the cells of small-cell carcinoma are pleomorphic and arranged in noncohesive loose aggregates, their cytoplasm is scanty, and they show nuclear molding. Their nuclei are hyperchromatic with fine to coarsely granular chromatin. The cells of well-differentiated adenocarcinoma are arranged in three-dimensional clusters or loose aggregates of relatively uniform cells with a columnar configuration. The nuclei are uniformly round and hyperchromatic with finely granular chromatin. Macronucleoli are usually prominent. This study demonstrates that cytologic analysis of fine-needle aspirates can play a significant role in the evaluation and management of peripheral lung tumors.