Carotid body tumor mimicking adenocarcinoma on fine-needle aspiration.

We report an 86-year-old woman who presented with a 6-month history of a mass in the left side of her neck. MRI and MRI angiography favored a diagnosis of a neural tumor. FNAB showed a large cluster of cohesive, pleomorphic cells with intranuclear inclusion bodies; a diagnosis of adenocarcinoma was favored. At surgery, a 7 x 5 x 2.5 cm, firm, encapsulated mass was excised. Microscopically, the richly vascularized tumor had characteristics of a CBT, with large pleomorphic chief cells and spindle-shaped sustentacular cells in small, poorly formed nests. The chief cells were strongly immunoreactive for neuron-specific enolase and chromogranin, and focally positive for neurofilament, enkephalin, somatostatin, and beta-endorphin. The sustentacular cells were strongly immunoreactive for S-100 protein and glial fibrillary acidic protein and focally positive for vimentin. Ultrastructurally, the chief cells contained abundant neurosecretory granules. We emphasize that CBT must be included in the differential diagnosis of lateral neck masses. The distinction from adenocarcinoma is difficult on FNAB. The marked cytological atypia in an aspirate of a CBT does not indicate malignancy and may lead to an erroneous diagnosis.