Answer: Paraganglioma

Histology: The tumor is composed of distinct nests of cuboidal cells, separated by highly vascularized fibrous septa consistent with neuroectodermal origin.

The individual tumor cells have a moderate abundant granular and somewhat basophilic cytoplasm. Occasional large or even bizarre tumor cell nuclei may be found but this phenomenon is common in neuroendocrine neoplasms and, in the absence of excessive mitotic activity, is of no consequence.

Discussion: Paraganglioma is a broad term applied to tumors arising in paraganglia regardless of location. The tumor under discussion here would actually be subclassified as a chemodectoma because it appeared to arise from the carotid body.

Immunocytochemically, the tumor cells are surrounded by S-100 protein positive sustentacular cells in the periphery of the tumor cell nests. The tumor cells themselves will be reactive for chromogranin and negative for keratin, distinguishing this lesion from most of the other entities listed suggested as a diagnosis above. Alveolar soft part sarcoma (ASPS) has clearly been confused in the past with paraganglioma and with granular all tumor. Many malignant granular cell tumors on the older literature are probably ASPS. ASPS occurs in deep soft tissues and usually comprised of central nests of tumor cells surrounded by fibrous tissue rather than the fibrovascular septa of chemodectoma. The alveolar pattern arises from detachment of the central cells in the cell nests. The individual tumor cells are large with prominent nucleoli and a granular cytoplasm. Occasionally PAS stains reveal intracytoplasmic needle-like structures.

A specific chromosonal translocation has been described and the presence of aberrant nuclear expression of TFE3 can be demonstrated by immunohistochemistry.

Reference(s):
– Rosai J, Rosai and Ackerman’s Surgical Pathology, Ninth Edition, Mosby, New York, 2004, pp 153-154, pp 1142-1146 and pp 2318-2320.