Oncocytic and granular cell neoplasms of the central nervous system and pituitary gland.

Oncocytic transformation is an infrequent event within the central nervous system and is limited to neoplasms of the choroid plexus, meninges, and pituitary gland. Oncocytic modifications in choroid plexus tumors seem to occur predominantly in adult patients and in the fourth ventricle and do not seem to reflect any particular biological behavior. Meningiomas showing oncocytic differentiation have been recently described and this variant probably behaves more aggressively. Pituitary oncocytomas are regarded as a subtype of null cell adenomas. Oncocytic tumors have a significantly higher risk of progression with a higher recurrence rate after radiotherapy. Oncocytic changes in astrocytic neoplasms are rare. More frequently, astrocytomas can show granular changes that result in neoplasms composed of cells with granular cytoplasm and eccentric nuclei resembling foamy macrophages. Granular cell astrocytomas may mimic non-neoplastic lesions such as cerebral infarction and demyelinating disease. Cells with granular bodies are frequent in pilocytic astrocytoma, pleomorphic xanthoastrocytoma, and ganglion cell tumors. Their presence is considered a useful diagnostic finding to distinguish these low-grade lesions from malignant gliomas. A rare neoplasm is the granular cell tumor of the infundibulum that, when symptomatic, has to be differentiated from pituitary adenomas and other more common lesions of the sellar region.