Aggressive small cell tumor of the skull base

A 40-year-old Black man presenting with increasing nasal discharge of bloody, mucoid pus as well as nasal obstruction over a 2-month period is described. Magnetic resonance imaging of the skull showed a tumor eroding through the skull base into the clivus and extending into the sphenoid sinus. Endoscopy of the sphenoid sinus demonstrated a polypoid mass extending into the posterior choanae. The lesion was partially resected. Histologic evaluation showed a cellular small blue cell tumor punctuated by bland, epithelial-lined microcysts. Electron microscopy revealed epithelial cells with abundant rough endoplasmic reticulum and electron-dense membrane-bound endocrine granules, some undergoing misplaced exocytosis. Immunohistochemical evaluation demonstrated cytoplasmic reactivity for neuron-specific enolase, synaptophysin, and prolactin. Stains for leukocyte common antigen, HMB-45, desmin, cytokeratin, chromogranin, and the remaining spectrum of pituitary hormones including growth hormone, corticotropin, luteinizing hormone, follicle-stimulating hormone, and thyrotrophic hormone were negative. In contrast, the epithelium lining the cysts was cytokeratin positive and synaptophysin negative. This ostensibly small cell tumor therefore represented a remarkably extensive and aggressive prolactin cell adenoma with unusual light microscopic features. Characterization of the lesion required electron microscopy and further confirmation by immunocytology. The distinction of pituitary adenomas and particularly of prolactin cell tumors from other adenoma types and from other small cell lesions markedly affects therapy and patient prognosis.