Pituitary adenoma as an unsuspected clival tumor.

Pituitary adenomas are common tumors that account for about 10% of intracranial neoplasms. Most arise from the adenohypophysis and are confined to the region of the sella turcica. Other sites may be involved as a result of extension, infiltration, or ectopic location. However, posterior extension or ectopic involvement of the clivus of the sphenoid and occipital bones is rare. Seven patients with destructive clival masses were referred to our institution with presumptive diagnoses of chordomas. In all cases, histologic workup revealed pituitary adenomas. Because they represent a subset of adenomas, the histologic features of the tumors were studied, and the clinical histories of the patients were reviewed. Five of the patients were men, aged 31 to 67 years, and two were women, aged 55 and 67 years. Four patients had extremely high plasma concentrations of prolactin (8,132-22,424 ng/ml, nl < 15). Four tumors resembled usual sellar adenomas; however, three exhibited nuclear pleomorphism, mitotic figures, and other morphologic features, suggesting alternate diagnoses. Three required immunoperoxidase stains in addition to those for pituitary hormones, and three required electron microscopy for diagnosis. Destructive invasion of the clivus by pituitary adenomas is rare, and anaplastic features of some of the tumors may lead to difficult diagnoses.