The pathology of nonfunctional pituitary adenomas

The nonfunctional adenomas also known as undifferentiated, null cells, or nonsecretory adenomas are endocrinologically silent neoplasms of the anterior lobe of the pituitary gland. They constitute 50% of all pituitary adenomas in the present report. Most tumors are large, often growing beyond the confines of the sella turcica and characterized anatomically by displacement and compression of the adjacent sellar structures including the optic chiasm, hypothalamus, and third ventricle. Others may be truly invasive when they locally or diffusely infiltrate the adjacent structures. They may grow through the dura and the bone into the cranial cavity and/or the sphenoidal sinus and the nasopharynx or infiltrate one or both cavernous sinuses. Seventy-six adenomas were divided into 48 nononcocytic adenomas and 28 oncocytic adenomas or oncocytomas occurring in older patients. By light microscopy using conventional histologic stains, the majority of nononcocytic tumors were chromophobic. The oncocytomas were slightly acidophilic with a large granular cytoplasm. With the peroxidase-anti-peroxidase (PAP) method with anti-sera for the anterior pituitary hormones, the adenoma cells show no immunostaining. Ultrastructurally, the nononcocytic tumors possess a modest number of small secretory granules but no specific ultrastructural features. The oncocytic tumors are characterized by an excessive number of mitochondria in their cytoplasm. With the PAP method using cytochrome C oxidase antiserum, specific identification of mitochondria can be made. As the nonfunctional adenomas are devoid of anterior pituitary hormones they have been called "null cell" adenomas. However, most of the null-cell adenomas are positive for chromogranin. The diagnosis of nonfunctional adenoma can be suspected clinically when in the absence of signs of hypersecretion of pituitary hormones, there is radiologic evidence of ballooning of the sella and bulging of its diaphragm. An invasive adenoma can be detected by radiologic signs of destruction of the sella turcica and its boundaries or by neurosurgical intervention when there are findings of invasion of the dura, the parasellar, and suprasellar structures.