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.