Neoplasms which arise from or metastasize to the pituitary gland. The majority of pituitary neoplasms are adenomas, which are divided into non-secreting and secreting forms. Hormone producing forms are further classified by the type of hormone they secrete. Pituitary adenomas may also be characterized by their staining properties (see adenoma, basophil; adenoma, acidophil; and adenoma, chromophobe). Pituitary tumors may compress adjacent structures, including the hypothalamus, several cranial nerves, and the optic chiasm. Chiasmal compression may result in bitemporal hemianopsia.