The pituitary gland is the master gland of the body because it controls most of the body's endocrine functions by means of the hypothalamic-pituitary axis. The anterior lobe of the pituitary gland secretes 6 hormones: thyroid-stimulating hormone (TSH), previously adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), leuteinizing hormone (LH), growth hormone (GH), and prolactin (PRL). The posterior pituitary gland secretes vasopressin and oxytocin.
Pituitary adenomas are almost always benign with no malignant potential. In general, pituitary lesions can be subdivided into nonsecretory and secretory tumors of the pituitary gland, other intrasellar tumors, and parasellar tumors. The last group occurs in the vicinity of the sellar turcica and can mimic the pituitary tumors in terms of the symptoms they cause. Nonsecretory pituitary tumors are called null-cell tumors. Small null-cell tumors measuring a few millimeters are common and found in up to 25% of autopsied pituitary glands. These may grow slowly, destroying normal pituitary function (hypopituitarism), or they may compress nearby structures and cause neurologic problems.
Functioning pituitary adenomas can be clinically classified by means of the hormone they elaborate. These tumors become symptomatic because they secrete hormones, and they are less likely than like null-cell tumors to become large enough to compress adjacent structures. As pituitary tumors grow, destruction of normal pituitary tissue results in various hormonal deficiencies. In rare cases, these tumors may spontaneously hemorrhage or become infarcted. The pressure they exert on nearby structures can produce double vision and facial numbness. The optic chiasm is directly above the pituitary gland, and upward growth of pituitary tumors frequently causes progressive visual loss. This visual loss typically begins from each side of the field of vision and leads to tunnel vision and then blindness.