Treatment paradigms for pituitary adenomas: defining the roles of radiosurgery and radiation therapy
Pituitary adenomas represent one of the most common types of intracranial tumors. While their macroscopic appearance and anatomical location are relatively homogeneous, pituitary tumors have the potential to generate a wide variety of clinical sequelae. Treatment options for pituitary tumors include medical therapy, microscopic or endoscopic surgical resection, radiosurgery, radiation therapy, or observation depending on the biochemical profile and clinical status of the patient. Radiosurgery and external beam radiation therapy (EBRT) are most commonly as adjunctive treatments following incomplete surgical resection leaving residual tumor, tumor recurrence, or failure of medical therapy. We present a comprehensive literature review of the radiosurgery series for pituitary tumors including nonfunctioning adenomas, ACTH- and GH-secreting adenomas, and prolactinomas. While post-radiosurgery radiographic tumor control for nonfunctioning adenomas is excellent, typically around 90 %, the rates of biochemical remission for functioning adenomas are lower than the tumor control rates. The highest endocrine remission rates are achieved patients with Cushing’s disease and the lowest in those with prolactinomas. Although EBRT has been largely supplanted by radiosurgery for the vast majority of pituitary adenomas cases, there remains a role for EBRT in select cases involving large tumor volumes in close proximity to critical neural structures. By far the most common complication after radiosurgery or EBRT is delayed hypopituitarism followed by cranial neuropathies. The effect of suppressive medications on radiosurgery outcomes remains controversial. Due to the rare but well-documented occurrence of late recurrence following endocrine remission, long-term and rigorous clinical and radiographic follow-up is necessary for all pituitary adenoma patients treated with radiosurgery or EBRT.