Pituitary adenomas comprise 10 - 12% of intracranial tumors in the United States and may be classified as either microadenomas, 1 cm or less, or macroadenomas and functioning or non-functioning.
The usual initial treatment is surgery to establish a diagnosis and relieve pressure, especially on the optic chiasm. Radiation therapy has been used in the management of pituitary tumors since the first published studies in 1909. It is used in the case of recurrent adenomas following surgery as well as for persistent syndromes of hyperfunction.
Patients unsuitable for surgery may also be treated with irradiation when the clinical picture is compatible and surgery contraindicated.
The role of radiosurgery, such as with the Gamma Knife, is to treat small residual functioning adenomas after surgery or prevent regrowth of macroadenomas which have been subtotally resected. It is also be used for salvage treatment of recurrent adenomas following previous fractionated irradiation.
Treatment strategies would include repeat surgery, medical management or interval follow-up if the patient is asymptomatic. Pituitary adenomas have a variable recurrence rate ranging from 6 – 69% (median 23%) with surgery alone and a similar rate after irradiation only. The combination of surgery and postoperatrive irradiation can reduce the recurrence rate by approximately one-half to about 11%. Long term follow-up is necessary because of late relapses at 10 and 20 years.
Complications and Outcomes
Side-effects of Gamma knife treatment include a 15% incidence of hypopituitarism. Injury to the visual apparatus is extremely rare, less than 1% when the recognized dose limits are maintained.
Gamma Knife radiosurgery thus remains a valuable therapeutic option for patients with pituitary adenomas.
Becker et al. Strahlentherapie und Onkologie 2002, 4:173-186.