Background: Gamma knife treatment outcome of large pituitary tumors which are only partially irradiated secondary to immediate proximity to critical structures such as the optic apparatus have not been rigorously studied.
Materials and methods: From July 2003 to December 2013, there were 41 cases of recurrent or residual nonfunctioning pituitary macroadenoma partially treated with gamma knife radiosurgery (GKRS) because the adenoma obscured part of the optic apparatus on planning SRS MR imaging.
Results: The follow up period after GKRS was 92.3 ± 5.6 months. The percentage of tumor coverage with the full dose was 88.5 ± 0.7%. Five of 43 (11.6%) patients experienced a transient visional decrease and one patient experienced a permanent visual field defect. During the follow up, two patients underwent transphenoidal surgery and one patient had a craniotomy due to tumor progression. Seven patients (16.2%) developed cortisol and thyroxine deficiencies. In multiple variant analyses, transient visual decline was correlated to the tumor volume (> 3.5 cc), percentage of tumor coverage (< 90%), the distance from the optic apparatus to the pituitary stalk (> 15 mm) and percentage of tumor above the orbital apex (65%).
Conclusion: In the limited case of this cohort, we found that partially treated pituitary nonfunctioning macroadenoma yielded a high tumor control rate. However, visual decline as a result of tumor progression or radiation effect can occur in a minority of patients. The radiosurgical technique warrants further study to better define the long-term risk to benefit profile for its use in complex pituitary macroadenoma obscuring part of the optic apparatus.
Keywords: Gamma knife radiosurgery; Irradiation optic nerve neuropathy; Pituitary macroadenoma.