Debulking surgery of pituitary adenoma as a strategy to facilitate definitive stereotactic radiosurgery

Neil Forster, Ronald Warnick, Vinita Takiar, Luke Pater, John Breneman

In patients with pituitary adenomas (PA) who are unable to undergo complete surgical resection, radiation therapy (RT), specifically stereotactic radiosurgery (SRS), results in excellent local control. However, the utility of radiosurgery may be limited by the proximity of the lesion to the optic chiasm (OC). We evaluate the efficacy of debulking surgery in increasing the PA-OC separation to convert patients into SRS candidates. From 2007 to 2015, 31 patients with PA < 2 mm from the OC underwent debulking surgery followed by RT within 2 years of resection. Coronal and sagittal T1-pre- and post-contrast sequences were used to determine PA-OC separation. Time interval between postoperative and pre-radiotherapy MRI scans and type of radiation therapy were analyzed. Functional tumor status, tumor characteristics [cavernous sinus (CS) or suprasellar (SS) involvement, chiasm/nerve encasement (NE)], and presence of ≥ 2 of these characteristics (multiple factors, MF) was also noted. Surgery converted 9 of 31 patients (29%) to SRS candidates. Median time from surgery to pre-RT planning MRI was 8 months (range 2-20). Of the 31 patients initially ineligible for SRS, 6 became eligible immediately after surgery, and another 3 were deemed eligible on follow-up. Mean PA-OC separation was 0.3 mm preoperative, 1.4 mm postoperative, and 2.1 mm at time of SRS (p = 0.002). Preoperative SS, NE, and MF involvement predicted pre-RT separation < 2 mm. Debulking surgery of unresectable pituitary tumors is a successful strategy for converting select radiosurgery-ineligible patients to radiosurgery candidates. Absence of preoperative SS, NE, and MF predicts for successful conversion.