CASE REPORT - BRAIN TUMORS Radiosurgery for infundibulum adenoma: stalk dose implications Jennifer D. Sokolowski 1 & Or Cohen-Inbar 1,2 & Jason P. Sheehan 1 Received: 20 June 2016 /Accepted: 4 July 2016 # Springer-Verlag Wien 2016 Abstract Treating pituitary adenomas in the infundibulum with stereotactic radiosurgery (SRS), achieving tumor volume control while preserving pituitary endocrine function and vi- sual function, is challenging. We present a case of a recurrent remnant infundibular lesion treated with Gamma Knife sur- gery (GKS). The mass was treated with microsurgical resec- tion twice, and the residual stalk lesion was treated with single-session SRS employing a margin dose of 15 Gy to the infundibulum. Five years after GKS, tumor regression persists without visual dysfunction or hypopituitarism. Radiosurgical doses of 30 Gy to the pituitary stalk may be tolerated by patients while maintaining endocrine function. Keywords Stereotactic radiosurgery . Gamma Knife surgery . Infundibulum . Pituitary stalk . Pituitary adenoma Introduction Stereotactic radiosurgery (SRS) has been used to treat pitui- tary adenomas for over 20 years. However, treating pituitary adenomas residing in the infundibulum, achieving tumor vol- ume control while preserving pituitary endocrine function and visual function, is challenging. The optic pathways residing at the superior extent of the infundibulum are known to be ex- traordinarily radiosensitive structures, and dogma has been that even relatively low dose radiation exposure to the infun- dibulum carries the risk of hypopituitarism [1, 2, 4, 11]. Studies done by one group looking at radiation dose to the infundibulum noted a mean dose of 7.7 ± 3.7 versus 5.5 ± 3 in patients with and without post-treatment deficits, respectively [1], and another study from that group noted mean treatment dose of 6.5 versus 4.1 Gy in patients with and without deficits, respectively [2]. These stalk threshold radiation doses are low- er than thresholds for the pituitary gland, and these data have led to the belief that the stalk is more sensitive to radiation, but specific rates of side effects after SRS aimed at pituitary stalk lesions have not been reported. There are limited data proving that stalk dose is an independent factor that predicts risk of hypopituitarism post SRS [4, 8]. Herein, we present a case of a SRS treatment of residual pituitary adenoma involving the entire infundibulum that was treated with stereotactic radiosurgery without incurring visual deficits or hypopituitarism. The dose used to treat the adeno- ma was substantially higher than previously reported safe thresholds for the infundibulum. Materials and methods The patient was diagnosed with a pituitary macroadenoma after he was noted to have elevated prolactin levels at age 64. The prolactin was reportedly mildly elevated, not consistent with prolactinoma. He presented 3 years later with complaints of sub- jective haziness in the temporal fields bilaterally, and he subse- quently underwent a formal visual field test, which was normal, but a visual-evoked response study was abnormal, prompting an MRI study. The MRI revealed a macroadenoma, now with suprasellar extension abutting the optic chiasm (Fig. 1a–b). His prolactin at this time was 28.9 ng/ml. Other measured hormones were normal preoperatively, including serum free T4, cortisol, adrenocorticotropic hormone, and insulin-like growth factor 1. The patient underwent transsphenoidal resection in February 2009 at age 67, which demonstrated a nonfunction- ing lesion that was negative for adrenocorticotropic hormone, prolactin, growth hormone, follicle-stimulating hormone, * Jennifer D. Sokolowski soko@virginia.edu 1 Department of Neurological Surgery, University of Virginia, PO Box 800212, Charlottesville, VA 22908, USA 2 Department of Neurosurgery, Rambam Health Care Center, Haifa Israel Molecular Immunology &Tumor Immunotherapy Laboratory, Technion Institute of Technology, Haifa, Israel Acta Neurochir DOI 10.1007/s00701-016-2894-1