Revisiting radioresistance: a systematic review of outcomes of Stereotactic radiosurgery (SRS) in functional head and neck paragangliomas.

This systematic review evaluates the role of stereotactic radiosurgery (SRS) in managing functional head and neck paragangliomas (FPG), which pose unique challenges due to catecholamine secretion and associated functional symptoms. Currently there are no established management guidelines for FPG because of their rarity. We explore clinical, radiological and hormonal outcomes of SRS and conventional radiotherapy (RT), challenging traditional assumptions of radioresistance in FPG. Following PRISMA guidelines, databases including PubMed, Scopus, Web of Science, ResearchGate, Google Scholar, and Embase were searched for English-language studies on SRS for head and neck paragangliomas (HNPG) up to December 2024. Keywords included "Glomus," "SRS," "Gamma Knife Radiosurgery," and "CyberKnife." Studies reporting clinical, radiological, or hormonal outcomes for FPG treated with SRS were included. Data extraction focused on tumor location, SRS parameters, clinical symptoms, and follow-up results. We included eight studies, documenting 10 cases of FPG treated with SRS. Tumors were located in the jugular (6 cases), Jugulo-tympanic (3 cases), and carotid body (1 case). Seven cases were treated with Gamma Knife Radiosurgery (GKRS), while CyberKnife was used in three. Primary SRS was performed in three cases, and five underwent secondary SRS for residual or recurrent disease. Hormonal outcomes showed normalization of catecholamine levels in six cases 30-36 months post-SRS. There was resolution of functional symptoms in all cases treated with high-dose SRS. SRS is a viable alternative or adjunct to surgical intervention in FPG, achieving favorable clinical, hormonal, and radiological outcomes with minimal morbidity. Our findings challenge the conventional view of the radioresistance of FPG, highlighting the potential for sustained biochemical and symptomatic control. The limited number of cases underscores the need for future studies with standardized outcome reporting to refine therapeutic strategies for this rare condition.