Background and Purpose— We evaluated risk factors associated with the development of adverse radiation effects (ARE) after stereotactic radiosurgery (SRS) for cerebral arteriovenous malformations (AVMs). Methods— We evaluated 755 patients with AVM who underwent a single Gamma Knife SRS procedure with at least a 2-year minimum follow-up. Eighty-seven patients (12%) underwent previous resection and 128 (17%) had previous embolization. The median target volume was 3.6 mL (range, 0.1–26.3 mL). The median margin dose was 20 Gy (range, 13–27 Gy). Results— Fifty-five patients (7%) developed symptomatic ARE at a median follow-up of 75 months. The cumulative rates of symptomatic ARE were 3.2%, 5.8%, 6.7%, and 7.5% at 1, 2, 3, and 5 years, respectively. Factors associated with a higher rate of developing symptomatic ARE included larger AVM volume, higher margin dose, larger 12-Gy volume, higher Spetzler–Martin grade, and higher radiosurgery-based score. The rates of developing symptomatic ARE were higher in the brain stem (22%) or thalamus (16%), compared with AVMs located in other brain locations (4%–8%). Nineteen patients (3%) sustained irreversible new neurological deficits related to ARE, and 1 patient died. The rates of irreversible symptomatic ARE were 0.8%, 1.9%, 2.1%, and 2.8% at 1, 2, 3, and 5 years, respectively. The 5-year cumulative rates of irreversible symptomatic ARE were 9.1% in thalamus, 12.1% in brain stem, and 1.4% in other locations. Conclusions— The knowledge of ARE risk rates after AVM radiosurgery can assist informed consent for patients with AVM, their families, and healthcare providers.

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This is a retrospective longitudinal study that uses data from the National Health Insurance Research Database (NHIRD) of Taiwan of which hypothyroid patients who received a diagnosis between 2000 and 2010 were selected and followed up until 2011. The primary outcome of this study was the occurrence of tinnitus (ICD-9-CM code 388.3). The relevant comorbidities were selected as potential confounders according to the literature, which included vertigo (ICD-9-CM code 386), insomnia (ICD-9-CM code 780), anxiety (ICD-9-CM code 300.00), and hearing loss (ICD-9-CM code 388–389). The overall incidence of tinnitus was significantly higher in the hypothyroidism cohort than in the non-hypothyroidism cohort (9.49 vs. 6.03 per 1000 person-years), with an adjusted HR of 1.35 (95% CI 1.18–1.54) after adjusting potential confounders. The incidences of tinnitus, as stratified by gender, age, comorbidity, and follow-up time, were all significantly higher in the hypothyroidism cohort than those in the non-hypothyroidism cohort. The incidence of tinnitus significantly increased with age (aHR = 1.01, 95% CI 1.01–1.02). In conclusion, we report the relationship between hypothyroidism and the increased risk for tinnitus. We also found that hypothyroidism patients are at increased risk of developing tinnitus when associated with comorbidities including vertigo, hearing loss, and insomnia.

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