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Background: Repeat stereotactic radiosurgery (SRS) for persistent cerebral arteriovenous malformation (AVM) has generally favorable patient outcomes. However, reporting studies are limited by small patient numbers and single-institution biases. The purpose of this study was to provide the combined experience of multiple centers, in an effort to fully define the role of repeat SRS for patients with arteriovenous malformation., Methods: This multicenter, retrospective cohort study included patients treated with repeat, single-fraction SRS between 1987 and 2022. Follow-up began at repeat SRS. The primary outcome was a favorable patient outcome, defined as a composite of nidus obliteration in the absence of hemorrhage or radiation-induced neurological deterioration. Secondary outcomes were obliteration, hemorrhage risk, and symptomatic radiation-induced changes. Competing risk analysis was performed to compute yearly rates and identify predictors for each outcome., Results: The cohort comprised 505 patients (254 [50.3%] males; median [interquartile range] age, 34 [15] years) from 14 centers. The median clinical and magnetic resonance imaging follow-up was 52 (interquartile range, 61) and 47 (interquartile range, 52) months, respectively. At last follow-up, favorable outcome was achieved by 268 (53.1%) patients (5-year probability, 50% [95% CI, 45%-55%]) and obliteration by 300 (59.4%) patients (5-year probability, 56% [95% CI, 51%-61%]). Twenty-eight patients (5.6%) experienced post-SRS hemorrhage with an annual incidence rate of 1.38 per 100 patient-years. Symptomatic radiation-induced changes were evident in 28 (5.6%) patients, with most occurring in the first 3 years. Larger nidus volumes (between 2 and 4 cm 3 , subdistribution hazard, 0.61 [95% CI, 0.44-0.86]; P =0.005; >4 cm 3 , subdistribution hazard, 0.47 [95% CI, 0.32-0.7]; P <0.001) and brainstem/basal ganglia involvement (subdistribution hazard, 0.6 [95% CI, 0.45-0.81]; P <0.001) were associated with reduced probability of favorable outcome., Conclusions: Repeat SRS confers reasonable obliteration rates with a low complication risk. With most complications occurring in the first 3 years, extending the latency period to 5 years generally increases the rate of favorable patient outcomes and reduces the necessity of a third intervention., Competing Interests: Disclosures Dr Palmer has received grants from Genentech Inc. and Varian Medical Systems Inc, speaking fees from Varian Medical Systems Inc, and is a consultant for Novocure Inc. Dr Lunsford has ownership interest (shareholder) in Elekta AB and is a consultant Chair DSMB for Insightec Inc. Dr Cifarelli has received a speaking honorarium from Carl Zeiss Meditech AG. Dr Liscak is a consultant for Elekta AB. Dr McInerney has received funding from Elekta AB for research unrelated to this study. The other authors report no conflicts.

Objective: Clinically significant spinal hemorrhage is an extremely rare but potentially devastating complication of spinal epidural steroid injection. We report a rare case of cauda equina syndrome after spinal epidural injection that inadvertently penetrated an unrecognized spinal paraganglioma., Methods: The clinical records for a patient presenting with cauda equina syndrome were retrospectively reviewed. A literature search was performed to identify reports of cauda equina syndrome in patients undergoing spinal epidural steroid injection, as well as recent large series describing complications associated with these injections., Case Report: A 37-year-old man presented to our emergency department with severe low back pain radiating bilaterally to the lower extremities and urinary incontinence. His pain had greatly intensified 1 day after spinal epidural steroid injection. He had a 1-year history of low back pain diagnosed as disk herniation and managed conservatively but had experienced recent onset of a similar pain and new onset of nocturnal back pain causing sleep disturbance. Epidural injection had been administered based on the earlier diagnosis of disk herniation. Examination using magnetic resonance imaging revealed a previously unrecognized oval hemorrhagic mass lesion at L2-3, which had been inadvertently penetrated during epidural injection. Emergent en bloc resection resolved the patient's neurological symptoms. At histopathologic analysis, the tumor was diagnosed as a spinal paraganglioma., Discussion: The presented case indicates the importance of a thorough history, physical examination, and imaging assessment before spinal epidural steroid injection.