Natural course and treatment outcomes of arteriovenous shunts below the conus medullaris

OBJECTIVE: Arteriovenous shunts below the conus medullaris (AVS-BC) have an unstudied natural history. The aim of this study was to elucidate the natural history of AVS-BC and to clarify the clinical onset, progression, and treatment outcomes for management strategy optimization. METHODS: A prospectively maintained database was retrospectively reviewed for consecutive symptomatic patients with AVS-BC between January 2000 and July 2023. Onset and deterioration patterns were categorized as acute or gradual and assessed using the modified Aminoff-Logue Scale (mALS) and modified Denis Pain and Numbness Scale (mDS). Time to deterioration before and after treatment was evaluated using Kaplan-Meier analysis, restricted cubic splines, and Cox and logistic regression modeling. RESULTS: The analysis included 132 patients (113 male, median age 54.5 years) with AVS-BC, with a median observational period of 9.00 months (IQR 5.25-12.00 months). Acute onset occurred in 18.2% of patients, with 16.7% experiencing acute deterioration. The overall pretreatment deterioration rate was 6.5% per month. Deterioration risk was highest shortly after the initial onset. Patients aged 50-70 years were less likely to experience deterioration (p = 0.02). Half the patients underwent embolization and 43.9% underwent microsurgery, with an anatomical cure achieved in most patients. The overall monthly deterioration rate after treatment was 0.5%. The mALS grade at admission was a significant risk factor for spinal motor deterioration (HR 0.60, 95% CI 0.45-0.79; p < 0.001). For sensory deterioration, risk factors included dural AVS-BC (HR 2.98, 95% CI 1.02-8.69; p = 0.046), a drainage diameter of 1.5-2.0 mm (HR 2.48, 95% CI 1.05-5.84; p = 0.038), and the admission mDS score (HR 1.66, 95% CI 1.24-2.21; p < 0.001). Deeper segments (L5-S1, HR 2.70, p = 0.024; S2-5, HR 13.00, p < 0.001) predicted embolization as the treatment modality. CONCLUSIONS: Rapid deterioration was observed among patients with AVS-BC, particularly after onset. While early treatments were beneficial for most patients, gradual deterioration after treatment warrants further research.