The Para-ISS Dural Space Enhancement Sign: A Novel MRI Finding Independently Associated With Intracranial Atherosclerotic Burden

Background: No dural enhancement sign centered on the inferior sagittal sinus (ISS) has been characterized. We observed a frequent, previously undescribed finding - para-ISS dural space enhancement (PISE) - at the free inferior margin of the falx cerebri. Objective: To define PISE, determine its detection rate in a large cross-sectional cohort, and characterize its correlates, in particular whether the pattern of association is compatible with an atherosclerosis-related dural mechanism. Methods: Consecutive contrast-enhanced intracranial vessel-wall MRI (VWI) examinations (May 2015-December 2025) were reviewed; 835 of 875 examinations were evaluable, corresponding to 811 patients. The first outcome-evaluable examination for each patient was used for all primary analyses. PISE was defined as dural enhancement strictly at the falx free margin adjacent to the ISS, exceeding the ISS vascular lumen. Forty-seven demographic, clinical-history, and imaging variables were tested univariately with Benjamini-Hochberg false discovery rate (FDR) correction; multivariable logistic regression with patient-grouped 5-fold cross-validation was triangulated with LASSO and random forest. Dose-response across plaque grades was assessed with the Cochran-Armitage trend test, and circulation-specific associations were compared in models adjusted for age and sex (inter-reader Cohen's kappa = 0.93). Results: PISE was detected in 609/811 patients (75.1%); detection rose from 50.0% (<40 years) to 81.7% (>70 years; trend p = 5.6 x 10^-6). The strongest univariate correlate was vulnerable intracranial plaque (OR=8.29, 95% CI 5.54-12.40). Detection increased across plaque grades 0/1/2 (38.7% -> 77.2% -> 90.3%; Z=11.09). Anterior-circulation plaque showed a stronger association than posterior-circulation plaque (OR=4.42 vs 2.76). Vulnerable plaque (OR=2.37), plaque grade (OR=2.84 per grade), age (OR=1.38 per SD), and inpatient status (OR=3.18) remained independently associated (patient-grouped cross-validated AUC=0.755). Moyamoya disease was inversely associated (OR=0.25). Findings were consistent across imputation and all-examination sensitivity analyses. Conclusions: PISE is a frequently detected novel dural enhancement sign whose independent, graded, anatomically concordant association with intracranial atherosclerotic burden supports an atherosclerosis-related dural mechanism and warrants prospective validation.