Abstract DP365: Differentiating Small Vessel CNS Vasculitides: Comparative MRI Features of Primary Angiitis of the Central Nervous System and Susac Syndrome

Background: Primary angiitis of the central nervous system (PACNS) and Susac syndrome are rare, immune-mediated small-vessel vasculitides with overlapping clinical and imaging features. PACNS is a T-cell–mediated disorder confined to the CNS, while Susac syndrome is a B-cell–mediated endotheliopathy involving CNS, retinal, and cochlear microangiopathy. Accurate differentiation is critical, especially in patients presenting with isolated CNS findings and without angiographic abnormalities, as management differs substantially. Objective: To compare MRI features between Susac syndrome and PACNS in order to identify distinguishing imaging markers that aid diagnostic accuracy in CNS-predominant presentations. Methods: This retrospective study included two Cleveland Clinic cohorts. The Susac cohort (n=61) was drawn from the Susac Syndrome Retrospective Cohort (2004–2025), encompassing patients meeting established diagnostic criteria based on clinical, imaging, and ophthalmologic/audiologic findings. The PACNS cohort (n=31) included only small-vessel subtype patients from the Cerebral Vasculitis Clinic (2015–2024), requiring biopsy- or angiography-supported diagnosis and exclusion of systemic vasculitis. MRI brain imaging was reviewed for corpus callosum involvement, white matter enhancement, infarct patterns, cerebellar lesions, leptomeningeal enhancement, and gray matter involvement. Fisher’s exact test was used for categorical comparisons. Results: Corpus callosum lesions were significantly more common in Susac (83.6%) than PACNS (19.4%) (p<0.001, OR=0.05). Cerebellar involvement also favored Susac (45.9% vs 19.4%, p=0.013). PACNS patients more frequently showed enhancing white matter lesions (65.5% vs 27.3%, p=0.001, OR=5.07) and lacunar infarcts (29.0% vs 11.5%, p=0.045). Periventricular/subcortical white matter involvement was nearly universal in both groups. No significant differences were observed in acute infarcts, leptomeningeal enhancement, or deep gray matter lesions. Conclusions: Despite shared small-vessel pathology, Susac syndrome and PACNS demonstrate distinct imaging patterns. Corpus callosum and cerebellar involvement suggest Susac, while white matter enhancement and lacunar infarcts support PACNS. These imaging markers may improve diagnostic precision and guide immunotherapy.