To describe a potential novel imaging biomarker in a series of patients with suspected primary angiitis of the central nervous system (PA-CNS).

Primary angiitis of the central nervous system (PA-CNS) is a rare and heterogeneous disease notoriously difficult to diagnose. PA-CNS had been classically associated with ischemic or hemorrhagic strokes as well as contrast-enhancing lesions. Subcortical and brainstem cavitary lesions with surrounding T2 hyperintensity on magnetic resonance imaging (MRI) can be seen in lacunar strokes, but they have not traditionally been associated with PA-CNS.

This is a case series involving a retrospective chart review of 9 patients (April 2013-January 2024) selected based on high degree of clinical and neuroradiological suspicion for PA-CNS and presence of one or more prominent subcortical or brainstem cavitary lesions on MRI.

All 9 cases demonstrated a constellation of clinical and neuroradiologic features of PA-CNS, including headache, stroke, multiple parenchymal lesions, and vessel abnormalities. Each patient had one or more cavitary lesions with low central T1/FLAIR, high central T2, and high surrounding T2/FLAIR signal. Lesions were located in subcortical and brainstem regions.

We report a series of patients suspected to have PA-CNS with multiple subcortical and brainstem lesions on MRI, characterized by central encephalomalacia and a surrounding rim of FLAIR hyperintensity. While the differential for these lesions includes chronic small vessel strokes or demyelinating disease, they have several atypical features. This observation could represent an opportunity to delineate a new radiographic biomarker to aid in diagnosis of PA-CNS. Future study is needed with consistent use of diagnostic methods for PA-CNS, such as brain biopsy, to confirm this novel association.