Tiny spots, big diagnosis: the hidden face of primary CNS angiitis

Abstract Background Primary angiitis of the central nervous system (PACNS) is a rare, idiopathic vasculitis limited to the CNS, with a wide spectrum of clinical and radiological manifestations. Its diagnosis is often delayed due to overlap with infectious, demyelinating, and neoplastic conditions. Neuroimaging plays a crucial role in raising suspicion and guiding further investigation. Case presentation We report the case of a 38-year-old man who presented with subacute cognitive decline, behavioral changes, and gait disturbance. Magnetic resonance imaging (MRI) of the brain revealed bilateral periventricular and subcortical white matter hyperintensities with prominent perivascular miliary/punctiform enhancement on post-contrast 3D T1-weighted imaging. Extensive laboratory evaluation ruled out infectious, autoimmune, and neoplastic causes. A definitive diagnosis of PACNS was established through brain biopsy, which demonstrated transmural inflammation of small- to medium-sized leptomeningeal and intraparenchymal vessels. The patient was treated with corticosteroids, resulting in progressive improvement. Conclusion This case highlights the diagnostic value of high-resolution MRI (3D T1-weighted sequences) in demonstrating punctiform perivascular enhancement and associated microhemorrhages in PACNS, findings that may be overlooked on conventional 2D post-contrast imaging. A high index of suspicion, in combination with histopathological confirmation, is essential for timely diagnosis. Early immunosuppressive therapy can lead to favorable clinical outcomes.