Primary Angiitis of the Central Nervous System and Its Mimics: A Pattern-Based Approach to Biopsies for Central Nervous System Vasculitis

A diagnosis of CNS vasculitis is dependent on the identification of transmural inflammation and vascular wall damage, preferentially affecting leptomeningeal and superficial cortical vessels. Where a diagnosis of vasculitis is not made, granulomatous, lymphocytic, and necrotizing patterns of inflammation present alternative differential diagnoses. The appropriate application of immunohistochemistry, special stains, and other diagnostic tools is critical in resolving these diagnoses.