CNS limited ANCA-associated vasculitis presenting as an isolated intraparenchymal mass

The authors report a 34-year-old male with antineutrophil cytoplasmic autoantibody (ANCA) associated vasculitis (AAV) which only involved the central nervous system and presented with an isolated mass in the left parietal lobe. Constitutional symptoms were lacking and the only symptom was progressive right-sided hemiparesis. Pathology suggested necrotizing vasculitis without eosinophils and granulomas. Cytoplasmic ANCA was elevated to 103.9 IU/ml (>5 times the upper limit) in serum. He obtained a regression following treatment of cyclophosphamide and steroids. Prompt diagnosis of AAV is essential since early and aggressive initiation of immunosuppressive therapy can avoid further neurological sequelae.