Tumefactive brain lesion with rapid cavity formation associated with anti-aquaporin-4 antibody

A 54-year-old woman with no medical history presented with left hemiparesis and hemianopsia. Brain MRI showed an extensive lesion without enhancement in the right parietal lobe, followed by rapid cavity formation (figure 1). Brain biopsy performed 55 days after disease onset revealed decreased glial fibrillary acidic protein and aquaporin-4 (AQP4) immunoreactivity, though we could not show the activated complement due to the paucity of the sample (figure 2). Brain biopsy results revealed that the patient was positive for anti-AQP4 antibody. She received methylprednisolone pulse therapy, followed by plasmapheresis. Progression was inhibited. Based on anti-AQP4 antibody-seropositive cases, the concept of neuromyelitis optica spectrum disorders is becoming broader. These disorders should be considered in differential diagnoses when tumefactive brain lesions are observed. Our case highlights the importance of examining AQP4 immunoglobulin G, because it could result in an early diagnosis without performing biopsy.