Extradural petromastoid calcifying pseudoneoplasm of the neuraxis (CAPNON): Case report and literature review

•Calcifying pseudoneoplasm of the neuraxis is a rare intracranial tumor.•We report a case of intracranial-extradural CAPNON in the mastoid region.•Patient was managed with surgical resection with good early result.•Tumor usually affects bony sinuses benignly but mimics common lesions.•Consider CAPNON in the differential diagnosis of skull base tumors. Calcifying pseudoneoplasm of the neuraxis (CAPNON) is a very rare tumor with fewer than 70 cases reported in the literature. In general, this tumor occurs intracranially either within the brain parenchyma or in an extra-axial location, but it has also been described within the spine as an extra-axial lesion. We describe an unusual case of intracranial-extradural CAPNON involving the mastoid region. This may be only the second such case reported in the literature, as one patient with CAPNON has been reported involving the sinonasal region. Our patient was managed with surgical resection through a translabyrinthine approach with good early result. We describe an unusual case of extradural CAPNON involving the mastoid bone. It appears that when located extradurally, this tumor may have a predilection for the bony sinuses. This little-known, generally benign entity can mimic more common lesions such as meningiomas, and should be considered in the differential diagnosis of skull base tumors, particularly when associated with heavy calcification.