Calcifying pseudoneoplasm of the neuraxis ( <scp>CAPNON</scp> ) associated with neurenteric cyst. An autopsy case showing unusual fatal outcome

Background Calcifying pseudoneoplasm of the neuraxis (CAPNON) is a rare calcified tumefactive lesion that can occur in the brain or spine. Although the aetiology and natural course of CAPNON has not yet been fully established, recent study reported that many CAPNON cases have dual pathology, which may be associated with its aetiology. Case presentation A 53-year-old man with a history of an untreated brain mass was taken to a hospital by emergency transport. A computed tomography scan revealed an intracranial hypo-attenuated mass exhibiting mass effect. Several calcified foci were observed around the lesion. He suddenly showed tonic seizure after admission, therefore an emergency craniotomy was performed. However, he unfortunately died due to advanced cerebral oedema. Microscopic findings of the surgically obtained materials were consistent with neurenteric cyst (NC). Intracranial hard masses were found adjacent to NCs and the masses were composed of fibrous cartilage-like matrix with massive linear calcification and surrounding round-to-oval epithelioid cells. Conclusion CAPNON associated with NC was considered to be most appropriate diagnosis of present case. To the best of our knowledge, this is the first report of such case. The present case suggests that delay of treatment may cause a poor outcome, at least in CAPNON associated with NC. Careful investigation, including of the underlying pathology, may be essential for deciding treatment strategies for CAPNON.