LAUSR

BACKGROUND Epidermoid cysts are rare, slow growing, benign tumors. They commonly occur at the cerebellopontine angle or the suprasellar region, and they can also occur in the skull. Intradiploic epidermoid cysts are often detected incidentally, but their progression can cause various symptoms. CASE DESCRIPTION The patient was a 49-year-old woman who was diagnosed with otitis media with effusion based on a reported sensation of left ear blockage. Thorough examination revealed a mass lesion in the left occipital bone. Computed tomography depicted a mass lesion on the left occipital bone, part of which reached the inner table of the skull and eroded the mastoid air cell. On magnetic resonance imaging, T1-weighted signal was low but T2-weighted signal and diffusion-weighted signal were high. Intradiploic epidermoid cyst was suspected based on the imaging results, and it was surmised that mastoid cellulitis by the mass lesion accompanied by bone destruction had progressed to otitis media with effusion. The pathological diagnosis was epidermoid cysts. Six months after the operation the otitis media with effusion had improved, and there had been no recurrence of epidermoid cysts. CONCLUSIONS We experienced a case of occipital bone intradiploic epidermoid cysts diagnosed in conjunction with otitis media with effusion.