[Small epidermoid induced trigeminal neuralgia unrecognized by conventional CT and MRI for over 25 years]

A 65-year-old woman had been conservatively treated as idiopathic trigeminal neuralgia for over 25 years, because conventional computed tomography (CT) and magnetic resonance imaging(MRI) showed no abnormality in the cerebello-pontine(CP) angle cistern. She received a detailed MRI by constructive interference in steady state and diffusion weighted image(DWI) sequences. Those sequences on MRI well demonstrated a epidermoid tumor in the CP angle cistern, and the removal of the tumor completely resolved the neuralgia. Since a small epidermoid in the CP angle cistern seems to be unrecognized by conventional CT and MRI, detailed evaluation by DWI sequence, which has been widespread recently, is required for patients with trigeminal neuralgia.