[A case of painful tic convulsif due to cerebellopontine angle epidermoid tumor which could not be clearly detected by MRI].

A case of painful tic convulsif (trigeminal neuralgia and ipsilateral hemifacial spasm) caused by cerebellopontine angle epidermoid tumor is presented. This tumor was compressed to the trigeminal nerve, and became attached to the facial and auditory nerves. The facial nerve exit-zone of brain stem was also compressed by the tumor along with a branch of the posterior inferior cerebellar artery. Total removal of the tumor was carried out and neuralgia and facial spasm disappeared. Painful tic convulsif caused by brain tumor is rare (eight cases in the literature plus our case), but epidermoid tumor is not rare as a cause of this complaint (seven in eight cases). In preoperative examination of this case, we could not detect this epidermoid in the cerebellopontine angle, because this tumor was the same intensity as CSF liquid on magnetic resonance imaging (T1 and T2 weighted image) and exerting hardly any mass effect on the brainstem. On encountering a case of painful tic convulsif of unknown origin despite the usual preoperative examinations, it may be useful that same kind of brain tumor, especially, epidermoid might be concealed in the cerebellopontine angle lesion.