Dermoid cyst in the facial nerve--a unique diagnosis.

Facial nerve paralysis in children may occur as a complication of infections, trauma, or rarely from benign or malignant tumors of the facial nerve. We present the first reported case of a dermoid tumor in the facial nerve causing facial paralysis in a child. Case report at a tertiary Children's Hospital. A 9-month-old was referred to our institution for evaluation of persistent, complete right sided facial paralysis three months after receiving a diagnosis of Bell's palsy. A workup at our institution including MRI and CT revealed marked widening of the facial canal in the mastoid segment consistent with facial nerve schwannoma or hemangioma. Surgical exploration via mastoidectomy and facial nerve decompression revealed keratinous material containing hair that had fully eroded the facial nerve, disrupting it completely. The entire tumor was removed along with the involved segment of facial nerve, and the missing facial nerve segment was cable grafted. Histological examination of the tumor confirmed a ruptured dermoid cyst in the facial nerve. Facial nerve tumors are rare causes of facial paralysis in children, accounting for fewer than 10% of cases of facial paralysis in the pediatric population. Dermoid cyst can occur throughout the head and neck region in children, but a dermoid tumor in the facial nerve has not been described in the literature prior to this report. This represents a new and uncommon diagnostic entity in the evaluation of facial nerve paralysis in children. Appropriate imaging studies and pathology slides will be reviewed.