Intradiploic Epidermoid of the Tegmen Tympani With Cochlear Invasion

Intradiploic epidermoid cysts are benign tumors that account for ∼1% of all intracranial space occupying lesions. Because of the indolent growth, symptoms are usually gradual in onset with a prolonged duration. While they can originate from any part of the skull, temporal bone epidermoids are rare. We describe a case of an unusual presentation of a temporal bone epidermoid cyst. A 64-year-old male presented with sudden right-sided hearing loss and worsening right eyelid ptosis was found to have a nonenhancing lobulated mass above the right tegmen tympani with complex signal and possible communication with the apical turn of the cochlea on magnetic resonance imaging (MRI). He underwent subtemporal craniotomy with excision of the cyst lining and matrix without any complications and was discharged home on postoperative day 1. Complete excision was not possible given that the facial nerve and cochlea were improved. He had subjective improvement in his hearing immediately after surgery. Intradiploic epidermoid cysts are benign tumors that can present anywhere in the skull with variable presentation. While complete excision is the goal, neurovascular involvement may make this challenging. The use of computed tomography scan and MRI can prove to be invaluable in determining accurate diagnosis and size for surgical planning.