Tension Pneumocephalus With Acute Cerebellar Symptoms Due to an Intradiploic Epidermoid Cyst Eroding the Mastoid Bone

This case report presents a unique presentation of an intradiploic epidermoid cyst (IDEC) in a 55-year-old female. She presented with acute cerebellar symptoms triggered by a Valsalva maneuver. IDECs are a rare type of intracranial epidermoid cysts. They are benign and have a slow growth pattern that translates into progressively developing symptoms instead of acute symptoms. Symptoms include local deformities, focal neurologic deficits, and pain. This patient developed acute cerebellar symptoms due to erosion of the mastoid bone that created a pathway between the eustachian tube and the intracranial space via the mastoid air cells. Consequently, tension pneumocephalus emerged via a ball-valve effect that caused a significant mass effect in the posterior fossa. Surgical resection of the IDEC and closing of the mastoid air cells resulted in symptom relief by restoring the integrity of the intracranial-extracranial barrier. This case highlights that a higher level of vigilance is warranted for an IDEC in the proximity of aerated bone structures, such as the mastoid air cells and the paranasal sinuses, and that a more proactive approach is advocated.