Endoscopic‐assisted transmastoid decompression of petrous apex cholesterol granuloma

Cholesterol granuloma is one of the most common abnormalities of the petrous apex. It is a benign slowgrowing expanding cystic mass that contains fluid, lipid, and cholesterol crystals and is surrounded by a fibrous lining. The granuloma arises from a pneumatized petrous apex that becomes obstructed. It most commonly arises from the central petrous apex; however, it has been found at other subsites of the temporal bone. The obstruction creates a vacuum that causes blood to be drawn into the air cells. Cholesterol in the hemoglobin is released as red blood cells are broken down. The immune system reacts to the cholesterol as a foreign body producing an inflammatory response. Associated small blood vessels rupture as a result of the inflammation. Recurrent hemorrhaging causes the mass to expand. Most patients present with subtle symptoms of headache and pain; however, larger lesions can present with cranial neuropathies, tinnitus, and hearing loss. Asymptomatic patients in whom petrous apex cholesterol granuloma (PACG) is incidentally discovered do not need treatment. Treatment for symptomatic lesions is primarily surgical, with the goal of decompressing and draining the lesion, thereby providing aeration to the petrous apex while avoiding or minimizing destruction of normal structures. The traditional approaches to these tumors is via a corridor created by a surgical dissection through the temporal bone employing the infralabyrinthine, infracochlear, middle fossa, and/or retrolabyrinthine approaches. In severe cases, the translabyrinthine and/or transcochlear approaches may be employed. With the recent advancement in endoscopic anterior skull base surgery, medial approaches to the petrous apex via a transsphenoid or transpterygoid approach have been described. This is used when there is excellent pneumatization of the ipsilateral sphenoid sinus and the carotid artery is not between the sphenoid sinus and the lesion. Unlike cholesteatoma, PACGs only require drainage and do not need complete removal. The approach to these lesions is dependent on patient anatomy and the size and location of the cholesterol granuloma. Each approach carries its own set of risks, which can be as great as complete hearing loss, facial nerve palsy or paralysis, necessity for brain retraction, and cranial nerve or neurovascular injury. We describe a technique in which we approached the lesion via an infralabyrinthine approach through the temporal bone, and employed a 30-degree endoscope and angled instrumentation to access and drain the lesion.