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CSF leak complicating the infralabyrinthine approach to petrous apex: lessons learnt

© BMJ Publishing Group Limited 2022. No commercial reuse. See rights and permissions. Published by BMJ. DESCRIPTION A young adult man presented to the otolaryngology department having progressive hearing loss in his right ear for 3 months after a febrile illness. There were no associated reports of ear pain, ear discharge, vertigo or trauma. On otoscopic examination, there was a minimal retraction of the tympanic membranes on either side. The rest of the clinical examination was unremarkable. A pure tone audiogram revealed a profound sensorineural hearing loss of 90 dB on the right, with a normal hearing threshold on the left. Tympanometry was unremarkable. A highresolution CT of the temporal bones showed an expansile smoothwalled lesion of size 7 mm × 10 mm in the right petrous apex, with overlying cortical thinning (figures 1 and 2). No other abnormality was noted in the middle ear or inner ear. The patient subsequently underwent an MRI of the brain with contrast, which confirmed the presence of a welldefined cystic lesion of the right petrous apex. It was hyperintense on both T1 and T2, suggesting a cholesterol granuloma or a cholesteatoma (figure 3). The only possible surgical approach to the lesion was a cell tract, beginning in the hypotympanum, inferior to the basal turn of the cochlea. The patient was counselled regarding surgical drainage of the cyst but the irreversibility of his hearing loss. The patient underwent a posterior tympanotomy and drilling was done along the infralabyrinthine cell tracts to the petrous apex. Drilling for the infralabyrinthine approach was done in a roughly triangular space inferior to the basal turn of the cochlea, posterior to the internal carotid artery and anterior to the jugular bulb (figure 4). No welldefined tract was visualised, and the solid bone was drilled to a depth of 12 mm when a dome of a cystlike structure appeared in the view. When this cystlike structure was opened, there was a gush of cerebrospinal fluid. A misaligned trajectory of the drilling appeared to have led to the posterior fossa dura and not the petrous apex. The track was closed with fat harvested from the abdominal wall and reinforced with temporalis fascia and fibrin glue. A postoperative CT scan (figure 5) showed the trajectory of the surgical tract was more posteriorly angled by around thirty degrees, leading to the posterior fossa dura and not the petrous apex. The postoperative course was uneventful, and the patient is planned for a repeat procedure after about 6 months when the tract will hopefully be fibrosed. Cholesterol granulomas encompass the most frequent destructive lesion of the petrous apex. Cholesterol granulomas form when the aeration of the petrous apex is hindered, thus creating a vacuum into which blood is drawn, causing foreign body giant cell reaction to cholesterol deposits, with fibrosis. They are ten times more common than cholesteatomas and forty times more common than petrous apex mucoceles. They are usually clinically silent but can bring about local mass effects, resulting in headaches, hearing loss, diplopia and vertigo. Five approaches were traditionally employed to gain surgical access to the petrous apex: middle cranial fossa, translabyrinthine, transotic, infracochlear and infralabyrinthine. In patients with serviceable hearing, lesions encroaching the posterior wall of the sphenoid sinus can be approached via the transsphenoidal route also. The infralabyrinthine approach via the Figure 1 Preoperative HRCT temporal bone (axial section). The yellow asterisk depicts the cavity in the right petrous apex. HRCT, highresolution CT.