To present a case of progressive sensorineural hearing loss (SNHL) caused by labyrinthine erosion secondary to expanding geniculate ganglion cerebrospinal fluid (CSF) diverticulum extending along the path of the facial nerve. Thirteen-year-old man with no past medical history or risk factors presented with unilateral progressive SNHL and no other otologic or neurologic symptoms. Audiological data as well as imaging studies including a magnetic resonance imaging (MRI) of the brain and internal auditory canal and a temporal bone computed tomography (CT) are presented. Partial labyrinthectomy, CSF leak closure, and cochlear implantation were performed. A lumbar puncture was obtained 2 months postoperatively. Closure of the CSF leak. Mastoidectomy revealed a wide area of CSF leak through the geniculate ganglion and fallopian canal with partial destruction of the superior and lateral semicircular canals by an expanding diverticulum. This is an unusual presentation of progressive SNHL due to partial labyrinthine erosion due to a meningocele of the geniculate ganglion along the fallopian canal. It is likely that the patient had a congenital open pathway through the labyrinthine segment of the facial nerve and CSF pulsations created the meningocele over a few years. This case argues for early closure of such CSF diverticula to prevent possible SNHL due to labyrinthine erosion.