Labyrinthitis ossificans.

A 32-year-old man came to us for evaluation of a profound bilateral sensorineural hearing loss. The patient's hearing had been normal until he experienced an episode of meningitis when he was 13 years old. He had no history of ear infection or trauma.

An audiogram confirmed that the man had a profound bilateral hearing loss and no sound perception. Because he was not a candidate for hearing aids, computed tomography (CT) of the temporal bones was performed to investigate the feasibility of placing cochlear implants. CT revealed that the inner ear had been completely replaced by dense cortical bone (figure). This finding is consistent with a diagnosis of severe labyrinthitis ossificans. Because of the extent of the osteoneogenesis and the complete absence of sound perception, cochlear implantation was not pursued.

Labyrinthitis ossificans is a pathologic ossification in the cochlea and labyrinth. It is usually caused by an infection that reaches the inner ear via a tympanogenic (most common), meningogenic, or hematogenic route.[1] Chronic otitis media can cause labyrinthitis via either the oval or round window. Bacterial meningitis is the most common cause of meningogenic labyrinthitis. The infection spreads to the inner ear via subarachnoid spaces, such as the cochlear aqueduct and the internal auditory canal. Ossification is typically bilateral and can be seen as early as 3 to 4 months following an episode of acute bacterial meningitis. Between 8 and 24% of all cases of profound deafness in school-aged children are caused by bacterial meningitis.[2] Approximately 2 to 5% of children and adults who survive bacterial meningitis develop a profound bilateral sensorineural hearing loss.[3] Hematogenic labyrinthitis is rare (mumps and measles are the most common pathogens).[2,3]

Labyrinthitis ossificans typically involves the perilymphatic space and spares the endolymphatic space. Inflammatory injury results in fibrosis, which is followed by the formation of new bone. CT is used in the preoperative assessment of possible cochlear implantation because it can detect sclerosis, irregularity, or obliteration of the cochlea, vestibule, and semicircular canals. The basal turn of the cochlea is the most frequently affected site, and this can make cochlear implantation difficult or impossible. Depending on the degree of ossification, the electrode can be inserted completely or partially.[34]

References

(1.) deSouza C, Paparella MM, Schachern P, Yoon TH. Pathology of labyrinthine ossification. J Laryngol Otol 1991;105:621-4.

(2.) Nadol JB, Jr., Hsu WC. Histopathologic correlation of spiral ganglion cell count and new bone formation in the cochlea following meningogenic labyrinthitis and deafness. Ann Otol Rhinol Laryngol 1991;100:712-6.

(3.) Weissman JL, Kamerer DB. Labyrinthitis ossificans. Am J Otolaryngol 1993;14:363-5.

(4.) Mabrie DC, Niparko JK. Quiz case 1. Meningitis-related labyrinthitis ossificans. Arch Otolaryngol Head Neck Surg 1999;125:912, 914.