TITLE: Infections of the Labyrinth SOURCE: Grand Rounds Presentation, UTMB, Dept. of Otolaryngology DATE: February 25, 2004

Labyrinthitis, or inflammation of the inner ear, may be caused by a variety of agents. It may be part of a systemic process or may be the result of an invading agent. Non-infectious causes of labyrinthitis, such as autoimmune labyrinthitis or that resulting from other systemic processes have been covered in other Grand Round presentations. The focus of this presentation is that of infections of the labyrinth. A variety of organisms may infect the labyrinth, resulting in vestibular manifestations, cochlear manifestations, or both. Agents affecting the labyrinth include bacterial, viral, and fungal infections. Pathogenesis: Labyrinthine infection usually occurs by one of the three most common routes. These include hematogenous spread, from the meninges, or from the middle ear space. Meningogenic labyrinthitis occurs through the internal auditory canal (IAC), the cochlear aqueduct or both and occurs more frequently in the pediatric population. The immature immune system of infants is not developed enough to prevent spread from a meningo-encephalitis to the nearby inner ear. Also, the patency of the cochlear aqueduct found at younger ages facilitates spread of infection. It has been estimated that 82% of children less than 16 years of age will have an open aqueduct as compared to 30% over age 60. Temporal bone studies have demonstrated invasion of leukocytes and bacteria through the subarachnoid space in the IAC and along perineural and perivascular spaced following the eighth cranial nerve. The ganglion, canal, and modiolar spaces also become involved with eventual penetration of the perlymphatic scalae. In similar studies, inflammation and fibrosis was found to involve the cochlear aqueduct and the region of the scala tympani adjacent to the cochlear aqueduct. Hematologic labyrinthitis occurs from blood borne infections and is the least common route of spread to the labyrinth. Tympanogenic labyrinthitis results from extension of infection from the middle ear, mastoid air cells, or petrous apex. The most common of these is otitis interna following an acute or chronic otitis media from spread through the round or oval window. The round window is the more common of the two. Large intercellular spaces in the round window are the proposed route