Labyrinthitis ossificans

Findings

Figure 1: Axial CT image through the left temporal bone shows complete ossification of the left superior semicircular canal.
Figure 3: Axial CT image at the level of the internal auditory canal shows non-erosive soft tissue attenuation lateral to the malleus and incus as well as partial ossification of the lateral semicircular canal.


Diagnosis: Labyrinthitis ossificans


Labyrinthitis ossificans (LO) is the end result of suppurative labyrinthitis where inflammation of the membranous labyrinth progresses to fibrosis and ossification. Suppurative labyrinthitis typically arises following meningitis, although other causes include direct infection from hematogenous sources or trauma.

LO is the most common cause of acquired childhood deafness and can be detected by CT as early as 2 months following an episode of meningitis. Following meningitis, approximately 6% to 30% of children develop some degree of sensorineural hearing loss which is typically bilateral.

On CT, osseous deposition is seen within the membranous labyrinth. On MRI, loss of the normal high signal on T2-weighted images from displacement of the endolymphatic fluid is suggestive of this diagnosis. It is important to the clinician to distinguish between cochlear involvement, non-cochlear involvement, or both as prognosis is determined by response to cochlear implantation. The degree of ossification is important in surgical planning and severe LO may preclude cochlear implantation.