Section Editor: Sandy Cheng-Yu Chen, M.D.
Taipei Medical University Hospital, Taipei, Taiwan
Labyrinthitis ossificans (LO) represents pathological ossification of the membranous labyrinth due to prior inner ear insult. The most common cause is prior inner ear inflammation/infection. Less common causes are prior surgery, trauma, tumor, autoimmune disease, vascular, hematologic disorders, etc. LO usually results in marked sensorineural hearing loss and could be unilateral or bilateral. LO consists of fibrous and osseous stages. CT scan classically shows increased density/ossification (arrows) in the membranous labyrinth at osseous stage. MRI shows low signal intensity foci within high signal fluid of membranous labyrinth on T2 MR images and is considered more sensitive than the CT scan in the fibrous stage.