Labyrinthitis is inflammation of the membranous labyrinth.
Pathology
Labyrinthitis can be divided according to etiology.
Tympanogenic
Labyrinthitis is a potential complication of acute otomastoiditis with the spread of infection or of toxins from the middle ear to the inner ear via either the round window or oval window. It is therefore typically unilateral. Typically patients will have sensory neural hearing loss (SNHL) and vertigo. When SNHL is fluctuating, a perilymphatic fistula should be suspected - typically seen in the setting of coexistent cholesteatoma or previous ossicular surgery (e.g. prosthetic stapedectomy)
When toxins only, then the term "acute toxic labyrinthitis" or " acute serous labyrinthitis" is used. MRI may be negative.
When bacteria actually enter the labyrinth, then "acute suppurative labyrinthitis" applies, and MRI is positive.
Post-traumatic
Post-traumatic labyrinthitis is seen usually seen in the setting of temporal bone fracture with a resulting perilymphatic fistula.
Meningogenic
Meningitis, most frequently bacterial, typically causes bilateral labyrinthitis, and is seen most frequently in children. It is the most common cause of acquired deafness. Spread is thought to occur through the lateral aspect of the internal acoustic meatus, into the cochlea. In HIV immunocompromised patients cytomegalovirus (CMV) has also been described.
Haematogenic
Viral labyrinthitis is common, with respiratory tract infections being most frequent. Whether these spread hematogenously or via the middle ear is debatable. Measles and mumps are said to be hematogenously spread to the labyrinth (although the two references cited disagree). It is a much less frequent cause of labyrinthitis. Syphilis involvement of the labyrinth, known as otosyphilis is also re-emerging as a result of increased numbers of immunocompromised patients.
Autoimmune
Infrequent cause, associated with Takayasu arteritis.
Radiographic features
Prior to MRI, no imaging findings were described, however, now enhancement of the labyrinth on post-contrast T1WI enable the diagnosis to be made with confidence.