Labyrinthitis ossificans (LO)

Timothy C. Hain, MD • Page last modified: December 27, 2022

Labyrinthitis Ossificans
CT scan of labyrinthitis ossificans. On the left (right inner ear) is a normal labyrinth. On the right, (left inner ear), is a similar level but the lateral semicircular canal shows no loop.

The inner ear contains the labyrinth, which consists of a set of interconnected channels in the bone that contain fluid, membranes, and neural cells that respond to sound and motion. In LO, the labyrinth is replaced by bone, almost always as a result of a bacterial infection. This typically results in profound deafness and loss of vestibular function on the affected side. If there is bilateral LO, patients are completely deaf and have no vestibular sensation.

Taxat and Ram (2020) wrote "Labyrinthitis ossificans is the pathological ossification of the membranous labyrinthine spaces in response to an insult to the inner ear involving membranous labyrinth or the endosteum of the otic capsule."

Little is known as to why some patients develop LO and others don't. Aminpour (2005) suggested that TNF-alpha may play an important role in an animal model of meningitis.

Mineralization in animals is rapid, and begins 3 days after infection (Tinling et al, 2004). Nabili et al (1999) reported that mineralization started at 3 weeks, and continued over a 12 month course.

Frequency of Labyrinthitis ossificans

Labyrinthitis ossificans is rare, occurring in only about 2% of persons who have had mastoidectomy. (Lin et al., 2014). Meningitis, the usual cause of LO, is extremely rare as well, perhaps accounting for the rareness of LO.

In our experience, most patients with LO are completely deaf, have no vestibular function, and developed this as a child as a result of meningitis. However, other causes are reported (see below), of which chronic mastoiditis appears to be common. LO might theoretically occur as a result of a cochlear implant, but this is rarely reported. Meningitis appears to be a much more common source of LO. (Yune et al, 1991)

We have encountered only one patient who developed this as a result of otitis media (i.e. middle ear infection). This is likely due to the current propensity for patients with otitis media to get antibiotics.

Causes of Labyrinthitis ossificans

Buch et al wrote about 44 cases(2019) : "RESULTS: Forty-four patients (58 ears) with labyrinthitis ossificans were identified and evaluated. The most common risk factors were chronic otomastoiditis (n = 18), temporal bone surgery (n = 9), temporal bone trauma (n = 6), sickle cell disease (n = 5), and meningitis (n = 4)."

Most of the other data about this rare syndrome comes from case reports.

Bacterial meningitis, the most frequent cause of LO, was reviewed in JAMA by Hasbun (2022). It affects about 1/100,000 to 80/100,000 persons/year, depending largely on the income of persons living in the country -- High-income countries have less meningitis. Income affects meningitis, according to Hasbun who states "The incidence ranges from approximately 0.9 per 100,000 individuals per year to approximately 10 to 80 per 100 000 individuals per year in low-income and middle-income patients. The most common bacteria are H Influenzae, Neisseria meningititis, and streptococcus pneumonae.

Diagnosis of Labyrinthitis ossificans

Imaging studies are needed to diagnose LO. The CT scan of the temporal bone is the most straightforward, as it shows bone replacing the labyrinth. MRI scan of the inner ear area can show the loss of fluid in the labyrinth, but cannot distinguish plugging from soft tissue from bone. MRI has the advantage of being no radiation exposure.

Treatment (prevention) of Labyrinthitis ossificans

Hartnick et al (2001) reported that patients treated with steroids had less LO. According to Hasbun who reviewed meningitis (2022), "First-line therapy is prompt empirical intravenous antibiotic therapy and adjunctive dexamethasone."

There is considerable literature concerning cochlear implant in LO patients (e.g. Helmstaeder et al, 2018). The question is whether or not the electrodes can be threaded into a cochlea that is blocked by bone.