Labyrinthitis is inflammation of the inner ear structures (cochlea, vestibule, and semicircular canals) and is one of the most common causes of sensorineural hearing loss (SNHL). Etiology may be viral (most common — herpes simplex, CMV, rubella), bacterial (tympanogenic or meningitic spread), or autoimmune. The disease progresses through three stages: acute (fluid) stage — inflammatory fluid and edema within the inner ear; fibrous stage — narrowing of the labyrinthine lumen with granulation tissue and fibrosis; ossified stage — filling of the labyrinthine lumen with bone. MRI shows labyrinthine wall enhancement in the acute stage, decreased labyrinthine fluid signal on T2 3D sequences in the fibrous stage. CT detects intracochlear calcification in the ossified stage — critically important in cochlear implant planning because electrode placement may not be possible with complete ossification.
Age Range
5-70
Peak Age
40
Gender
Equal
Prevalence
Uncommon
Labyrinthitis pathogenesis is based on the spread of inflammatory cascade to inner ear structures. Three main routes of infection exist: (1) Tympanogenic route — bacterial/viral spread from otitis media to the inner ear through the round or oval window; (2) Meningitic route — spread from the subarachnoid space through the cochlear aqueduct or internal acoustic canal (most common after pediatric bacterial meningitis); (3) Hematogenous route — bloodborne spread during viremia. The inflammatory process affects inner ear fluid compartments (perilymphatic and endolymphatic). In the acute stage, inflammatory mediators (cytokines, prostaglandins) create mucosal edema and fluid exudation — seen on MRI as enhancing inflamed labyrinthine wall. Gadolinium passes through the disrupted blood-labyrinth barrier and causes T1 shortening. In the fibrous stage, fibroblasts and collagen deposition replace inflammatory cells — labyrinthine fluid signal decreases on T2 3D sequences because fibrous tissue (short T2 time) replaces free fluid. In the ossified stage, calcification of fibrous tissue and new bone formation occurs — seen on CT as high-density calcification/bone within the cochlear lumen. Ossification starts earliest and most commonly in the basal turn (can begin within 2-4 weeks in meningitic labyrinthitis). This process is critical for cochlear implant planning because basal turn ossification makes electrode placement difficult or impossible.
Labyrinthine wall enhancement on post-contrast T1 fat-sat in the acute stage and intracochlear calcification on CT in the chronic/ossified stage are the two cardinal imaging findings of labyrinthitis. Enhancement in the acute stage represents blood-labyrinth barrier disruption, calcification in the ossified stage represents ossification of fibrous tissue. Together, these two findings determine the stage of labyrinthitis and provide critical information for cochlear implant planning.
Abnormal enhancement along the labyrinthine wall is observed on post-contrast T1 fat-sat sequences. Enhancement may involve one or more of the cochlea, vestibule, and semicircular canals. Asymmetric enhancement is conspicuous when compared with the normal side. This finding is the most sensitive MRI indicator of acute labyrinthitis. Enhancing structures represent inflammatory exudation and blood-labyrinth barrier disruption.
Report Sentence
Abnormal enhancement of the right/left cochlea/vestibule/semicircular canals is identified on post-contrast T1 fat-sat sequences, consistent with acute labyrinthitis; asymmetry is conspicuous compared with the contralateral normal labyrinth.
Decreased or absent fluid signal in the labyrinthine lumen is observed on T2 3D CISS/FIESTA sequences. Normal labyrinth shows bright hyperintense signal on T2 as it is filled with fluid. In the fibrous stage, fibrous tissue filling the labyrinthine lumen reduces or completely eliminates free fluid signal. This finding is best evaluated by comparison with the normal side. Assessment of cochlear lumen patency is mandatory in cochlear implant planning.
Report Sentence
Decreased/absent labyrinthine fluid signal in the right/left cochlea/vestibule is identified on T2 3D CISS sequences, consistent with fibrous stage labyrinthitis; patency evaluation is recommended for cochlear implant planning.
Calcification/new bone formation within the cochlear lumen is seen on CT. Ossification most commonly starts in the basal turn and progresses toward the apical turn over time. In complete ossification, the cochlear lumen appears entirely filled with bone. In partial ossification, focal calcified foci are observed. Ossification may also develop in semicircular canals and vestibule. This finding is critically important for cochlear implant surgery planning — basal turn ossification makes electrode placement difficult or impossible.
Report Sentence
Calcification/ossification in the basal turn/all turns of the right/left cochlea is identified on CT, consistent with ossified stage labyrinthitis; cochlear lumen patency should be evaluated for cochlear implant planning.
In acute labyrinthitis, intralabyrinthine hyperintense signal on non-contrast T1 may be observed due to proteinaceous exudation or hemorrhagic component. This finding is rare but when present suggests bacterial labyrinthitis and suppurative complication. In hemorrhagic labyrinthitis, methemoglobin causes T1 hyperintensity. Comparison with the normal side evaluates symmetry.
Report Sentence
Intralabyrinthine hyperintense signal on non-contrast T1 of the right/left ear is identified, suggesting proteinaceous exudation/hemorrhagic component; suppurative labyrinthitis should be excluded.
Calcification/ossification in the semicircular canals may be observed. Lateral, posterior, and superior semicircular canals should each be evaluated separately. Semicircular canal ossification is a sign of vestibular function loss. The presence of ossification in semicircular canals along with the cochlea indicates widespread labyrinthine involvement.
Report Sentence
Calcification/ossification in the semicircular canals is identified, consistent with widespread labyrinthine involvement.
Criteria
Most common form. HSV, CMV, rubella, mumps, VZV. Bilateral involvement possible. SNHL usually unilateral and sudden onset.
Distinct Features
Ossification rarely develops. Usually limited to acute and fibrous stages. Treatment antiviral + steroid.
Criteria
Following bacterial meningitis (especially pediatric Streptococcus pneumoniae, Haemophilus). Spread through cochlear aqueduct. Most aggressive form.
Distinct Features
Ossification develops fastest in this form (2-4 weeks). Bilateral involvement common. Cochlear implant should be planned earliest in this group.
Criteria
Autoimmune: bilateral, fluctuating SNHL, steroid response. Tympanogenic: as complication of otitis media, spread through round window.
Distinct Features
Serum anti-cochlear antibody may be positive in autoimmune form. Accompanying middle ear inflammation findings in tympanogenic form.
Distinguishing Feature
Cholesterol granuloma: focal lesion at petrous apex, T1+T2 hyperintense. Labyrinthitis: diffuse involvement along labyrinthine structures, T1 generally hypointense, enhancement diffuse.
Distinguishing Feature
Cholesteatoma: focal mass in middle ear, DWI bright, no enhancement. Labyrinthitis: diffuse enhancement along inner ear structures, no focal mass.
Distinguishing Feature
IAC meningioma: focal dural-based mass, homogeneous enhancement. Labyrinthitis: diffuse enhancement along labyrinthine wall, no focal mass.
Urgency
urgentManagement
medicalBiopsy
Not NeededFollow-up
3-monthEarly treatment (antibiotic/antiviral + steroid) in the acute stage is critical for hearing preservation. In meningitic labyrinthitis, cochlear implant evaluation should be performed urgently because ossification begins within 2-4 weeks — placing the electrode before complete ossification is the most important factor simplifying surgery and improving outcomes. CT evaluates ossification degree, MRI evaluates active inflammation and nerve status. Cochlear implant is the most effective rehabilitation method for bilateral severe SNHL. Electrode placement is possible with drill-out technique in partial ossification, but may not be possible in complete ossification.
Medical treatment in the acute stage (anti-inflammatory, antiviral/antibiotic). Cochlear implant evaluation in bilateral or severe SNHL. Implant electrode placement is difficult in ossified labyrinth — preoperative CT patency assessment is mandatory. The more advanced the ossification, the worse the prognosis.