Serous labyrinthitis is a non-suppurative inflammation of the inner ear, secondary to circumscribed labyrinthitis or caused by bacterial or viral toxins from otitis media entering the inner ear through the oval or round window. A labyrinthine reaction similar to serous labyrinthitis may also occur following fenestration surgery or stapedectomy.
Pathology
The primary pathological changes include hyperemia of the inner ear, increased capillary permeability, and the presence of serous or serofibrinous exudates and lymphocytic infiltration in the perilymphatic space. The hair cells of the inner ear are generally undamaged, allowing for the restoration of inner ear function after recovery. However, if the condition progresses, it may develop into suppurative labyrinthitis.
Clinical manifestations
A history of otitis media or middle ear cholesteatoma is present.
Vertigo is accompanied by nystagmus, nausea, and emesis. Nystagmus is horizontal or rotatory. In the early stages, nystagmus is directed toward the affected side, indicating vestibular hyperfunction on that side. If the inflammation persists, nystagmus shifts to the contralateral side, suggesting vestibular hypofunction on the affected side. The fistula test may be positive.
Severe cases may exhibit sensorineural hearing loss, though complete hearing loss is not observed. Mild cases may present with cochlear symptoms such as recruitment and diplacusis.
Differential diagnosis
In suppurative labyrinthitis, the labyrinth is completely destroyed, resulting in nystagmus directed toward the healthy side, with complete loss of vestibular and auditory function on the affected side. Due to the separation of the cochlea and vestibule by the membranous perilymphatic space, in rare cases of complete semicircular canal fistula destruction, cochlear function may still be preserved.
Early acute diffuse serous labyrinthitis is challenging to differentiate from the active phase of circumscribed labyrinthitis. If spontaneous nystagmus changes direction from the affected side to the healthy side, vertigo worsens, hearing loss becomes more pronounced (though not complete), and vestibular function tests show reduced function (but not complete loss), the condition can be diagnosed as serous labyrinthitis when improvement or stabilization occurs with treatment.
Treatment
With appropriate treatment, inner ear function can generally be restored to near-normal levels.
For serous labyrinthitis caused by acute suppurative otitis media or mastoiditis, systemic anti-infective therapy is the primary approach.
For cases associated with chronic suppurative otitis media, mastoiditis, or middle ear cholesteatoma, mastoidectomy should be performed under adequate antibiotic coverage to remove the pathological lesion. Opening the labyrinth is generally unnecessary.
Sedatives and dehydrating agents can be used to manage vertigo. Appropriate doses of glucocorticoids may also be administered.