||Serous labyrinthitis is the mildest form of labyrinthitis, and represents reactive changes in response to an irritation of the labyrinth caused by an otitic or meningeal infection without actual bacterial invasion of the inner ear.
Histologically these changes manifest as a mild endolymphatic hydrops or by the formation of an eosinophilic granular precipitate within the scalae. The osseous and cytoarchitecture of the inner ear remain intact.
Clinically, serous labyrinthitis is associated with varying degrees of vertigo and hearing loss, which are the result of bacterial toxins or of biochemical alterations caused by infection. When serous labyrinthitis occurs in a mild form there may be a complete recovery of function, whereas in severe forms the cytotoxic effects may produce permanent damage to the sensory structures, resulting in a partial or complete loss of hearing and/or vestibular function.
Serous labyrinthitis may develop as a complication of either acute or chronic otitis media. When this occurs it seems likely that the bacterial toxins have entered the inner ear via the round or oval windows, or, rarely, through a pathologic, bony labyrinthine fistula.
Histologically, serous labyrinthitis is characterized by a fine, homogeneous, granular or fibrillar, eosinophilic precipitate in the perilymphatic spaces. In more severe cases the precipitate may also be present in the endolymphatic spaces, and there may be a slight hydrops of the endolymphatic system.