Labyrinthine otosclerosis and sensorineural deafness. Pathologic findings of the spiral ligament.

In severe labyrinthine otosclerosis, spiral ligament changes occur predominantly adjacent to the stria vascularis, and consist of a decrease or loss of the capillary-perilymph system. It is suggested that this results in increased concentrations of metabolic products in the cochlear fluids that can no longer be absorbed effectively. If vascular shunts form they might represent collateral channels, with the flow of blood from the cochlea into the otosclerotic focus, bypassing the deficient capillary network in the spiral ligament. The zone of dense collagenization is described as a widening of the soft tissues endosteum of the cochlear capsule due to erosion of the bone, with the bone surface now set further back. This may result in greater mobility or loosening of the suspension mechanism of the basilar membrane.