Pathogenesis and pathophysiology of Meniére's disease.

Meniére's disease, neither spontaneous nor inducible in animals, is studied only in patients. Natural history (epidemiology) shows a triad of major symptoms: vestibular, auditory, and aural pressure. One in 3 patients has bilateral Meniére's; over full lifespans, bilaterality approaches 50%. Aural pressure (74.1%) and positional vertigo during/between attacks (85.9%) are common. Clinical variants can persist for 25+ years. All forms have delayed onset and can occur years after incitement, after otosclerosis, infections like otitis media, syphilis, or trauma. Endolymphatic hydrops is found in all, most importantly in pars inferior (cochlear duct and saccule). Some (not most) cases show ruptures. The saccule can distend into the lateral semicircular canal. Symptomatic attacks are explained on physical/biochemical bases. Both longitudinal (slow) and radial (fast) flow seem operational, longitudinal in advanced Meniére's where membranous labyrinth replaces perilymph in scala vestibuli and vestibule. All forms result from endolymphatic absorptive dysfunction (in duct and sac), with mastoid and periaqueductal hypocellularity, hypodevelopment of Trautmann's triangle, and anterior displacement of lateral sinus. Secondary obstructions in ductus reuniens or utricolo-endolymphatic valve may explain atypical Meniére's (vestibular or cochlear alone).