This animation illustrates cyclical changes in the dilation of the membranous labyrinth that may correspond to symptoms of fullness, tinnitus, decreased hearing, and disequilibrium when dilation is great and diminished symptoms when dilation subsides. Also shown is a “membrane break” in which potassium rich endolymph causes a conduction block of the vestibular nerves resulting in violent vertigo. The conduction block resolves spontaneously. Cycles of dilation and incapacitating “membrane break” events follow a unique and random pattern in time and intensity in each patient. These changes likely are a result of disorders of ion homeostasis in the cochlea. Although scientifically controversial, this simple model is helpful to patients who often feel intense frustration with their inability to conceptualize their problem.
The resting tone of the vestibular nerves may be interrupted by acute inflammation of the nerves resulting in violent spinning with nausea and vomiting. Resting tone returns after the acute episode ends but often at a decreased level. Compensation for the reduced tone can be promoted with vestibular therapy and inhibited by the prolonged use of vestibular suppressant medications.
Benign Paroxysmal Positional Vertigo
An initial event causes displacement of otoconia from the macula of the utricle. When the patient lies down the loose otoconia displace to the posterior canal. On rising, the otoconia displace further into the canal and while in transit displace the ampulla in an inhibitory direction. Tipping the head back or lying down will displace the ampulla in the stimulatory direction resulting in the most intense symptoms.
Horizontal Canal Fistula
Erosion of the horizontal semicircular canal by cholesteatoma may result in sound transit across the horizontal canal. This can cause a Tullio phenomenon in which the patient experiences horizontal turning provoked by loud sounds. Patients may also experience autophony as patients with superior canal dehiscence syndrome do.