Underlying Mechanisms of Sound-Induced Vertigo
The inner ear is a closed system responsible for both hearing and balance. Normally, sound pressure is managed by two openings covered by flexible membranes: the oval window and the round window. These structures convert sound vibrations into nerve signals in the hearing organ, the cochlea, while keeping the balance, or vestibular, system isolated from this acoustic energy. This separation ensures sound is perceived correctly without interfering with our sense of equilibrium.
Sound-induced vertigo occurs when this system is compromised by a third, abnormal opening, a phenomenon explained by the “third window” theory. When a hole or thinning develops in the bone surrounding the inner ear, it creates a pathway for pressure to escape. This defect allows acoustic energy from sounds to leak from its normal pathway and displace fluid within the balance canals.
This misdirected energy stimulates nerve receptors in the vestibular system that are meant to detect head motion. The brain receives these signals and misinterprets them as actual movement, even though the head is still. This conflict results in the sensation of vertigo, imbalance, and involuntary eye movements known as nystagmus.
Medical Conditions That Cause the Symptom
A primary cause of sound-induced vertigo is Superior Canal Dehiscence Syndrome (SCDS). This condition is an absence or thinning of the bone that covers the superior semicircular canal. This bony defect creates the “third window” that allows sound and pressure changes to stimulate the balance organ, leading to dizziness. SCDS can be present from birth due to developmental issues or can result from physical trauma to the head.
Other medical conditions can also lead to similar symptoms. Meniere’s disease, a disorder of the inner ear, is characterized by an excessive buildup of fluid. This can make the entire system more susceptible to pressure fluctuations from sound, causing the inner ear membranes to become more sensitive to acoustic stimuli.
Another cause is a perilymphatic fistula, which is a small tear or defect in the membrane separating the middle and inner ear. This tear allows inner ear fluid to leak into the middle ear, disrupting normal pressure dynamics. Such a fistula can be caused by head injury, barotrauma from flying or scuba diving, or complications from ear surgery. In these cases, loud noises can cause pressure waves to stimulate the vestibular system through the tear.
The Diagnostic Process
Confirming the cause of sound-induced vertigo involves a specialized diagnostic approach. A patient’s medical history provides initial clues, but objective testing is required for a definitive diagnosis. The process focuses on visualizing the inner ear’s structure and measuring its functional response to sound and pressure.
A high-resolution computed tomography (CT) scan of the temporal bone is a standard imaging procedure. This scan can produce images detailed enough to identify a bony dehiscence characteristic of SCDS. The imaging allows clinicians to visually confirm the presence, location, and size of the anatomical defect.
Functional tests are also performed to measure the ear’s sensitivity. Vestibular Evoked Myogenic Potential (VEMP) testing assesses the vestibular system’s response to sound. In affected individuals, the threshold for eliciting these potentials is often lower than normal. A hearing test, or audiogram, is also performed, and a physician might conduct a Tullio test by presenting sound to the ear while observing for nystagmus.
Treatment and Management Strategies
Once a diagnosis is confirmed, treatment is tailored to the severity of symptoms and the specific underlying cause. The approach includes non-surgical management for milder cases and surgical intervention for more debilitating symptoms. The goal is to reduce or eliminate the abnormal stimulation of the balance system by sound.
For individuals with less severe symptoms, management begins with conservative, non-surgical methods. This involves lifestyle adjustments aimed at avoiding the triggers of vertigo. Patients are advised to stay away from environments with loud noises, and using earplugs or noise-canceling headphones can prevent symptoms when exposure is unavoidable.
In cases where symptoms significantly impact a person’s quality of life, surgical intervention may be considered, particularly for SCDS. The surgical procedures are designed to repair the defect and restore the inner ear’s normal pressure system. Two common techniques are canal plugging and resurfacing. Canal plugging occludes the dehiscent semicircular canal, while resurfacing involves placing a graft over the bony opening.