Hearing internal bodily functions, such as the sound of your own eyes blinking, footsteps, or heartbeat, can be startling. This amplified self-hearing is medically known as autophony. While the body constantly produces these subtle vibrations, perceiving them clearly suggests an issue with the inner ear’s sound dampening system. This symptom often points toward an uncommon condition that disrupts the normal mechanics of hearing and balance.
Superior Semicircular Canal Dehiscence
The most frequent explanation for this hypersensitivity to internal sound is Superior Semicircular Canal Dehiscence (SSCD). This disorder involves a structural defect in the bone encasing the inner ear’s balance organs. The temporal bone that normally covers the superior semicircular canal is either abnormally thin or completely absent, a defect referred to as a “dehiscence.”
The superior semicircular canal is one of three fluid-filled loops that help track rotational movement and maintain balance. In healthy individuals, a thick layer of bone protects this canal from pressure changes inside the skull. SSCD is rare; only a small percentage of the population, estimated at one to two percent, has the underlying anatomical defect, and even fewer develop the full syndrome of symptoms.
The Full Spectrum of Auditory and Balance Symptoms
SSCD manifests as symptoms affecting both hearing and equilibrium. Autophony is a defining characteristic; patients hear their eye movements, and experience their own voice and chewing sounds as distorted and excessively loud. This also includes hearing the rush of blood or a rhythmic thumping sound, known as pulsatile tinnitus, synchronized with their heart rate.
The condition often causes hyperacusis, a heightened sensitivity to external sounds. Normal environmental noises can become physically painful or overwhelming. The balance system is also impacted by the dehiscence, leading to the Tullio phenomenon, where loud noises trigger episodes of vertigo or dizziness.
Changes in intracranial pressure can also induce vertigo, commonly experienced when coughing, sneezing, straining, or lifting heavy objects. These pressure-induced episodes are a direct consequence of the structural defect, creating unsteadiness or disequilibrium. The combination of these auditory and vestibular issues significantly interferes with daily life.
How the “Third Window” Effect Amplifies Internal Sounds
The anatomical problem of SSCD is described as creating a “third window” in the inner ear. The inner ear normally operates with two compliant points—the oval window and the round window—which regulate fluid pressure during sound transmission. This two-window system ensures sound energy reaching the cochlea is processed efficiently.
The dehiscence acts as an abnormal third opening, disrupting the hydraulic balance of the inner ear fluid, perilymph. This defect creates an alternative, low-resistance pathway for pressure and vibration. The result is a shunting of sound energy away from the cochlea’s normal hearing pathway.
The third window dramatically amplifies vibrations transmitted through the skull bone, which is how internal body noises travel. Bone-conducted sound energy is channeled directly into the superior semicircular canal, bypassing normal dampening mechanisms. This makes the inner ear overly sensitive to minute movements. This abnormal pressure relief is why subtle movements, such as muscles pulling on the skull bone during an eye blink, are perceived as audible events.
Diagnostic Testing and Confirmation
Confirming SSCD requires combining clinical history with objective testing. The gold standard for visualizing the bony defect is a high-resolution computed tomography (CT) scan of the temporal bones. This imaging technique uses thin slices to identify the absence or thinning of the bone overlying the superior semicircular canal.
An audiogram, or comprehensive hearing test, is performed to assess hearing function. SSCD patients commonly exhibit a low-frequency conductive hearing loss, sometimes called a pseudo-conductive loss, characteristic of the third window’s effect. Vestibular Evoked Myogenic Potential (VEMP) testing measures the inner ear’s response to sound. SSCD patients often show abnormally low thresholds for VEMP responses, indicating hypersensitivity to acoustic stimulation.
Treatment and Management Strategies
Once SSCD is confirmed, treatment is tailored to the severity of symptoms. For individuals with mild or intermittent symptoms, a conservative management strategy is recommended. This involves behavioral modifications, such as avoiding triggers like loud noises, strenuous activity, or rapid pressure changes.
If symptoms are debilitating and affect the quality of life, surgical intervention may be considered. The primary goal is to repair the bony defect and restore the normal mechanics of the inner ear. The two main surgical techniques are canal plugging and canal resurfacing. Plugging closes the superior semicircular canal with bone wax or tissue to eliminate the third window effect. Resurfacing covers the dehiscent area with bone cement without entirely closing the canal.