An acoustic neuroma is a noncancerous tumor, also called a vestibular schwannoma, that develops on the main nerve leading from the inner ear to the brain. This tumor originates from Schwann cells, which support and protect nerve cells. Sensorineural hearing loss is a hearing impairment resulting from issues within the inner ear or the nerve pathway to the brain. An acoustic neuroma is linked to this hearing loss because the tumor’s growth exerts pressure on the hearing nerve.
How an Acoustic Neuroma Disrupts Hearing
The vestibulocochlear nerve connects the inner ear to the brain and has two parts: the vestibular nerve for balance and the cochlear nerve for sound transmission. An acoustic neuroma begins to grow on the vestibular portion of this nerve. Despite originating on the balance nerve, its location is what affects hearing.
Both nerve branches travel together through a narrow, bony channel called the internal auditory canal. As the acoustic neuroma enlarges within this confined space, it presses against the adjacent cochlear nerve. This physical compression damages the delicate nerve fibers of the cochlear nerve.
The damage from this sustained pressure disrupts the nerve’s ability to transmit electrical signals from the inner ear. The tumor may also interfere with the blood supply to the cochlear nerve, further contributing to its malfunction and causing hearing loss.
Distinctive Symptoms and Progression
The hearing loss from an acoustic neuroma affects only one ear, a condition known as unilateral hearing loss. This one-sided nature helps differentiate it from other types of hearing decline. The progression is slow and gradual, developing over months or years, which can lead individuals to attribute the change to normal aging.
Beyond hearing loss, the tumor’s pressure on the vestibulocochlear nerve causes other symptoms. Tinnitus, a persistent ringing or buzzing in the affected ear, is a common complaint. Because the tumor grows on the balance portion of the nerve, issues with equilibrium are also frequent, and patients may experience dizziness, unsteadiness, or vertigo.
As the tumor expands, it can press on other nearby cranial nerves. Some individuals may experience numbness or tingling on one side of the face if the trigeminal nerve is compressed. If the facial nerve is affected, it can cause twitching or weakness in the facial muscles on the same side as the tumor.
Diagnostic Procedures
The diagnostic process begins with a hearing test called an audiogram. An audiologist conducts this test to measure a person’s ability to hear sounds at various pitches and volumes and their capacity to understand speech. The results may reveal a pattern of high-frequency sensorineural hearing loss in one ear, which is a strong indicator of a possible acoustic neuroma.
While an audiogram can suggest a tumor, the definitive diagnosis is made using medical imaging. Magnetic Resonance Imaging (MRI) with a contrast agent called gadolinium is the standard for identifying these tumors. The contrast material is injected into the bloodstream, and because tumors absorb more of the dye than healthy tissue, they appear as a bright mass on the MRI scan.
This imaging technique allows physicians to visualize the tumor with detail. The MRI confirms the diagnosis and reveals the tumor’s size, location on the nerve, and proximity to surrounding brain structures. This information helps determine the most appropriate course of action for treatment.
Treatment Approaches and Hearing Restoration
Once diagnosed, treatment decisions depend on the tumor’s size, growth rate, and the patient’s health. For small, slow-growing tumors with minimal symptoms, a “watch and wait” approach with regular MRI monitoring may be recommended. Another option is stereotactic radiosurgery, which uses focused radiation to stop the tumor’s growth. For larger tumors, microsurgical removal may be necessary to alleviate pressure on nerves and the brainstem.
A primary goal during treatment is preserving existing hearing, but this is not always achievable, and pre-existing hearing loss may persist or worsen. For individuals with significant or complete hearing loss in one ear, several rehabilitation technologies are available. These options do not restore natural hearing but help mitigate the effects of single-sided deafness.
Contralateral Routing of Signal (CROS) hearing aids capture sound from the deaf side and transmit it to a device worn on the hearing ear. Bone-anchored hearing systems (BAHS) use a small, surgically placed titanium implant to send sound vibrations through the skull bone to the functioning inner ear of the opposite side. In cases where the cochlear nerve remains intact after surgery but hearing is lost, a cochlear implant may be an option to directly stimulate the nerve and provide a sense of sound.