Definition
An acoustic neuroma is a benign tumor on the eighth cranial nerve (vestibulocochlear), which runs from the brainstem to the ear and carries hearing and equilibrium. These tumors grow slowly.
Acoustic neuromas occur sporadically or as part of von Recklinghausen neurofibromatosis, where the neuroma takes one of two forms. In neurofibromatosis type I, a schwannoma may sporadically involve the 8th nerve, usually in adult life, but can involve any cranial nerve or the spinal root; bilateral acoustic neuromas are rare in this type. In neurofibromatosis type II, bilateral acoustic neuromas are the hallmark and typically present before age 21, tend to involve the entire nerve, and show strong autosomal dominant inheritance. Bilateral tumors account for only about 5 to 10% of cases; the large majority are sporadic and unilateral. Sporadic acoustic neuromas are diagnosed in roughly 1 in every 100,000 people per year, and more than 90% of patients develop one-sided hearing loss, which is why a new unilateral hearing change always earns a workup (National Institute on Deafness and Other Communication Disorders).
Causes
The exact cause is unknown.
Risk Factors
Age 30 to 60 (average age of diagnosis is 50). History of neurofibromatosis type 2 (for bilateral neuromas only, which are very rare).
Symptoms
First signs: gradual hearing loss in one ear, decreased sound discrimination (especially on the telephone), and ringing in the ears (tinnitus).
As the neuroma enlarges: balance problems, facial numbness and tingling, and weakness of the facial muscles.
Diagnosis
Audiogram. Measures hearing in both ears.
Auditory Brainstem Response Test (ABR, BAER, or BSER). Measures the rate of electric impulses traveling from the inner ear to the brainstem. A slowed or absent impulse suggests an acoustic neuroma, and this test is almost always abnormal when one is present.
Electronystagmography. A balance test. Cold and warm water or air is introduced into the ear canal, and the resulting dizziness and rapid eye movement (nystagmus) is recorded.
MRI scan. Uses magnetic waves to image the inside of the body.
CT scan. An x-ray that uses a computer to image the inside of the body.
Nursing Diagnoses
Risk for Falls related to loss of balance. Disturbed Sensory Perception (auditory). Risk for Imbalanced Nutrition: Less Than Body Requirements related to weak facial muscles.
Treatment
Observation. If the tumor is very small, the physician may just monitor growth. This is common in people over age 70.
Microsurgical removal. As the tumor grows or hearing worsens, removal may be necessary. The surgical approach depends on tumor size and location. Complications can include permanent hearing loss and paralysis of the facial muscles on the affected side.
Radiation therapy (radiotherapy). Radiation kills cells and shrinks the tumor, and is expected to halt further growth. It may be used when tumors are small and surgery is not possible, and may preserve hearing.
Frequently Asked Questions
What is the first sign of an acoustic neuroma? The classic opener is gradual one-sided hearing loss, often with ringing in that ear (tinnitus) and trouble hearing on the phone. Because the tumor sits on the vestibulocochlear nerve, more than 90% of patients develop unilateral hearing loss, so any new asymmetric hearing change should be evaluated.
Is an acoustic neuroma cancer? No. It is a benign (noncancerous) schwannoma that does not spread to other parts of the body. It causes problems by slowly pressing on nearby nerves and, if it grows large, on the brainstem, not by metastasizing.
Why is fall prevention the nursing priority? The tumor disrupts the balance (vestibular) portion of the eighth cranial nerve, so patients lose equilibrium as it grows. Keeping the path clear, assisting with ambulation, and teaching slow position changes protect a patient whose balance and hearing are both eroding.
How is an acoustic neuroma diagnosed? An audiogram measures hearing, and the auditory brainstem response test screens nerve conduction, but MRI with contrast is the definitive study because it shows even small tumors on the eighth nerve.
What are the treatment options? Three paths: watchful waiting with serial imaging for small or slow tumors (common in older adults), microsurgical removal, and focused radiation (radiosurgery). The choice depends on tumor size, hearing status, age, and surgical risk.
Can both ears be affected? Bilateral acoustic neuromas are uncommon and are the hallmark of neurofibromatosis type 2, an inherited condition that usually presents before age 21. Most acoustic neuromas are sporadic and affect only one ear.