Case Study of the Week: Acoustic Neuroma

Acoustic neuroma is a diagnosis I have yet to make in my life as a nurse practitioner but one that's always in the back of my mind when a patient presents with hearing difficulties.  While diagnosing an acoustic neuroma is rare, NPs and PAs need to keep it in mind as it can have some serious implications.An acoustic neuroma, also called a vestibular schwannoma, is a benign and usually slow growing tumor that develops on the eighth cranial nerve (vestibulocochlear nerve).  Because this nerve is responsible for linking the ear and the brain, acoustic neuromas may disrupt hearing, their primary symptom.  While these tumors are benign, if they grow large enough they may affect vital areas of the brain making their prompt diagnosis and treatment imperative.

Case Presentation

A 32 year old male presents to your clinic with a chief complaint of sudden hearing loss in his left ear for two days.  He reports occasional ringing in this ear as well as a slight headache.  He denies tingling, numbness and weakness.  He denies visual changes, nausea and vomiting and vertigo. 

On exam, the patient's vital signs are within normal limits.  Other than pronounced hearing loss in the left ear, his cranial nerve and cerebellar exams are normal.  The patient's ENT exam is normal.  You know that unilateral hearing loss is caused by acoustic neuroma until proven otherwise and order an MRI to further evaluate the patient.

Diagnosis and Treatment

Most patients with acoustic neuroma present with hearing loss.  Most often, hearing loss is gradual but can occur suddenly.  Patients may also experience tinnitus in the affected ear, loss of balance, headache and facial numbness or weakness. 

Acoustic neuroma is diagnosed primarily with contrasted MRI.  While a CT scan can pick up an acoustic neuroma, tumors as large as 1.5cm can be missed making MRI the preferred diagnostic test. 

Management and Outcome

Acoustic neuroma can be managed in three different ways.  First, the tumor may simply be monitored closely.  This is the preferred method of management in elderly patients, patients with small tumors, especially if their hearing remains good, and in patients whose other medical problems increase risk of operation.

The second treatment option for patients with acoustic neuroma is radiation therapy known as stereotactic radiosurgery.  This involves making a small incision near the tumor site and directing radiation at the tumor.  The goal of radiation is to preserve hearing, preserve function of facial nerves and stop tumor growth.  For most patients this treatment is temporary and they lose hearing gradually within about 10 years of stereotactic radiosurgery treatment.

The final method for treating acoustic neuroma is surgical removal.  Depending on the size of the tumor and severity of symptoms, this may be the best option for some patients.  As with any surgery, this presents potential complications including hearing loss, facial weakness, tinnitus and stroke.

Outcomes of acoustic neuroma treatment are varied, but removal or stopping growth of the tumor typically prevents symptoms from becoming worse.  For example, in 6-20% of patients experiencing tinnitus with acoustic neuroma, symptoms worsen after removal.  However, tinnitus improves in 25-60% of patients.  Similar outcomes are found with facial function.  In most patients with facial weakness or paralysis, symptoms improve after tumor removal.  However for some patients, facial function may worsen. 

After surgical excision of an acoustic neuroma, a follow-up MRI should be obtained 6-12 months after surgery to make sure the tumor has been removed completely.  If the tumor has been entirely excised, a follow-up MRI should be obtained at 5 years and 10 years post removal.

Discussion

While acoustic neuromas are benign tumors, they can result in debilitating consequences such as tinnitus, facial weakness and hearing loss.  Nurse practitioners and physician assistants must diagnose these tumors promptly and make an appropriate referral for treatment to prevent complications.