Acoustic Neuroma
Overview

Acoustic Neuromas and Vestibular Schwannomas (another term for the same diagnosis) are slow growing tumors consisting of benign, non-cancerous, tissue.  These originate behind the ear directly beneath the brain and reside within the eighth cranial nerve, also known as the vestibulocochlear nerve or acoustic nerve. Acoustic Neuromas occur over time when the buildup of cells in the acoustic nerve sheath become larger than the normal anatomy allows.

The word acoustic is derived from the Greek work for "to hear" - akoustik├│s, while vestibular refers to the vestibule which is in reference to the first cavity of the inner ear. Because of this, the acoustic nerve has two primary functions - first to transmit sound, and second to facilitate balance to and from the inner ear and the brain.

Directly adjacent to the acoustic nerve is the seventh cranial nerve, or the facial nerve, which supplies the facial mussels for expressions. The overproliferation of cells from the acoustic neuromas on the sheath of the acoustic nerve cause a compression of the facial nerve throughout the two centimeter canal that separates both nerves. 

Although acoustic neuromas and vestibular schwannomas are fairly uncommon occurring in one to two people for every 100,000, they can occur at any age, in any sex, and in any ethnicity. The cause of acoustic neuromas can be tied to a genetic defect that normally resists tumor formation; however the cause of this genetic defect is unknown. The link that has been shown, however, is between people who have a history of neurofibromatosis type 2 (NF2), which is genetic disorder that causes tumors to form within the central nervous system.       

Symptoms

Because acoustic neuromas and vestibular schwannomas are slow growing tumors, often symptoms do not present until the earliest age of the late 20's into the early 30's. Like most tumors, the exact symptoms depend on the specific size and location of the tumor; however, most of the possible symptoms in order of prevalence include:

  1. Hearing loss
  2. Tinnitus or ringing in the ear
  3. Headache that worsens during specific activities (lying down, standing up, coughing, sneezing, vomiting, etc.)
  4. Loss of balance or vertigo
  5. Facial weakness, numbness, or pain
  6. Lower cranial nerve palsy and a single dilated pupil 
 


 

Diagnosis

Similar to most cases, the first steps for diagnosis an acoustic neuroma involve going over the patient's medical history and family genetic history as well as a physical examination and observation of symptoms. If after this initial step additional testing is required, a gadolinium-enhanced head MRI should be undergone. This is preferred over both thin-cut CT scans (which can miss tumors as large as 1.5 cm) and audiometric tests (which miss a quarter to a third of similar sized acoustic neuromas). 


Treatment

At the Florida Center for Minimally Invasive Brain Surgery, treatment options for acoustic neuromas are individualized relative to the specific characteristics of the tumor.  This includes - the size of the tumor, the growth speed of the tumor, the relationship of the tumor to adjacent sensitive brain structures, the health and medical history of the patient, as well as the existing symptoms. Once all of these variables have been evaluated and discussed with the patient, there are three treatment options for consideration:

  •  Observation only
           If the acoustic is small and has few of no symptoms, it may be best to follow the tumor with regular MRI scans in the future and leave it untreated for the time. 

  •  Neurosurgical tumor extraction
           Acoustic neuromas can be fully extracted a variety of neurosurgical approaches. Some of these approaches include a retrosigmoid approach, translabyrinthe approach, and a middle cranial fossa approach. 
  •  Stereotactic radiosurgery
           Stereotactic radiosurgery is considered to be a form of radiation therapy and not a surgical procedure due to the fact there is no incision made. In an outpatient setting, radiation is administered through a machine, such as a Gamma Knife┬«, CyberKnife, or BrainLAB, that targets the diseased brain tissue without damaging the surrounding areas. 

 

Gamma Knife Radiosurgery

 

Prognosis

The outcome and prognosis for individuals with acoustic neuromas is generally very good when diagnosis happens at an appropriate stage. After treatment, hearing loss stabilizes, ringing in the ears as well as facial function is often eliminated or improved, and tumor recurrence is generally less than five percent for those without NF2. 

While acoustic neuromas are not cancerous, treatment should often be considered once diagnosis or symptoms occur. The nerve compression an acoustic neuroma can cause may lead to non-reversable hearing loss as well as life-threatening hydrocephalus if grown large enough. 

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