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Acoustic Neuroma
(Vestibular Schwannoma) |
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By Jeffrey P. Harris, M.D., Ph.D.
About Acoustic neuroma
Acoustic neuroma is the name commonly applied to a benign tumor arising from the sheath cells of the vestibular component of the 8th cranial nerve. The correct name is vestibular schwannoma.
However, since the prominent early symptoms are unilateral hearing loss and tinnitus (ringing in the ears) due to compression of the auditory component of the 8th cranial nerve, the name acoustic neuroma appears to be here to stay.
The tumors originate inside the bony canal through which the 8th cranial nerve passes on its way to the inner ear. The 7th cranial nerve (facial nerve) which supplies the muscles of the face passes through the same canal. As the tumor enlarges, it extends into an intracranial space at the base of the brain referred to as the cerebello-pontine angle (CPA). Since other types of tumors can be seen in this location,
tumors here are usually referred to as a cerebello-pontine angle tumor until a definite diagnosis is made.
Once the tumor has extended into the cerebello-pontine angle, it may encroach on other cranial nerves such as the 5th cranial nerve, causing facial numbness, or compress the brain stem, causing ataxia (problems with coordination and balance).
Diagnosis
- Acoustic neuromas are most frequently diagnosed by MRI scan in a patient with unilateral hearing loss. MRI can determine:
- The distance the tumor extends laterally in the auditory canal
- The extent to which the tumor expands in the cerebello-pontine angle
- Whether or not the brain stem is contacted or distorted
Other important diagnostic tests are the audiogram and the recordable brain stem audio evoked responses (BAERs) because these will provide indicators of the possibility of saving hearing.
Classification
Based on the MRI scan, acoustic neuromas fall into three classifications:
- Entirely intracanalicular, which means the entire tumor is no bigger than a bean and is completely within the bony canal.
- Intracranial extension without brain stem distortion, which means the intracranial portion of the tumor is small, i.e. 1-2 cm.
- Intracranial extension with brain stem distortion, which means the intracranial portion of the tumor is bigger than 2 cm and pressing on the bone of the brain.
Read a sample consultation with an accoustic neuroma patient
Read about treatment options for acoustic neuroma
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