ACOUSTIC NEUROMA (Vestibular Schwannoma)

What is an acoustic neuroma or vestibular schwannoma?

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An acoustic neuroma or vestibular schwannoma refers to a benign tumor that grows from the vestibular nerve. The vestibular nerve is responsible for balance and equilibrium and runs from the brainstem out towards the ear canal. Along this course, it is in close proximity to three other nerves: a second vestibular nerve, the cochlear nerve (responsible for hearing), and the facial nerve (responsible for muscle movement of the face).

As acoustic neuromas grow, they stretch the adjacent nerves. The cochlear nerve is much more sensitive to stretching compared to the facial nerve. As a result, hearing loss or tinnitus (ringing) are common symptoms.

As tumors get larger, they can displace and cause pressure and swelling in the adjacent brain (brainstem and cerebellum), which can cause headaches, weakness, balance difficulty, and incoordination.



How are acoustic neuromas diagnosed?

Acoustic neuromas are commonly found on evaluation for hearing changes. When suspected, an MRI of the brain is performed with special high-resolution sequences through the ear canal. Consultation with an otologist with careful hearing tests are necessary to evaluate the precise nature of hearing dysfunction.

How are acoustic neuromas treated?

Each patient requires careful individual evaluation and consideration by an experienced skull base team to determine the best treatment option. In general, treatment falls in three categories: observation, surgery, or focused radiation (radiosurgery). Small tumors that are found incidentally and are not causing symptoms can often be observed with repeat MRI scans. Small tumors that are causing hearing loss can be treated with surgery or radiation, depending on individual patient and tumor characteristics. Large tumors are best treated with surgery. Occasionally, in the setting of large tumors, small amounts of tumor are left behind during surgery to protect critical brainstem and nerve function. This residual tumor may be treated with radiation if necessary.

What does surgery involve?

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In general, there are three approaches to surgery: retrosigmoid, translabyrinthine, and middle fossa approaches. All three approaches are performed by a team of two surgeons: a skull base neurosurgeon and a skull base otologist.

1. Retrosigmoid
A retrosigmoid approach involves a C-shaped incision behind the ear. An approximately 2-inch craniotomy (opening of the skull) at the base of the brain is performed. The cerebellum is gently retracted to expose the tumor and a combination of tumor removal and careful dissection of the nerves and brain is performed.

The retrosigmoid approach is used in small and medium sized tumors in order to preserve hearing or in large tumors for better exposure and visualization.

2. Translabyrinthine
A translabyrinthine approach involves a C-shaped incision behind the ear. The mastoid bone (the bone that can be felt directly behind the ear) is then drilled and removed in order to expose the internal ear canal and the tumor. A combination of tumor removal and careful dissection of the nerves and brain is then performed.

The translabyrinthine approach sacrifices hearing. This approach is used when hearing is already poor or if the tumor size makes hearing preservation unlikely after surgery.

3. Middle fossa
The middle fossa approach involves a linear incision above the ear. A 2-inch craniotomy (opening of the skull) is performed. The temporal lobe (the part of the brain that lays on the skull base above the ear) is then gently lifted. The bone of the skull base that covers the internal ear canal is then drilled and removed allowing access and visualization of the tumor. A combination of tumor removal and careful dissection of the nerves and brain is then performed.

The middle fossa approach is used in small tumors and to preserve hearing.