Brain tumour Acoustic Neuroma

An acoustic neuroma is a noncancerous growth that develops on the eighth cranial nerve. Also known as the vestibulocochlear nerve, it connects the inner ear with the brain and has two different parts. One part is involved in transmitting sound; the other helps send balance information from the inner ear to the brain.

Progression to malignancy in this kind of tumor is rare. They normally develop gradually over a period of years, expanding at their site of origin roughly 1–2 mm each year.

Tumors are typically described as small (less than 1.5 cm), medium (1.5 cm to 2.5 cm), large (2.5 cm to 4 cm), or giant (greater than 4 cm).

Most schwannomas start out as intracanalicular, and growth compresses the nerve against the bony canal, so the first symptoms of the tumor are unilateral sensorineural hearing loss or disturbances in balance.

As intracanalicular tumors grow, they tend to expand into the cerebellopontine angle (CPA), leading to their characteristic “ice-cream-cone like” appearance on a radiograph.

As the schwannoma expands into the CPA, it may infringe on cranial nerve V (controls facial sensation, chewing and swallowing) and cranial nerve VII (controls facial expression and taste)

There are two types of acoustic neuroma: a sporadic form and a form associated with a syndrome called neurofibromatosis type II (NF2). NF2 is an inherited disorder characterized by the growth of noncancerous tumors in the nervous system. NF2 is a rare disorder. It accounts for only 5% of acoustic neuromas

Diagnosis and management

The definitive diagnostic test for patients with acoustic tumors is gadolinium-enhanced magnetic resonance imaging (MRI). Gadolinium contrast is critical because nonenhanced MRI can miss small tumors. Audiometry is done to measure amount and type of deafness.

Acoustic Neuroma Treatments

There are three main courses of treatment for acoustic neuroma:

Observation
Surgery
Radiation therapy

Observation is also called watchful waiting. Because acoustic neuromas are not cancerous and grow slowly, immediate treatment may not be necessary. Often monitoring of the tumor is done with periodic MRI scans. Simple observation without any therapeutic intervention has been used in the following groups of patients:

Elderly patients
Patients with small tumors, especially if their hearing is good
Patients with medical conditions that significantly increase the risk of operation.
Patients with a tumor on the side of an only hearing ear or only seeing eye.

Surgery: The goals of surgery are to control the tumor, and preserve function of the involved nerves. Preservation of hearing is an important goal for patients who present with functional hearing. Surgery cannot restore hearing already lost. Microsurgical techniques and instruments, along with the operating microscope, have greatly reduced the surgical risks of total tumor removal.

Microsurgical tumor removal can be done at one of three levels: subtotal removal, near total removal or total tumor removal. Subtotal removal is indicated when anything further risks life or neurological function. In these cases the residual tumor should be followed for risk of growth (approximately 30%). Periodic MRI studies are important to follow the potential growth rate of any tumor. Near total tumor removal is used when small areas of the tumor are so adherent to the facial nerve that total removal would result in facial weakness. The piece left is generally less than 1% of the original and poses a risk of regrowth.

The surgical approach taken depends on the location of the tumour, its size and the relative importance of hearing preservation. Complete removal is possible in most cases. The risks of surgery include,

Mortality (risk about 1%)
CSF leak and meningitis
Hydrocephalus
Cerebellar injury
Stroke
Epilepsy
Facial paralysis (either partial or complete)
Hearing loss
Balance impairment
Persistent headache

Radiation therapy is recommended in some cases for acoustic neuromas. Radiation therapy for this condition is usually delivered in one of two ways:

Single fraction stereotactic radiosurgery , in which many hundreds of small beams of radiation are aimed at the tumor in a single session.
Multi-session fractionated stereotactic radiotherapy (FRS), which delivers smaller doses of radiation daily, generally over several weeks. Early studies suggest multi-session therapy may preserve hearing better than SRS.

Possible complications due to treatments for acoustic neuroma:

Damage to the facial nerve, causing a facial nerve palsy. The facial nerve is the nerve in the brain that controls movements in the muscles of the face. If an acoustic neuroma has grown quite large, removal during surgery can potentially lead to damage of this neighbouring nerve. If the nerve is damaged, there will be paralysis of part of the face. This can cause a problem with drooping of one side of the face. In some cases, physiotherapy will help but, in others, the damage is permanent. Obviously, during surgery, great care is taken to identify and avoid damage to surrounding nerves.
Damage to the vestibulocochlear nerve, leading to deafness. As mentioned, a degree of hearing loss is normal after treatment for acoustic neuroma. If you have NF2 and bilateral tumours, there is a strong chance that after surgery, you will completely lose the hearing in both of your ears.
Damage to the trigeminal nerve, leading to loss of feeling (facial numbness). In the same way that the facial nerve can be damaged during surgery to remove an acoustic neuroma, the trigeminal nerve can also be injured. If this occurs, there is loss of sensation to parts of
Regrowth (recurrence) of acoustic neuromaFewer than 5 in every 100 acoustic neuromas come back. So it is uncommon, but possible.