Schwannoma

Schwannoma is a rare, slow-growing tumor that affects the nervous system. Also known as a neurilemmoma, it originates in Schwann cells, or neurolemmocytes, which are responsible for producing the myelin required to facilitate nerve conduction.

There are different types of schwannomas depending on the area in which they are located:

• Intracranial schwannoma: develops in nerves located within the skull.
• Vestibular schwannoma or acoustic neuroma: the most common type. It arises in the vestibular nerve, which extends from the inner ear to the brain.
• Trigeminal schwannoma: affects the trigeminal nerve, which is responsible for controlling mastication and providing facial sensation.
• Vagal schwannoma: very rare. It develops in the vagus nerve, which connects the brainstem to the body's vital organs (heart, lungs, stomach, intestines, pancreas, liver, kidneys, and spleen).
• Hypoglossal schwannoma: extremely uncommon. It affects the hypoglossal nerve, which controls tongue movements.
• Spinal schwannoma: affects the spinal cord and most commonly occurs in the cervical or thoracic regions.
• Intradural schwannoma: located within the dura mater, the outer protective layer surrounding the meninges, causing compression of the spinal cord or its nerve roots.
• Extradural schwannoma: a rarer type located outside the dura mater.
• Dumbbell schwannoma: grows both inside and outside the spinal canal, with one portion intradural and the other extradural. The name derives from its characteristic shape, which narrows centrally as it passes through the intervertebral foramen.
• Peripheral schwannoma: originates in nerves located outside the brain and spinal cord. It most commonly occurs in:
• Upper and lower extremities.
• Trunk.
• Brachial plexus: a network of nerves that originates in the neck and extends through the arm from the shoulder to the hand.
• Lumbar plexus: a network of spinal nerves arising from vertebral levels L1 to L4.
• Lumbosacral trunk: the connection between the lumbar and sacral plexuses, including the L4 and L5 nerve roots.
• Sacral plexus: the sacral nerves between S1 and S4.

The prognosis of schwannoma is generally very favorable when diagnosed early, as the vast majority of these tumors are benign. In the rare cases in which malignant cells are present, the likelihood of cure depends on the stage at diagnosis and the tumor's degree of aggressiveness.

Symptoms

Symptoms of neurilemmoma vary depending on its location:

• Vestibular schwannoma: may damage both branches of the vestibulocochlear nerve—the cochlear branch, responsible for hearing, and the vestibular branch, responsible for balance. Common manifestations include:
• Hearing: loss of hearing in one ear.
• Tinnitus: perception of a persistent internal ringing or buzzing sound.
• Loss of balance.
• Unsteadiness.
• Vertigo.
• Facial paralysis.
• Ataxia: lack of coordination or clumsiness of movement.
• Dysphagia: difficulty or inability to swallow.
• Headache.
• Intracranial hypertension.
• Spinal schwannoma: may produce symptoms in the cervical, thoracic, or lumbar regions:
• Radicular pain radiating along the affected nerve.
• Limb weakness.
• Spasticity: increased muscle tone resulting in stiffness and persistent muscle tension.
• Difficulty walking.
• Numbness at the base of the skull.
• Urinary retention or incontinence.
• Altered bowel function.
• Peripheral schwannoma: although it can occur anywhere in the body, it is more common in the arms, legs, head, and neck:
• A palpable mass along the course of a nerve. Although slow-growing, it may become large enough to be visibly noticeable.
• Tenderness on palpation.
• Tingling.
• Numbness.
• Weakness.
• Loss of motor function.

Causes

Although the exact causes of neurilemmoma are not fully understood, it is believed to result from a genetic alteration. Specifically, it is associated with mutation or inactivation of the NF2 gene on chromosome 22, which encodes the protein merlin. This abnormality prevents proper regulation of cell growth and therefore impairs protection against tumor formation.

Risk Factors

The risk of developing schwannoma increases in the following situations:

• Having a genetic syndrome that causes alterations in the NF2 gene, such as:
• Neurofibromatosis type 2.
• Schwannomatosis.
• Carney complex.
• Excessive exposure to radiation.
• Previous radiotherapy treatment.

Complications

The most significant complication of schwannoma is nerve compression caused by the tumor. When this occurs, it may result in pain, weakness, numbness, or even loss of function in the affected area.

Prevention

Because schwannoma is a condition of genetic origin, it cannot be prevented.

What specialist treats schwannoma?

Schwannoma is primarily managed within the Neurosurgery specialty, although in some cases specialists in Physical medicine and Rehabilitation may also be involved.