What Is A Schwannoma?

Every nerve is surrounded by a layer of lipids, which functions to provide them with electrical insulation from the surrounding fluid. The term for this is called a sheath, with Schwannomas being a type of nerve sheath tumour formed by Schwann cells. Schwannomas are typically non-cancerous (benign), however, in rare cases, they can be cancerous (malignant), and when this occurs, the condition is termed neurofibrosarcoma. Despite Schwannomas rarely degenerating into malignant cancer, the size of the tumours exerts pressure on the nerve and surrounding tissues. This can lead to nerve damage and loss of muscle control, potentially leading to long-term muscle weakness or hearing loss, depending on the location and size of the schwannomas.¹

Location and symptoms

Schwannomas commonly occur in the head and neck, the flexor surfaces of the upper and lower extremities, the posterior mediastinum in the thorax, and the trunk.² Depending on the location of Schwannomas, symptoms can vary.³

One common type of schwannoma is vestibular schwannoma, which is a benign brain tumour that starts in the vestibulocochlear nerve, which connects the brain to the ear. Symptoms include hearing loss, tinnitus, dizziness, balance problems, and trouble moving the eye.³

Schwannomas that develop on the nerves in the arm or leg can cause muscle pain and weakness and carpal tunnel syndrome or tarsal tunnel syndrome.³

Schwannomas that develop on the nerves in the face and neck can result in facial muscle pain or paralysis, problems swallowing or moving an eye, and loss of the sense of taste.³

When a schwannoma grows on a nerve root in the spinal cord, it can cause symptoms similar to those associated with spinal problems such as a herniated disk. Symptoms may include tingling, severe pain, bowel or bladder dysfunction, and even paralysis in severe cases.³

What are the causes of schwannomas?

The cause of schwannomas is not known in most cases, as 90% of cases occur sporadically, which are termed solitary schwannomas.⁴

Despite the majority of cases of this rare disease occurring randomly, certain genetic mutations and diseases can affect an individual’s ability to develop Schwannomas. The mutations commonly occur in SMARCB1 and LZTR1 genes, as they produce proteins that act as tumour suppressors, preventing cells from growing and dividing too rapidly, or in an uncontrolled way.⁵ The genetic diseases associated with the increased likelihood of schwannomatosis include neurofibromatosis type 2 and Carney complex. Neurofibromatosis type 2 is a dominantly inherited syndrome, and when this occurs, tumours usually develop on both sides of the brain (bilateral), in both ears, or in the spinal cord.¹ Those who suffer from schwannomatosis develop multiple schwannomas on the nerves in multiple parts of their body, most commonly in the head, spine, or limbs, therefore distinguishing itself from neurofibromatosis type 2.¹

When should I see a doctor?

You should see a doctor if you are experiencing any pain associated with schwannomas, unusual lumps or numbness in any limbs, or have a genetic condition in which you have an increased likelihood of developing schwannomas. 

How are schwannomas treated?

When schwannomas grow large enough, they can create strain on the nerves or nearby structures. Therefore, treatment may be necessary to remove the tumour. These tumours are commonly treated using surgery. The surgeon uses precise microsurgical techniques to separate the schwannoma from the nerve tissue. Due to the size of the schwannomas, separation may not be achievable. Therefore, radiotherapy may be required, and this will be either stereotactic radiotherapy or radiosurgery. Malignant schwannoma is usually treated with radiotherapy or chemotherapy.¹

Another type of treatment is observation/watch and wait; this is a common treatment with benign tumours if you are not experiencing any symptoms or only mild symptoms. If the tumour eventually grows larger and/or causes symptoms, doctors will likely recommend medical treatment for it.⁴

Diagnosis

Commonly, individuals with schwannomas may not even know they have the condition. Usually, schwannomas are spotted accidentally when analysing imaging test results that were captured when investigating other medical conditions. These imaging tests include Magnetic Resonance Imaging (MRI): which is a painless test that produces very clear images of the organs and structures within your body using a large magnet, radio waves, and a computer to produce detailed images. Computed Tomography (CT) scan: This is a CT scan using X-rays and computers in order to produce images of the structures inside of your body. Ultrasound is a diagnostic technique that utilises high-frequency sound waves to create real-time pictures or videos of internal organs or other soft tissues. These imaging scans help you determine where the tumour is located in the body, as well as establish its size.⁵

After a schwannoma has been detected, your healthcare provider may perform a biopsy, which involves using a needle to obtain a sample of the cells, in order to confirm the presence of a tumour. Schwannoma tissue has distinctive features that are good for diagnostic elements, such as Antoni A patterns where the cells are elongated as are their nuclei; Antoni B patterns where the cells are irregular and Verocay bodies between the Antoni A cells.⁶

Can schwannomas be prevented?

As most cases occur randomly and for unknown reasons, schwannomas can not be prevented by modern medicine, diet, or lifestyle. Less than 10% of individuals who develop schwannomas are linked to certain genetic conditions. If you have a family history where someone has been diagnosed with neurofibromatosis 2 (NF2), Schwannomatosis, or Carney complex, you may want to visit your local healthcare provider to receive genetic counselling, which should be able to determine whether an individual is carrying the genetic condition.⁴

Conclusion

Schwannomas are a type of nerve sheath tumour that are formed by Schwann cells, and their cause is generally unknown. While schwannomas are not generally benign, they can be malignant in certain rare cases which are termed neurofibrosarcomas. Symptoms are commonly dependent on the size of the tumour, as larger lesions exert increased pressure on nerves and surrounding tissues. Symptoms commonly vary depending on the location of the tumour. While medical advancements lack the ability to treat schwannomas, surgery is the most common approach to medical care in order to eliminate the mass and relieve nerve pressure.