Schwannomas, also known as neurinomas or neurilemmomas, are a common peripheral nerve sheath tumour (PNSTs) in adults, and develop from Schwann cells in the peripheral nervous system. Schwann cells are a type of glial (or supportive) cell that helps form the myelin sheath surrounding nerve fibres.
PNSTs are tumours that arise from the protective layer of peripheral nerves. More specifically, they develop from nerve sheaths, which are layers of myelin and connective tissue that provide insulation to nerve fibres within the nervous system.
The nervous system is made up of two primary components: the central nervous system (CNS), and the peripheral nervous system (PNS). The CNS is made up of the brain and spinal cord, and is responsible for all sensory and motor functions in the body. The PNS encompasses all nerves outside of the CNS, and is responsible for all involuntary functions in the body. The PNS is further subdivided into the autonomic nervous system (ANS) and the somatic nervous system (SNS). The ANS controls involuntary processes and glands, such as heart rate, blood pressure, respiration, and digestion. Comparatively, the SNS is responsible for voluntary and involuntary muscle movements, as well as transmitting sensory information to the CNS.
Schwannomas are generally diagnosed in people between the ages of 50-70, and are generally diagnosed equally among the sexes. However, anyone can develop this disease.
Types of Schwannomas
There are several types of Schwannomas, which can be categorised by their location within the PNS, as well as their cellular appearance under the microscope.
Schwannoma Subtypes Based on Location
Schwannomas can be classified by their location within the PNS.
Intracranial Schwannoma
Intracranial schwannomas, also known as neurinomas, are a common type of schwannoma that develop within the skull. Unlike most schwannomas, intracranial schwannomas are slightly more common in women, however anyone can develop this disease. Most intracranial schwannomas are benign, and can have a good prognosis.
Common types of intracranial schwannomas include:
- Vestibular schwannoma (develops on vestibular nerves, which is responsible for transmitting sound from the ear to the brain, as well as information related to balance).
- Trigeminal schwannoma (develops on trigeminal nerves, which is responsible for providing sensation to the face).
- Facial nerve schwannoma (develops on facial nerves, which controls facial muscles and expression).
- Jugular foramen schwannoma (develops on nerves that run through the jugular foramen, which is a bony structure that allows important vessels and nerves to pass from the head to the rest of the body).
Orbital Schwannoma
Orbital schwannomas, also known as intraorbital schwannomas, are a rare subtype of schwannoma that develops in optic nerves, which are responsible for relaying information from your eyes to your brain and enabling us to see. These tumours are generally benign, and can have a good prognosis.
Spinal Schwannoma
Spinal schwannomas are a relatively common subtype of schwannoma that develops within the spinal canal, most commonly spinal nerve roots. Spinal nerves are primarily responsible for stimulating movement and feeling to various parts of the body. Most spinal schwannomas are benign, and can have a good prognosis.
Intercostal Nerve Schwannoma
Intercostal nerve schwannomas, also known as intercostal nerve neurilemmomas or intercostal nerve neurinoma, are a rare subtype of schwannoma that develops in intercostal nerves in the trunk. More specifically, these nerves are found in the intercostal spaces, which are the spaces between each rib. These nerves assist in the contraction of muscles, as well as relaying sensory information from the skin to the brain. Intercostal nerve schwannomas are generally benign, and can have a good prognosis.
Rare Schwannoma Locations
These types of schwannoma are very rare:
- Gastrointestinal schwannoma.
- Posterior mediastinal schwannoma.
- Retroperitoneal schwannoma.
- Thoracic schwannoma.
- Schwannomas occurring in the limbs.
Schwannomas Subtypes Based on Cellular Appearance
In addition to their location, schwannomas can also be categorised based on their cellular appearance.
Ancient Schwannoma
Ancient schwannomas are a rare subtype of schwannoma characterised by degenerative changes within the tumour. These tumours are most commonly found in the head, neck, chest, abdomen, pelvis, and/or ribs. While ancient schwannomas are typically benign and slow growing, they show minimal and non-specific symptoms, often leading to a delayed diagnosis.
Cellular Schwannoma
Cellular schwannomas are a rare subtype of schwannoma characterised by large quantities of abnormal tissue (more specifically Antoni type A tissue) within the tumour. These tumours are most commonly found in the paravertebral regions, which are the areas directly next to the spine. While cellular schwannomas are generally benign, they can be misdiagnosed as a malignant schwannoma due to their similar cellular appearances. These tumours are often slow growing, and can have a good prognosis.
Epithelioid Schwannoma
Epithelioid schwannomas are a rare subtype of schwannoma that develops from Schwann cells in the epithelial tissue, which are the layers of tissue that cover organs, line body cavities, and is the main component of glands in the body. These tumours are often difficult to diagnose, and may be benign or malignant. Generally, most epithelioid schwannomas are benign and can have a good prognosis.
Microcystic/Reticular Schwannoma
Microcystic/reticular schwannomas are a rare subtype of schwannomas that was only recently discovered. It is most commonly found within the viscera (internal organs of the body, especially in the chest or abdomen), often in the gastrointestinal tract. Because of how rare these tumours are, there has been limited research done into the general prognosis of this disease.
Plexiform Schwannoma
Plexiform schwannomas are a rare subtype of schwannoma that develops in a nerve plexus, which is a complex network of intersecting nerves within the body. Unlike most types of schwannoma, this subtype is generally diagnosed at birth or in childhood. Most plexiform schwannomas are found in the skin or in subcutaneous tissue (fatty tissue just beneath the skin). These tumours are generally benign, and can have a good prognosis.
Neuroblastoma-type Schwannoma
Neuroblastoma-type schwannoma, also known as neuroblastoma-like schwannoma, is a rare subtype of schwannoma that is characterised by large, collagenous structures arranged in a rosette (circular) pattern that is surrounded by Schwann cells. These tumours are so named as they resemble neuroblastomas, which are neuroendocrine tumours that develop from neuroblast cells in nerve tissue. These tumours are often benign.
Vestibular Schwannoma
Vestibular schwannomas, also known as acoustic neuromas, are the most common type of schwannoma. It develops from the vestibular nerves, which play important roles in both hearing and balance. These tumours are generally benign, and can have a good prognosis.
Malignant Schwannoma
While most schwannomas are benign, in rare instances they may undergo a malignant transformation and become a cancerous soft tissue sarcoma or a malignant peripheral nerve sheath tumour (MPNST). Once a schwannoma has undergone a malignant transformation, they can become aggressive and metastasise to other parts of the body. Malignant schwannomas may not have as good of a prognosis as benign schwannomas, and are often treated differently.
For more information on MPNSTs, please refer to the Rare Cancers Australia Peripheral Nerve Sheath Tumour (Malignant) page.
Treatment
When cancers are detected, they are staged and graded based on size, metastasis (whether the cancer has spread to other parts of the body), and how the cancer cells look under the microscope. Staging and grading helps your doctors determine the best treatment for you. However, as most schwannomas are considered benign, these tumours are generally considered low-grade and not staged.
Once your tumour has been diagnosed, your doctor may recommend genetic testing, which analyses your tumour DNA and can help determine which treatment has the greatest chance of success. They will then discuss the most appropriate treatment option for you.
Treatment is dependent on several factors, including location, age, stage of disease and overall health.
Treatment options for schwannomas may include:
- Surgery to remove as much of the tumour as possible.
- Watch and wait.
- Radiation therapy.
- Clinical trials.
- Palliative care.
For more information on the treatment options, please refer to the Rare Cancers Australia treatment options page.
Risk factors
While the cause of schwannomas remains unknown, the following factors may increase the likelihood of developing the disease:
Not everyone with these risk factors will develop the disease, and some people who have the disease may have none of these risk factors. See your general practitioner (GP) if you are concerned.
Early symptoms
Many patients with schwannomas may appear asymptomatic in the early stages of disease. As the tumour grows, symptoms may appear, and often vary based on location. Some of these symptoms include:
- Hearing loss/ringing in the ears.
- Cranial nerve dysfunction, which carries its own set of symptoms:
- Intense pain in the head.
- Vertigo (dizziness).
- Weakness.
- Paralysis of affected area.
- Hydrocephalus (rare).
- Difficulties swallowing.
- Difficulties with eye movement.
- Numbness and/or tingling in affected areas.
- Muscle weakness in affected areas.
- Facial nerve palsy.
- Ocular proptosis (bulging of one or both eyes).
- Pain in affected area(s).
- Abdominal discomfort.
- Upper gastrointestinal bleeding, which caries its own set of symptoms:
- Nausea and/or vomiting, potentially containing blood.
- Diarrhoea.
- Abdominal cramping.
- Rectal bleeding.
- Bloating.
- Heartburn.
- Myelopathy (spinal cord injury caused by severe compression – rare).
Not everyone with the symptoms above will have cancer, but see your general practitioner (GP) if you are concerned.
Diagnosis/diagnosing
If your doctor suspects you have a schwannoma, they may order the following tests to confirm the diagnosis and refer you to a specialist for treatment.
Physical examination
Your doctor will collect your overall medical history, as well as your current symptoms. Following this, they may examine your body to check for any abnormalities.
Neurological examination
A neurological examination assesses sensory and motor functions, and can generally be done in your GPs office. The doctor may check your vision, hearing, balance, coordination, strength, and reflexes, depending on the signs and symptoms you have described. Any problem that is detected in this exam can help determine which portion of the CNS needs further investigation.
Imaging & Blood tests
The doctor will take images of your body using magnetic resonance imaging (MRI), a computed tomography scan (CT scan), x-rays, bone scan and/or positron emission tomography (PET scan), depending on where it is suspected the cancer is. The doctor may also look at other parts of the body and look for signs of metastasis. Additionally, a blood test may be taken to assess your overall health and help guide treatment decisions.
Electromyogram (EMG)
An electromyogram is a diagnostic procedure used to measure the response of nerves and skeletal muscles to electrical activity. For this test, small needles are inserted into your muscle and records the electrical activity in the muscle as you try to move it. This procedure is often performed by a specialist, and is often performed while you are awake.
Nerve Conduction Study
A nerve conduction study, also known as a nerve conduction velocity test, is a diagnostic procedure used to measure the speed of electrical impulses through a nerve. The test involves stimulating the nerves via small electrode patches on the skin with a very small electrical impulse. Nerve conduction studies are often performed alongside an EMG.
Biopsy
Once the location of the cancer has been identified, the doctor will perform a biopsy to remove a section of tissue using a needle. This tissue will then be sent to the lab and analysed for cancer cells.
Prognosis (Certain factors affect the prognosis and treatment options)
While it is not possible to predict the exact course of the disease, your doctor may be able to give you a general idea based on the rate and depth of tumour growth, susceptibility to treatment, age, overall fitness, and medical history. Generally, benign schwannomas have a better prognosis and survival rates. However, if the tumour has become malignant and/or has spread, the prognosis may not be as good, and there may be a higher risk of recurrence. It is very important to discuss your individual circumstances with your doctor to better understand your prognosis.
References
Some references are to overseas websites. There may be references to drugs and clinical trials that are not available here in Australia.