Peripheral nerve sheath tumours (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.
This page will primarily focus on benign (non-cancerous) peripheral nerve sheath tumours (BPNSTs). BPNSTs are more common than malignant (cancerous) peripheral nerve sheath tumours (MPNSTs), however they can lead to nerve and/or muscle damage. In rare cases, BPNSTs can undergo a malignant transformation when left untreated. For more information on MPNSTs, please refer to the Rare Cancers Australia Peripheral Nerve Sheath Tumours (Malignant) page.
In general, the average age of diagnosis varies between BPNST subtypes.
Types of Benign Peripheral Nerve Sheath Tumours
There are several types of BPNSTs, which are categorised by the type of cells they develop from, and their cellular appearance under the microscope.
Schwannoma
Schwannomas, also known as neurinomas or neurilemmomas, are the most common BPNST in adults, and develop from Schwann cells in the PNS. Schwann cells are a type of glial (or supportive) cell that helps form the myelin sheath surrounding nerve fibres. Schwannomas are more common in people between the ages of 50 and 70, and tends to be diagnosed equally between the sexes.
For more information on schwannomas, please refer to the Rare Cancers Australia Schwannoma page.
Neurofibroma
Neurofibromas are a common type of BPNST that tends to develop along the nerves and contain fibrous or connective tissue. They are generally diagnosed equally among the sexes, and are often diagnosed between the ages of 20-40.
For more information on neurofibromas, please refer to the Rare Cancers Australia Neurofibroma page.
Perineuroma
Perineuromas are a rare type of BPNST that develops from perineural cells, a type of cell that surrounds the peripheral nerve sheath. These tumours are generally found in deeps soft tissues, the peripheral nerves of the limbs, or cranial nerves, however they can develop anywhere in the body. There are two main types of perineuroma, which are classified on their location and their proximity to large nerves.
Intraneural Perineuroma
Intraneural perineuromas are perineuromas that develop from within the nerve, such as peripheral nerves of the limbs and cranial nerves. These tumours are most commonly found in children and young adults, are generally benign, and can have a good prognosis.
Extraneural Perineuroma
Extraneural perineuromas, also known as soft tissue perineuromas, are perineuromas that develop next to nerves, most notably deep in soft tissue. These tumours are not generally associated with large nerves nearby, and are generally diagnosed in patients between the ages of 16-70. Extraneural perineuromas are generally benign, and can have a good prognosis.
Hybrid Nerve Sheath Tumour
Hybrid nerve sheath tumours, also known as hybrid peripheral nerve sheath tumours (HPNSTs), are a rare subtype of BPNSTs that show characteristics of two or more types of BPNST. The most common combinations include:
- Schwannoma and perineuroma.
- Schwannoma and neurofibroma.
- Neurofibroma and perineuroma.
While these are the most commonly recognised hybrid tumours, they can occur in any combination. HPNSTs are more common in young adults, however they can develop at any age. These tumours are generally benign, and can have a good prognosis.
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 the PNSTs mentioned 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 BPNSTs 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 BPNSTs 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 BPNSTs 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:
- Pain in the affected area.
- Numbness and/or tingling in affected area.
- Itching and/or burning sensation in affected area.
- Weakness and/or loss of function in affected area.
- A mass that may be firm and/or palpable.
- Dizziness.
- Loss of balance.
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 BPNST, 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, BPNSTs have a good 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.