Schwannoma

Schwannomas, also known as neurinomas or neurilemmomas, are a common peripheral nerve sheath tumoura tissue mass that forms from groups of unhealthy cells (PNSTs) in adults, and develop from Schwann cellsthe basic structural and functional unit of all living things 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 tissuea group of cells that work together to perform a function 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, bloodthe red bodily fluid that transports oxygen and other nutrients around the body 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 benignnot cancerous, can grow but will not spread to other body parts, and can have a good prognosisto predict how a disease/condition may progress and what the outcome might be.

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, abdomenstomach, stomach area, belly, 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 diagnosisthe process of identifying a disease based on signs and symptoms, patient history and medical test results.

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 malignantcancerous, may grow and spread to other areas of the body 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 subcutaneousunder the skin 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 tissuetissue/the material that joins, holds up or surrounds inside body parts such as fat, muscle, ligaments and lining around joints sarcomacancer arising from bones and/or soft tissue 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, metastasiswhen the cancer has spread to other parts of the body, also known as mets, and how the cancera disease where abnormal cells split without control and spread to other nearby body tissue and/or organs cells look under the microscope. Stagingthe process of determining how big the cancer is, where it started and if it has spread to other areas 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 testinga procedure that analyses DNA to identify changes in genes, chromosomes and proteins, which can be used to analyse tumour DNA to help determine which treatment has the greatest chance of success, 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:

• Surgerytreatment involving removal of cancerous tissue and/or tumours and a margin of healthy tissue around it to reduce recurrence to remove as much of the tumour as possible.
• Watch and waitthe close monitoring of a cancer without giving treatment until symptoms appear or worsen.
• Radiation therapya treatment that uses controlled doses of radiation to damage or kill cancer cells.
• Clinical trialsresearch studies performed to test new treatments, tests or procedures and evaluate their effectiveness on various diseases.
• Palliative carea variety of practices and exercises used to provide pain relief and improve quality of life without curing the disease.

Risk factors

While the cause of schwannomas remains unknown, the following factors may increase the likelihood of developing the disease:

• Genetic mutations.
• Being diagnosed with schwannomatosis (a rare type of neurofibromatosis).
• Being diagnosed with neurofibromatosis type 2 (NF2).
• Being diagnosed with Carney complex.

Not everyone with these riskthe possibility that something bad will happen 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.

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 dysfunctionimpaired or abnormal function; not working properly, which carries its own set of symptoms:
  • Intense pain in the head.
  • Vertigodizziness, a sensation of spinning or moving.
  • Weakness.
  • Paralysis of affected area.
• Hydrocephalusa build up of cerebrospinal fluid (CSF) in the brain, causing pressure and potentially damaging brain tissue (rare).
• Difficulties swallowing.
• Difficulties with eye movement.
• Numbness and/or tingling in affected areas.
• Muscle weakness in affected areas.
• Facial nerve palsy.
• Proptosisbulging or protrusion of one or both of the eyes out of the eye sockets, also known as exophthalmos.
• Pain in affected area(s).
• Abdominal discomfort.
• Upper gastrointestinal bleeding, which caries its own set of symptoms:
  • Nauseato feel sick or likely to vomit and/or vomiting, potentially containing blood.
  • Diarrhoeafrequent discharge of watery or loose stools from the body.
  • Abdominal cramping.
  • Rectal bleeding.
  • Bloating.
  • Heartburn.
• Myelopathyan injury to the spinal cord 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

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 examinationan examination of your current symptoms, affected area(s) and overall medical history.
• Neurological examinationan assessment of sensory and motor functions, such as vision, balance and coordination.
• Imagingtests that create detailed images of areas inside the body tests, potentially including:
  • CT (computed tomography) scana type of medical imaging that uses x-rays and computer technology to create detailed images of the body.
  • MRI (magnetic resonance imaging)a type of medical imaging that uses radiowaves, a strong magnet and computer technology to create detailed images of the body.
• Blood teststesting done to measure the levels of certain substances in the blood.
• Electromyogram (EMG)a diagnostic procedure used to measure the response of nerves and skeletal muscles to electrical activity.
• Nerve conduction studiesa diagnostic procedure used to measure the speed of electrical impulses through a nerve.
• Biopsyremoval of a section of tissue to analyse for cancer cells.

References

• Johns Hopkins Medicine
• Mayo Clinic
• Radiopaedia