Schwannoma

Common Questions about Schwannoma

How common are Schwannomas?

Schwannomas are rare, with less than 200,000 diagnosed cases yearly in the United States. However, they are the most common tumors of peripheral nerves in adults. The exact incidence of schwannomas in the general population is not clearly defined due to their rarity and the fact that they often remain asymptomatic and undiagnosed. However, some general insights can be provided:

• Vestibular Schwannomas (Acoustic Neuromas): These are the most common types of schwannomas arising from the nerve that connects the inner ear to the brain. They account for about 6-8% of all primary brain tumors. The estimated incidence is about 1 per 100,000 individuals per year.
• Spinal Schwannomas: These are less common than vestibular schwannomas. They can occur within the spinal canal and may cause symptoms related to compression of spinal nerves. The incidence rate of spinal schwannomas is not well documented. Still, it is considered to be lower than that of vestibular schwannomas.
• Schwannomatosis: This is a rare disorder characterized by developing multiple schwannomas throughout the nervous system, excluding the vestibular nerve. The incidence of schwannomatosis is estimated to be about 1 in 40,000 individuals.
• Neurofibromatosis Type 2 (NF2): This is a genetic disorder that makes it more likely that people will develop multiple tumors in their nervous system, including schwannomas, particularly on the cranial and spinal nerves. The incidence of NF2 is approximately 1 in 25,000 to 1 in 40,000 births.

Schwannomas can occur at any age but are most commonly diagnosed in adults between 20 and 50. They are slightly more common in women than in men. Most schwannomas are solitary and sporadic, although individuals with certain genetic conditions like NF2 are at a higher risk of developing multiple tumors.

Given their benign nature, schwannomas often grow slowly and may not cause symptoms for many years. As such, some individuals may have schwannomas that remain undetected throughout their lives, potentially making the true incidence of these tumors higher than what is documented.

Who gets Schwannomas?

Schwannoma can occur in people of all ages. However, they are more common in people with the genetic disorders neurofibromatosis type 2 (NF2) and schwannomatosis. Schwannomas rarely run in families, but these same genetic disorders in a family may increase a family member’s risk of schwannoma.

What is the prognosis for those diagnosed with schwannoma?

Schwannomas are typically benign (non-cancerous) tumors that grow on the sheaths of nerves throughout the body. Because they are benign, discussing survival rates in the context often used for cancer patients—such as five-year survival rates—is not entirely applicable. Instead, the focus with schwannomas is usually on successful removal, management of symptoms, and preservation of nerve function.

The prognosis for individuals with schwannomas is generally excellent, especially when the tumors are detected early and are accessible for surgical removal. The outcomes of surgery or other treatments depend on the location of the tumor, its size, and whether it affects critical structures or nerve functions. For most patients, complete removal of the schwannoma is possible, which typically results in a cure of the condition associated with the tumor.

For schwannomas in locations that make surgery more complex, such as vestibular schwannomas (also known as acoustic neuromas) that affect the nerves related to hearing and balance, treatment goals include maximizing tumor removal while minimizing impacts on hearing, balance, and facial nerve function. Even in these more complex cases, modern surgical techniques and other treatment modalities (like stereotactic radiosurgery) have significantly improved outcomes, allowing many patients to maintain a good quality of life.

In cases where schwannomas are associated with genetic conditions, such as Neurofibromatosis Type 2 (NF2), the management might be more complicated due to the presence of multiple tumors. Even then, the focus remains on managing symptoms, reducing tumor size, and preserving nerve function to the greatest extent possible.

Overall, the survival rate for individuals with schwannomas is excellent since these tumors are benign. The key challenges typically revolve around managing symptoms and preventing or addressing functional impairments related to the tumors. Regular follow-ups and monitoring are essential, especially in cases where complete tumor removal isn’t possible or in individuals with conditions that predispose them to develop multiple schwannomas.

What is the most common location for a schwannoma?

The most common location for a schwannoma is on cranial nerve VIII, also known as the vestibular nerve. This nerve is part of the nerve system connecting the inner ear to the brain. Tumors in this location are specifically referred to as vestibular schwannomas or acoustic neuromas. Given the vestibular nerve’s role in these functions, these tumors are notable for affecting hearing and balance.

Other relatively common locations for schwannomas include the spinal nerves, where they can grow within the spinal canal or on nerves that branch out from the spinal cord. These spinal schwannomas can lead to symptoms depending on their size and location, including pain, weakness, or numbness in the limbs or trunk, and issues with bladder or bowel control.

The location of a schwannoma largely determines the approach to treatment and management, as well as the potential impacts on the patient’s health and function.

Where are cancerous schwannomas most likely to form?

Cancerous schwannomas, known as malignant peripheral nerve sheath tumors (MPNSTs), are sporadic. These malignant tumors arise from the nerve sheath cells surrounding peripheral nerves and are more aggressive than their benign counterparts. They can develop anywhere in the body but are most common in the following locations:

• Deep Tissue of the Arms and Legs: MPNSTs often occur in the proximal regions of the limbs, closer to the body. This is partly because the larger peripheral nerves from which these tumors originate are located in these areas.

• Trunk: The trunk of the body, including the chest and abdominal areas, is another common location for these tumors. Here, the tumors can affect the larger nerve plexuses.

• Head and Neck: Though less common than in the limbs or trunk, malignant schwannomas can also occur in the head and neck region, affecting the associated nerves.
• Pelvic Region: MPNSTs can develop in the pelvic region, involving the nerves that supply this area.

These tumors are often associated with genetic conditions, such as neurofibromatosis type 1 (NF1), which significantly increases the risk of developing MPNSTs. In individuals with NF1, these malignant tumors may arise from preexisting benign neurofibromas that undergo malignant transformation.

The prognosis for MPNSTs can be challenging, as these tumors tend to be more aggressive and have a higher risk of recurrence and metastasis compared to benign schwannomas. Treatment typically involves a combination of surgery, radiation therapy, and chemotherapy aimed at removing the tumor, controlling its spread, and managing symptoms.

Given their rarity, any new or worsening symptoms in individuals with a history of neurofibromatosis or other nerve-related tumors should prompt immediate medical evaluation to rule out malignancy and determine the most appropriate course of action.

Information and Resources for Schwannoma

National Cancer Institute: Schwannoma

Cancer Research UK