Schwannoma tumors
Schwannoma tumors, also known as neurilemmomas, are benign (noncancerous) tumors formed from Schwann cells, which are the glial cells that insulate peripheral nerves. They typically arise in cranial, spinal, and autonomic nerves, with common types including vestibular schwannoma, which affects hearing and balance, and others associated with cranial nerves like the trigeminal and facial nerves. While these tumors are generally slow-growing and painless, they can grow large and occasionally cause symptoms such as hearing loss, dizziness, or nerve dysfunction depending on their location. Schwannomas are more prevalent in older adults, with a notable incidence in children linked to neurofibromatosis, a genetic condition that predisposes individuals to multiple nerve tumors.
Diagnosis involves a combination of medical history, physical examination, and imaging tests such as MRI or CT scans, sometimes accompanied by hearing tests for vestibular schwannomas. Treatment typically includes surgical removal or radiotherapy, as other methods have limited effectiveness. Although schwannomas cannot be prevented, early detection and intervention lead to a favorable prognosis; however, untreated tumors can lead to significant complications, including nerve damage and, in severe cases, life-threatening scenarios.
Subject Terms
Schwannoma tumors
ALSO KNOWN AS: Schwann cell tumors
RELATED CONDITIONS: peripheral nerve sheath tumors (MPNSTs), neurofibromatosis, schwannomatosis
DEFINITION: Schwannoma is a benign (noncancerous) encapsulated solitary tumor formed by Schwann cells of the peripheral nerves: cranial nerves, spinal nerves, and autonomic nerves. Schwannomas generally occur in the head, neck, and upper and lower limbs. A common cranial nerve schwannoma is the vestibular schwannoma (unilateral and nonhereditary), which affects the eighth cranial nerve, which governs hearing and balance. Other schwannommas include trigeminal, facial, and hypoglossal. Around 5 percent of schwannomas become cancerous. When schwannomas are found in children, they are usually associated with neurofibromatosis. Schwannomatosis is a newly identified neurofibromatosis of multiple schwannomas.
Risk factors: There are no known risk factors for schwannomas.
Etiology and the disease process: The etiology of schwannomas is unknown. The nerve fiber, or axon, of peripheral nerves, is sheathed in glial cells called Schwann cells. Sometimes Schwann cells abnormally proliferate to form a tumor, or schwannoma. The cells of schwannomas are spindle-shaped neoplastic Schwann cells.
Incidence: Schwannoma is generally a disease of older adults. The incidence rate for vestibular schwannoma is 4 to 5 adult cases per 100,000 people yearly. In children, the incidence rate is .44 per 100,000. Spinal schwannoma has an incidence rate of .24 per 100,000. The incidence rate for both rises with age.
Symptoms: Schwannomas are generally slow-growing, small, painless tumors, although sometimes they can be painful and be as large as 10 centimeters. Subcutaneous tumors (under the skin) can be palpated during physical examination. In vestibular schwannoma, additional symptoms are hearing loss, dizziness, and ringing in the ears. Other cranial nerve schwannomas can have symptoms related to the function of that nerve.
Screening and diagnosis: A medical history and physical examination of the patient plus X-rays, ultrasound, computed (CT) scans, (MRI) scans, and are used to diagnose schwannoma. Vestibular schwannoma also requires a hearing test (audiogram). According to the World Health Organization (WHO), schwannoma is a grade I tumor, and malignant peripheral nerve sheath tumors are grades III and IV.
Treatment and therapy: is usually not effective. Radiotherapy and surgery are the main treatments. Rarely occurring malignant tumors may also require chemotherapy. In the 2020s, two new drugs, VT1 and VT2, were discovered to arrest the growth and shrink schwannomas. An additional drug, Everolimus, was in clinical trials for the treatment of vestibular schwannoma.
Prognosis, prevention, and outcomes: Schwannomas cannot be prevented. The prognosis is good with early diagnosis and surgery but worsens if the tumor is detected at a later stage. For example, an untreated vestibular schwannoma can cause pressure on the neighboring facial nerve, causing paralysis of the face on the affected side, and can further press on the brain stem, even resulting in death. The recurrence rate of malignant peripheral nerve sheath tumors after surgery is high.
“Schwannoma.” Johns Hopkins Medicine, www.hopkinsmedicine.org/health/conditions-and-diseases/nerve-sheath-tumor/schwannoma. Accessed 16 June 2024.
“Step Taken Towards Non-surgical Treatment for Schwannomas.” Brain Tumour Research, braintumourresearch.org/en-us/blogs/research-campaigning-news/step-taken-towards-non-surgical-treatment-for-schwannomas. Accessed 16 June 2024.
Williams, Alan. “New Experimental Treatment Can Stop the Growth of Schwannoma Tumours.” University of Plymouth, 8 Nov. 2022, www.plymouth.ac.uk/news/new-experimental-treatment-can-stop-the-growth-of-schwannoma-tumours. Accessed 16 June 2024.