Acoustic neuroma (schwannoma)
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Acoustic neuroma (schwannoma)
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Acoustic neuroma (schwannoma)
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Acoustic schwannomas p. 719
Bilateral acoustic schwannomas p. 719
Schwannomas p. 509, 543, 731
Vestibular schwannomas p. 543
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Transcript
Content Reviewers
Rishi Desai, MD, MPHContributors
Simone Taylor
Evan Debevec-McKenney
Tanner Marshall, MS
Schwannoma, sometimes called neurilemmoma, is a tumor that develops from Schwann cells.
Schwann cells belong to a category of cells called glial cells, which surround and support the neurons of the nervous system, and get their name from Theodor Schwann, a nineteenth-century physicist who first discovered them.
Neurons are made up of three main parts.
The dendrites, which are little branches off of the neuron that receive signals, which is essentially an electrical impulse, from other neurons; the soma, or cell body, which has all of the neuron’s main organelles like the nucleus; and the long axon, which transmits the signal to the next neuron in the series.
In the peripheral nervous system, Schwann cells synthesize a fatty substance made of lipoproteins called myelin, which forms insulating sheaths at along parts of the axon.
The myelin sheath plays an important role in conducting electrical impulses or action potentials.
Action potentials propagate along the axon when sodium ions move into the cell through ion channels.
In sections with a myelin sheath, there are no ion channels, but sections in between, called nodes of Ranvier, have a ton of ion channels.
The action potential therefore doesn’t have to move along each section of the neuron, but rather from node to node, resulting in super fast saltatory conduction.
Also, the Schwann cells express a gene called neurofibromin 2, or NF2, which encodes a protein called merlin.
In schwann cells, merlin acts as a tumor suppressor, meaning it prevents the Schwann cells from dividing uncontrollably.
And that’s exactly what happens with a schwannoma, the schwann cells start dividing uncontrollably.
No one knows what causes most schwannomas from developing. The majority of schwannomas are solitary tumors of Schwann cells which are found around peripheral nerves.
They are usually benign meaning that the cells don’t invade surrounding tissue structures, and schwannomas therefore don’t metastasize to distant locations.
Most often, they arise around cranial nerve 8, the vestibulocochlear nerve, and are known as vestibular schwannomas, or acoustic neuromas, though acoustic neuroma is not that precise a description.
Summary
Acoustic neuroma is a benign tumor that arises from the Schwann cells that surround the eighth cranial (vestibulocochlear) nerve. The symptoms of acoustic neuroma vary depending on the size and location of the tumor, but they can include hearing loss, tinnitus (ringing in the ears), dizziness, and facial weakness. The cause of acoustic neuroma is not fully understood, but it appears to be due to a combination of environmental and genetic factors.
Sources
- "Robbins Basic Pathology" Elsevier (2017)
- "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
- "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
- "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
- "The tumour-suppressor genes NF2/Merlin and Expanded act through Hippo signalling to regulate cell proliferation and apoptosis" Nature Cell Biology (2005)
- "Clinical Features and Treatment of Penile Schwannoma: A Systematic Review" Clinical Genitourinary Cancer (2016)
- "Extracranial head and neck schwannomas—A 10-year review" Auris Nasus Larynx (2007)
- "News on the genetics, epidemiology, medical care and translational research of Schwannomas" Journal of Neurology (2006)
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