Acoustic neuroma pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2]
Overview
On microscopic histopathological analysis, acoustic neuroma is characterized into two types, Antoni A and Antoni B based on growth patterns.[1]
Pathophysiology
Acoustic neuromas are benign tumors (WHO grade 1), which usually arise from the intracanalicular segment of the vestibular portion of the vestibulocochlear nerve (CN VIII), near the transition point between glial and Schwann cells (Obersteiner-Redlich zone) 8. In over 90% of cases these tumors arise from the inferior division of the vestibular nerve 8. An acoustic neuroma arises from a type of cell known as the Schwann cell. These cells form an insulating layer over all nerves of the peripheral nervous system (i.e., nerves outside of the central nervous system) including the eighth cranial nerve. The eighth cranial nerve is separated into two branches the cochlear branch, which transmits sound to the brain and the vestibular branch, which transmits balance information to the brain. Most acoustic neuromas occur on the vestibular portion of the eighth cranial nerve. Because these tumors are made up of Schwann cells, and usually occur on the vestibular portion of the eighth cranial nerve, many physicians prefer the use of the term vestibular schwannoma. However, the term acoustic neuroma is still used more often in the medical literature.[2]
They are well circumscribed encapsulated masses, which unlike neuromas, arise from but are separate from nerve fibers 7, which they usually splay and displace rather than incorporated.
Microscopic Pathology
They can display two types of growth pattern:
- Antoni A
- Elongated cells with cytoplasmic processes arranged in fascicles 7
- Little stromal matrix
- Verocay bodies: nuclear free zones of processes lying between regions of nuclear palisading
- Antoni B
- Loose meshwork of cells
- Less densely cellular
- Microcysts and myxoid change
