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==Pathophysiology==
==Pathophysiology==
Acoustic neuromas may occur sporadically, or in some cases occur as part of [[Neurofibromatosis type I|von Recklinhausen neurofibromatosis]], in which case the neuroma may take on one of two forms.
*Acoustic schwannomas are benign tumours (WHO grade 1), which usually arise from the intracanalicular segment of the vestibular portion of the vestibulocochlear nerve (CN VIII) 2,4, near the transition point between glial and Schwann cells (Obersteiner-Redlich zone) 8. In over 90% of cases these tumours arise from the inferior division of the vestibular nerve 8.  
*In '''Neurofibromatosis type I''', a schwannoma may sporadically involve the 8th nerve, usually in adult life, but may involve any other cranial nerve or the spinal root. Bilateral acoustic neuromas are rare in this type.
*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.  
*In '''Neurofibromatosis type II''', bilateral acoustic neuromas are the hallmark and typically present before the age of 21. These tumors tend to involve the entire extend of the nerve and show a strong [[autosomal dominant]] inheritance. Incidence is about 5 to 10%.
*They can display two types of growth pattern:
 
**Antoni A
The usual tumor in the adult presents as a solitary tumor, originating in the nerve. It usually arises from the vestibular portion of the 8th nerve, just within the internal auditory canal. As the tumor grows, it usually extends into the posterior fossa to occupy the angle between the cerebellum and the pons ([[cerebellopontine angle]]). Because of its position, it may also compress the 5th, 7th, and less often, the 9th and 10th cranial nerves. Later, it may compress the pons and lateral medulla, causing obstruction of the [[cerebrospinal fluid]] and increased [[intracranial pressure]].  
*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.


==References==
==References==

Revision as of 13:04, 14 September 2015

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Pathophysiology

  • Acoustic schwannomas are benign tumours (WHO grade 1), which usually arise from the intracanalicular segment of the vestibular portion of the vestibulocochlear nerve (CN VIII) 2,4, near the transition point between glial and Schwann cells (Obersteiner-Redlich zone) 8. In over 90% of cases these tumours arise from the inferior division of the vestibular nerve 8.
  • 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.
  • 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.

References


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