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{{Acoustic neuroma}}
{{Acoustic neuroma}}
{{CMG}}{{AE}} {{Simrat}}
{{CMG}}{{AE}} {{Simrat}} {{M.B}}


==Overview==
==Overview==
Acoustic neuroma may be [[Classification|classified]] according to the findings on [[magnetic resonance imaging]] ([[Magnetic resonance imaging|MRI]]) or it can also be [[Classification|classified]] based on [[microscopic]] [[histopathology]], and whether or not they are associated with [[Neurofibromatosis type II|neurofibromatosis type 2]]. Based on [[microscopic]] [[histopathology]], acoustic neuroma may be [[Classification|classified]] into four subtypes: conventional [[schwannoma]], cellular schwannoma, plexiform schwannoma, and melanotic schwannoma. While acoustic neuromas are benign [[Tumor|tumors]], there is no established system for the [[Cancer staging|staging]] of acoustic neuromas. Koos [[Grading (tumors)|grading]] scale provides four [[Grading (tumors)|grades]] based on extrameatal extension and compression of the [[brain stem]] , a reliable method for [[tumor]] [[classification]] which is used in practice.
==Classification==
===Classification based on the association with neurofibromatosis type 2:===
'''Not associated/Sporadic'''
*The vast majority are the sporadic form. 95% of all the cases of acoustic neuroma are sporadic. The cause of sporadic form is unclear 
'''Associated with Neurofibromatosis type II (NF2)'''<ref>{{Cite journal
| author = [[D. Gareth R. Evans]]
| title = Neurofibromatosis 2 &#91;Bilateral acoustic neurofibromatosis, central neurofibromatosis, NF2, neurofibromatosis type II&#93;
| journal = [[Genetics in medicine : official journal of the American College of Medical Genetics]]
| volume = 11
| issue = 9
| pages = 599–610
| year = 2009
| month = September
| doi = 10.1097/GIM.0b013e3181ac9a27
| pmid = 19652604
}}</ref>
*[[Neurofibromatosis type II|NF2]] is a rare disorder and it accounts for 5% of acoustic neuromas
*Acoustic neuroma associated with [[neurofibromatosis type II]] are typically [[bilateral]] and cause gradually progressive [[Hearing impairment|hearing loss]], [[tinnitus]],  and balance dysfunction
===Classification based on the [[MRI scan]]:===
*Entirely intracanalicular: The entire [[tumor]] is completely within the [[Bone|bony]] canal
*[[Cranium|Intracranial]] extension without [[brain stem]] distortion: [[Cranium|Intracranial]] portion of the [[tumor]] is 1.5 - 2.5 cm. (Some references mentioned 1 - 2 cm) 
*[[Cranium|Intracranial]] extension with [[brain stem]] distortion: [[Cranium|Intracranial]] portion of the [[tumor]] is greater than 2.5 cm. (Some references mentioned more than 2 cm)


==Calssification==
=== Classification based on Microscopic Histopathology:<ref name="pmid12792904">{{cite journal| author=Kurtkaya-Yapicier O, Scheithauer B, Woodruff JM| title=The pathobiologic spectrum of Schwannomas. | journal=Histol Histopathol | year= 2003 | volume= 18 | issue= 3 | pages= 925-34 | pmid=12792904 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12792904  }} </ref><ref>{{Cite journal|last=Sho Hashimoto|first=|date=2003|title=Classification of vestibular schwannoma|url=|journal=Springer Japan|volume=|pages=|via=}}</ref> ===
Unilateral vestibular schwannomas affect only one ear. They account for approximately 8 percent of all tumors inside the skull; one out of every 100,000 individuals per year develops a vestibular schwannoma. Symptoms may develop at any age but usually occur between the ages of 30 and 60 years. Unilateral vestibular schwannomas are not hereditary.
*Conventional [[schwannoma]]: It is the most common schwannoma
*[[Cellular]] schwannoma: It may mimic [[malignant]] peripheral [[Neuron|nerve sheath]] [[tumor]]
*Plexiform schwannoma: It may mimic [[malignant]] peripheral [[Neuron|nerve sheath]] [[tumor]] if cellular, especially in childhood
*Melanotic schwannoma


Bilateral vestibular schwannomas affect both hearing nerves and are usually associated with a genetic disorder called neurofibromatosis type 2 (NF 2). Half of affected individuals have inherited the disorder from an affected parent and half seem to have a mutation for the first time in their family. Each child of an affected parent has a 50 percent chance of inheriting the disorder. Unlike those with a unilateral vestibular schwannoma, individuals with NF2 usually develop symptoms in their teens or early adulthood. In addition, patients with NF2 usually develop multiple brain and spinal cord related tumors. They also can develop tumors of the nerves important for swallowing, speech, eye and facial movement, and facial sensation. Determining the best management of the vestibular schwannomas as well as the additional nerve, brain, and spinal cord tumors is more complicated than deciding how to treat a unilateral vestibular schwannoma. Further research is needed to determine the best treatment for individuals with NF2.
=== Staging ===
Acoustic neuromas  are [[benign]] [[Tumor|tumors]] ([[WHO]] [[Grading (tumors)|grade]] 1), but there is no established system for the [[Cancer staging|staging]] of acoustic neuromas. Numerous [[Cancer staging|stage]] [[Grading (tumors)|grading]] systems have been reported according to [[tumor]] size. [[Tumor]] size is more important and can be measured by measuring the maximum [[diameter]] of the [[tumor]].<ref>{{Cite journal|last=Sterkers JM, Morrison GA, Sterkers O, El-Dine MM.|first=JM|date=1994|title=Preservation of facial, cochlear, and other nerve functions in acoustic neuroma treatment.|url=|journal=Otolaryngol Head Neck Surg|volume=|pages=|via=}}</ref><ref>{{Cite journal|last=Hitselberger WE, House WF|first=|date=1966|title=classification of acoustic neuromas|url=|journal=Arch Otolaryngol|volume=|pages=|via=}}</ref><ref>{{Cite journal|last=Koos WT, Day JD, Matula C, Levy DI|first=|date=|title=Neurotopographic considerations in the microsurgical treatment of small acoustic neurinomas|url=|journal=J Neurisurg|volume=|pages=|via=}}</ref>


Scientists believe that both unilateral and bilateral vestibular schwannomas form following the loss of the function of a gene on chromosome 22. (A gene is a small section of DNA responsible for a particular characteristic like hair color or skin tone). Scientists believe that this particular gene on chromosome 22 produces a protein that controls the growth of Schwann cells. When this gene malfunctions, Schwann cell growth is uncontrolled, resulting in a tumor. Scientists also think that this gene may help control the growth of other types of tumors. In NF2 patients, the faulty gene on chromosome 22 is inherited. For individuals with unilateral vestibular schwannoma, however, some scientists hypothesize that this gene somehow loses its ability to function properly.
According to the Koos grading scale, there are 4 [[Grading (tumors)|grades]] of acoustic neuroma based on the findings on [[magnetic resonance imaging]] ([[Magnetic resonance imaging|MRI]]), extrameatal extension and compression of the [[brain stem]]:<ref>{{Cite journal
| author = [[Nicholas J. Erickson]], [[Philip G. R. Schmalz]], [[Bonita S. Agee]], [[Matthew Fort]], [[Beverly C. Walters]], [[Benjamin M. McGrew]] & [[Winfield S. 3rd Fisher]]
| title = Koos Classification of Vestibular Schwannomas: A Reliability Study
| journal = [[Neurosurgery]]
| year = 2018
| month = August
| doi = 10.1093/neuros/nyy40
| pmid = 30169695
}}</ref>
{| {{table}} cellpadding="4" cellspacing="0" style="border: 1px;solid margin: 1em 1em 1em 0; border-collapse: collapse;"
! colspan="2" align="center" style="background:#4479BA;" |{{fontcolor|#FFF|Koos Classification for Acoustic Neuroma}}
|-
! style="background: #DCDCDC; " |Grade!!Definition
|-
! style="background: #DCDCDC;" |I
| style="background: #F5F5F5;" |[[Tumor]] involves only the [[Internal ear|internal auditory canal]]
|-
! style="background: #DCDCDC;" |II
| style="background: #F5F5F5;" |[[Tumor]] extends into the cerebellopontine angle, but does not encroach on the [[brain stem]].
|-
! style="background: #DCDCDC;" |III
| style="background: #F5F5F5;" |[[Tumor]] fills the entire cerebellopontine angle
|-
! style="background: #DCDCDC;" |IV
| style="background: #F5F5F5;" |[[Tumor]] displaces the [[brain stem]] and adjacent [[cranial nerves]]
|-
|}


There are two types of acoustic neuroma: unilateral and bilateral. Unilateral acoustic neuromas affect only one ear. They account for approximately 8 percent of all tumors inside the skull. Symptoms may develop at any age but usually occur between the ages of 30 and 60 years.
'''Below table summarizes the current grading systems used in practice:''' 
{| style="border: 3px; font-size 190%; margin: 1px; width: 700px; align=“ left”"
! colspan="6" style="background: #5579FF; width: 600px:" | {{fontcolor|#FFF|Main grading systems for acoustic neuromas}}
|-
! style="background: #4479BA; " | {{fontcolor|#FFF| Tumor size (CPA Maximum diameter)}}
! style="background: #4479BA; " | {{fontcolor|#FFF| Sterker}}
! style="background: #4479BA; " | {{fontcolor|#FFF| House}}
! style="background: #4479BA; " | {{fontcolor|#FFF| Koos}}
! style="background: #4479BA; " | {{fontcolor|#FFF| Samii}}
! style="background: #4479BA; " | {{fontcolor|#FFF| Tumor Description}}
|-
! style="padding: 10px 10px; background: #ABCDEF; " | 0
(intracanalicular)
! style="padding: 10px 10px; background: #ABCDEF; " |Tube type
! style="padding: 10px 10px; background: #ABCDEF; " |Intracanalicular
! style="padding: 10px 10px; background: #ace123; " |Grade I
! style="padding: 10px 10px; background: #eee000; " |T1
! style="padding: 10px 10px; background: #eee000; " |Confining to internal acoustic canal
|-
! style="padding: 10px 10px; background: #ABCDEF; " | ≤ 10 mm
! rowspan="2" style="padding: 10px 10px; background: #ABCDEF; " | Small
! style="padding: 10px 10px; background: #ABCDEF; " | Grade 1
(Small)
! rowspan="3" style="padding: 10px 10px; background: #ace123; " | Grade II
! style="padding: 10px 10px; background: #eee000; " | T2
! style="padding: 10px 10px; background: #eee000; " | Superpassing internal acoustic canal
|-
! style="padding: 10px 10px; background: #ABCDEF; " | ≤ 15 mm
! rowspan="2" style="padding: 10px 10px; background: #ABCDEF; " | Grade 2
(Medium)     
! rowspan="2" style="padding: 10px 10px; background: #eee000; " | T3a
! rowspan="2" style="padding: 10px 10px; background: #eee000; " | [[Tumor]] occupying [[Cerebellopontine angle|CPA]]
|-
! style="padding: 10px 10px; background: #ABCDEF; " | ≤ 20 mm
! rowspan="2" style="padding: 10px 10px; background: #ABCDEF; " | Mild
|-
! style="padding: 10px 10px; background: #ABCDEF; " | ≤ 30 mm
! style="padding: 10px 10px; background: #ABCDEF; " | Grade 3
(Moderately Large)
! style="padding: 10px 10px; background: #ace123; " | Grade III
! style="padding: 10px 10px; background: #eee000; " | T3b
! style="padding: 10px 10px; background: #eee000; " | [[Tumor]] occupying [[Cerebellopontine angle|CPA]] and contacting
the [[Brain stem|brainstem]] without compression
|-
! style="padding: 10px 10px; background: #ABCDEF; " | ≤ 40 mm
! style="padding: 10px 10px; background: #ABCDEF; " | Large
! style="padding: 10px 10px; background: #ABCDEF; " | Grade 4
(Large)
! rowspan="2" style="padding: 10px 10px; background: #ace123; " | Grade IV
! style="padding: 10px 10px; background: #eee000; " | T4a
! style="padding: 10px 10px; background: #eee000; " | [[Tumor]] compressing the [[Brain stem|brainstem]]
|-
! style="padding: 10px 10px; background: #ABCDEF; " | > 40 mm
! style="padding: 10px 10px; background: #ABCDEF; " | Huge
! style="padding: 10px 10px; background: #ABCDEF; " | Grade 5
(Giant)
! style="padding: 10px 10px; background: #eee000; " | T4b
! style="padding: 10px 10px; background: #eee000; " | Severe [[Brain stem|brainstem]] displacement and deformation of fourth [[Ventricle (brain)|ventricle]] under [[tumor]] compression
|-
! colspan="6" style="padding: 10px 10px; background: #DCDCDC; " |Main grading systems for [[Acoustic neuroma|acoustic neuromas]].  
The classifications on the left side (blue area) are mainly based on tumor size, while those on the right side (yellow area) are based on the [[Anatomy|anatomical]] relationship around the tumor. Koos classification (green area) combines the [[tumor]] size and anatomical relationship for larger tumors.
|}
<ref>{{Cite journal|last=Hao Wu, Liwei Zhang, Dongyi Han, Ying Mao, Jun Yang, Zhaoyan Wang, Wang Jia, Ping Zhong, Huan Jia|first=|date=2016|title=Summary and consensus in 7th International Conference on acoustic neuroma: An update for the management of sporadic acoustic neuromas|url=|journal=World Journal of Otorhinolaryngology-Head and Neck Surgery|volume=|pages=|via=}}</ref>


Bilateral acoustic neuromas, which affect both ears, are hereditary. Inherited from one's parents, this tumor results from a genetic disorder known as neurofibromatosis-2 (NF2). Affected individuals have a 50 percent chance of passing this disorder on to their children. Unlike those with a unilateral acoustic neuroma, individuals with NF2 usually develop symptoms in their teens or early adulthood. Because NF2 patients usually have multiple tumors, the surgical procedure is more complicated than the removal of a unilateral acoustic neuroma. Further research is needed to determine the best approach in these circumstances.
==References==
{{reflist|2}}
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In addition to tumors arising from the hearing and balance nerves, NF2 patients may develop tumors on other cranial nerves associated with swallowing, speech, eye and facial movement, and facial sensation. NF2 patients may also develop tumors within the spinal cord and on the brain's thin covering.
[[Category:Types of cancer]]
 
[[Category:Disease]]
Both types of acoustic neuroma occur following a loss of the function of a gene on chromosome 22. A gene is a small section of DNA responsible for a particular trait like hair color or skin tone. This particular gene on chromosome 22 suppresses the growth of Schwann cells. When this gene malfunctions, Schwann cells can grow out of control. This gene may help suppress other types of tumor growth. In NF2 patients, the faulty gene on chromosome 22 is inherited.
[[Category:Up-To-Date]]
 
[[Category:Oncology]]
Acoustic neuroma is also called an acoustic neurinoma or a vestibular schwannoma.
[[Category:Medicine]]
 
[[Category:Otolaryngology]]
 
[[Category:Neurology]]
 
[[Category:Neurosurgery]]
Cytologically, no differences have been found between the vestibular schwannomas of NF2 and those found in sporadic cases. Histologically, however, the tumors in NF2 often appear as grape-like clusters that can infiltrate the fibers of individual nerves and may adumbrate a polyclonal origin. Both unilateral and bilateral tumors vary in their precise location along the vestibular nerve, tending to arise at the border between the central and peripheral segments of the nerve. Why tumors arise at this transition zone is not known, but variation in the site at which a tumor is located can have a major influence on the symptoms it produces.
 
For clinical management, the most useful classification of vestibular schwannomas is by size, location, and growth rate. However, tumors tend to enlarge unpredictably. Some do not change in size for many years, while others may grow at a rate of up to 20mm in diameter per year. Currently, the best method to monitor tumor growth is with gadolinium-enhanced MRI. To facilitate the interpretation of clinical studies, both the greatest diameter of the tumor within the posterior fossa and the extent of penetration into the intracanalicular space should be documented.
 
A second important classification is between familial and sporadic cases. All cases of vestibular schwannomas are thought to result from the functional loss of a tumor-suppressor gene that has been localized to the long arm of chromosome 22. In at least 95 percent of patients, however, the disease is unilateral and the majority of these cases are sporadic, resulting from somatic mutations that are not associated with an increased risk for other tumors either in the individual or in close relatives. About 5 percent of patients exhibit bilateral disease or other features that define NF2. These patients are thought to carry a single germline mutation of the chromosome 22 linked gene and sustain the loss of the remaining normal allele as a somatic event in those cells that give rise to the tumor. Thus, the trait is recessive at the cellular level but exhibits a dominant pattern of genetic transmission in families. Even when a thorough family history is obtained, in about one half of all recognized cases of NF2, no evidence of other affected family members can be found. These may patients represent new germline mutations and are at risk of transmitting the disease to their offspring.
 
Patients with NF2 who carry new mutations tend to be more severely affected than familial cases, and some recent studies have raised the possibility that in familial cases the onset of symptoms may be earlier and the severity greater when the disease is inherited from the mother. Such effects can arise from genomic imprinting, and although the precise genetic mechanism for this phenomenon is unknown, a growing number of examples of such parental origin effects now have been documented. If confirmed, these findings could have practical implications for the management of families with NF2.
 
Molecular studies on NF2 and on unilateral tumors are at an exciting juncture. The gene for NF2 should soon be identified and may provide molecular explanations for clinical differences among families with NF2 as well as differences in the growth rate among tumors. Further studies on the molecular biology of the gene may suggest treatments for vestibular schwannomas, both in NF2 and in patients with unilateral diseases.
 
Patients with NF2 may have associated meningiomas and spinal root schwannomas as well as cafe-au-lait spots and peripheral Schwann cell tumors and often develop posterior subcapsular cataracts at an early age. The prevalence of these findings varies greatly among families.

Latest revision as of 18:00, 19 April 2019

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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] Mohsen Basiri M.D.

Overview

Acoustic neuroma may be classified according to the findings on magnetic resonance imaging (MRI) or it can also be classified based on microscopic histopathology, and whether or not they are associated with neurofibromatosis type 2. Based on microscopic histopathology, acoustic neuroma may be classified into four subtypes: conventional schwannoma, cellular schwannoma, plexiform schwannoma, and melanotic schwannoma. While acoustic neuromas are benign tumors, there is no established system for the staging of acoustic neuromas. Koos grading scale provides four grades based on extrameatal extension and compression of the brain stem , a reliable method for tumor classification which is used in practice.

Classification

Classification based on the association with neurofibromatosis type 2:

Not associated/Sporadic

  • The vast majority are the sporadic form. 95% of all the cases of acoustic neuroma are sporadic. The cause of sporadic form is unclear

Associated with Neurofibromatosis type II (NF2)[1]

Classification based on the MRI scan:

Classification based on Microscopic Histopathology:[2][3]

Staging

Acoustic neuromas are benign tumors (WHO grade 1), but there is no established system for the staging of acoustic neuromas. Numerous stage grading systems have been reported according to tumor size. Tumor size is more important and can be measured by measuring the maximum diameter of the tumor.[4][5][6]

According to the Koos grading scale, there are 4 grades of acoustic neuroma based on the findings on magnetic resonance imaging (MRI), extrameatal extension and compression of the brain stem:[7]

Koos Classification for Acoustic Neuroma
Grade Definition
I Tumor involves only the internal auditory canal
II Tumor extends into the cerebellopontine angle, but does not encroach on the brain stem.
III Tumor fills the entire cerebellopontine angle
IV Tumor displaces the brain stem and adjacent cranial nerves

Below table summarizes the current grading systems used in practice:

Main grading systems for acoustic neuromas
Tumor size (CPA Maximum diameter) Sterker House Koos Samii Tumor Description
0

(intracanalicular)

Tube type Intracanalicular Grade I T1 Confining to internal acoustic canal
≤ 10 mm Small Grade 1

(Small)

Grade II T2 Superpassing internal acoustic canal
≤ 15 mm Grade 2

(Medium)

T3a Tumor occupying CPA
≤ 20 mm Mild
≤ 30 mm Grade 3

(Moderately Large)

Grade III T3b Tumor occupying CPA and contacting

the brainstem without compression

≤ 40 mm Large Grade 4

(Large)

Grade IV T4a Tumor compressing the brainstem
> 40 mm Huge Grade 5

(Giant)

T4b Severe brainstem displacement and deformation of fourth ventricle under tumor compression
Main grading systems for acoustic neuromas.

The classifications on the left side (blue area) are mainly based on tumor size, while those on the right side (yellow area) are based on the anatomical relationship around the tumor. Koos classification (green area) combines the tumor size and anatomical relationship for larger tumors.

[8]

References

  1. ↑ D. Gareth R. Evans (2009). "Neurofibromatosis 2 [Bilateral acoustic neurofibromatosis, central neurofibromatosis, NF2, neurofibromatosis type II]". Genetics in medicine : official journal of the American College of Medical Genetics. 11 (9): 599–610. doi:10.1097/GIM.0b013e3181ac9a27. PMID 19652604. Unknown parameter |month= ignored (help)
  2. ↑ Kurtkaya-Yapicier O, Scheithauer B, Woodruff JM (2003). "The pathobiologic spectrum of Schwannomas". Histol Histopathol. 18 (3): 925–34. PMID 12792904.
  3. ↑ Sho Hashimoto (2003). "Classification of vestibular schwannoma". Springer Japan.
  4. ↑ Sterkers JM, Morrison GA, Sterkers O, El-Dine MM., JM (1994). "Preservation of facial, cochlear, and other nerve functions in acoustic neuroma treatment". Otolaryngol Head Neck Surg.
  5. ↑ Hitselberger WE, House WF (1966). "classification of acoustic neuromas". Arch Otolaryngol.
  6. ↑ Koos WT, Day JD, Matula C, Levy DI. "Neurotopographic considerations in the microsurgical treatment of small acoustic neurinomas". J Neurisurg.
  7. ↑ Nicholas J. Erickson, Philip G. R. Schmalz, Bonita S. Agee, Matthew Fort, Beverly C. Walters, Benjamin M. McGrew & Winfield S. 3rd Fisher (2018). "Koos Classification of Vestibular Schwannomas: A Reliability Study". Neurosurgery. doi:10.1093/neuros/nyy40. PMID 30169695. Unknown parameter |month= ignored (help)
  8. ↑ Hao Wu, Liwei Zhang, Dongyi Han, Ying Mao, Jun Yang, Zhaoyan Wang, Wang Jia, Ping Zhong, Huan Jia (2016). "Summary and consensus in 7th International Conference on acoustic neuroma: An update for the management of sporadic acoustic neuromas". World Journal of Otorhinolaryngology-Head and Neck Surgery.

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