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


==Overview==
==Overview==
Acoustic neuroma may be classified into several subtypes based on [[MRI scan]], microscopic [[histopathology]], and whether or not they are associated with [[neurofibromatosis]] type 2.
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.  
Acoustic neuroma may be classified based on MRI scan into three subtypes: entirely canalicular, intracranial extension without [[brainstem]] distortion, and intracranial extension with brain stem distortion. Based on microscopic histopathology, acoustic neuroma may be classified into four subtypes: conventional [[schwannoma]], cellular schwannoma, plexiform schwannoma, and melanotic schwannoma.<ref name="libre">Schwannoma. Librepathology(2015) http://librepathology.org/wiki/index.php/Schwannoma Accessed on October 2 2015</ref>
==Classification==
==Classification==
Acoustic neuroma may be classified into two subtypes, based on whether or not they are associated with neurofibromatosis type 2.
===Classification based on the association with neurofibromatosis type 2:===
*'''Sporadic'''  
'''Not associated/Sporadic'''  
**The vast majority are the sporadic form. Ninety five % of all cases of acoustic neuroma are sporadic. The cause of sporadic form is unclear.  
*The vast majority are the sporadic form. 95% of all the cases of acoustic neuroma are sporadic. The cause of sporadic form is unclear   
*'''Acoustic neuroma associated with neurofibromatosis type II (NF2)'''
'''Associated with Neurofibromatosis type II (NF2)'''<ref>{{Cite journal
**NF2 is a rare disorder and it accounts for 5% of acoustic neuromas.  
| 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)


Based on the [[MRI scan]], acoustic neuromas can be classified into three subtypes:
=== 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> ===
*Entirely intracanalicular: The entire tumor is completely within the bony canal
*Conventional [[schwannoma]]: It is the most common schwannoma
*Intracranial extension without [[brain stem]] distortion: intracranial portion of the tumor is 1.5-2.5 cm. (Some references mentioned 1-2 cm) 
*[[Cellular]] schwannoma: It may mimic [[malignant]] peripheral [[Neuron|nerve sheath]] [[tumor]]
*Intracranial extension with brain stem distortion: intracranial portion of the tumor is greater than 2.5 cm. (Some references mentioned more than 2 cm)
*Plexiform schwannoma: It may mimic [[malignant]] peripheral [[Neuron|nerve sheath]] [[tumor]] if cellular, especially in childhood
Based on microscopic [[histopathology]], acoustic neuroma can be classified into four subtypes:<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>
*Melanotic schwannoma
*Conventional [[schwannoma]]: It is the most common schwannoma.
 
*[[Cellular]] schwannoma: It may mimic [[malignant]] peripheral nerve sheath tumor.
=== Staging ===
*Plexiform schwannoma: It may mimic malignant peripheral nerve sheath tumor if cellular- especially in childhood.[[File:Plexiform_schwannoma_with_high_magnifaction.jpg|thumb|none|800px|Plexiform schwannoma with high magnifaction]]   
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>
*Melanotic schwannoma: It may be confused with [[melanoma]]. [[File:Psammomatous_melanotic_schwannoma.jpg|thumb|none|800px|Psammomatous melanotic schwannoma]]
 
It is associated with psammomatous form (psammomatous melanotic schwannoma) and with a heritable disorder (Carney complex).
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
The [[Carney complex]], also known as [[Carney syndrome]], NAME syndrome and LAMB syndrome, is an autosomal dominant syndrome associated with endocrinopathy, endocrine and nonendocrine tumors, and spotty pigmentation of the skin including the following:<ref name="libre">Schwannoma. Librepathology(2015) http://librepathology.org/wiki/index.php/Schwannoma Accessed on October 2 2015</ref>
  | author = [[Nicholas J. Erickson]], [[Philip G. R. Schmalz]], [[Bonita S. Agee]], [[Matthew Fort]], [[Beverly C. Walters]], [[Benjamin M. McGrew]] & [[Winfield S. 3rd Fisher]]
*[[Cutaneous]] lentigines
| title = Koos Classification of Vestibular Schwannomas: A Reliability Study
*Myxomas (skin ([[subcutaneous]]), subcutanous, [[heart]])
| journal = [[Neurosurgery]]
*Endocrine [[neoplasms]]
| 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]]
|-
|}
 
'''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>


==References==
==References==

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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