Acoustic neuroma classification
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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]
- 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 loss, tinnitus, and balance dysfunction
Classification based on the MRI scan:
- Entirely intracanalicular: The entire tumor is completely within the bony canal
- Intracranial extension without brain stem distortion: Intracranial portion of the tumor is 1.5 - 2.5 cm. (Some references mentioned 1 - 2 cm)
- Intracranial extension with brain stem distortion: Intracranial portion of the tumor is greater than 2.5 cm. (Some references mentioned more than 2 cm)
Classification based on Microscopic Histopathology:[2][3]
- Conventional schwannoma: It is the most common schwannoma
- Cellular schwannoma: It may mimic malignant peripheral nerve sheath tumor
- Plexiform schwannoma: It may mimic malignant peripheral nerve sheath tumor if cellular, especially in childhood
- Melanotic schwannoma
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. | |||||
References
- ↑ 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) - ↑ Kurtkaya-Yapicier O, Scheithauer B, Woodruff JM (2003). "The pathobiologic spectrum of Schwannomas". Histol Histopathol. 18 (3): 925–34. PMID 12792904.
- ↑ Sho Hashimoto (2003). "Classification of vestibular schwannoma". Springer Japan.
- ↑ 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.
- ↑ Hitselberger WE, House WF (1966). "classification of acoustic neuromas". Arch Otolaryngol.
- ↑ Koos WT, Day JD, Matula C, Levy DI. "Neurotopographic considerations in the microsurgical treatment of small acoustic neurinomas". J Neurisurg.
- ↑ 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) - ↑ 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.