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]
Overview
Acoustic neuroma may be classified according to findings on magnetic resonance imaging (MRI) or 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, but 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
- Acoustic neuroma may be classified into two subtypes, based on whether or not they are associated with neurofibromatosis type 2.
- 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
- Acoustic neuroma 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
- Sporadic
- Based on the MRI scan, acoustic neuromas can be classified into three subtypes:
- 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)
- Based on microscopic histopathology, acoustic neuroma can be classified into four subtypes:[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) According to the classification system known as the Koos grading scale there are 4 stages of acoustic neuroma based on findings on magnetic resonance imaging (MRI) and extrameatal extension and compression of the brain stem. The stages of acoustic neuroma are shown in the table below:[4]
| Koos Classification for Acoustic Neuroma | |
| Stage | Definition |
| I | Tumor involves only the internal auditory canal |
| II | Tumor extend into the cerebellopontine angle, but do not encroach on the brain stem. |
| III | Tumor fills the entire cerebellopontine angle |
| IV | Tumor displaces the brain stem and adjacent cranial nerves |
- : It may be confused with melanoma
- Cutaneous lentigines
- Myxomas (skin (subcutaneous), subcutanous, heart)
- Endocrine neoplasms
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.
- ↑ 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/nyy409. PMID 30169695. Unknown parameter
|month=ignored (help)