![]() ![]() May show erosion and widening of the internal acoustic canal (IAC). small tumors tend to be solid, but larger tumors commonly demonstrate cystic degeneration 2.the location and extension can be classified according to the Koos grading scale.rarely, small tumors may be confined to the labyrinth (see intralabyrinthine schwannoma) 4.a minority are purely extracanalicular, merely abutting the porus acusticus (~20%) 1,5.extracanalicular extension may result in an " ice cream cone" appearance, presumed to represent tumor growth inwards along a path of least resistance.involvement of the IAC fundus is associated with decreased rates of hearing preservation.a small "CSF cap" typically remains, separating intracanalicular tumor from the cochlea however, growth laterally through the cochlea (transmodiolar) or vestibule (transmacular) into the middle ear may occasionally occur.most have an intracanalicular component, often widening the porus acusticus ( trumpeted IAM sign) (up to 90%) 5. ![]() Immunohistochemical staining is usually positive for S-100 protein 11.
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