Acoustic neuroma MRI

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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

Gadolinium-enhanced MRI scan is diagnostic of acoutic neuroma. On brain MRI, acoustic neuroma characterized by hypointense mass on T1-weighted MRI, and hyperintense mass on T2-weighted MRI.[1]

MRI

  • Magnetic resonance imaging (MRI) using gadolinium as an enhancing contrast material is the preferred diagnostic test for identifying acoustic neuromas. The image formed clearly defines an acoustic neuroma if it is present and this technique can identify tumors measuring only a few millimeters in diameter. Tumors as small as 1-2 mm in diameter can be demonstrated by well performed MRI scanning. Nonenhanced MRI can miss small tumors.[1]
  • Most vestibular schwannomas have an intracanalicular component, and often result in widening of the porus acusticus resulting in the trumpeted IAM sign, which is present in up to 90% of cases.
  • In a minority of cases (~20%) they are purely extracanalicular, only abutting the porus acousticus.
  • Usually there is a small CSF cap between intracanalicular portion and the cochlea; occasionally, these tumors grow laterally through the cochlea (transmodiolar) or vestibule (transmacular) into the middle ear. Rarely they are small and confined to the vestibule (intravestibular) or to the cochlea (intracochlear) or both (vestibulocochlear).
  • Extracanalicular extension into cerebellopontine angle (path of least resistance) can lead to "ice-cream-cone" appearance. Small tumors tend to be solid whereas cystic degeneration seen commonly in larger tumors. Haemorrhagic areas may also be seen. Calcification is typically not present.[2]
MRI component Features
T1
  • Slightly hypointense cf. adjacent brain (63%)
  • Isointense cf. adjacent brain (37%)
  • May contain hypointense cystic areas
T2
  • Heterogeneously hyperintense cf. to adjacent brain
  • Cystic areas fluid intensity
  • May have associated peritumoural arachnoid cysts
T1 C+ (Gd)
  • Contrast enhancement is vivid
  • But heterogeneous in larger tumors

Post-op MRI: Linear enhancement may not indicate tumor, but if there is nodular enhancement suspect tumor recurrence (needs follow up MRI).[2]

MRI showing Intracanalicular acoustic neuroma[3]
MRI showing Intrameatal vestibularis schwannoma[4]

References

  1. 1.0 1.1 Vestibular Schwannoma. Wikipedia(2015) https://en.wikipedia.org/wiki/Vestibular_schwannoma Accessed on October 2 2015
  2. 2.0 2.1 Acoustic Schwannoma. Radiopedia(2015) http://radiopaedia.org/articles/acoustic-schwannoma Accessed on October 2 2015
  3. Image courtesy of Dr Frank Gaillard. Radiopaedia (original file here).[http://radiopaedia.org/licence Creative Commons BY-SA-NC
  4. Image courtesy of Dr. Roberto Schubert Radiopaedia (original file here).[http://radiopaedia.org/licence Creative Commons BY-SA-NC

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