Acoustic neuroma MRI
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Acoustic neuroma MRI On the Web | |
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American Roentgen Ray Society Images of Acoustic neuroma MRI | |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Contrast-enhanced CT will detect almost all acoustic neuromas that are greater than 2.0 cm in diameter and project further than 1.5 cm into the cerebellopontine angle. Those tumors that are smaller may be detected by MRI with gadolinium enhancement. Audiology and vestibular tests should be concurrently evaluated using air conduction and bone conduction threshold testing to assess for sensorineural versus conduction hearing loss.
MRI
Acoustic neuromas are most frequently diagnosed by MRI scan in a patient with unilateral hearing loss. Important information to be determined from the MRI scan are distance the tumor extends laterally in the auditory canal, the extent to which the tumor expands in the cerebello-pontine angle, and whether or not the brain stem is contacted or distorted The definitive diagnostic test for patients with acoustic tumors is gadolinium-enhanced MRI.
- Well-performed scanning can demonstrate tumors as small as 1-2 mm in diameter. On the other hand, thin-cut CT scanning can miss tumors as large as 1.5 cm even when intravenous contrast enhancement is used.
- Gadolinium contrast is critical because nonenhanced MRI can miss small tumors.
- Fast-spin echo techniques do not require gadolinium enhancement and can be performed very rapidly and relatively inexpensively. However, such highly targeted techniques risk missing other important causes of unilateral sensory hearing loss, including intra-axial tumors, demyelinating disease, and infarcts.
- MRI is contraindicated in individuals with ferromagnetic implants.
- Fine-cut CT scanning of the internal auditory canal with contrast can rule out a medium-size or large tumor but cannot be relied upon to detect a tumor smaller than 1-1.5 cm.
- If suspicion is high and MRI is contraindicated, air-contrast cisternography has high sensitivity and can detect relatively small intracanalicular tumors.
MRI findings of acoustic neuroma include:
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 tumours
Post-up MRI:Linear enhancement may not indicate tumour, but if there is nodular enhancement suspect tumour recurrence (needs follow up MRI).