From the Guidelines
IAC MRI should include contrast-enhanced T1-weighted scans, as well as standard T1- and T2-weighted sequences, diffusion-weighted imaging (DWI), and fluid-attenuated inversion recovery sequences, to provide a comprehensive evaluation of the internal auditory canal and cerebellopontine angle. When evaluating the internal auditory canal (IAC) using MRI, it is essential to use a combination of sequences to accurately diagnose conditions such as vestibular schwannomas 1. The MRI protocol should include:
- Standard T1- and T2-weighted sequences
- Diffusion-weighted imaging (DWI) to differentiate vestibular schwannomas from arachnoid or epidermoid cysts
- Fluid-attenuated inversion recovery sequences
- Axial submillimetric heavily T2-weighted sequence to evaluate the vestibulocochlear nerve and its branches
- Thin slice spin echo or turbo spin echo/fast spin echo T1-weighted sequences or submillimetric T1-weighted 3D gradient echo sequences before and after gadolinium administration 1. Vestibular schwannomas typically present as a solid nodular mass with an intracanalicular component in the internal acoustic canal (IAC), often resulting in its widening, and are usually isointense on T1-weighted imaging with strong enhancement after gadolinium administration 1. The use of gadolinium-based contrast is still considered the gold standard in the diagnostic workup of vestibular schwannomas, despite the current debate about omitting post-gadolinium T1-weighted sequences 1. This comprehensive MRI protocol allows for accurate diagnosis and evaluation of conditions affecting the internal auditory canal and cerebellopontine angle, ultimately guiding treatment decisions and improving patient outcomes.
From the Research
IAC MRI Studies
- The study 2 found that MRI is the preferred method for assessing the internal auditory canal (IAC) due to its ability to provide excellent visualization of the canal and its contents.
- The study 3 determined that non-contrast high-resolution T2-weighted imaging (T2WI) alone can detect intralabyrinthine schwannomas (ILSs) with 84-100% sensitivity, suggesting that gadolinium may be unnecessary for screening MRI.
- The study 4 established normative size measurements for the IAC using MRI, finding that the mean IAC diameters were 5.93 mm (anteroposterior) and 5.70 mm (craniocaudal), with no significant differences between males and females or with age groups.
MRI Sequences and Techniques
- The study 5 provided an overview of the most useful MRI sequences for internal auditory canal and labyrinthine imaging, including the expected appearances of common pathologic entities.
- The study 3 used non-contrast T2WI and post-contrast T1WI to evaluate the IAC, while the study 4 used 1.5-T MRI to obtain anteroposterior and craniocaudal measurements of the IAC.
Gadolinium Contrast Agents
- The study 6 investigated the effects of gadolinium MRI contrast agents on DNA damage and cell survival when used in combination with radiation, finding a significant increase in initial levels of DNA damage, but no significant decrease in cell survival.
- The study 3 suggested that gadolinium may be unnecessary for screening MRI of the IAC, which could reduce costs, time, and adverse events associated with gadolinium administration.