Contrast-Enhanced CISS MRI Improves Visualization and Planning in Vestibular Schwannomas

Background Preoperative visualization is essential in planning of vestibular schwannoma operations. Still, there is often a considerable discrepancy between measured tumor size in MRI and intraoperative findings, especially regarding the intrameatal part of the tumor. Furthermore, cranial nerves are mostly invisible. Improving the quality and reliability of imaging in these respects might be helpful for the surgical strategy.

Methods In a consecutive series of 50 patients (28 women, 22 men, mean age: 51 years), planned for surgery of vestibular schwannomas, contrast-enhanced CISS MRI (Gd-Ciss) was performed in addition to standard Gd-enhanced T1 MRI (Gd-T1). Data by either technique were compared with regard to tumor size and extension, especially to the auditory meatus, along the nerve axis and perpendicular to it as well as tumor-induced changes (fundus filling and cochlear sign), and to possible identification of nerve structures.

Results Additional Gd-Ciss MRI was easily feasible in all patients and necessitated no additional contrast administration. Gd-Ciss showed larger tumor extensions than Gd-T1 MRI, especially and significantly in the coronal plane, that is, along the nerve axis, with 23.4 versus 19.1 mm (p < 0.03), 18.9 versus 18.2 mm in sagittal and 17.6 versus 17.3 mm in craniocaudal extensions. In three cases of seemingly absent intrameatal tumor extension in Gd-T1 images, Gd-Ciss demonstrated intrameatal tumor growth and was confirmed at surgery. Also in tumors at advanced stages, Gd-Ciss MRI allowed to identify parts of the cranial nerves which remain nonvisible in the majority of Gd-T1 imaging.

Conclusion In comparison to the Gd-MRI, Gd-Ciss provides better preoperative visualization of tumor localization and size and is more reliable in predicting the real tumor extension as found at surgery. Gd-T1 sequences underestimate the tumor extension in the coronal plane compared with Gd-Ciss sequences. By this technique, the advantage of the native CISS technique with better evaluation of the cranial nerves is combined with the chance to visualize all tumor parts, also the intra-meatal tumor portion. A realistic preoperative identification of tumor borders and of nerve displacement is essential for preoperative planning.