High-resolution T2-weighted MRI versus tractography to predict cranial nerve anatomy in skull base tumors: a retrospective 132-case series

OBJECTIVE Skull base tumors are difficult to approach because of their deep location and their entrapment by cranial nerves (CNs), arteries, and veins. CN trajectories can be challenging to describe by conventional MRI when they are deformed by skull base tumors. High-resolution (HR) T2-weighted MRI (T2) has been able to depict normal CN cisternal paths; however, tractography has demonstrated value in CN reconstruction when the nerves are displaced by skull base tumors. In the present study, the authors aimed to compare HR T2 to tractography in the detection of CNs displaced by skull base tumors. METHODS From a case series of various complex skull base tumors managed between July 2015 and December 2023 in a single department, HR T2 scans were acquired, as were diffusion images with dedicated postprocessing, including distortion correction, region of interest design, probabilistic fiber tracking, and three-plane visualization. The positions of CNs displaced by skull base tumors were then compared between HR T2 and tractography. RESULTS A total of 132 patients were included in the study. They presented with various skull base tumors: vestibular schwannomas (n = 47), cerebellopontine angle (CPA) meningiomas (n = 46), CPA epidermoid cysts (n = 12), cavernous sinus schwannomas (n = 8), cavernous sinus meningiomas (n = 3), and 16 less frequent histological types. A total of 442 CNs were identified as being displaced by skull base tumors. Of these nerves, 236 (53.4%) were identifiable using HR T2, and 358 (81.0%) were successfully reconstructed using tractography (p < 0.001, McNemar test), although not significantly for the abducens nerve, lower nerves, and hypoglossal nerve. Interestingly, the identification rate of the abducens nerve was higher on HR T2 than tractography (43.5% vs 34.8%). CONCLUSIONS The present study revealed that tractography is more effective in predicting the position of most nerves displaced by skull base tumors, whereas HR T2 can identify the smallest CNs such as the abducens nerve.