Background & objective: Cranial nerve schwannomas originate frequently in posterior cranial fossae and have various and complex MRI performances, some of which are still not well known. This study was to explore MRI performances and features of schwannomas from cranial nerves in posterior cranial fossae.
Methods: The MRI performances of 75 cases of schwannoma from cranial nerves in posterior cranial fossae, including trigeminal (n=9), facial (n=1), acoustic (n=53), 9th-11th (n=9) and hypoglossal (n=3) schwannomas, confirmed by surgical and pathologic findings, were analyzed retrospectively.
Results: Most of schwannomas in posterior cranial fossae were solid-cystic lesions when their sizes were larger than 1.5 cm in diameter. Small lesions (less than 1.5 cm in diameter) may be completely solid, which were closely related to cranial nerves. On T1WI, the solid part of tumor appeared iso- or slightly hypointense, while cystic part was hypointense. On T2WI, solid part appeared high or slightly high signal intensity, but cystic part appeared very high signal intensity. On contrast-enhanced T1WI, there was obvious enhancement in the solid part, but not in the cystic part. Some typical signs were very useful to infer tumor origin, such as, dumbbell-shaped trigeminal schwannoma extended across the middle and posterior cranial fossa, enlargement of internal auditory canal, widened jugular foramen and hypoglossal foramen caused by acoustic schwannoma, the 9th-11th shcwannoma, and hypoglossal schwannoma, respectively. The correct ratio for qualitative diagnosis of schwannoma was 92% using MRI, but the incorrect ratio for identifying the nerve of tumor origin was 8.7%.
Conclusion: MRI is a good method in qualitative diagnosis of schwannoma and identifying cranial nerves of tumor origin in posterior cranial fossae.