后颅窝颅神经鞘瘤的MRI表现与诊断

MRI Performance and Diagnosis of Schwannomas from Cranial Nerves in Posterior Cranial Fossae

背景与目的:颅神经鞘瘤好发于后颅窝,其MRI表现较复杂、多样,有些还未完全为人们所熟悉。本研究拟探讨后颅窝颅神经鞘瘤的MRI表现及特征。方法:回顾性分析总结75例经手术、病理证实的后颅窝神经鞘瘤的MRI表现,其中三叉神经鞘瘤9例,面神经鞘瘤1例,听神经鞘瘤53例,舌咽、迷走和副神经鞘瘤9例,舌下神经鞘瘤3例。结果:后颅窝神经鞘瘤直径大于1.5cm的多呈囊实性,小于1.5cm的肿瘤可呈均匀实性,但与颅神经关系密切。肿瘤的MRI信号具有的特点:T1WI,肿瘤实质多呈等或稍低信号,囊性部分呈低信号;T2WI,实性部分呈稍高或高信号,囊性部分信号更高;增强扫描,实性部分呈明显强化,囊性部分不强化。跨中、后颅窝哑铃形肿块、内听道扩大及听神经增粗、颈静脉孔及舌下神经孔扩大等表现分别对推测肿瘤是否来自三叉神经、听神经、舌咽、迷走和副神经以及舌下神经有帮助。术前MRI确定神经鞘瘤的准确率是92%,肿瘤神经起源定位误诊率为8.7%。结论:MRI是后颅窝神经鞘瘤定性诊断和确定颅神经起源的良好方法。

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 hypoglassal （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 contrastenhanced 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.