Wiggins R H, Harnsberger H R, Salzman K L, Shelton C, Kertesz T R, Glastonbury C M
Department of Radiology, Division of Neuroradiology, University of Utah, Salt Lake City, Utah 84132-1140, USA.
AJNR Am J Neuroradiol. 2006 Mar;27(3):694-9.
The imaging appearance of facial nerve schwannomas (FNSs) has been described as an enhancing tubular mass (using T1-enhanced MR) within an enlarged facial nerve canal (using CT). The purpose of this study is to identify how often the FNS imaging findings conform to this description and determine whether there are underlying anatomic explanations for the discrepant imaging appearances identified.
The clinical, pathologic, and radiologic records of 24 FNS in 23 patients were retrospectively reviewed. Each FNS was evaluated for location along the facial nerve. The lesions were cataloged by facial nerve segment with the imaging characteristics of each segment described.
The average age at time of first imaging was 39 years (age range, 10-70 years). Eighteen (71%) of the 24 FNSs were pathologically confirmed, while the others were determined intraoperatively or diagnostically by the presence of both enlargement of the facial nerve canal and enhancement on contrast-enhanced T1 MR examination. The most common location was in the geniculate fossa (83%), followed by the labyrinthine and tympanic segments of the facial nerve (both 54%). The most common clinical presentation was facial neuropathy (42%).
The classic description of FNS on enhanced T1 MR is that of a well-circumscribed fusiform enhancing mass along the course of the intratemporal facial nerve with bone algorithm CT showing sharply defined bony canal enlargement. Modern imaging techniques, however, demonstrate the importance of the surrounding anatomic landscape, leading to various imaging appearances. Lesions traversing the labyrinthine segment can demonstrate a dumbbell appearance. When FNSs track along the greater superficial petrosal nerve, they may present as a round mass projecting up into the middle cranial fossa. FNS of the tympanic segment of the facial nerve preferentially pedunculate into the middle ear cavity, clinically presenting as a middle ear mass. When the mastoid segment of the facial nerve is involved, irregular and "invasive" tumor margins seen on MR can be explained on CT as tumor breaking into surrounding mastoid air cells.
面神经鞘瘤（FNS）的影像学表现被描述为在扩大的面神经管内（使用CT）出现强化的管状肿块（使用T1增强磁共振成像）。本研究的目的是确定FNS的影像学表现符合该描述的频率，并确定对所发现的不一致影像学表现是否存在潜在的解剖学解释。
回顾性分析23例患者24个FNS的临床、病理和放射学记录。对每个FNS沿面神经的位置进行评估。根据面神经节段对病变进行分类，并描述每个节段的影像学特征。
首次成像时的平均年龄为39岁（年龄范围为10 - 70岁）。24个FNS中有18个（71%）经病理证实，其他则通过面神经管扩大和对比增强T1磁共振成像检查时的强化在术中或诊断时确定。最常见的位置是膝状窝（83%），其次是面神经的迷路段和鼓室段（均为54%）。最常见的临床表现是面神经病变（42%）。
增强T1磁共振成像上FNS的经典描述是沿颞内面神经走行的边界清晰的梭形强化肿块，骨算法CT显示面神经管明显扩大。然而，现代成像技术表明了周围解剖结构的重要性，导致了各种影像学表现。穿过迷路段的病变可表现为哑铃状。当FNS沿岩浅大神经走行时，它们可能表现为向上突入中颅窝的圆形肿块。面神经鼓室段的FNS优先长入中耳腔，临床上表现为中耳肿块。当面神经乳突段受累时，磁共振成像上可见的不规则和“浸润性”肿瘤边缘在CT上可解释为肿瘤侵入周围乳突气房。
