OBJECTIVE To examine the CT and MRI characteristics of extraneural perineuriomas. MATERIALS AND METHODS With IRB approval, our institutional imaging database was retrospectively reviewed for cases of pathologically proven extraneural perineuriomas. CT and MRI features were recorded, correlative imaging analyzed, and the electronic medical record cross-referenced. RESULTS We identified ten patients [(seven males, three females, mean age 49.4 ± 18.3 years (range, 16-70 years)]. All cases were pathologically confirmed. Nine cases were conventional soft tissue extraneural perineuriomas, including one with "reticular" features and one with histologic features of malignancy; the tenth case contained admixed Schwann cells (hybrid perineurioma/schwannoma). Six out of ten patients underwent CT and ten of ten MRI evaluation. Nine out of ten MRIs were performed with IV contrast. Five lesions were subcutaneous, four intermuscular, and one intramuscular. Mean lesion diameter was 4.3 ± 2.7 cm (range, 0.9-10.2 cm). Nine out of ten lesions were well circumscribed; one had irregular margins. On CT, five of six were hypodense and one isodense compared to skeletal muscle. Most lesions were T1 isointense (5/10) or hypointense (4/10) and T2 hyperintense (7/10) relative to skeletal muscle, and demonstrated solid enhancement (6/9). There was no evidence of muscular denervation on any MRI exam, and a nerve of origin was identified in two out of ten cases. CONCLUSIONS Extraneural perineuriomas have a distinctly different imaging appearance from intraneural perineuriomas, manifesting as rounded or ovoid soft tissue masses, without evidence of muscular denervation, and usually without an apparent nerve of origin. Because these features mimic other benign and malignant soft tissue lesions, including sarcomas, biopsy or excision is needed for definitive diagnosis.

中文翻译：

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神经外神经鞘膜瘤：CT和MRI成像特征。

目的探讨神经外神经鞘膜瘤的CT和MRI特征。材料与方法经IRB批准，我们对机构影像数据库进行了病理学证实的神经外神经鞘膜瘤病例的回顾性回顾。记录CT和MRI特征，分析相关成像，并交叉引用电子病历。结果我们确定了10例患者（男7例，女3例，平均年龄49.4±18.3岁（范围16-70岁）），所有病例均经病理证实，其中9例为常规软组织神经外神经鞘瘤，其中1例为“网状”。具有恶性肿瘤的特征和一种具有恶性组织学特征；第十例包含混合的雪旺细胞（混合性神经内膜瘤/神经鞘瘤），十名患者中有六名接受了CT检查，十名患者接受了MRI评估。十个MRI中有九个进行了IV对比。皮下有五个病变，肌间有四个，肌内有一个。平均病变直径为4.3±2.7 cm（范围0.9-10.2 cm）。十个病变中有九个受到良好限制；一个人的边距不规则。在CT上，与骨骼肌相比，六分之五为低密度，而等密度为一。相对于骨骼肌，大多数病变为T1等强度（5/10）或低强度（4/10）和T2高强度（7/10），并表现出实体增强（6/9）。在任何MRI检查中都没有肌肉神经支配的证据，十分之二的病例中发现了起源神经。结论神经外神经鞘瘤具有与神经内神经鞘瘤明显不同的影像学表现，表现为圆形或卵形软组织肿块，没有肌肉神经支配的证据，而且通常没有明显的起源神经。由于这些特征可模仿其他良性和恶性的软组织病变（包括肉瘤），因此需要进行活检或切除才能明确诊断。