外周型原始神经外胚层肿瘤的CT和MRI影像学表现

CT and MRI imaging features of peripheral primitive neuroectodermal tumors

目的探讨外周型原始神经外胚层肿瘤（pPNETs）的CT和MRI表现，以提高pPNETs诊断的准确性。方法9例经手术病理证实的pPNETs患者中，4例术前经螺旋CT或多排螺旋CT平扫或增强扫描；6例经自旋回波T1WI、快速自旋回波T2WI和屏气扰相梯度回波T1WI3个序列平扫，动态增强采用屏气快速多层面扰相位梯度重聚成像T1WI快速扫描序列。将CT和MRI表现与手术病理结果进行对照分析。结果pPNETs位于肌肉6例，盆腔2例，胸腔1例。肿瘤呈椭圆形4例，不规则形5例。肿瘤直径7．4～18．3cm，平均11．6cm，境界不清。2例病灶信号和密度均匀，无明显坏死和囊变；7例病灶有明显的坏死和囊变，其中位于胸腔和盆腔的3例肿瘤均可见显著坏死和囊变。CT平扫肿瘤密度与邻近肌肉相仿，增强扫描呈中等程度以上的强化，双期增强呈进行性持续强化，强化不均匀。MRI T1WI序列肿瘤实体成分呈不均匀等信号或略低信号，T2WI呈不均匀略高信号或高信号，MRI增强强化程度较CT强化显著，强化更不均匀。位于肌肉的6个病灶均位于神经路径，可见明显软组织肿块包绕骨骼，3例骨骼破坏轻微，2例骨骼破坏明显，直径与软组织肿块相仿，1例骨骼破坏直径超过软组织肿块。骨质破坏位于骨髓腔，为溶骨性骨质破坏，无肿瘤成骨，无明显骨膜反应。结论pPNETs多见于儿童或青少年，多位于四肢、躯干的神经路径上，肿瘤体积较大，边缘不规则，境界很不清楚，强化显著且不均匀；位于胸、腹、盆腔的肿瘤坏死和囊变显著，位于四肢的肿瘤包绕骨骼，或坏死和囊变，或密度、信号相对均匀。pPNETs不仅具有神经源性肿瘤坏死和囊变及明显强化的特征，还具有小细胞恶性肿瘤浸润生长的特征。

Objective To investigate the CT and MRI features of peripheral primitive neuroectodermal tumors （pPNETs） and evaluate its diagnostic value. Methods The clinicopathological data of 9 surgically treated patients with peripheral primitive neuroectodermal tumors confirmed by pathology were collected, spiral CT （4/9）and MRI （6/9） plain scanning and dynamic enhancement scanning were performed preoperatively. Both CT and MRI scannings were performed in 1 case. Those CT and MR images were retrospectively reviewed and analyzed together with clinicopathological findings. Results The 9 lesions were located in skeletal muscles （ n = 6） , pelvic cavity （ n = 2 ） and thoracic cavity （ n = 1 ）. The tumor size was 7.4-18.3 cm in diameter with a mean diameter of 11.6 cm. The shape of those lesions was round or ellipse （4 lesions） and irregular （5 lesions）. The tumor usually presented as ill-defined masses, with homogeneous （n = 2） or inhomogeneous density （n = 7 ）. Seven cases, including the 3 lesions located in the chest and pelvis, showed obvious necrosis and multilocular cyst formation. The tumors showed iso-density as that of the adjacent muscles on CT plain scans and moderate heterogeneous enhancement after intravenous injection of contrast agents. The features of the tumors on the MRI including slightly low signal intensity on SE T1- weighted imaging, iso-signal intensity or slightly high signal intensity on FSE T2-weighted imaging and heterogeneous dynamic delayed contrast-enhancement with obvious necrosis in most of them. Six cases had a lesion in the skeletal muscles, presented as a giant ill-defined masse surrounding bone and extended along neural route with bone destruction to varying degrees. Conclusion Primitive neuroectodermal tumor is a kind of malignant tumor with proliferation of small, undifferentiated neuroectodermal cells, usually occurring in children or adolescent and frequently located in the extremities, chest cavity, pelvic cavity and chest wall. It typically presents as a large, ill-defined masse extending along neural route with heterogeneous and obvious enhancement after intravenous injection of contrast agents. The tumors located in the chest and pelvic cavities and some in the extremities show obvious necrosis and muhilocular cyst formation, while some of the tumors in the extremities appear as homogeneous solid masses.