原发性肛管直肠恶性黑色素瘤的CT和MRI表现

CT and MRI manifestations of primary anorectal malignant melanoma

目的：探讨原发性肛管一直肠恶性黑色素瘤（AMM）的CT和MRI表现。方法：回顾性分析本院经病理证实的15例AMM患者的临床、CT、MRI和病理资料。11例行CT检查，3例行MRI检查，1例行CT和MRI检查。结果：15例AMM中，10例病变位于直肠远端与肛管交界处，2例位于直肠，3例位于肛管。肿瘤形态呈蕈伞形肿块9例，肠壁环形增厚4例，肠壁未见明显增厚2例。4例有肺部或者肝脏转移，5例有周围淋巴结转移。15例患者均未见明星的肠梗阻征象。CT平扫示肿块呈稍低密度，最大径约2～4cm，增强后强化方式不一，以中度强化为主。MRI示肿瘤在T2wI上以等信号为主，T2wI上以稍高信号为主，DWI上呈高信号，增强后均有明显强化。结论：AMM的CT和MRI表现具有一定特征性；但AMM病灶较大时，MRI信号不具有黑色素瘤特异性的典型信号。CT检查有助于发现远处转移灶，MRI检查对其鉴别诊断有提示价值。

Objective：To analyze the CT and MRI findings of primary anorectal malignant melanoma （AMM）. Methods： The clinical,CT and MRI materials of 15 cases with AMM confirmed by surgery and pathology were analyzed retrospective- ly. Of them, 11 patients had CT scanning,3 had MR imaging and 1 had both CT and MRI performed. Results：Of the 15 pa- tients with AMM, tumor located at the junction of distal rectum and anal canal （10 cases） ,rectum （2 cases） and anal canal （3 cases）. Tumors usually appeared as intraluminal fungiform masses （n= 9）, circumscribed thickening of bowel wall （n= 4） and with no bowel wall thickening （n=2）. Pulmonary or hepatic metastasis could be assessed in four patients. Five pa- tients had perirectal lymph node metastasis. There was no evidence of bowel obstruction in any of the patients. Tumor on non-enhanced CT appeared hypo-attenuation, the maximum diameter ranged from 2em to 4era. The enhanced pattern of tumor varied,most of them showed moderate enhancement, On MRI, tumors mainly appeared iso-intense on T~ WI, slightly hyper-intense on T2WI, hyper-intense on DWI, and showed markedly heterogeneous enhancement on contrast enhanced T1 WI. Conclusion：Some CT and MRI characteristics of AMM could be revealed： However, no typical MRI features could be assessed in large lesion. CT scanning was helpful to identify distant metastases and MRI was valuable in differential diagnosis.