原发性肛管直肠恶性黑色素瘤影像学诊断

Imaging diagnosis of anorectal malignant melanoma

目的探讨原发性肛管直肠恶性黑色素瘤（AMM）的CT和MRI诊断价值。方法回顾性分析经组织病理学证实的AMM7例，其中男3例，女4例。6例行CT检查，1例行MRI检查。结果AMM表现明显蕈伞型肿块充满肠腔不伴肠梗阻（n=5），肠壁明显增厚（n=2）；3例伴肠周脂肪浸润，其中1例延伸至骶前间隙；5例伴淋巴结转移，其中1例淋巴结直径〉3cm。CT平扫示肿块呈稍低密度影，轻度强化2例、中度强化4例；AMM及其转移灶在MRIT1WI均呈高信号，T2WI为低信号。抑脂T1WI能更好的显示病灶范围及转移灶。结论肛门直肠部AMM可表现为腔内较大蕈伞型肿块，虽充满肠腔，但不伴肠梗阻，同样具转移淋巴结转移及明显肠周脂肪浸润。MRI对鉴别黑色素性AMM有提示价值。

Objective To discuss the diagnostic value of CT and MRI for primary anorectal malignant melanoma（AMM）. Methods Seven patients（3 males and 4 females） with AMM confirmed pathologically were analyzed retrospectively,which were examined by CT（ n =6） and 1.5T MRI（ n = 1 ）. Results AMM presented as bulky intraluminal fungating masses without causing obstruction（ n =5） and irragular rectal wall thickening（ n = 2 ）. Three cases had perirectal infiltration with 1 case extended to the presacral space, Five cases had perirectal enlarged lymph nodes with 1 case larger than 3 cm in diameter. Nonenhanced CT showed a hypodense lesion and En hanced CT manifested slight enhancement （n = 2） and mild enhancement （n = 4）. The tumor scanned by MRI depicted high intensity on T1WI and low intensity on T2WI, so did the enlarged lymph nodes and bone metastasis. Fat-saturation T1WI significantly improved the extention of tumor and detection of metastasis. Conclusion Bulky intraluminal fungating masses without causing obstruction,perirectal infiltration and enlarged lymph nodes may be helpful to diagnose AMM. MRI is especially useful for differentiating melanotic AMM from other rectal tumors.