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目的:分析经手术切除的最大径≤4 cm肾脏血管平滑肌脂肪瘤（AML）的MRI征象特点。方法:回顾性分析2014年1月至2020年11月解放军总医院第一医学中心经术后病理证实的最大径≤4 cm的112例AML患者，其中5例为上皮样血管平滑肌脂肪瘤（EAML）。根据MRI上能否观察到脂肪成分，分为含脂肪AML和乏脂肪AML。评估MRI征象，包括肿瘤最大径、肿瘤位置、生长方式、形状、鸟嘴征、劈裂征、假包膜、出血、囊变、坏死、血管流空影、Tn 2WI及DWI信号强度及均匀性、强化峰值所在期相。含脂肪和乏脂肪AML病灶最大径的比较采用Mann-Whitney n U检验，采用χ2检验或Fisher确切概率法比较MRI征象的差异。n 结果:112例患者共123个病灶，其中96个为含脂肪AML，27个为乏脂肪AML。82个表现为圆形或类圆形，112个为外生性生长，71个强化峰值位于皮髓质期，出现劈裂征、鸟嘴征、囊变、假包膜、出血的病灶数分别为30、49、1、1、1个，未见坏死征象。乏脂肪AML均为单发，含脂肪AML与乏脂肪AML病灶最大径分别为2.5（1.7，3.5）、1.8（1.4，2.3）cm，差异有统计学意义（n Z=-2.80，n P=0.005）。含脂肪与乏脂肪AML中，分别有65、12个Tn 2WI呈不均匀信号，鸟嘴征、劈裂征的个数分别为44、5和26、4个，DWI上分别有57、10个信号不均匀，在生长方式上完全内生、部分外生、完全外生的个数分别为5、44、47和6、8、13个。2组间鸟嘴征、Tn 2WI和DWI均匀性、生长方式差异有统计学意义（n P均0.05）。5例EAML患者共8个病灶，其中1例多发为4个含脂肪病灶。另外4例均为单发，其中2个为含脂肪病灶，2个为乏脂肪病灶。1个乏脂肪病灶中可见出血。n 结论:手术切除的≤4 cm的AML常表现为外生性生长的圆形或类圆形病灶，强化峰值多位于皮髓质期，可出现劈裂征及鸟嘴征，少见囊变、假包膜、出血征象，无坏死征象。相对于含脂肪AML，乏脂肪AML常为单发直径较小的肿瘤，更易内生性生长，多无鸟嘴征。EAML可表现为乏脂肪伴出血或多发含脂肪病灶两种模式。“,”Objective:To analyze the MRI characteristics of surgical resected renal angiomyolipoma (AML) smaller than 4 cm.Methods:A total of 112 patients with surgical pathology confirmed renal AML of which the maximum diameter was smaller than 4 cm were analyzed retrospectively in the First Medical Centre, Chinese PLA General Hospital from January 2014 to November 2020, 5 of which were epithelioid angiomyolipoma (EAML) patients. According to the presence or absence of visible fat in lesions on MRI, the lesions were divided into AML with fat group and AML without visible fat (AMLn wovf) group. The MRI features were evaluated, including maximum diameter, location, growth pattern, shape, beak sign, angular interface with renal parenchyma, pseudo-capsule, hemorrhage, cystic degeneration, coagulative necrosis, flowing void in the tumor, signal intensity and homogeneity on Tn 2WI and diffusion weighter imaging (DWI), the peak enhanced phase. The differences of maximum diameter of AML with fat and AMLn wovf were analyzed using Mann-Whitney n U test, and the differences of MRI features were analyzed using χn 2 test or Fisher′s exact probability test.n Results:There were 123 lesions found in 112 patients, and 96 lesions contained fat and 27 lesions were AMLn wovf. 82 lesions showed round and round-like shapes, 112 lesions showed exophytic growth pattern, 71 lesions with peak enhancement in corticomedullary phase. And the numbers of lesions with angular interface with renal parenchyma, beak sign, cystic degeneration, pseudo-capsule, hemorrhage were 30, 49, 1, 1, 1, respectively. There was no coagulative necrosis in all lesions. Compared with AML with fat, AMLn wovf was single lesion. The diameters of AML with fat and AMLn wovf were 2.5 (1.7, 3.5) and 1.8 (1.4, 2.3) cm respectively, with statistically significant difference (n Z=-2.80, n P=0.005). In the AML with fat and AMLn wovf, 65 and 12 cases were heterogeneous in Tn 2WI, 44 and 5 lesions showed beak sign, 26 and 4 lesions showed angular interface with renal parenchyma, 57 and 10 cases were heterogeneous in DWI. And there were 5 and 6 lesions showed the endophytic, 44 and 8 lesions showed partly exophytic, 47 and 13 lesions showed exophytic in patterns of tumor growth respectively. The beak sign, homogeneous in Tn 2WI and DWI, patterns of tumor growth showed statistical differences in AML with fat and AMLn wovf (all n P0.05). A total of 5 EAML patients were with 8 lesions. One patient had 4 lesions with fat, other patients had single lesion in which 2 lesions with fat, 2 lesions without visible fat. One lesion without visible fat showed hemorrhage.n Conclusions:Surgical resected AML smaller than 4 cm is often exophytic round and round-like, enhanced in corticomedullary phase, showing angular interface with renal parenchyma and beak sign, with rare cystic degeneration, pseudo-capsule, hemorrhage and improbable coagulation necrosis. AMLn wovf is single smaller lesion which often shows endophytic growth pattern, and beak sign is infrequent. EAML seems to be present in two modes, multiple lesions with fat and AMLn wovf with hemorrhage.n