脂肪坏死MR表现的实验研究

Empirical study on fat necrosis with MRI

目的:探讨脂肪坏死的MR表现、演变规律及其病理基础。方法:采用射频消融技术在5只实验用猪(约克夏)项背部浅表脂肪层内制作脂肪坏死模型。于造模后1周开始,在不同时间点(7 d～6个月)对脂肪坏死区域进行MR扫描。MR成像序列包括T1WI、T2WI、T2STIR、灌注成像及常规T1WI增强扫描。分析病灶的MR表现,并与病理结果对照。结果:5只猪共成功制作出22个脂肪坏死病灶模型,依据病理特征将脂肪坏死演变过程分为早、中、晚期。全部病灶早期在T1WI及T2WI均呈不均匀稍低信号,边缘可见环形低信号。随时间推移,病灶T1WI及T2WI信号均逐渐减低,T1WI部分病灶内可见点片状高信号。所有时间点病灶T2STIR均呈明显高信号,信号强度随时间推移略有降低。灌注曲线表现为逐渐上升型及平台型,未见速升速降型。强化特点早期以环形强化为主,中后期以不均匀轻度强化为主。病理显示病灶早期边缘主要是由纤维母细胞、吞噬脂质的泡沫细胞及混合性炎症细胞组成,内见脂肪崩解后残存的空泡状轮廓,中后期纤维成分逐渐增多,直至完全替代坏死的脂肪细胞。结论:不同时期脂肪坏死MR表现具有一定的特征性,能够反映其病理特征。

Objective： To observe the appearance of fat necrosis in pig model after radio frequency ablation on MRI and to study the relevant pathologic basis.Methods： The model of fat necrosis was made in superficial fat layer of five pigs by radio frequency ablation,MRI including T1WI,T2WI,T2STIR,PWI and T1WI contrast-enhanced scan were performed at different times（from seven days to six months） after radio frequency ablation one week.The MRI findings in fat necrosis model was analyzed and compared with pathological results.Results： 22 lesions of fat necrosis were made in 5 pigs.Based on pathological features,the evolution of fat necrosis was divided into three stages.22 lesions manifested heterogeneous low intensity which were in different degree in T1WI and T2WI,ring-shaped lower intensity was found in periphery of fat necrosis lesions.As the time went,the signal intensity of fat necrosis lesions was lower in T1WI and T2WI,patchy and dot-linear high signal were found in part of fat necrosis lesions;22 lesions manifested high intensity in T2STIR and the signal intensity was lower lightly.Perfusion curves were rapid ascending and slow descending,there was not rapid ascending and rapid descending.The enhancement characteristic of fat necrosis was mainly early ring enhancement,and mainly in the late heterogeneous mild enhancement.Histopathlolgically,it was characterized by anuclear fat cells surrounded by phagocytic lipid-laden histiocytes（foam cells） initially,with an accumulation of multinucleated giant cells and fibroblast at the edges of the lesion.During the subsequent reparative phase,fibrosis may replace the areas of necrotic fat and debris.Conclusion： The MRI findings in fat necrosis model is characteristic,and can reflect the pathological features.