低位直肠癌侵犯肛提肌的MRI评价

MRI evaluation of lower rectal carcinoma invading levator ani muscle

目的通过对低位直肠癌侵犯肛提肌的MRI征象与手术对照分析,探讨直肠癌侵犯肛提肌(耻骨直肠肌、髂骨尾骨肌)的MRI表现。方法 16例低位直肠癌,经手术证实癌肿均有不同程度侵犯肛提肌,其中男11例,女5例,年龄39～75岁,平均55岁。结果本组16例肛提肌受累的低位直肠癌患者中,耻骨直肠肌及髂骨尾骨肌两者均显示同时受侵犯。在横断面观察显示受累的耻骨直肠肌周围脂肪间隙消失16例;耻骨直肠肌增粗12例;病变区域内不规则形T2信号增高9例。在冠状面观察显示受累髂骨尾骨肌不规则增粗14例;肌束不连续11例;肌束边缘呈锯齿状改变10例;肿物与髂骨尾骨肌间隙消失16例。本组16例患者中,肿物下缘与齿状线距离均小于5cm,其中小于1cm者5例,1～2cm者5例,2～3cm者4例,3～5cm者2例。4例盆腔淋巴结增大,其中包括盆壁淋巴结增大2例,直肠周围淋巴结增大2例;3例腹股沟淋巴结增大。16例患者均显示直肠肌层受累,其中10例直肠周围筋膜增厚。结论 MRI检查对低位直肠癌侵犯肛提肌具有一定的优势,其主要征象包括:a)肿物与肛提肌之间脂肪间隙模糊或消失;b)耻骨直肠肌受累以横断位显示为佳,肌束中断及T2WI信号增高为主要表现;c)髂骨尾骨肌受侵则以冠状位显示较好,肌束增粗、连续性中断及其边缘呈锯齿状为主要表现。

Objective To analyze the MRI findings of lower rectal carcinoma（LRC） invading levator ani muscle（LAM） which comprised puborectalis muscle and iliococcygeus muscle and to compare with the intraoperative findings.Methods sixteen patients（11 men,5 women;aged 39-75 years;mean age,55 years） with surgically proved LRC invading LAM to variant degrees were evaluated by using MR imaging.Results Among the 16 patients,the puborectalis muscle and iliococcygeus muscle were simultaneously involved.Axial MR images showed that the disappearance of fat space around the involved puborectalis in 6 cases;the thickening of puborectalis muscle in 12 cases;irregular T2 hyperintense signals within the lesion region in 9 cases.Coronal MR images demonstrated that irregular thickening of involved iliococcygeus muscle in 14 cases;discontinuity of muscle bundle in 11 cases;muscle bundle with serrated margin in 10 cases;T 2 hyperintense signals within the lesion region in 2 cases;the space between mass and iliococcygeus muscle disappeared in 16 cases.Among the 16 cases,the distance from the inferior margin of the mass to the dentate line was less than 5 cm,of whom,less that 1 cm in 5 cases,1-2 cm in 5 cases,2-3 cm in 4 cases,and 3-5 cm in 2 cases.Four patients associated with pelvic lymph node enlargement,which comprised pelvic wall lymph nodes and perirectal lymph nodes in 2 each.Three patients associated with inguinal lymph node enlargement.All the 16 patients appeared muscularis recti involvement,of whom,10 cases associated with perirectal fascia thickening.Conclusion MRI examinations have certain advantages for the diagnosis of LRC invading LAM and the main signs include：a） fat space between the mass and the LAM blurred or disappeared;b） the involvement of puborectalis may best display in cross section and the main findings are muscle bundle interruption and T2 hyperintensity signal;the invasion of iliococcygeus muscle is showed better in coronal plane and the main findings are muscle bundle thickening and continuous interruption as well as its jagged margin.