MRI Study Of Rectum And Perirectal Structures

Objective:To investigate the MRI characteristics of the rectum and perirectal structures and the ability of MRI to demonstrate the rectum and perirectal structures, and to provide more objective radiologic evidence for anatomic and radiologic differences of some structures.Materials and methods:30 healthy volunteers(17 males and 13 females) were firstly scanned by conventional axial T1WI,T2WI,T2W SPAIR,sagittal T2WI sequences, from which the images obtained were used to plan small FOV T2WI axial,sagittal,coronal scans. Overall image quality of all sequences were firstly graded, then displaying rate of rectum and perirectal structures recorded, rectum and perirectal structures graded independently by two experienced radiologists. All analyses were performed with SASS17.0.Results:Small FOV coronal,transverse images with quality superior to that of others can display anatomical structures clearly.Rectal wall can be divided into 1-3 layers.21,5,30,5cases can not be layered on the T1WI,T2WI,T2W SPAIR,small FOV T2WI sequences, respectively. The scores on each sequence were compared, the differences among T1WI,T2W SPAIR,T2WI/small FOV T2WI were statistically significant, P<0.05.The mesorectum,mesorectal fascia,Denonvilliers fascia,prescaral fascia,peritoneal fold of 30 cases can not be displayed on the T2W SPAIR sequences, while 100% inner structures of mesorectum can be displayed.100% mesorectum and inner structures of mesorectum can be displayed on the T1WI,T2WI,small FOV T2WI sequences.83.3%,83.3%,96.7% front fascia of mesorectum,36.7%,36.7%,100% rear fascia,83.3%,83.3%,96.7% left fascia,83.3%,83.3%,93.3% right fascia, 83.3%,83.3%,96.7% Denonvilliers fascia,36.7%,36.7%,100% prescaral fascia, 63.3%,63.3%,70.0% peritoneal fold were displayed on the T1WI,T2WI,small FOV T2WI sequences, respectively. The scores of the above structures on each sequence were compared, both the differences of inner structures of mesorectum between T2W SPAIR and T1WI/T2WI,小FOV T2WI and T, WI/T2WI, and the differences of others among T2W SPAIR,T1WI/T2WI,small FOV T2WI were statistically significant, P<0.05.Lateral ligament of 30 cases can not be displayed on the conventional T1WI,T2WI,T2W SPAIR,small FOV T2WI sequences.Pelvic plexuse of 30 cases can not be displayed on the conventional T1WI,T2WI,T2W SPAIR sequences, while 80% left pelvic plexus and 83.3% right pelvic plexus were displayed on the small FOV T2WI sequence. The scores on each sequences were compared, the differences among T2W SPAIR/T1WI/T2WI and small FOV T2WI were statistically significant, P<0.05; The differences of left and right pelvic plexus on each sequence were not statistically significant, P>0.05.Mesorectum was wrapped around the rectum, and connected to the surrounding fat of sigmoid colon upward. Below the peritoneal level the mesorectal fascia around the mesorectum formed a tubular sleeve, at the peritoneal level the mosorectal fascia became fused with peritoneal on the front and sides of mesorectum.Boundaries among levator ani muscle, puborectal muscle, external anal sphincter can clearly be demonstrated on the small FOV T2WI sequences.Conclusions:Using small FOV T2WI sequence clearly showed the rectum and periretal structures was important to rectal cancer preoperative staging and selection of surgical procedures, and provided a more objective radiologic evidence for radiologic and anatomical differences.