The Value Of High Resolution MRI In Preoperative Staging Of Primary Rectal Cancer

Objective Colorectal cancer(CRC)is one of the most common malignant gastrointestinal tumors and 65% of colorectal cancer patients is rectal cancer patients.Total mesorectal excision(TME)is an effective surgical procedure for middle and lower rectal cancer:surgeons can effectively reduce the local recurrence rate of rectal cancer through resection of the tumor and all the small cancer foci in the mesorectal fascia.The circumferential margin(CRM)is the shortest distance between the depth of tumor invasion and the boundary of the mesorectal excision.The TME principle will loses its value if the tumor infiltrates the circumferential margin,so it is important to observe whether is there tumor invasion in the circumferential margin,which is an important criterion to evaluate the effect of TME.Neoadjuvant therapy can effectively improve the R0 resection rate and reduce the risk of local recurrence in patients.There is approximately 20% of the patients can obtain pathological complete remission(p CR)from neoadjuvant therapy[1,2].At present,the focus of the development of cancer treatment is individualized treatment.Accurate preoperative staging is essential for screening patients who require neoadjuvant chemoradiotherapy and who can be operated directly.High resolution magnetic resonance imaging(HR-MRI)can clearly show the level of the rectal wall,so it is particularly important for patients with rectal cancer to be proceed with high resolution MRI before surgery to help doctors determine their individualized treatment strategies.The purpose of this study was to assess utility of high resolution MRI in preoperative staging of rectal carcinoma,mesorectal fascia involvement and circumferential resection margin.Methods This prospective study included 40 patients(26 male,14 female,mean age 52.3 years,range 32~74 years,all given informed consent).All patients were proved pathologically to have cancer rectum.MRI using high resolution sequences was done to all patients with an average of 10 + /-4.3 days before surgery was done.The standard in the study of imaging and pathological staging are from the seventh edition of "AJCC cancer staging manual".MRI findings were correlated with pathological and surgical outcome.Results1.Twenty-one tumors were located in the upper rectum(55.3%),7 in the mid rectum(18.4%),and 10 in the distal rectum(26.3%);2.MRI based T staging showed sensitivity,specificity,PPV and NPV of 95.8%,87.5%,92% and 93.3% respectively with weighted kappa 0.84 and P value 0.000.The sensitivity,specificity,PPV and NPV of MRI based assessment of circumferential resection margin(CRM)were 90.0%,96.7%,90% and 96.7% respectively with weighted kappa 0.86 and P value 0.000.The accuracy,sensitivity,specificity,PPV and NPV of nodal staging by MRI were 85%,73.3%,92%,84.6% and 96.7% respectively.Conclusion Preoperative MRI utilizing high resolution sequences is an accurate modality for pre-operative grading of rectal carcinoma,delineation of affection of the mesorectal fascia and circumferential resection margin which are the main factors affecting the outcome of surgery thus helping to categorize patients who can go directly for surgery from patients who may go for neo-adjuvant therapy to avoid overtreatment.