OBJECTIVETo evaluate the accuracy of 3.0T high-resolution magnetic resonance imaging(MRI) in definition of tumor invasion depth staging (T staging) before operation.

METHODSClinical and radiographic data of 49 rectal cancer patients who underwent radical resection within two weeks after 3.0 T high-resolution MRI examination without preoperative neoadjuvant chemotherapy in Peking University People's Hospital between February 2015 and November 2015 were retrospectively collected. Two radiologists reviewed the MRI imagines and evaluated the location and T staging of rectal cancer independently(radiologist A and B). The kappa statistics was used to evaluate the interobserver agreement, and kappa value greater than 0.81 indicated excellent agreement. The accuracy, sensitivity and specificity of high-resolution MRI in definition of rectal cancer T staging were assessed with pathological result as golden standard.

RESULTSAccording to pathological result of 49 rectal cancer patients, 3 were pT1, 17 were pT2, 22 were pT3, and 7 were pT4a. In 2 cases of mucinous adenocarcinoma, MRI T2WI showed focal or diffuse significantly higher signal close to perirectal fat. And in other 47 patients of non-mucinous adenocarcinoma, MRI T2WI showed equal or higher signal compared with pelvic muscle. Interobserver agreement was excellent in diagnosis of T staging of rectal cancer with 3.0T high-resolution MRI(Kappa=0.87). The accuracy, sensitivity and specificity of both radiologists for T1 staging was 95.9%(47/49), 1/3 and 100%(46/46) respectively, besides, 1 case was both diagnosed correctly and 2 cases were overstaged. For 2 radiologists, the accuracy of T2 staging was 87.8%(43/49) and 91.8%(45/49) respectively, the sensitivity was both 88.2%(15/17), and the specificity was 87.5%(28/32) and 93.5%(30/32) respectively, besides, 15 cases were both diagnosed correctly and 2 cases were overstaged. The accuracy for T3 staging was 89.8%(44/49) and 93.9%(46/49) respectively, the sensitivity was 86.4%(19/22) and 95.5%(21/22) respectively, and the specificity was both 92.6%(25/27). Radiologist A made correct diagnosis for 19 cases, understaged 2 cases and overstaged 1 case. Radiologist B made correct diagnosis for 21 cases and only overstaged 1 case. The accuracy, sensitivity and specificity of both radiologists for T4a staging was 98.0%(48/49), 7/7 and 97.6%(41/42) respectively, besides, 7 cases were both diagnosed correctly. The overall accuracy of T staging was 85.7%(42/49) and 89.8%(44/49) by two radiologists respectively. The accuracy for differentiating T1/T2 from T3/T4 was 91.8%(45/49) and 95.9%(47/49) by two radiologists respectively. Radiologist A overstaged 2 cases and understaged 2 cases, and radiologist B overstaged 2 cases.

CONCLUSIONHigh-resolution MRI can accurately evaluate preoperative T staging of rectal cancer and help select the high-risk rectal cancer patients with over T3 to receive neoadjuvant treatment.