Value of MR imaging in the staging of rectal carcinoma]

Correlative studies of MRI and pathologic specimens were done in 35 patients with rectal cancer. The MR manifestations of the primary tumor and its invasion into the surrounding structures were investigated with reference to the staging of rectal cancer. Prone positioning and the procedure of hypotonic air-distension of rectum was the method of choice to depict the primary tumor and tumor invasion. The spin-echo (SE)pulse sequence with TR/TE: 500/32 ms (T1-weighted image) was selected to show the anatomical structures in the pelvis and tumor spread in the surrounding fatty space and lymph node metastasis. Owing to the reduced contrast between tumor invasion and fatty tissue and decreasing signal intensity on multi-echo T2-weighted images the long repetiting time (TR) pulse sequence could not provide significant contribution in tumor staging. The MR appearance of rectal carcinoma was categorized as polypoidnodular, cauliflowermassive and protuberant-ring types. Ulceration was often seen in the latter two types. Peripheral invasion often manifested as spotty-nodular, sawtoothed-wavy and tumefied shape with medium signal intensity on T1-weighted images. The presence of a lump of small nodes, round or oval nodules within 2 cm from the rectal wall or nodular mass in the perirectal fatty space could be considered as possible lymph node metastasis. Following the modified Dukes Staging System of rectal cancer proposed by Astler-Coller all patients were staged preoperatively and correlated with surgical specimens. The accuracy of staging was 74.3%, compatible with the results of studies published.