Purpose: The purpose of this study was to assess the potential role of diŠusion-weighted imaging (DWI) using low and high b-values to detect rectal cancer.Methods: The subjects were 15 patients diagnosed endoscopically with rectal cancer (m in 1 patient, sm in 0, mp in 3, ss in 7, se in 1, a in 3) and 20 patients diagnosed endoscopically with colon cancer and no other lesions (control group). Magnetic resonance imaging was performed using a 1.5T system. DWI was performed in the axial plane using echo planar imaging sequence (repetition time W echo time 1200 W 66,ˆeld of view 306×350 mm, reconstruction matrix 156×256, pixel size 2.0×1.4×8.0 mm) and acquired with 2 b-values (50 and 800 s W mm 2 ). Low and high b-value DW images were analyzed visually. A lesion was positive by detection of a focal area of high signal in the rectum in high b-value images. The apparent diŠusion coe‹cient (ADC) values of areas of high signal in high b-value images were calculated from the low and high b-value images.Results: High b-value images enabled visualization of all 15 rectal cancers. In the control group, 13 cases were classiˆed as negative and 7 cases as positive for rectal cancer. Sensitivity for detection of rectal cancer was 100z (15 W 15), and speciˆcity was 65z (13 W 20). The mean ADC values in 7 patients with false-positive lesions and in 15 patients with rectal cancer were 1.374×10 -3 mm 2 W s (standard deviation [SD]: 0.157) and 1.194×10 -3 mm 2 W s (SD: 0.152), respectively (P=0.026).Conclusion: DWI with low and high b-values may be used to screen for rectal cancer.
Preoperative diagnosis of tumor in the pelvic cavity is not easy. The present case was diagnosed as lymph node metastasis in a lower rectal carcinoid tumor, however, histologically it was Schwannoma in the pelvic cavity. A 65-year old man with melena underwent colonoscopy and was diagnosed as having a lower rectal carcinoid tumor. After endoscopic submucosal resection, low anterior resection with radical lymphadenectomy was performed for carcinoid tumor with pelvic lymph node metastasis. As a result, the pelvic tumor was a benign Schwannoma with S-100 protein positive, CD34 positive.
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