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Hypothesis: Rectal cancer can be accurately staged preoperatively by magnetic resonance imaging (MRI) with external phase-arrayed coils. Design: Comparison of MRIs with pathologic staging. Setting: University hospital. Patients: Twenty-eight consecutive patients with biopsyproven rectal cancer who did not undergo irradiation. Intervention: Patients underwent imaging using a 1.5-T MRI scanner with external phase-arrayed surface coils. Streaking of the perirectal fat and disruption of the bowel wall margin were interpreted as transmural invasion. Lymph nodes were defined as metastatic when they had a diameter of at least 0.5 cm. Tumors were staged according to the TNM staging system (American Joint Committee on Cancer guidelines) as confined to the bowel wall (T1-T2) and invading through the bowel wall (T3-T4). Patients underwent anterior resection (n = 15), abdominoperineal resection (n = 11), or local excision (n = 2). Main Outcome Measures: Calculation of sensitivity, specificity, and accuracy for invasion through the bowel wall and lymph node status. Results: Sensitivity of MRI in detecting invasion through the bowel wall was 89% (16/18), specificity was 80% (8/10), and accuracy was 86% (24/28). Sensitivity for malignant lymphadenopathy was 67% (8/12), specificity was 71% (10/14), and accuracy 69% (18/26). Conclusion: Although more costly and not as accurate as endoscopic ultrasound, MRI with phase-arrayed coils had excellent sensitivity at detecting transmural penetration of rectal cancer.

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Morphology is a clinical guide to prognosis after local excision. Non-exophytic cancers are associated with high-risk histopathological features that render tumours of this type unsuitable for local excision.