Rectal tumor stage: correlation of endorectal MR imaging and pathologic findings.

PURPOSE: To develop magnetic resonance (MR) imaging criteria for staging rectal cancer. MATERIALS AND METHODS: Thirty-six patients with rectal tumors underwent MR imaging with an endorectal surface coil. MR images were compared with specimens from the resected tumor. RESULTS: Rectal wall layers were reliably demonstrated. The MR imaging-determined tumor stage agreed with pathologic findings in 81% of cases. A retrospective review found the integrity of the rectal wall layers at the lesion center an accurate criterion for interpreting the local extent of the lesion. Lymph nodes as small as 2 mm were demonstrated. Although sensitive for demonstrating perirectal adenopathy, MR imaging had a specificity of only 72% for N1 disease. CONCLUSION: Endorectal surface coil MR imaging shows promise for staging rectal lesions. Additional studies are necessary to further establish criteria for interpreting the images.