LAUSR

Purpose To retrospectively assess the accuracy of magnetic resonance imaging (MRI) in predicting dentate line invasion in low rectal cancer. Materials and methods Eighty-one patients with primary rectal cancer were assessed by dynamic contrast-enhanced MRI. The location of the dentate line was assessed on MRI in 27 patients with upper-mid rectal cancer. Two observers independently evaluated the distance between the distal tumor edge and the MRI-defined dentate line in 54 patients with low rectal cancer, and the imaging and histological findings were compared. Results The MRI-defined dentate line was 24.0 ± 3.8 mm above the anal verge in patients with upper-mid rectal cancer. The dentate line invasion status agreed with the histological findings in 49/54 (91%) patients ( κ  = 0.72 [95% CI 0.50–0.95]) for observer 1, and in 51/54 (94%) patients ( κ  = 0.83 [0.65–1.00]) for observer 2 in patients with low rectal cancer. Interobserver agreement was good ( κ  = 0.83 [0.65–1.00]). The MRI-derived distance between the distal tumor edge and the dentate line had significant correlation with the histological distance ( r  = 0.86 for reader 1 and 0.75 for observer 2). Conclusion MRI demonstrates high accuracy in predicting dentate line invasion in low rectal cancer.