Preoperative evaluation of the depth of anal canal invasion in very low rectal cancer by magnetic resonance imaging and surgical indications for intersphincteric resection.

PURPOSE

The present study was performed to evaluate the depth of anal canal invasion (DACI), and determine whether magnetic resonance imaging (MRI) assessment of the conjoined longitudinal muscle (CLM) can be used to identify the surgical indication for intersphincteric resection.

METHODS

Sixty-six patients with T1 (n = 2), T2 (n = 20), T3 (n = 39), and T4 (n = 5) lower rectal cancer were included. Depth of anal canal invasion was defined as extension of the tumor to the anal canal. The outline of the CLM on MRI was assessed as clear, unclear, or absent (indicating invasion).

RESULTS

A comparison of overall T-stage and DACI of 22 pT1-pT2 tumors revealed that none had a higher T-stage within the anal canal, and 16 of 39 pT3 tumors had only pT0-pT2 invasion within the anal canal. The CLM was clear in 30 cases of T0-T2 DACI, unclear in 5 cases of T0-T2 DACI, and 3 cases of T3-T4 DACI, and showed invasion in 3 cases of T2 DACI and 25 cases of T3-T4 DACI. The sensitivity, specificity, positive predictive value, and negative predictive value of using a clear CLM outline for determining T0-T2 DACI was 78.9, 91.9, 100, and 77.8%, respectively.

CONCLUSIONS

Preoperative evaluation of DACI was compatible with the surgical indications. A clear CLM accurately indicates T0-T2 DACI.