ABSTRACT
BACKGROUND: Three-dimensional anorectal ultrasound (3-DAUS) scanning provides accurate information on tumor size and its relation to the anal muscles. The purpose of this study was to evaluate the ability of 3-DAUS to assess response to radiochemotherapy (RCT) for rectal cancer by comparing 3-DAUS images to pathological findings. METHODS: Twenty-five patients (mean age 52.4 years), staged as T2 (n = 3), T3 (n = 16) or T4 (n = 6), with lymph node metastases in 12 cases, were submitted to neoadjuvant RCT, followed by a second 3-DAUS scan 7 weeks later. The patients were grouped according to the distance (cm) between the distal tumor edge and the proximal border of the internal anal sphincter (IAS) (group I, presenting anal canal invasion; group II, < or =2.0 cm; group III, >2.0 cm). All patients were operated on and the pathological findings were compared to post-RCT 3-DAUS scanning results. RESULTS: Four (16%) patients (three in group I, one in group II) experienced complete tumor regression. Fourteen (56%) tumors (six in group I, seven in group II, and one in group III) regressed partially. Distance to the IAS was >2.0 cm in eight patients (seven in group II and one in group III). The remaining six (24%) patients (all group I) experienced no regression. 3-DAUS and pathological findings were concordant in 24 (96%) patients, with only one (4%) nonconclusive post-RCT 3-DAUS result found to be a residual tumor. Tumor regression made sphincter-saving surgery possible in 13 patients (eight in group III, four complete tumor regression, and one nonconclusive on 3-DAUS). Pathological examination revealed free distal margins in all cases. The index of agreement between lymph node metastases on post-RCT 3-DAUS and surgical specimens was moderate (84%). CONCLUSION: 3-DAUS can aid significantly in the choice of surgical approach following RCT. However, a greater sample of patients is required to establish sufficiently accurate post-RCT 3-DAUS parameters.
