MRI-defined height of rectal tumours.

BACKGROUND: There is no standard for reporting rectal cancer distances from the distal resection margin in the literature. The objective was to demonstrate the importance of rectal cancer measurement from a standardized point.
METHODS: Review of databases at two international institutions identified 50 patients with rectal adenocarcinoma within 15 cm of the anal verge (AV), who had preoperative magnetic resonance imaging (MRI) and underwent surgery with curative intent. Expert radiologists reviewed the magnetic resonance images for anatomical distances from the anorectal ring (ARR) to the AV, from the ARR to the dentate line (DL), and from the DL to the AV. Anatomical measurements were compared with preoperative measurements to assess reporting inconsistencies.
RESULTS: Fifty patients with rectal adenocarcinoma were included in the study. The mean(s.d.) anatomical distance was 1.66(0.61) cm from the ARR to the DL, 3.78(0.61) cm from the ARR to the AV (maximum 5.5 cm) and 2.11(0.10) cm from the DL to the AV. The mean radiological distance from the distal tumour was 2.90(1.60) (median 3.2, range 0-7.5) cm to the ARR, 4.36(3.20) (median 4.2, range -0.5 to 12.8) cm to the DL and 6.13(3.39) (median 6.0, range 0-14.1) cm to the AV. There was a significant difference in the distal tumour margin between measurements made by the expert radiologists and reported preoperative measurements (P < 0.001). Significant differences were also found between the expert radiologists' MRI and rigid proctoscopic measurements (P = 0.025).
CONCLUSION: There was up to 5.5 cm variation, depending on which landmark was chosen for reporting the distal margin of rectal cancer. This has potential implications for surgical planning, interpreting radiological images and comparative studies.