Diagnostic accuracy of preoperative magnetic resonance imaging in predicting curative resection of rectal cancer: prospective observational study

Abstract

Objective: To assess the accuracy of preoperative staging of rectal cancer with magnetic resonance imaging to predict surgical circumferential resection margins.

Design: Prospective observational study of rectal cancers treated by colorectal multidisciplinary teams between January 2002 and October 2003.

Setting: 11 colorectal units in four European countries.

Participants: 408 consecutive patients presenting with all stages of rectal cancer and undergoing magnetic resonance imaging before total mesorectal excision surgery and histopathological assessment of the surgical specimen.

Main outcome measures: Accuracy of magnetic resonance imaging in predicting a curative resection based on the histological yardstick of presence or absence of tumour at the margins of the specimen.

Results: 354 of the 408 patients had a clear circumferential resection margin (87%, 95% confidence interval 83% to 90%). Specificity for prediction of a clear margin by magnetic resonance imaging was 92% (327/354, 90% to 95%). High resolution scans were technically satisfactory in 93% (379/408). Surgical specimens were histopathologically graded as complete or moderate in 80% (328/408), and the median lymph node harvest was 12 (range 0-49). Magnetic resonance imaging predicted clear margins in 349 patients. At surgery 327 had clear margins (94%, 91% to 96%).

Conclusion: High resolution magnetic resonance imaging accurately predicts whether the surgical resection margins will be clear or affected by tumour. This technique can be reproduced accurately in multiple centres to predict curative resection and warns the multidisciplinary team of potential failure of surgery, thus enabling selection of patients for preoperative treatment.

Fig 1

Recruitment of patients and treatment arms (MRI=magnetic resonance imaging)

Fig 2

Assessment of circumferential resection margins. Oblique axial thin section magnetic resonance imaging and corresponding gross tissue slice. The scan depicts an intermediate signal intensity (grey) upper third rectal tumour (outlined in white). The mesorectal fascia (red line) is shown as a thin low signal intensity (black) line enveloping the mesorectum posteriorly with the peritoneal reflection anteriorly (yellow line). The scan shows a malignant lymph node (blue line) close to the mesorectal fascia. The potential circumferential margin is defined as clear on the scan because this distance is 2 mm. The tissue slice shows the malignant node (arrow) close to the margin with a distance >1 mm. The margin is therefore clear

Fig 3

Involved circumferential resection margin predicted by magnetic resonance imaging. Oblique axial thin section imaging and corresponding gross tissue slice. The scan depicts an intermediate signal intensity (grey) mid-third rectal tumour (outlined in white). The mesorectal fascia is shown as a thin low signal intensity dark line enveloping the mesorectum (red line). The scan shows a tongue of tumour lying against the mesorectal fascia (arrow). The potential circumferential margin is defined as affected on the preoperative magnetic resonance imaging because the distance to the mesorectal fascia is <1 mm. The tissue slice shows tumour affecting the surgical circumferential margin. The margin is therefore affected as predicted by magnetic resonance imaging