Shorter pelvic distances on MRI are associated with harder rectal cancer surgery

Design

Systematic review and meta-analysis of observational studies

Population

36 studies, 8,364 patients having total mesorectal excision (6 studies, 769 patients pooled)

Primary outcome

Association of MRI pelvic distances with surrogate measures of surgical difficulty

Effect

Interspinous distance MD -5.13 mm (95% CI -6.61 to -3.65); intertuberous MD -7.32 mm (-10.24 to -4.39)

A systematic review of 36 studies with 8,364 patients examined preoperative MRI pelvimetry before total mesorectal excision for rectal cancer. Studies used different pelvic measurements and different definitions of surgical difficulty, including operating time, blood loss, conversion to open surgery, specimen quality and complications.

Risk of bias assessment raised some concerns in 30 studies, high risk in five and insufficient information in one. A meta-analysis of six studies with 769 patients found that shorter interspinous distance (mean difference -5.13 mm, 95% CI -6.61 to -3.65) and shorter intertuberous distance (-7.32 mm, 95% CI -10.24 to -4.39) were associated with surrogate measures of difficulty, with no heterogeneity.

The authors say pelvimetry may help predict difficulty but that protocols need standardising. For radiologists, the practical step is to report consistent pelvic measurements on staging MRI when the surgical team asks for them, and to say how they were taken.

• Interspinous and intertuberous distances were the measures most consistently linked to surgical difficulty.
• Measure at standard landmarks and state the method in the report.
• Difficulty was judged by surrogates, so these distances predict a harder operation, not a worse outcome.
• Agree with the colorectal team whether pelvimetry belongs in the staging template.

Why it matters

It moves a measurement surgeons already discuss informally towards something radiologists can report consistently.

Don't overread it

Difficulty was judged by surrogates, and the pooled analysis covered only 6 of 36 studies.

The statistics, in plain English

A mean difference of about 5 mm means patients with harder operations had pelvises that were on average 5 mm narrower at that level. I² of 0% means the six studies agreed closely, but six studies from a literature with varying definitions is still limited.

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