Rectal cancer — local staging and restaging

ESGAR rectal MRI consensus; NICE NG151

A geometry problem more than a contrast problem. The answer depends on slices angled perpendicular to the tumour at high in-plane resolution, and gadolinium adds nothing — which makes "MRI pelvis with contrast" the classic mis-specified request here.

Biopsy-proven rectal adenocarcinoma before treatment selection, or reassessment after neoadjuvant therapy.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

MRI Rectum — primary staging

MRI Rectum

What we'd amend, and why

Everything depends on resolving a two-millimetre distance between the outermost tumour and a thin fascial layer, so the study is built for spatial resolution rather than for contrast: thin, small-field-of-view, high-matrix T2 acquisitions angled strictly perpendicular to the tumour axis, with no fat suppression so that the interface between dark tumour, bright fat and the fine dark line of the mesorectal fascia remains visible. Intravenous gadolinium blurs that interface by enhancing tumour and inflammation alike and has not been shown to improve either T staging or margin assessment, which is why the protocol deliberately omits it.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayadult — Adults
rulerule-mr-device-screening — MR safety screening for implants and foreign bodies; checked by Radiographer at the scanner

Decision support only. Local protocol takes precedence.

Handled at the scanner(1)nothing for you to do

Settled and owned downstream. Each returns to a radiologist only on the stated trigger.

MR safety screening for implants and foreign bodies
Complete the MR safety questionnaire, verify implant labelling and its stated conditions of use against this scanner and this protocol, and ensure no ferromagnetic object enters Zone IV.
Radiographer at the scannerBefore the scan
Flags back if: An implant or retained foreign body that is MR Unsafe, unlabelled, or cannot be identified; or an MR Conditional device whose stated conditions this scanner or the requested protocol cannot satisfy; or a credible unexcluded intraocular metallic foreign body history.
Device screening is the only real safety gate on this pathway, and it is worth resolving early rather than at the scanner: this is a long examination with several high-resolution acquisitions, and a patient who cannot complete it produces motion-degraded images that cannot answer a two-millimetre question.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

Adults

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	MRI Rectum MRI Rectum — primary staging usually appropriate	Everything depends on resolving a two-millimetre distance between the outermost tumour and a thin fascial layer, so the study is built for spatial resolution rather than for contrast: thin, small-field-of-view, high-matrix T2 acquisitions angled strictly perpendicular to the tumour axis, with no fat suppression so that the interface between dark tumour, bright fat and the fine dark line of the mesorectal fascia remains visible. Intravenous gadolinium blurs that interface by enhancing tumour and inflammation alike and has not been shown to improve either T staging or margin assessment, which is why the protocol deliberately omits it.
Second line	MRI Rectum MRI Rectum — restaging after neoadjuvant therapy	After chemoradiotherapy the question changes from extent to response, and diffusion carries more weight because residual viable tumour restricts while post-treatment fibrosis and oedema do not. The oblique planes must be planned from the pre-treatment tumour bed rather than from whatever abnormality remains, or the comparison is not valid.
Second line	CT Abdomen and Pelvis CT Abdomen and Pelvis — Portal Venous Phase	CT covers distant staging and is the fallback for local assessment when MRI is genuinely contraindicated, but it cannot resolve the mesorectal fascia or distinguish tumour from desmoplastic reaction, so a CT-based local stage should be reported as an approximation.

Pitfalls

Accepting a request for a contrast-enhanced pelvic MRI. Gadolinium is not part of the staging protocol and its addition can obscure the fascial interface.
Allowing a routine axial pelvic acquisition instead of oblique axials perpendicular to the tumour. Off-axis slices systematically overstate extramural spread through partial volume.
Cropping the field of view above the sacral promontory in a proximal tumour, or above the anal verge in a low one.
Reporting nodes by size alone; border irregularity and internal heterogeneity carry more weight in the mesorectum.
Restaging too soon after radiotherapy, when treatment oedema exaggerates residual disease.

Priors — what to pull first

Obtain the endoscopy report for the height of the tumour above the anal verge; it tells the radiographer where to angle.
For restaging, the baseline study must be on the workstation at the time of planning, not merely available afterwards.

What makes a good request

The report drives the treatment decision: distance to the mesorectal fascia, extramural depth of spread, extramural venous invasion, nodal status and, for low tumours, the relationship to the sphincter complex.
Restaging must replicate the geometry of the baseline study, since the comparison is the point.

Scoring this once it is done

The classification and risk tools this question ends in.

RECIST 1.1 Tumor Response C-RADS v2023 (CT Colonography Reporting & Data System)

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

MRI Rectum — primary staging MRI Rectum — restaging after neoadjuvant therapy CT Abdomen and Pelvis — Portal Venous Phase

Confirm locally

MRI Rectum — primary staging: timings are typical — confirm against local protocol.
Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.