Suspected acute mesenteric ischaemia

ACR AC Imaging of Mesenteric Ischemia; ACR AC Radiologic Management 2022; WSES AMI 2017

The most time-critical abdominal CT there is, and the one most often ordered as the wrong protocol. A routine single portal-venous abdomen is not a mesenteric CT angiogram, and the difference decides whether the occlusion is seen.

Severe abdominal pain with unremarkable examination findings, often with atrial fibrillation, recent myocardial infarction, low cardiac output or a thrombophilic state, and a rising lactate or unexplained acidosis.

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

CT Mesenteric Angiogram — Biphasic

CT Angiogram — Mesenteric

What we'd amend, and why

Two acquisitions answer two different questions and the study is not the study without both. The arterial acquisition shows the occlusion itself — an embolus lodged beyond the origin of the superior mesenteric artery, or an ostial thrombus on plaque — and it must be arterial because once the mesenteric veins opacify the intraluminal filling defect is masked. The portal venous acquisition shows the consequence: mural hypoenhancement in the affected territory, mesenteric venous thrombosis, and bowel wall changes. An unenhanced series is included because acute intravascular thrombus and haemorrhagic mural infarction are hyperdense before any contrast is given, and that density is lost once enhancement is added. One thing has to be said in the report and said plainly: a normal study does not exclude the diagnosis. Early in the course, before infarction, the bowel can look entirely normal; the non-occlusive low-flow form has patent vessels by definition; and mural findings in venous occlusion are subtle and easily read as ileus. The scan is evidence, not a discharge decision — where the clinical suspicion stays high the next steps are re-imaging, catheter angiography or diagnostic laparoscopy, and the pathway is not closed by a clean CT.

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

How was this decided?

pathwayadult — Adults
rulerule-contrast-reaction-premed — Prior contrast reaction and elective premedication; checked by Nurse before the scan
rulerule-metformin — Metformin and iodinated contrast; checked by Radiographer at the scanner
rulerule-paeds-dose — Child-sized technique and contrast dose; checked by Radiographer at the scanner
rulerule-pregnancy-ionising — Pregnancy status before an ionising exposure; checked by Radiographer at the scanner
rulerule-renal-iodinated — Kidney function and intravenous iodinated contrast; checked by Radiographer at the scanner
rulerule-iv-access — Intravenous access adequate for the planned injection; checked by Radiographer at the scanner

Decision support only. Local protocol takes precedence.

Handled at the scanner(4)nothing for you to do

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

Metformin and iodinated contrast
Confirm whether the patient takes metformin or a metformin-containing combination, and if so whether ACR Category II applies (eGFR below 30, known or suspected AKI, or an arterial catheter study likely to cause renal embolisation). If Category I — that is, no AKI and eGFR at or above 30 — no action of any kind is needed.
Radiographer at the scannerAt the scanner
Flags back if: The patient takes metformin AND meets ACR Category II — eGFR below 30 mL/min/1.73 m2, known or suspected acute kidney injury, or an arterial catheter procedure with likely renal arterial embolisation. Metformin plus a normal or mildly reduced eGFR is explicitly NOT a flag-back: there is no need to stop metformin before or after intravenous iodinated contrast in Category I patients, and no need to re-check creatinine afterwards.
Child-sized technique and contrast dose
Confirm that a size- or weight-based protocol is selected — child-sized kV and mAs against size-based diagnostic reference ranges — and that contrast volume is calculated by weight rather than taken from an adult default. Weight-based iodinated contrast volumes of roughly 1.5–2.0 mL/kg are widely used in paediatric CT.
Radiographer at the scannerAt the scanner
Flags back if: No paediatric or size-based protocol exists on the scanner for the requested examination, or the requested coverage or number of phases exceeds what the clinical question needs — for example a multiphase study where a single phase answers it, or whole-body coverage for a focal question.
Pregnancy status before an ionising exposure
Make the pregnancy enquiry immediately before the exposure and record the answer. In the UK this is a statutory operator duty discharged at the time of exposure under the employer’s written procedures required by IR(ME)R 2017 — it is not something the vetting radiologist can perform or pre-empt, and a request is complete without it.
Radiographer at the scannerAt the scanner
Flags back if: The patient states that she is, or may be, pregnant AND the uterus is in or near the primary beam. The exposure is then paused for re-justification by the IR(ME)R practitioner before it proceeds.
Intravenous access adequate for the planned injection
Site and test a cannula that supports the protocol flow rate, preferring an antecubital or large forearm vein, and observe the injection for extravasation. A 20-gauge or larger cannula is preferred for flow rates of 3 mL/s or more.
Radiographer at the scannerAt the scanner
Flags back if: No cannula can be sited that supports the protocol flow rate — for example only a 22-gauge hand or foot cannula for a CT angiogram needing 4–5 mL/s; or the only available access is a central line or port that is not labelled power-injectable; or an extravasation occurs.

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	CT Angiogram — Mesenteric CT Mesenteric Angiogram — Biphasic usually appropriate	Two acquisitions answer two different questions and the study is not the study without both. The arterial acquisition shows the occlusion itself — an embolus lodged beyond the origin of the superior mesenteric artery, or an ostial thrombus on plaque — and it must be arterial because once the mesenteric veins opacify the intraluminal filling defect is masked. The portal venous acquisition shows the consequence: mural hypoenhancement in the affected territory, mesenteric venous thrombosis, and bowel wall changes. An unenhanced series is included because acute intravascular thrombus and haemorrhagic mural infarction are hyperdense before any contrast is given, and that density is lost once enhancement is added. One thing has to be said in the report and said plainly: a normal study does not exclude the diagnosis. Early in the course, before infarction, the bowel can look entirely normal; the non-occlusive low-flow form has patent vessels by definition; and mural findings in venous occlusion are subtle and easily read as ileus. The scan is evidence, not a discharge decision — where the clinical suspicion stays high the next steps are re-imaging, catheter angiography or diagnostic laparoscopy, and the pathway is not closed by a clean CT.
Second line	CT Abdomen and Pelvis CT Abdomen and Pelvis — Portal Venous Phase	A standard portal-venous abdomen still shows established infarction — pneumatosis, portal venous gas, mural thinning — but by the time those are present the bowel is usually already dead. It is an acceptable study only where a dedicated angiographic protocol cannot be delivered, and its limitation must be stated.

Pitfalls

Vetting this as a routine abdominal CT. Same body part, different study: without an arterial acquisition the occlusion is frequently invisible.
Allowing positive oral contrast to be added, which defeats the study.
Reading a normal-calibre, normally enhancing bowel as excluding ischaemia in the non-occlusive low-flow form, where the vessels are patent and the findings are subtle.
Reporting a normal early study as a negative study. Ischaemic bowel looks normal until it infarcts, so a clean CT in the first hours is compatible with an occlusion that has not yet declared itself — the report should say what it cannot exclude, and a patient whose clinical picture does not settle needs repeat imaging, catheter angiography or laparoscopy rather than reassurance.
Downgrading urgency because the abdomen is soft. Pain disproportionate to the examination is the classic presentation, not a reassuring one.
Treating isolated mesenteric venous thrombosis as a negative arterial study — the venous acquisition is where it is found.
Waiting for a creatinine before scanning. The delay costs bowel, the alternative to the study is not a safer study, and the renal risk is downstream and manageable.

Priors — what to pull first

A prior CT or echocardiogram may document atrial fibrillation, mural thrombus or known mesenteric arterial stenosis, all of which raise the pre-test probability sharply.
Compare mesenteric arterial calibre with any earlier arterial-phase study — chronic stenosis with new decompensation looks different from a fresh embolus.

What makes a good request

This is an emergency vetting decision. Bowel viability falls away over hours, so a scan placed in a routine list is effectively a negative decision.
Naming the suspected mechanism — embolic, thrombotic, venous or low-flow — helps, but the protocol covers all four, so uncertainty is not a reason to delay.
A normal CT angiogram does not exclude acute mesenteric ischaemia, particularly early, in the non-occlusive low-flow form, and in venous occlusion. Sensitivity is for established disease; the study is at its weakest at exactly the point where the bowel is still salvageable.
Renal impairment is not a reason to defer or dilute this study. Contrast is the examination, hypoperfusion is already injuring the kidney, and the accepted response is to scan with the lowest diagnostic volume and manage the kidneys afterwards.

Scoring this once it is done

The classification and risk tools this question ends in.

eGFR (CKD-EPI 2021 Creatinine)

How these studies are acquired

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

CT Mesenteric Angiogram — Biphasic CT Abdomen and Pelvis — Portal Venous Phase

Confirm locally

CT Mesenteric Angiogram — Biphasic: 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.