Suspected acute diverticulitis

ACR AC Left Lower Quadrant Pain (2023 update); WSES 2020

Left lower quadrant pain where the question is not only whether there is diverticulitis but whether it is complicated. Contrast-enhanced CT answers both in one pass; the vetting failure is accepting an unenhanced or oral-only study that cannot grade it.

Left iliac fossa pain and tenderness with raised inflammatory markers, often in a patient with known diverticulosis, where the management fork is antibiotics versus drainage versus surgery.

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

Haemodynamic state

The fact that lets a pathway waive its own requirements. A crashing patient does not wait for a score.

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 Abdomen and Pelvis — Portal Venous Phase

CT Abdomen and Pelvis

What we'd amend, and why

A portal-venous acquisition is what separates uncomplicated inflammation from a complication: the enhancing bowel wall and enhancing abscess rim stand out against non-enhancing pus and against pericolic fluid, and extraluminal gas is obvious against fat. The same series characterises the mimics — colonic carcinoma, epiploic appendagitis, ovarian pathology — that make up a large share of left iliac fossa pain.

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.

Haemodynamically unstable — complicated diverticulitis

Role	Study & protocol	Why this answers the question
First line	CT Abdomen and Pelvis CT Abdomen and Pelvis — Portal Venous Phase usually appropriate	Shock in left iliac fossa pain is not a more severe version of the same question — it is the complicated end of the disease, where the answer is source control and the scan exists to say where and by what route. A portal-venous acquisition delivers extraluminal gas, the site of the perforation, the size and drainability of a collection and the alternative diagnoses in a single pass, which is all the information the decision between percutaneous drainage and laparotomy needs. Two cautions travel with it. In pregnancy this arm deliberately overrides the ultrasound-first sequence, because graded compression is non-diagnostic in a substantial proportion of patients and each non-diagnostic study costs time this patient does not have, while a missed perforation threatens the pregnancy far more than one abdominal acquisition does. And the scan must not become the thing that delays treatment: resuscitation, antibiotics and the surgical review go on in parallel, and a decision already made on clinical grounds is not waiting for a report.

This arm changes the sequence, not the urgency of treatment. Nothing here withholds a study; it removes an ultrasound step that is a poor use of the minutes an unstable patient has.

Pregnant

Role	Study & protocol	Why this answers the question
First line	Ultrasound abdomen Ultrasound abdomen — full survey	Graded compression over the point of maximal tenderness can show a thick-walled inflamed segment, an inflamed diverticulum and surrounding echogenic fat, with no radiation to the fetus. It is the right first step even though a substantial proportion of studies are non-diagnostic because of body habitus or overlying gas.
Second line	MRI abdomen and pelvis MRI abdomen/pelvis — non-contrast rapid protocol	Fluid-sensitive T2 sequences show mural oedema and pericolic inflammatory fluid without ionising radiation, and the large field of view covers the alternative gynaecological and obstetric diagnoses that dominate this presentation in pregnancy. Gadolinium is not needed for this question.
Problem solving	CT Abdomen and Pelvis CT Abdomen and Pelvis — Portal Venous Phase	Reserved for the unwell patient where ultrasound and MRI have not answered the question or are unavailable. A missed perforated diverticulitis carries far more risk to a pregnancy than a single abdominal CT exposure, and the decision should be made explicitly rather than by default.

Under-imaging a pregnant patient with suspected complicated diverticulitis is a documented harm, not a safe default.

Adults

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	CT Abdomen and Pelvis CT Abdomen and Pelvis — Portal Venous Phase usually appropriate	A portal-venous acquisition is what separates uncomplicated inflammation from a complication: the enhancing bowel wall and enhancing abscess rim stand out against non-enhancing pus and against pericolic fluid, and extraluminal gas is obvious against fat. The same series characterises the mimics — colonic carcinoma, epiploic appendagitis, ovarian pathology — that make up a large share of left iliac fossa pain.
Reasonable alternative	Ultrasound abdomen Ultrasound abdomen — full survey	Reasonable as a first test in a slim young adult with focal tenderness where dose avoidance matters, accepting that it neither excludes a small perforation nor reliably grades a collection, so a negative study in a patient who remains unwell must escalate.

Pitfalls

Accepting an unenhanced study for a request whose real purpose is to find a drainable collection.
Adding positive oral contrast by reflex — it delays the scan by an hour and obscures the mural enhancement that grades the disease.
Treating an apparently uncomplicated first episode as a closed question: a stricturing sigmoid carcinoma can present identically, and interval luminal assessment is part of the pathway.
Vetting on the pain alone. Peritonism or shock makes this an urgent complicated-disease question, and the scan should not sit in a routine slot.

Priors — what to pull first

Check for a previous sigmoid colectomy and for prior episodes: recurrent disease changes the surgical conversation.
A recent colonoscopy or CT colonography report may already have documented the diverticular burden and excluded a stricturing carcinoma.

What makes a good request

The management question is complication, not diagnosis: an abscess, a contained perforation or free gas changes the pathway on the day.
A request that states current observations, inflammatory markers and whether there is peritonism lets the reporting emphasis be set correctly.

Scoring this once it is done

The classification and risk tools this question ends in.

eGFR (CKD-EPI 2021 Creatinine)C-RADS v2023 (CT Colonography Reporting & Data System)

How these studies are acquired

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

CT Abdomen and Pelvis — Portal Venous Phase Ultrasound abdomen — full survey MRI abdomen/pelvis — non-contrast rapid protocol

Confirm locally

CT Abdomen and Pelvis — Portal Venous Phase: 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.