Suspected appendicitis

ACR AC Right Lower Quadrant Pain (2022 rev); WSES Jerusalem appendicitis guidelines 2020

The archetypal age- and pregnancy-forked pathway: contrast-enhanced CT for most adults, ultrasound first in children, and ultrasound then MRI in pregnancy. The same request deserves three different answers.

Right iliac fossa pain with raised inflammatory markers where the diagnosis is uncertain enough to need imaging.

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 Abdomen and Pelvis — Portal Venous Phase

CT Abdomen and Pelvis

What we'd amend, and why

Contrast-enhanced CT has the highest accuracy in adults and, just as importantly, characterises the alternative diagnoses that account for a large share of right iliac fossa pain. A single portal-venous phase answers the question — extra phases add dose without yield. The protocol detail that most often goes wrong is the one nobody writes down: no routine positive oral contrast. Intravenous contrast alone gives equivalent accuracy for appendicitis, the sixty to ninety minutes needed to opacify the terminal ileum is delay in a patient who may be going to theatre that evening, it is unsafe in anyone with an unprotected airway, and dense luminal contrast forecloses converting the study if the clinical picture changes. Low-dose or reduced-dose technique is a reasonable default in a slim young adult, where it has been shown not to cost diagnostic accuracy for this question. The report should say more than yes or no: whether the appendix has perforated, whether there is a drainable collection, and whether there is an appendiceal mass, because those answers point at three different operations or at none.

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.

Worth asking the referrer (1)

None of these hold the request up. They sharpen the protocol or the plan that follows.

Is the patient pregnant, or could she be?
A confirmed pregnancy selects an entirely different pathway rather than merely modifying the protocol. A possible pregnancy is resolved by a beta-hCG before the exposure, not by defaulting either to CT or to a slower test.

Pathways

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

Pregnant

Role	Study & protocol	Why this answers the question
First line	Ultrasound right iliac fossa (appendix) Graded-compression ultrasound of the right iliac fossa usually appropriate	No ionising radiation, and diagnostic when the appendix is seen. It is the right first step even though it fails to visualise the appendix in a substantial minority, and that minority grows with gestation as the gravid uterus displaces the caecum upwards and laterally — so a non-visualised appendix in the third trimester is an expected result and never a negative study. Graded compression is still the technique, applied over the point of maximal tenderness rather than over McBurney's point, and the same examination looks at the ovaries and the renal tracts because ovarian torsion, a degenerating fibroid and an obstructing stone are the pregnancy-specific mimics.
Second line	MRI abdomen and pelvis MRI abdomen/pelvis — non-contrast rapid protocol	Resolves the non-diagnostic ultrasound without radiation, and it is the second step rather than an optional extra — a pregnant woman whose ultrasound did not see the appendix has not been investigated. Sensitivity and specificity approach those of CT. Gadolinium is not required for this question and is avoided in pregnancy: it crosses the placenta and is the one contrast agent whose use here needs a specific justification, whereas the unenhanced protocol answers the question. It is acceptable in any trimester. What has to be protected is the timescale — an MRI slot that arrives tomorrow is not a second-line study for suspected appendicitis, and if that is what is on offer the pathway moves to CT rather than waiting.
Problem solving	CT Abdomen and Pelvis CT Abdomen and Pelvis — Portal Venous Phase	Reserved for when ultrasound and MRI are non-diagnostic or unavailable and the clinical concern persists — and then done without hesitation. Conceptus dose from a single abdominopelvic CT is of the order of tens of milligray, below the roughly 50 mGy at which the ACR–SPR parameter says no increase in pregnancy loss or malformation has been shown, and far below the level at which deterministic effects are discussed at all; the stochastic risk is real but small and should be stated alongside the reassurance rather than instead of it. Set against that, perforated appendicitis in pregnancy carries a substantial risk of fetal loss and of preterm delivery, and that risk rises with every hour of diagnostic delay. A single portal-venous pass, collimated to the abdomen and pelvis, dose-optimised, with the conceptus dose recorded. Do not put lead over a uterus inside the imaged volume — it does nothing about internal scatter and can confuse automatic exposure control.

Do not withhold imaging a pregnant patient needs. Under-imaging suspected appendicitis in pregnancy is a documented harm, and the dominant hazard to the fetus is undiagnosed maternal disease.
The sequence is ultrasound, then MRI, then CT — but it is a sequence measured in hours, not days. Each rung is skipped when it cannot be delivered inside a timescale the appendix will tolerate.

Children and adolescents

Role	Study & protocol	Why this answers the question
First line	Ultrasound right iliac fossa (appendix) Graded-compression ultrasound of the right iliac fossa usually appropriate	Ultrasound is nearly as accurate as CT for appendicitis in children and avoids radiation in the group whose lifetime attributable risk is highest — a child has higher organ radiosensitivity, decades for a stochastic effect to express itself, and a smaller body in which any given acquisition is proportionally more of them. The appendix is also more accessible in a slim abdomen. The corollary is a discipline about what a negative study means: a non-visualised appendix is non-diagnostic, and the right next move in a child who is otherwise well is often active observation with repeat examination and a repeat ultrasound in six to twelve hours rather than an immediate CT. Escalation is for the child who is deteriorating, is systemically unwell, or whose ultrasound is equivocal with persistent clinical concern.
Second line	MRI abdomen and pelvis MRI abdomen/pelvis — non-contrast rapid protocol	Where available, MRI resolves an equivocal ultrasound without radiation. Access, not evidence, is usually what limits this step.
Problem solving	CT Abdomen and Pelvis CT Abdomen and Pelvis — Portal Venous Phase	Reserved for equivocal ultrasound where MRI is unavailable and concern persists — and then it happens, because a child with a perforating appendix is not made safer by a pathway that runs out of rungs. Child-sized kV and mAs against size-based reference ranges, a weight-calculated contrast volume, a single portal-venous pass, and coverage limited to the abdomen and pelvis. No routine positive oral contrast: intravenous contrast alone is of equivalent accuracy, and an hour and a half of drinking is an hour and a half a child with appendicitis spends undiagnosed, quite apart from being unsafe in a child heading for theatre.

A non-visualised appendix in a well child is a reason to observe and rescan, not a reason to reach for CT. Escalate on the child, not on the report.
Where a child is transferred for a surgical opinion, transfer the images with them — repeating an adequate ultrasound or CT at the receiving unit is avoidable dose and avoidable delay.

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	Contrast-enhanced CT has the highest accuracy in adults and, just as importantly, characterises the alternative diagnoses that account for a large share of right iliac fossa pain. A single portal-venous phase answers the question — extra phases add dose without yield. The protocol detail that most often goes wrong is the one nobody writes down: no routine positive oral contrast. Intravenous contrast alone gives equivalent accuracy for appendicitis, the sixty to ninety minutes needed to opacify the terminal ileum is delay in a patient who may be going to theatre that evening, it is unsafe in anyone with an unprotected airway, and dense luminal contrast forecloses converting the study if the clinical picture changes. Low-dose or reduced-dose technique is a reasonable default in a slim young adult, where it has been shown not to cost diagnostic accuracy for this question. The report should say more than yes or no: whether the appendix has perforated, whether there is a drainable collection, and whether there is an appendiceal mass, because those answers point at three different operations or at none.
Reasonable alternative	Ultrasound right iliac fossa (appendix) Graded-compression ultrasound of the right iliac fossa	Reasonable as a first test in slim young adults where dose avoidance is a priority, accepting a higher non-diagnostic rate — and in a woman of reproductive age it does a second job, because ovarian torsion, a ruptured ovarian cyst and a tubo-ovarian abscess all present as right iliac fossa pain and are pelvic ultrasound diagnoses rather than CT ones. A positive study ends the pathway; a non-visualised appendix does not, and the escalation to CT should be arranged at the time rather than left to the next clinician.

Pitfalls

Treating a non-visualised appendix on ultrasound as a negative study. It is non-diagnostic, and the pathway should escalate rather than stop.
Adding non-contrast or delayed phases to an adult CT for this question — dose without diagnostic yield.
Adding routine positive oral contrast. Intravenous contrast alone is of equivalent accuracy for appendicitis, the sixty to ninety minute preparation delays a patient who may be going to theatre the same evening, and it is unsafe in anyone with a reduced conscious level or an unprotected airway.
Defaulting a child or a pregnant patient straight to CT because that is what the request said.
Treating "could be pregnant" as either a reason to scan or a reason to refuse. It is a reason to send a beta-hCG, which answers it in minutes; a possible pregnancy that reaches the scanner unresolved is the failure, in whichever direction it then goes.
Forgetting the other time-critical diagnoses in the same anatomical field in a woman of reproductive age. A ruptured ectopic pregnancy and ovarian torsion both present as right iliac fossa pain, neither is reliably answered by a CT protocolled for the appendix, and a normal arterial Doppler signal does not exclude torsion.
A normal proximal appendix does not exclude inflammation confined to the tip.
Reading a phlegmon or an established periappendiceal abscess as "appendicitis" and stopping there. Perforation with a contained collection is a different management pathway — antibiotics with or without percutaneous drainage, and a decision about interval appendicectomy — so the report should say which picture it is.
Calling appendicitis in an older adult without looking at the caecum and the appendiceal base. An obstructing caecal or appendiceal tumour, and appendiceal mucinous neoplasm, present exactly like this, and a first episode of appendicitis over about fifty warrants that comment and usually colonic follow-up.

Priors — what to pull first

A documented previous appendicectomy ends the question — check before imaging.
Recurrent right iliac fossa pain with prior negative imaging shifts the pre-test probability and the differential.

What makes a good request

A declared pregnancy selects the pathway. "Could be pregnant" does not, and it is not meant to: the answer to a possible pregnancy is a serum or urine beta-hCG, which takes minutes and resolves the question outright, rather than routing the large majority of women who are not pregnant onto a slower and less accurate test. Vetting flags an undeclared or possible pregnancy for resolution before the exposure; it does not silently accept a pelvic CT in a woman whose status nobody has established.
In a woman of reproductive age with right iliac fossa pain, appendicitis is not the only time-critical diagnosis in the field. A beta-hCG is part of the work-up rather than part of the radiology request, because a ruptured ectopic pregnancy and ovarian torsion both present this way, both are missed by a scan protocolled purely for the appendix, and torsion in particular is a Doppler-and-clinical diagnosis that a normal arterial signal does not exclude.
A good request states the duration of symptoms, the white cell count and CRP, whether there has been a previous appendicectomy, and — in a woman — the pregnancy status and the date of the last menstrual period. Duration matters because a perforated appendix with an established abscess is a different management pathway from early appendicitis, and the report should say which it is.

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.

Graded-compression ultrasound of the right iliac fossa MRI abdomen/pelvis — non-contrast rapid protocol CT Abdomen and Pelvis — Portal Venous Phase

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.