Suspected gastrointestinal perforation

WSES perforated peptic ulcer 2020; ACR AC Acute Nonlocalized Abdominal Pain

Free gas is easy; the site of perforation is the useful answer. CT provides both, and the common vetting errors are settling for an erect chest radiograph and forgetting that a suspected anastomotic leak needs luminal contrast from the correct end.

Sudden severe abdominal pain with peritonism, or a post-operative patient deteriorating with sepsis and a rising inflammatory response.

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

Fever or sepsis

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

CT detects volumes of extraluminal gas far below the threshold at which a radiograph shows anything, and because gas rises it localises the source by where it collects — periportal and perihepatic for a duodenal perforation, pericolic and retroperitoneal for a colonic one. The portal-venous injection adds the wall enhancement, mural defect and adjacent inflammatory change that identify the perforated segment, which is what determines the operative approach.

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.

Febrile or septic — peritonitis or a post-operative leak

Role	Study & protocol	Why this answers the question
First line	CT Abdomen and Pelvis CT Abdomen and Pelvis — Portal Venous Phase usually appropriate	The study is unchanged and the urgency is not. CT still detects volumes of extraluminal gas far below the threshold at which a radiograph shows anything, and the portal-venous injection still supplies the wall enhancement, mural defect and adjacent inflammatory change that name the perforated segment — which is exactly what source control has to act on, so in a septic patient the scan is an emergency acquisition rather than the next available slot. Fluids, blood cultures and antibiotics run alongside it rather than after it, and the scan is not a reason to keep a patient away from theatre once the surgeon has decided to operate on the clinical picture. Where free gas has already been demonstrated and the abdomen is rigid, imaging that adds only anatomical detail should not be what the operation is waiting for.
First line	Chest radiograph Chest radiograph — PA (± lateral)	In the febrile patient with peritonism the erect chest radiograph sits beside the CT rather than below it, because it is taken at the trolley in the minutes while the scanner is being cleared and it costs the pathway nothing. Gas under the diaphragm in this setting is enough to go to theatre, so a positive film converts a diagnostic problem into a surgical one with no further waiting. The asymmetry is the entire point and belongs in the report: a positive film settles the question, a negative film settles nothing. Published detection rates for free gas on plain radiography vary widely across series, so a normal film in a septic peritonitic abdomen does not exclude perforation, and the CT still follows to localise the segment.
Problem solving	CT Abdomen and Pelvis CT Abdomen and Pelvis — Rectal Contrast (Anastomotic Leak)	Sepsis after a colorectal resection is an anastomotic leak until something else explains it, and a leak is luminal contents escaping — intravenous contrast cannot show that. Gravity-fed water-soluble rectal contrast opacifies the anastomosis directly, it is instilled in minutes, and it asks nothing of a patient too unwell to cooperate with a preparation. Coverage must extend to the perineum so that a low anterior resection anastomosis is included.
Problem solving	CT Abdomen and Pelvis CT Abdomen and Pelvis — Positive Oral Contrast	Where an upper gastrointestinal leak is suspected and no free gas has been found, water-soluble oral contrast can demonstrate the site directly. It sits last on this arm for a practical reason rather than a diagnostic one: it needs a patient who can drink and a preparation period before the acquisition, so it belongs to the septic patient who is well enough to wait for it and not to the one on the way to theatre. Barium is avoided because extraluminal barium provokes a chemical peritonitis.

Two first-line rungs is a deliberate statement that both are right answers here, not an ordering accident. Asking for the erect film accepts, asking for the CT accepts, and the plan shows the other one standing next — which is what a septic peritonitic abdomen actually gets.
A negative erect film is not a result on this arm. Reporting it as one is the single commonest way this diagnosis is delayed in exactly the patient who can least afford the delay.
This arm is entered on fever or sepsis alone. It does not assume peritonism, and it is not a substitute for the surgical assessment that decides whether the patient goes to the scanner or to theatre first.

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	CT detects volumes of extraluminal gas far below the threshold at which a radiograph shows anything, and because gas rises it localises the source by where it collects — periportal and perihepatic for a duodenal perforation, pericolic and retroperitoneal for a colonic one. The portal-venous injection adds the wall enhancement, mural defect and adjacent inflammatory change that identify the perforated segment, which is what determines the operative approach.
Reasonable alternative	Chest radiograph Chest radiograph — PA (± lateral)	An erect chest radiograph is quick and can settle the question when it is positive, because gas under the diaphragm in the right clinical setting is enough to go to theatre. It is a poor rule-out: published detection rates for free gas on plain radiography vary widely across series, so a normal film in a patient with peritonism must not stop the pathway.
Problem solving	CT Abdomen and Pelvis CT Abdomen and Pelvis — Rectal Contrast (Anastomotic Leak)	For a suspected colorectal anastomotic leak, the diagnosis is contrast escaping the lumen, and intravenous contrast cannot show that. Gravity-fed water-soluble rectal contrast opacifies the anastomosis directly, and coverage must extend to the perineum so that a low anterior resection anastomosis is included.
Problem solving	CT Abdomen and Pelvis CT Abdomen and Pelvis — Positive Oral Contrast	Where an upper gastrointestinal leak is suspected and no free gas is seen, water-soluble oral contrast can demonstrate the site directly. Barium is avoided because extraluminal barium provokes a chemical peritonitis.

Pitfalls

Accepting an erect chest radiograph as the definitive test — a negative film does not exclude perforation and the delay is not free.
Missing that the request is really about an anastomotic leak, which needs rectal or oral luminal contrast rather than an intravenous study alone.
Scanning in lung windows only. Small volumes of free gas are found on wide windows, and this is the classic perceptual miss.
Attributing free gas to a recent laparotomy without checking how recent; the volume normally falls over the days after surgery.

Priors — what to pull first

Find the operative date before calling post-operative free gas abnormal.
A previous CT showing a known diverticular or malignant stricture points to the likely site.

What makes a good request

For a post-operative patient, the operation, the date and the site of any anastomosis change the protocol, not just the report.
Free intraperitoneal gas that is expected after recent laparotomy or laparoscopy is a common source of false alarm — the operative date resolves it.

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 Abdomen and Pelvis — Portal Venous Phase Chest radiograph — PA (± lateral)CT Abdomen and Pelvis — Rectal Contrast (Anastomotic Leak)CT Abdomen and Pelvis — Positive Oral Contrast

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.