Imaging in suspected appendicitis
- Finding
When the appendix may be inflamed, ultrasound looks first in children and pregnant women; CT answers fastest in most adults.
What it is
Appendicitis is still diagnosed clinically first, and a risk score (such as the Alvarado or the Pediatric Appendicitis Score) helps decide who needs imaging. Patients at low risk can often be observed and re-examined; those at high risk may go to the surgeon directly; those in between gain the most from imaging. Ultrasound with graded compression comes first in children, in pregnancy and in young, slim women, because it uses no radiation and also shows the ovaries, the uterus and an ectopic pregnancy. CT with intravenous contrast is the most accurate test in adults and shows complications and other diagnoses. MRI without gadolinium is the next step in pregnancy when ultrasound does not settle the question. An inflamed appendix is a swollen, blind-ending tube that does not compress, with a thick wall and inflamed fat around it; a stone in it (appendicolith), an abscess or gas outside the bowel point to a complicated case.
What it looks like
- Ultrasound: a blind-ending, non-compressible tubular structure off the caecum, outer diameter over about 6 mm, with a thick wall.
- Ultrasound: bright, inflamed fat around it, increased wall flow on colour Doppler and maximal tenderness under the probe.
- An appendicolith is a bright focus with an acoustic shadow on ultrasound and a dense calcified dot on CT.
- CT: a dilated appendix (over about 6 mm) with an enhancing thick wall and stranding of the surrounding fat.
- Perforation on CT: a defect in the enhancing wall, extraluminal gas, a free appendicolith, phlegmon or a rim-enhancing abscess.
- MRI in pregnancy: a distended appendix with high T2 signal in the wall and fluid around it; a normal appendix full of air is reassuring.
Why it looks that way
- The obstructed lumen fills with fluid and pus, so the appendix swells and cannot be squashed by the probe.
- Inflammation spreads through the wall into the fat, which becomes brighter on ultrasound and hazy on CT.
- A gangrenous wall stops enhancing and then breaks, letting gas and pus escape into the right lower quadrant.
| Study | Best for | Limits |
|---|---|---|
| Ultrasound (graded compression) | Children, pregnancy, young women; no radiation | Depends on the operator and the patient's build; appendix often not seen |
| CT with IV contrast | Most adults; complications and other diagnoses | Radiation; contrast |
| MRI without gadolinium | Pregnancy after an inconclusive ultrasound | Availability, time, needs an experienced reader |
Differential and pitfalls
- A normal appendix not seen on ultrasound does not exclude appendicitis: the study is inconclusive, not negative.
- Retrocaecal or pelvic appendices and tip appendicitis are easy to miss; follow the whole appendix to its tip.
- Mimics in the right lower quadrant: mesenteric lymphadenitis, terminal ileitis, right ureteric stone, Meckel diverticulitis, epiploic appendagitis.
- In women: ovarian cyst rupture or torsion, ectopic pregnancy and pelvic inflammatory disease; get a pregnancy test before imaging.
- In pregnancy the appendix moves up and out as the uterus grows, so pain may not be at McBurney point.
Next step
- Low clinical risk: observe and re-examine; image only if the picture changes.
- Child, pregnant woman or young woman: ultrasound first; if inconclusive, MRI in pregnancy, or CT or repeat ultrasound with observation in children.
- Adult, not pregnant, intermediate or uncertain risk: CT of the abdomen and pelvis with intravenous contrast.
- Any sign of perforation, abscess or peritonitis: call the surgeon at once; ask interventional radiology about drainage of an abscess.
- Inconclusive study and ongoing pain: discuss with the radiologist and repeat the exam or the imaging rather than discharge.
Test yourself
Think of the answer, then tap the question to see it.
Which imaging test comes first in a pregnant woman with suspected appendicitis?
Graded-compression ultrasound; if it is inconclusive, MRI without gadolinium.
What does an appendix that cannot be seen on ultrasound mean?
The study is inconclusive. It does not exclude appendicitis; observe and re-examine, or go on to MRI or CT.
What are the ultrasound features of acute appendicitis?
A blind-ending, non-compressible tube over about 6 mm, thick wall, bright inflamed fat around it, wall hyperaemia, sometimes a shadowing appendicolith.
Which CT findings suggest a perforated appendix?
A defect in the enhancing wall, gas outside the bowel, an extraluminal appendicolith, a phlegmon or a rim-enhancing abscess.
Elsewhere in DurgiPedia
Connections
Educational content; it does not replace a radiologist's report and is not a clinical instruction. Each study is ordered on the patient's assessment and your institution's protocols.
Sources: Appendicitis (StatPearls (NCBI Bookshelf), 2024); Pediatric Appendicitis (StatPearls (NCBI Bookshelf), 2025); Appendicitis in Pregnancy (StatPearls (NCBI Bookshelf), 2026).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.