Appendicitis
Appendicitis is inflammation of the appendix.
Acute, uncomplicated appendicitis
Acute, uncomplicated appendicitis means that the appendix is inflamed, but has not yet ruptured. Here are the key features:
- Wall thickening (> 3 mm)
The wall of the appendix is visibly thickened — greater than 3 mm. On post-contrast images, you may see enhancement of the wall, which helps it stand out. Thickened walls suggest inflammation. - Peri-appendiceal fat stranding
The fat around the appendix (normally black and clear) appears hazy or streaky — this is called “fat stranding” and indicates local inflammation spreading beyond the appendix itself. In early appendicitis, fat stranding may not have developed yet. - Diameter > 7 mm
The overall diameter of the appendix — measured outer wall to outer wall — is greater than 7 mm. A normal appendix is usually smaller than this. Large diameter alone is not specific — normal variants can sometimes exceed 6 mm — but large diameter with other findings is concerning. - Appendicolith
Look for one or more dense (bright white) foci of calcification in the lumen of the appendix — this is an appendicolith. You can see appendicolith in normal and appendicitis, but Its presence supports appendicitis but its presence informs treatment planning.
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If you see air within the appendix lumen on CT, this favors a normal appendix — appendicitis typically causes the lumen to fill with fluid and/or debris.
Ruptured appendicitis
When the appendix bursts, it's like a balloon that's exploded. It usually takes hours to days from the onset of appendicitis. Most of what you'll see is the aftermath of an exploded appendix, rather than the appendix itself:
- Free air
Air will look like scattered spots of black pixels (very low density). The air will be centered in the right lower quadrant. - Free fluid, right lower quadrant or lower pelvis
Free fluid looks like confluent grayish pixels. The region-of-interest (ROI) tool measures approximately 0-10 HU. The fluid might flow into the right lower quadrant or the lower pelvis. - Abscess, right lower quadrant
Look for a round or oval collection of fluid surrounded by a rind that isn't bowel wall. You might see spots of air inside the abscess, but that isn't required. - Absent or fragmented appendix
The burst appendix is deflated and collapsed. Sometimes, you might see an almost intact appendix with a discrete defect in the wall, but most of the time, you won't be able to see the appendix at all.
Other common conditions like ruptured ovarian cyst and diverticulitis can sometimes overlap with some of these findings. But the clinical picture together with these findings can narrow things down.