Free air — where's the hole?

Peritonitic abdomen or free air on the plain film; the surgeon wants the perforation localized before the incision.

Answer the surgeon

Laparotomy — and whether the surgeon heads for the upper or the lower GI tract.

Your answer must state:

Extraluminal gas present: amount and distribution
Most likely perforation site
Contained vs free
Peritonitis: free fluid, peritoneal enhancement

Key and direct findings

1.Extraluminal gas
Read on lung or wide windows; even a few bubbles count.
Pitfall: Tiny bubbles are invisible on soft-tissue windows — always check wide windows before excluding perforation.
2.Focal bowel-wall defect
A visible discontinuity of the enhancing wall is the most direct localizer; extraluminal enteric contrast, if given, is equally definitive.
3.Gas distribution can suggest the source
Falciform-ligament, periportal, or lesser-sac gas favors a gastroduodenal source; mesenteric-root gas may favor small bowel; pelvic or pericolic bubbles may favor colonic/diverticular disease; retroperitoneal gas suggests a retroperitoneal segment such as D2–D4 or posterior rectum. These patterns overlap, so integrate the focal wall and inflammatory findings.

Supportive signs & checks

1.The inflamed segment is the culprit
Wall thickening with adjacent fat stranding points at the perforated segment; extraluminal bubbles concentrate next to the defect.
2.Benign causes of free gas
Recent surgery, peritoneal dialysis, and mechanical ventilation all produce pneumoperitoneum without a perforation.
Pitfall: Post-operative free gas can persist for days — correlate with the surgical history before calling a leak.
3.Sealed perforation
A contained perforation may show only a few locules and localized inflammation with no ongoing leak — still name the site.

Wet-read snippets

Fill the blanks, then copy into your preliminary report.

Positive

Pneumoperitoneum with gas concentrated ___, focal wall defect / inflammation of ___ — findings favor perforation of ___.

Negative

No extraluminal gas on lung windows and no free fluid — no CT evidence of hollow-viscus perforation.

Sources

GI tract perforation: MDCT findings according to perforation site — Kim SH et al. Korean J Radiol (2009)
GI perforation: clinical and MDCT clues for identification of aetiology — Pouli S et al. Insights Imaging (2020)

Content review: Content pending clinical review · 2026-07-15

Educational reference for trained clinicians. Verify every result against the cited original guideline before use. Not a substitute for clinical judgment or medical advice.