Abdomen & acute series

Abdomen and the acute series

Exam category: Procedures → Thorax and Abdomen
Why it matters: The acute abdomen series reuses the exact same physics as the pneumothorax decubitus rule from the chest module — free air rises, and that single fact drives most of the positioning logic here. The other half of this module is the contrast-agent decision, which is a patient-safety question before it is an imaging question: pick barium when it could leak into the peritoneum and you cause peritonitis.

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Overview

A baseline abdomen image (KUB) is taken before any contrast is introduced. Beyond that baseline, this module covers two decisions: using gravity to reveal air and fluid where they shouldn't be, and choosing the right contrast agent — which one, and how much detail you need from it. The five fluoroscopic studies that use those agents are covered in Fluoroscopic GI studies. The last two sections cover a swallowed foreign body and checking where a gastric or enteric tube ends.

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1. KUB and the acute abdomen series

KUB (kidneys, ureters, bladder) — a plain AP supine abdomen, no contrast, taken as a baseline before contrast studies.

The acute abdomen series exists specifically to evaluate bowel obstruction or perforation, and requires a horizontal beam with the patient erect or in decubitus — because you're looking for air-fluid levels and free air (pneumoperitoneum), and both need gravity and a horizontal beam to show up. Free air rises to the highest point — under the diaphragm on an erect image, or along the upper lateral abdominal wall on a decubitus image. On the erect abdomen the specific look is a thin crescent of lucency under the right hemidiaphragm, away from the gastric bubble.