Detection of free intraperitoneal air on computed tomography after blunt abdominal trauma

Abstract

In patients who have sustained blunt abdominal trauma, detection of free intraperitoneal air on computed tomography (CT) is thought to be a fairly specific finding of bowel rupture. We devised a method to determine the accuracy of a radiologist in identifying this important finding on CT scans in patients with blunt abdominal trauma.

We retrospectively reviewed 50 CT scans and the radiologist’s report in patients who had undergone diagnostic peritoneal lavage (DPL) before the CT scan. We analyzed the report to see whether either free intraperitoneal air or the possibility of DPL was mentioned.

Thirty scans retrospectively demonstrated free intraperitoneal air. The radiologist detected this finding in 25 patients (83%). In 5 patients (17%), the radiologist did not detect the free air or raise the possibility of a previous lavage. The amount of air introduced postlavage was variable, depending on the surgical technique and the time interval between the lavage and the CT scan. Air was most often demonstrated (in order of frequency) anterior to the liver, in the rectus recesses adjacent to the lavage defect, and in the fissures of the liver. In the five patients in whom free air was not identified, the amount or location of the air did not contribute to the error. The findings of this study were reviewed with all of the radiologists at a physician quality assurance meeting. A follow-up study of 25 patients was then obtained, and free air was detected in 25 (100%) of the cases.

In summary, (a) free intraperitoneal air was missed in 17% of patients; (b) air preferentially collects beneath the diaphragm and in the rectus recesses; (c) there was no correlation between the amount or location of air and the error rate; (d) the most important variable is the examiner’s experience, and this can be improved markedly through education.