A Tale of Two Cases: A Lines in Abdominal POCUS - Reliable Sign or Potential Pitfall in Diagnosing Pneumoperitoneum?
Dr. Himanshu Gul Mirani, Consultant in Emergency Medicine, Midland Metropolitan University Hospital, SWBH NHS Trust, UK
Case Presentation:
Brief History:
Point-of-care ultrasound (POCUS) has emerged as an invaluable tool in emergency medicine. A lines, horizontal reverberation artifacts initially described in lung ultrasound, have been reported as potential indicators of pneumoperitoneum when observed in abdominal examinations.
Details of History:
We present two cases demonstrating the diagnostic utility and potential limitations of abdominal A lines. Case 1 involves a male in his 40s with alcoholism presenting with abdominal pain and jaundice. Case 2 features a 70-year-old male with acute abdominal distension, vomiting, and a history of infraumbilical laparotomy.
Examination:
Case 1 demonstrated peritonitis on physical examination with evidence of jaundice.
Case 2 presented with significant abdominal distension and tympany.
A lines in case of pneumoperitoneum
Management and Outcome:
Investigations:
Both patients exhibited high anion gap metabolic acidosis (HAGMA) on blood gas analysis. POCUS in Case 1 revealed A lines with "dirty" free fluid containing bowel contents and hyperechoic lines in pelvic windows suggesting trapped air. Case 2 also demonstrated diffuse A lines, raising concern for perforation. CT confirmed perforation with pelvic collection and trapped air locules in Case 1, while Case 2 showed toxic megacolon with compressed small bowel displaced posteriorly.
Misleading Elements:
The presence of A lines in Case 2 initially suggested pneumoperitoneum, but ultimately represented a false positive finding caused by significantly distended colon creating similar reverberation artifacts.
Actual Diagnosis:
Case 1: Bowel perforation with peritonitis, confirmed by CT.
Case 2: Toxic megacolon without perforation, despite the presence of A lines.
Key Learnings and Points:
Educational and Clinical Relevance:
These cases highlight both the utility and limitations of A lines in diagnosing pneumoperitoneum. While A lines can indicate free intraperitoneal air, they may also result from severely distended bowel creating similar reverberation artifacts. Clinicians must maintain vigilance regarding potential false positives and correlate POCUS findings with clinical context and additional imaging when appropriate. This case series emphasizes the importance of understanding sonographic pitfalls to prevent diagnostic errors in emergency settings where rapid, accurate assessment is crucial.