American Journal of Roentgenology, Vol 167, 731-734, Copyright © 1996 by American Roentgen Ray Society
CT evaluation of infradiaphragmatic air in patients treated with mechanically assisted ventilation: a potential source of error
EJ Balthazar and SL Moore
Radiology Department, New York University-Tisch Medical Center, NY 10016, USA.
OBJECTIVE: The purpose of this study was to describe the CT features of
infradiaphragmatic air that may develop in patients after mechanically
assisted ventilation, its location, its pathway of transdiaphragmatic
dissection, and its extension into the abdomen. MATERIALS AND METHODS: We
retrospectively evaluated six consecutive adult patients with
pneumomediastinum associated with positive end-expiratory pressure therapy
who developed intraabdominal air and were imaged with CT in our
institution-between 1993 and 1995. Abdominal CT examinations were reviewed
and correlated with the clinical findings, follow-up examinations, and
exploratory laparotomies in four patients. RESULTS: In four patients, air
present in the anterior mediastinum (endothoracic fascia) was seen to
extend into the anterior abdominal wall within the extraperitoneal space.
In a fifth patient, the air was located extraperitoneally and
intraperitoneally. In the remaining patient, air was present exclusively in
the peritoneal cavity. In only two patients did we detect small amounts of
air in the posterior retroperitoneum. In five patients, we also detected
subcutaneous emphysema and/or air dissection into the muscle planes of the
anterolateral abdominal wall. CONCLUSION: In patients on mechanically
assisted ventilation, anterior mediastinal air can dissect through the
diaphragm into the anterior abdominal extraperitoneal space. This anterior
pathway of infradiaphragmatic extension of air can be erroneously diagnosed
as intraperitoneal air, which may lead to unnecessary exploratory
laparotomies. Also, anterior mediastinal air can enter the peritoneal
cavity, particularly in patients with a history of median sternotomy.