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1 All authors: Department of Radiology, Mater Misercordiae Hospital, Eccles St., Dublin 7, Ireland.
Received September 25, 2000;
accepted after revision April 24, 2001.
Address correspondence to J. G. Murray.
Abstract
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MATERIALS AND METHODS. The study sample consisted of 28 consecutive patients (19 men, nine women) between 17 and 74 years old (mean age, 31 years) who had undergone abdominal CT and subsequent emergency laparotomy after a blunt trauma. Ten patients had a diaphragmatic rupture (six, right-sided; four, left-sided) at laparotomy. An experienced radiologist unaware of the surgical findings retrospectively reviewed the CT scans, and then a second radiologist reviewed the scans to provide interobserver agreement. Note was made of discontinuity of the diaphragm, intrathoracic herniation of abdominal contents, and waistlike constriction of bowel (the collar sign). Also noted was whether the upper one third of the liver abutted the posterior right ribs or whether the bowel or stomach lay in contact with the posterior left ribs. Either of these findings was termed the "dependent viscera" sign. The radiologists' detection rate of diaphragmatic rupture on the CT scans via observance of the dependent viscera sign was determined. Interobserver agreement was assessed using Cohen's kappa statistic.
RESULTS. The dependent viscera sign was observed on the CT scans of
100% of the patients with a left-sided diaphragmatic rupture and of 83% of the
patients with right-sided diaphragmatic rupture. Both observers missed one
case of right-sided diaphragmatic rupture. The radiologists' overall rate of
detecting diaphragmatic rupture was 90% using the dependent viscera sign. We
found excellent interobserver agreement (
= 1) for detection of the
dependent viscera sign and for the diagnosis of diaphragmatic tear on CT
scans.
CONCLUSION. The dependent viscera sign increases the detection at CT of acute diaphragmatic rupture after blunt trauma.
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CT is the imaging modality of choice in the evaluation of severe blunt abdominal trauma [10]. CT has a sensitivity of 61-71% and a specificity of 87-100% as an aid in the diagnosis of acute traumatic diaphragmatic rupture [11, 12]. The CT signs of diaphragmatic rupture include discontinuity of the diaphragm, visceral herniation, and waistlike constriction of the bowel, which has been called the collar sign [13,14,15]. We have observed that because patients lie supine at CT examination, if the diaphragm has been ruptured, the herniated viscera (bowel or solid organs) are no longer supported posteriorly by the injured diaphragm and fall to a dependent position against the posterior ribs. On the right side, the upper one third of the liver typically does not abut the posterior chest wall when the diaphragm is intact. On the left side, the stomach and bowel generally do not abut the left ribs when the diaphragm is intact, and the stomach or bowel does not usually lie posterior to the spleen. Therefore, the "dependent viscera" sign is present on the right side if the upper one third of the liver abuts the posterior ribs and on the left side if the stomach or bowel abuts the posterior ribs. This study was performed to assess the usefulness of the dependent viscera sign at CT as a means of detecting diaphragmatic rupture after severe blunt trauma.
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CT was performed on a helical scanner (Somatom Plus 4; Siemens Medical Systems, Erlangen, Germany). Standard protocol involved imaging from lung bases to pubic symphysis with 8-mm collimation and table speed of 8 mm/sec (pitch, 1). Patients received 150 mL of IV iohexol (Omnipaque 240; Winthrop-Breon Pharmaceuticals, Barcolenta, Puerto Rico). Patients drank 500 mL of 1% diatrizoate solution 1 hr before scanning and an additional 250 mL immediately before scanning. In patients with altered consciousness who were unable to drink, 1% diatrizoate solution was administered via a nasogastric tube.
CT scans were retrospectively reviewed by a radiologist who was unaware of the operative findings and who had no prior exposure to these CT scans. A second radiologist also independently reviewed the CT scans to establish interobserver agreement for the presence of the dependent viscera sign and the diagnosis of diaphragmatic rupture. Both radiologists had a minimum of 8 years' experience in abdominal radiology and have board certification or the equivalent. Note was made of discontinuity of the diaphragm, herniation of viscera or omental fat, focal constriction of bowel (the collar sign), and presence of the dependent viscera sign. Each hemidiaphragm was recorded as intact or ruptured. Results were compared using operative findings as the gold standard. The incidence of individual signs for diaphragmatic injury on CT was recorded. The radiologists' overall detection rate of diaphragmatic rupture using CT was determined. Interobserver agreement was assessed using Cohen's kappa statistic.
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= 1).
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Six patients had right-sided diaphragmatic ruptures diagnosed at laparotomy that involved the posterior surface (n = 4), anterior surface (n = 1), and dome (n = 1) of the right hemidiaphragm. Both radiologists correctly detected five of the six ruptures using CT. Both observers missed one case of right-sided diaphragmatic rupture because visualization of the diaphragm was completely obscured by the presence of hemothorax and hemoperitoneum. The dependent viscera sign was observed in five (83%) of the patients with right-sided diaphragmatic rupture. In four patients, the upper third or more of the liver lay against the posterior ribs (Fig. 3), and in one patient, the small-bowel loops were seen lying dependent on the right posterior ribs (Fig. 4). In all five patients, the viscera were in direct contact with posterior ribs superior to the level of the 10th thoracic vertebra. In one patient, the dependent liver was the only diagnostic feature of rupture of the hemidiaphragm visualized on CT.
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Four patients had left-sided diaphragmatic ruptures diagnosed at laparotomy that involved the posterior-posterolateral surface (n = 3) or both the anterior and posterior surfaces (n = 1) of the left hemidiaphragm. Both radiologists correctly detected all four diaphragmatic ruptures using CT. In all four patients, the stomach lay in a dependent position against the posterior ribs above the level of the 10th thoracic vertebra (Figs. 1 and 5). The detection rate for left-sided diaphragmatic rupture using the dependent viscera sign was 100%. Helical CT overall detected 90% of traumatic diaphragmatic ruptures in this study.
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In this study group, the dependent viscera sign was detected in 90% of patients with diaphragmatic rupture. The dependent viscera sign was observed in five of six patients with right-sided diaphragmatic rupture (detection rate of 83%). A dependent bowel was detected in 100% of patients with left-sided diaphragmatic rupture. The dependent viscera sign was the most common diagnostic finding of diaphragmatic rupture on CT in this series. On review of the CT scans of 18 patients with surgically proven intact diaphragms, we found no false-positive cases of the dependent viscera sign on CT. Overall, 90% of traumatic diaphragmatic ruptures were detected using the dependent viscera sign.
Prior studies have emphasized the importance of detecting diaphragmatic discontinuity for the diagnosis of diaphragmatic rupture [14]. Worthy et al. [15] reported that discontinuity of the diaphragm was found in 71% of acute cases of diaphragm rupture, whereas Murray et al. [12] reported this finding in 73% of cases of such ruptures. In our study, diaphragmatic defect was seen in 80% of patients with diaphragmatic rupture. We had one false-positive diaphragmatic defect in our series, which was recognized by the reviewers as a normal variant and was not misinterpreted as a diaphragmatic rupture. The patient had undergone laparotomy for treatment of a concomitant hepatic laceration, and, at that time, an intact diaphragm was confirmed. The false-positive diaphragmatic defect sign has been reported in other series [12, 18]. Posterolateral diaphragmatic defects are seen at CT in approximately 6% of healthy adults and are more common in women, patients with emphysema, and elderly patients [17].
Killeen et al. [11] found the collar sign to be the most sensitive indicator of diaphragmatic rupture, particularly when reformatted images were used; they reported a sensitivity of 67% for left-sided rupture and 50% for right-sided injuries, with specificity of 100% using this sign. Other studies report a lower incidence of 27-36% for this feature [12, 14]. In our study, we found the collar sign to have a similar incidence of only 30%. The low incidence of detecting the collar sign in our study may be partly explained by the fact that in our series only axial CT images were reviewed. Because ours was a retrospective study, sufficient stored data for each examination were not available for our radiologists to review multiplanar reconstructions. Furthermore, frequently in the acute setting, there is a low clinical suspicion for diaphragmatic injury because of concomitant injuries, and thus multiplanar reconstructions may not be obtained.
In this study, herniation of viscera into the thorax was observed on CT scans in 60% of patients with diaphragmatic ruptures, similar to rates reported in previous studies (32-64%) [12,13,14]. The stomach and colon commonly herniate on the left, whereas the liver herniates on the right [19, 20]. In our study, the stomach herniated on the left in all four patients with left-sided diaphragmatic ruptures. This finding was associated with renal herniation in two patients and splenic herniation in three patients. Right-sided diaphragmatic rupture was associated with small-bowel herniation in one patient and liver herniation in four patients. Visceral herniation, particularly of the liver, may not be present initially or easily diagnosed at CT examination, especially in patients undergoing positive pressure ventilation [21]. Difficulty in differentiating an elevated diaphragm from true herniation of viscera through a ruptured diaphragm may also interfere with diagnosing visceral herniation.
Although visceral herniation was detected at CT in 60% of patients with diaphragmatic rupture, the dependent viscera sign was observed on the scans in 90% of patients. This result suggests that the dependent viscera sign may be an early indicator of diaphragmatic tear before visceral herniation can be confidently diagnosed using cross-sectional imaging, likely reflecting the fact that the sign is dependent on the absence of posterior diaphragmatic support rather than on frank visceral herniation.
Rather than using exact rib or vertebral levels that may vary, we chose to use the upper one third of the liver on the right and the relationship of the viscera to the posterior chest wall on the left for establishing the presence of the dependent viscera sign. Although we used somewhat subjective criteria, our results indicate that the dependent viscera sign is a reproducible sign with exact correlation between the two reviewers. Althogh not encountered in our series, other abnormalities such as diaphragmatic eventration or congenital hernia may give a positive dependent viscera sign in the absence of blunt traumatic diaphragmatic rupture.
In this retrospective study, 10 cases of diaphragmatic rupture were confirmed at laparotomy. Six of the diaphragmatic tears confirmed at laparotomy were on the patient's right side, and the remaining four abnormalities were on the left. One study of patients with a similar predominance of right-sided ruptures has been reported, but most previous studies in the literature have reported a greater incidence of left-sided diaphragmatic rupture [10,11,12]. Postmortem studies, however, show an equal distribution of left- and right-sided diaphragmatic ruptures, suggesting that rupture of the right hemidiaphragm is probably underdiagnosed [22]. The higher incidence of right-sided ruptures in our series is probably to our advantage: right-sided diaphragmatic injuries are typically more difficult to detect radiologically and thus allow a better test of the dependent viscera sign.
The recent trend toward nonoperative management of stable patients with blunt hepatic and splenic injuries may result in diagnostic delays of concomitant diaphragmatic injuries. This trend increases the importance of the role of CT in the early detection of diaphragmatic tears that heretofore may have been detected at surgery for concomitant injuries. With improvements in CT technology such as the recent introduction of multidetector CT, cross-sectional imaging is routinely used to screen for internal injuries after blunt trauma. The sensitivity and specificity of CT in revealing diaphragmatic rupture has steadily improved with developing technology and greater radiologic experience [10,11,12]. Our results show that the dependent viscera sign is a valuable additional sign not previously described that increases the CT diagnosis of diaphragmatic rupture after blunt trauma.
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