APPEARANCE: The dependent viscera sign is seen at supine computed tomography (CT) in the thoracoabdominal area. The viscera (ie, the bowel or solid organs) are positioned against the posterior ribs, with obliteration of the posterior costo-phrenic recess (Figs 1,2).
EXPLANATION: The dependent viscera sign is seen with diaphragmatic rupture. The absence of posterior support by the diaphragm allows viscera to "fall" against the posterior ribs to a dependent position. On the right side, the upper one-third of the liver typically does not abut the posterior chest wall (ie, the right ribs) when the diaphragm is intact. On the left side, the stomach and bowel lie anterior to the spleen and generally do not abut the left ribs when the diaphragm is intact. Therefore, the dependent viscera sign is said to be 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 or lies posterior to the spleen (1).
DISCUSSION: Diaphragmatic rupture in acute blunt trauma occurs in l%-7% of patients (2-4). The most common site of diaphragmatic rupture is at the posterior-lateral aspect of the pleuroperitoneal membrane (5,6). There is disagreement as to the relative rates of left- and right-sided injury. Imaging studies suggest a predominance of left-sided injury, with postmortem studies indicating an equal distribution (3,7-9).
The diagnosis cannot be established at initial presentation on the basis of clinical and radiographic findings in 66% of patients (10-16). If the condition remains undiagnosed, patients may return with herniation and bowel strangulation. A delayed diagnosis is associated with 50% morbidity and mortality (17). Thus, surgical management with early repair of diaphragmatic defects is preferred. Because of the increase in conservative management of blunt trauma, more patients undergo noninvasive imaging with CT, which increases the rate of diagnosis. The presence of specific signs can also aid in diagnosis.
Chest radiographs have a sensitivity of 45% for left-sided ruptures and of 17% for right-sided ruptures (18). Attempts at increasing sensitivity by inserting nasogastric tubes and by using fluoroscopy have been unsuccessful (12,19). Ultrasonography is limited in the assessment of diaphragmatic integrity in the setting of acute trauma and is operator dependent (18,20). Magentic resonance imaging is not a viable method for examining trauma patients in the acute setting.
The dependent viscera sign is up to 100% sensitive as a sign of diaphragmatic rupture and 83% sensitive for right-sided injury (1). Other signs of diaphragmatic rupture have also been noted. Intrathoracic herniation of the abdominal contents is 32%-64% sensitive for diaphragmatic rupture and represents a late feature of this condition (9,21,22). Also, diaphragmatic discontinuity is 71%-80% sensitive for rupture (1,23). In 6% of the general population, discontinuity is a normal variant and is seen more commonly in older patients, in women, and in those with emphysema (24). The collar sign is seen when the diaphragm constricts the herniated bowel or solid organs in a waistlike manner. The collar sign is 67% sensitive for left-sided rupture and 50% sensitive for right-sided rupture when sagittal and coronal reconstruction is used (8).