Sinus cut-off sign: a helpful sign in the CT diagnosis of diaphragmatic rupture associated with pleural effusion.

The objective of our study was to describe the "sinus cut-off" sign at CT in the diagnosis of diaphragmatic rupture in patients with blunt abdominal trauma complicated with pleural effusion, and evaluate its utility in an experimental model. Between January 2004 and March 2005, we observed an unusual interruption of costophrenic sinus at CT in three patients with blunt abdominal trauma accompanied with pleural effusion. This observation prompted us to evaluate the utility of this sign in an experimental model. Laparotomically, we created 2 cm diapragmatic lacerations at each hemidiaphragm in two rabbits and pushed up the abdominal viscera with omentum through the defect. To simulate hemothorax, we also injected 5-10 mL of diluted contrast material into the pleural space. Using a dual-slice helical CT scanner, limited thoracoabdominal CT examination was performed before and after injection of intrapleural contrast material. The images were analyzed for the presence of CT signs for diaphragmatic injury. The left posterior costophrenic sulcus was interrupted in all of the three patients with left pleural effusion. While it was associated with other findings of diaphragmatic injury, the "sinus cut-off sign" was the sole finding in one patient. The sinus cut-off sign was observed on the CT scans of 100% of the rabbits with a left and right sided diaphragmatic rupture. The "sinus cut-off sign" is useful and can increase the CT detection of acute diaphragmatic injury associated with pleural effusion.