The circle sign : a new sonographic sign of pneumatosis intestinalis : clinical, pathologic and experimental findings

Pneumatosis intestinalis (PI) represents gas in the bowel wall. The appearance of PI using high-resolution ultrasound (HRUS) has not been well described. The purpose of this report is to describe a new ultrasound sign of pneumatosis seen in three patients. This sign, called the "circle sign", is indicative of bubbles of gas within the circumference of the bowel, producing an appearance of a continuous echogenic ring on ultrasound. Further studies of the sonographic characteristics of pneumatosis were performed with an in vitro model. HRUS was performed prospectively in three patients demonstrating extensive PI radiographically. The appearance of the gas was characterized and the behavior of the intramural bubbles was studied when the bowel was compressed with the ultrasound transducer. Either CT scan or pathologic correlation was obtained in all patients. Experimental models of PI using air injected into the wall of sausage casing were developed. The presence of echogenic gas bubbles within the circumference of the wall of the bowel seen with HRUS was shown to represent pneumatosis intestinalis at histologic examination or by CT scanning in the three study patients. In vitro studies confirmed the clinical impression that the use of compression is helpful in distinguishing intramural from intraluminal air. The presence of echogenic gas bubbles in the wall of the bowel, often seen as a circle within the circumference of the bowel, may be helpful in diagnosing PI on ultrasound using HRUS.