Gas normaly only occurs in the gastrointestinal system. Gas in the free abdominal compartment is a sign of perforation. But gas sometimes can also be seen in parenchymal organs (as abscess or covered perforation), also in the retroperitoneal room and very seldom in the wall of bowel or in vessels. Gas at wrong places (extragastral and extraintestinal) is an important sign in gastrointestinal diseases.
Perforation of the GIT is occuring very rarely (1-2%). Most frequently it is caused by ulcera of the stomach and the duodenum. X-ray, sonography and endoscopy are most important in the diagnosis of this complication. X-ray is farely reliable in detecting air but needs a greater immission of gas. Given optimal conditions during the examination ultrasound can detect small amounts of air (1-2 ml). In daily routine sensitivity of this method is low (approx. 50 %). The diagnosis of a covered perforation is very complicated as it is lacking the typical criteria of free air in X-ray and sonography.
Patients with strong epigastric pain who where suspected to have a perforation were examend by ultrasound before and after undergoing endoscopy. We payed special attention to the presence of criteria of free air as well as any sonographical changes in the surrounding of the stomach.
1. The detection of free air by sonography is better after endoscopy. 2. A covered perforation can only be visualized by enhancement of air. Criteria of a covered perforation are: *Echogenuous enhancement of a strictly limited cavity of perforation. *Reverberations of air within the cavity. *Detection of the leakage. (orifice of perforation) *Detection of airmotion. * Change of sonographical image after second look sonography.
The detection of a free or a covered perforation by endoscopy and other imaging methods is complicated. Second look sonography after insufflation of air by endoscopy can be usefull and shows sometimes the perforation cavity. Under optimal conditions even the leackage can be visualized. The principle of a complementory sonography is little incriminatory. It provides the examiner with additional information, escpecially in a diagnostic procedure that is marked by a pressure of time.