The response to medical litholytic treatment of gallstones according to their specific gravity.

The buoyancy of gallstones was observed by taking anterior-posterior scout X-ray films of two patients standing during endoscopic retrograde cholangiography. In case 1, the large and small gallstones differed in buoyancy, and ursodeoxycholic acid treatment dissolved the floating small stones while failing to dissolve the nonfloating large stone. In case 2, both the large and small stones floated and are being dissolved by ursodeoxycholic acid treatment. Since floating or nonfloating and the plane of flotation depend on the specific gravity of the gallstone, the above findings suggest that a gallstone with a low specific gravity is more readily dissolved than one with a high specific gravity. The present method of estimating the buoyancy of gallstones was therefore considered extremely useful in selecting patients for medical litholytic treatment.