Out of 13 cases, they discovered, three had originally been misdiagnosed. More to the point, seven of the sponges showed a pattern of air bubbles on a CT scan, and not one of them had caused an abscess. Kopka and his colleagues tried an experiment whose elegant simplicity is reminiscent of Richard Feynman's famous experiment with the O-ring of the space shuttle. They placed eight sponges in a sterile bath of water, performed CT scans of them after one hour and repeated the CT scans six months later. Even after six months underwater, the sponges still contained most of the air bubbles that had been present after an hour.
Dark patches are air bubbles.
Lots of objects have been left in unsuspecting patients by fallible surgeons, including forceps, needles and even the occasional scalpel. Lynn Volk, a vice president of the Risk Management Foundation of the Harvard Medical Institutions, published a survey of all the malpractice claims that were brought against Harvard-affiliated institutions from 1976 to 1993. Still, with roughly four cases a year occurring among all of the Harvard-affiliated hospitals, retained foreign bodies clearly do not present a high risk. It is remarkable, in fact, that surgeons do so well at keeping wayward sponges out of patients. With so many pads in a patient at once, it is easy to imagine losing track of one.