That witty aphorism of Will Rogers—It ain’t what you don’t know that’ll hurt you. It’s what you do know that ain’t so—is often true in life. It is certainly frequently true in medicine, and radiology is no exception. Like many things accepted as correct in medical science and given the status of “law” by students and practitioners, it actually turns out to be “lore”, which in many instances is really the product of bull times time. So often an official-sounding pronouncement is unquestioned but false. The job of an investigator and teacher in any discipline having at least a glimmer of scientific luster is twofold: the first is rare—it is discovery; the second is much more common—it is revision.

In this essay I endeavor to point out tried but not true notions, faithfully believed as being what you know but really they ain’t so. I will confine my task of rectification to the chest and abdomen.

Example (1) If one is asked to list the causes of air in the biliary tree, the standard differential includes operations on the bile ducts, previous ERCP, gallstone ileus and cholangitis caused by a gas-forming organism. The first three are for sure, the fourth alleged cause, infection, does occur in the drainage ducts leading from the liver to the duodenum. Pneumobilia exclusively in the ducts but not the gallbladder, due to infection, has been recorded in books and reviews as a clinical observation, but the last time I searched several years ago it has never actually been reported. And I scanned the major radiology journals for 50 years to seek out a reference. It is perhaps reasonable to assume that it would occur but we deal with empirical information not logical deductions. How many other differentials can we recall in which not every possibility has actually been verified. Perhaps there are many like “phantom” pneumobilia.