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Throwing stones

Yale Medicine Magazine, 1998 - Winter/Spring


Every day in any large emergency department around the country at least one person, and usually far more, arrives in terrible agony caused by a sharp pain in the side. Getting a correct diagnosis for the source of the pain is the first, all-important, step in relieving the misery. The likeliest cause for most cases of what physicians call "acute flank pain" is a kidney stone. Hardened collections of mineral salts, literally rocks, build up in the kidneys and then enter the ureters, the tubes that run from the kidneys to the bladder. These kidney stones can get stuck, blocking urine flow and causing a horrific pain that has been likened to childbirth in its severity. The trouble is that other possible causes for such pain—from appendicitis to tumorous masses—while less likely, are not rare. Until doctors find the actual cause of the pain, there is virtually nothing they can do to help. Pain relief medication might actually make matters worse in some cases or even prevent correct diagnosis.

For 60 years, physicians had only one method at hand for deciphering whether the pain originated with a blockage caused by a kidney stone, or not. They injected patients intravenously with an iodine solution that is rapidly excreted by the kidneys, and which then would appear white when exposed to X-rays. If there was a blockage, the stone itself might not be visible, but the distended section of ureter above it would be, giving physicians some good evidence about the site and potential danger represented by a stone. If it wasn't a stone, then other procedures could begin, such as exploratory surgery, to figure out what was wrong. Depending on the degree of obstruction, it would take anywhere from 10 minutes to 24 hours to get a clear picture of the ureters. Moreover, in a small number of cases, patients developed adverse reactions to the injected contrast material, and in rare cases, those reactions were life-threatening. Even when the pictures came in, at best, this long-standard diagnostic method, called intravenous pyelogram (IVP), provided only a partial map to the stone. Whether urologists should try an intervention of some sort or just wait to let the stone pass on its own was often a matter of educated guess work. Then, in 1993, Yale-New Haven Hospital acquired a new helical computed tomography (CT) scanner.

A standard CT scanner employs a doughnut-shape X-ray camera adapted to a computer to achieve high-resolution images quickly. It takes from three to five seconds to make each image, or cross-sectional slice, with any extended region of the body, such as a flank being examined for a source of pain, requiring 20 to 30 minutes. The patient needs to hold completely still throughout. As such, it wasn't a practical tool for figuring out why a patient was writhing in agony. The new helical CT scanner, however, took the basic CT technology and sped it up enormously. A partial body scan that previously took a half-hour can now be completed in less than a minute.

Beginning that summer, a team of Yale radiologists and urologists, headed up by Robert C. Smith, M.D., associate professor in the Department of Diagnostic Radiology, took patients arriving with symptoms of kidney stones and ran them through the new helical CT machine. They then compared them with a similar number who underwent a standard diagnostic procedure. Kidney stones will never look the same again. Without using any contrast material, soft tissue appears gray and all stones white under CT scans. "We not only see the blockage," says Dr. Smith, "we can see the stone perfectly fine as well. We were able to see the stone in virtually every case." And the helical CT scan could detect appendicitis, masses in ovaries and other less common sources of flank pain.

Over the next two years, Dr. Smith's team performed helical CT scans on more than 800 patients experiencing acute flank pain. Diagnostic accuracy proved higher than IVP, and the scans provided much more exact information about the size and location of any stones that were found, making treatment decisions more effective. Patients who once may have waited more than a day in the hospital before diagnosis could be made now start treatment in a matter of minutes. "Usually," says Dr. Smith, "we have an answer within five minutes. No matter how you look at it, CT is more accurate and faster, and there is no known harm other than the necessary low-level radiation exposure." As a result of the Yale study, helical CT scan is now the standard diagnostic procedure for flank pain in most major hospitals around the world.