The Risks of Scanning

Photo illustration to run with Prescriptives story in 2/17/08 Sunday mag Photo illustration to run with Prescriptives story in 2/17/08 Sunday mag Photo: Dorothy A. Yule Photo: Dorothy A. Yule Image 1 of / 1 Caption Close The Risks of Scanning 1 / 1 Back to Gallery

The saying "what you don't know can't hurt you" in modern medicine could apply to a trend in healthy adults receiving full body or cardiac CT (computer tomography) scans. In addition to radiation risks, unnecessary CT scans can expose you to a host of problems - from risks of invasive biopsies to aggressive treatments for misdiagnosed cancers.

When ordered by your doctor in the proper setting, any risks of CT scans are far outweighed by their potential benefits. They are one of modern medicine's greatest diagnostic tools, used to examine any part of your body and, increasingly, to guide minimally invasive procedures previously performed with surgery. CT rapidly rotates X-ray beams around you, obtaining images from different angles that a powerful computer then compiles to build, slice by slice, highly detailed pictures of your insides. Contrast material (which you either drink or receive through a vein) is used in some cases to enhance these images.

The impressive level of detail that CT provides can also cause confusion. In CTs of healthy adults, more than 90 percent of findings are "false positives." One of the most common reasons patients are referred to our pulmonary practice at Stanford is for evaluation of tiny lung nodules - detected either incidentally in full-body or cardiac CT scans or on upper slices of an abdominal CT scan. Studies show that even in smokers, 98 percent of these "incidentalomas" are benign. (They are often no more than signs of prior infection.) But to ensure they are not malignant, patients may need further tests or invasive biopsies. If the diagnosis remains uncertain, they may even end up receiving surgery or chemotherapy for a presumed cancer.

At best, patients with incidentalomas require only repeat CT scans - from every three months to every year (depending on individual cancer risk factors), to watch for growth or change in the abnormality. But even this follow-up is not without risk. A CT scan can provide up to 1,000 times the radiation of an X-ray. A November 2007 New England Journal of Medicine review noted that two to three CT scans could expose patients to the same amount of radiation and cancer risk as the 1945 Japanese nuclear bomb survivors, with relatively higher risk in women and young patients.

In the rare event that an incidentaloma is malignant, you should know that early detection does not necessarily equate with better outcomes. In a large Mayo Clinic study of lung CT scans in smokers, those with "early-detected" cancers had additional biopsies, surgery (and probably anxiety), but lived no longer than their non-CT high-risk counterparts.

Full-body CT scans cost $500 to $1,000. Insurance companies do not cover the cost, but may use any detected abnormality to raise your premiums or limit future coverage. There are no public health organizations that advocate the use of full body or cardiac CT scans in healthy adults, and the American College of Radiology and American Heart Association have released statements recommending against them. Before you decide to schedule your own diagnostic test, consult with your doctor and follow the guidelines of these organizations. They constantly review all available evidence so you don't have to.