(1) Because we do not have the body of knowledge that tells us how to predict an anomaly is not worth pursuing. It would require a lot of major, expensive, long-term studies involving non- negligible chemical exposures in$ asymptomatic people in order to get a good idea of what the “healthy” anomaly looks like.
$ many of these MRIs require contrast material.
(2) Malpractice for a missed cancer in most states has an enormous lookback period and an automatic “doctor loses.” It doesn’t matter if the doc made a statistically appropriate call. So docs follow-up on anything but the most unambiguously benign lesions.
No, it has to do with avoiding harm to patients. I don’t make one red cent more or less from sending someone to an MRI or not. I do care about wasteful testing that is more likely to stress out a patient and send them down a rabbit-hole of follow-up tests with potential complications and costs (to them), if there’s not a reasonable chance of an outweighing clinical benefit for them.
And of course we make statistical calls! When you’re deciding -prospectively- whether a course of testing or treatment is in a patient’s best interest, you have to look at the stats on likely benefits and harms of various courses of action. I’d love to know what my patients have before hand, so I could avoid dealing with probabilities, but I haven’t been blessed with that particular power. I’d love for the data to exist to tell me how to interpret a result in my precise patient rather than a larger population she belongs to, but “solitary pulmonary nodules in 33-year old men who smoked twice in college and live half a mile from a freeway with two episodes of bronchitis in their teens” is a study that hasn’t been conducted yet. One day perhaps it will be, and if so, I’ll be grateful for it. But right now that data doesn’t exist, so we use what we have, and use our judgment to tailor it to the patient in front of us - imperfectly.
I recommend reading “overdiagnosed” by Gilbert Welch.
$ many of these MRIs require contrast material.
(2) Malpractice for a missed cancer in most states has an enormous lookback period and an automatic “doctor loses.” It doesn’t matter if the doc made a statistically appropriate call. So docs follow-up on anything but the most unambiguously benign lesions.