The main benefit of imaging — the edge of the sword we wish was the whole story — is that it can produce diagnostic clues that may be difficult or impossible to get any other way. And so, sometimes, imaging leads to a “well there’s your problem” explanation, revealing a cause that is relatively obvious — if you look in the right place, in the right way.
The other edge of the sword is that the “obvious” problems revealed by scanners are routinely not actually the problem. Imaging notoriously reveals things that only look scary and important, but are actually “incidental findings.” The spectre of false positives, the result that isn’t as satisfying an explanation as it seems.
The special case of imaging to diagnose chronic pain
False positives are a hazard with all medical imaging, but it’s especially an issue with investigations of chronic pain, which dances to the tune of many variables, and often doesn’t not correlate neatly with things in the tissues. People often hurt when there’s nothing obvious wrong with them, and things that seem like obvious causes of pain do not always hurt.1
And so premature, excessive, and misleading imaging are huge problems with real consequences: misdiagnoses, and the treatments based on them. Plus, of course, unnecessary fear and anxiety (nocebo) — which can directly exacerbate pain, ironically.
Examples of imaging results that can lead to misdiagnosis
- Many mensical tears in the knee are painless.2
- Bipartite patella (a congenitally split kneecap) is fairly common, but is mostly only symptomatic in teens. When spotted on scans in adults with anterior knee pain, it may be falsely accused of being the cause, and/or mistaken for a stress fracture, when in fact the cause is something else.3
- The back is the king of misleading MRI results. While some MRI results do indeed correlate with symptoms,4 it’s truly amazing how many of them do not. For instance, a big longitudinal study found virtually no correlation between most degenerative spinal changes and pain.5 For more on this topic, see MRI and X-Ray Often Worse than Useless for Back Pain.
“Well there’s your problem”: imaging at its best
Imaging can be misleading, but it can also just deliver the answer. Many surprisingly "obvious" problems can only be discovered by imaging, or only are in practice.
Metal rod embedded in arm. Art Lampitt had a serious car accident in 1965 — and then, fifty years later, his arm started to ache and swell. An x-ray revealed a strange, thin third arm bone: the turn signal lever from the 1963 Thunderbird he had crashed in. It had been embedded in his forearm, nestled between his ulna and radius, invisible and asymptomatic for decades.6
Tendon rupture: not as obvious as you’d think! Tendons connect muscles to bones — until they don’t. When the tendon tears away from the bone, that’s an "avulsion." Not a subtle injury! Especially if the muscle is big, you wouldn’t think that an avulsion would be hard to diagnose, but it can be. According to O’Laughlin et al, hamstring avulsions "can be difficult to diagnose due to swelling and patient guarding, which may mask a visibly palpable defect and lead to delays in diagnosis."7 ………In this case study, the only diagnosis was "hamstring pain" for several days, before the avulsion was finally confirmed by MRI, and surgically repaired on day 13. It’s not hard to imagine cases where the diagnosis would have taken much longer.………This is a good example of imaging at its most clinically useful. Premature, excessive, and misleading imaging are all major problems, but sometimes looking inside tissues is exactly what you need to get to "well, there’s your problem!"
"Benign" tumours in awkward places. Alex suffered for years from relentless back pain before a little tumour was finally discovered: it was benign, but it was growing on a nerve in his back (a “neuroma”), and it had just about ruined him. At his worst, Alex could barely walk. Eventually, after an easy surgery, he was basically completely cured, just like that. Boom. Alex had seen many, many healthcare professionals who had failed to diagnose the real problem, thrown up their hands, and chalked it all up to “non-specific back pain.” I was one of those healthcare professionals. A chiropractor finally suggested the right kind of spinal imaging … which easily identified the neuroma. Once it was revealed, that was the end of any discussions about how strange and unexplained chronic back pain is! He just needed surgery to remove a little blob of uninvited tissue from a nerve root. And that surgery worked immediately and permanently.
The other major benefit
The other imaging superpower is that it can also reduce fear and anxiety about a stubbornly painful problem by eliminating the worst-case scenarios — even while potentially causing worry about less ominous findings.
Sometimes persistent musculoskeletal pain is the tip of a pathological iceberg, and sometimes there just aren’t any clear indications that something more serious is going on. Imaging is the only way to be fairly sure that there isn’t a disturbing explanation for the problem.
I suffer from a bizarre problem known as "thunderclap headaches" — intense headaches that explode into existence, from no pain at all to agony in about three seconds (and, fortunately, rarely last for more than a few minutes). In 2016 I had a brain scan that showed no obvious or common cause of that problem. The relief I felt was substantial and lasting. Years later, I still don’t know for sure that my thunderclap headaches don’t have some sneaky ominious cause the scan missed … but it’s unlikely. Six years later, I am still taking comfort from that negative CAT scan.
When should you imaging be considered?
Obviously some suspected diagnoses, like fractures, are much more likely to be good candidates for imaging. In the absence of a specific diagnostic reason for imaging, the main general reasons to consider imaging are:
- Recalcitrance. Stubborn symptoms. When recovery isn't going as well as it should, imaging is often a reasonable way to look for an explanation.
- Diagnostic uncertainty. If there are too many strong candidates, imaging might help narrow it down.
- Higher stakes. For instance, it’s much more appropriate to consider imagine. One common example of that in pain medicine…
- Bilateral symptoms may suggest not only a need for imaging, but for spinal imaging.
All the risks with scans: radiation, reliability, and more
I’ve already covered the main one: misleading results are particularly a problem when trying to diagnose pain. Here’s everything, the complete list of “what could possibly go wrong”:
- Radiation exposure, of course. Bone scans and CT involve much more than radiation than x-ray. MRI and ultrasound are great alternatives for this reason.
- However, MRI cannot be used on people with implants.
- Injections of tracers and contrast agents always involve the risks of most injections, primarily allergies and infection, both rare but serious complications.
- Not nearly as much diagnostic clarity as you’d think. Imaging is surprisingly fallible in many ways. Both false positives and negatives abound, for various reasons:
- Perceptual errors, especially inattentional blindness,8 results in missing things that seem amazingly obvious in retrospect — like the loose screw in my wife’s back.9
- Scan selection can result in missing things that would be obvious on another type of scan. There are many types and sub-types of scans, with intricate pros and cons for detecting different kinds of lesions.
- Interpretation errors, especially the evaluation of the clinical importance of findings, errors in how the results are understood and communicated. The most common scenario is overestimating the importance of findings, but certainly the opposite can happen too — like the time that I was told point blank by a doctor that I did not have a finding that absolutely was there (and did prove to be significant). He was editorializing: he said the finding wasn’t there not because it wasn’t there, but because he was convinced that it didn’t matter.
Types of medical imaging
- X-ray shines electromagnetic radiation at x-ray wavelengths straight through tissue; it mostly goes through soft tissue and is mostly reflected by bone, so x-ray images mostly reveals bony features and relationships.
- CT or CAT scan (computed axial tomography) — A CT scan is basically a fancy x-ray that can reveal soft tissue detail by shining X-rays through tissues repeatedly from multiple angles. Soft tissues are only partially transparent
- MRI is superficially similar in that it also puts patients in a tube, but it is a radically different and exotic tech. MRI is basically an atom detector, specifically a proton detector (hydrogen nuclei). We are full of hydrogen. Every tissue has lots of hydrogen in it. The MRI makes protons “light up” by first polarizing them with a powerful magnetic field, and then exciting them with radio waves, revealing a person-shaped cloud of proton. The differences in the density of protons alone can show a lot, but a lot more information can be extracted from how the protons “shine” (that is, exactly how they respond to radio waves).
- Ultrasound bounces sound waves off layers of tissue; changes in tissue density reflect sound waves differently. Ultrasound is technologically complex and can be "tuned" for different tissue and diagnostic priorities. It’s the only kind of imaging that is also routinely used therapeutically (and especially in musculoskeletal medicine).
- Bone scan or bone scintigraphy detects an injected radioactive tracer molecule which is preferentially absorbed by cells that are producing new bone 1tissue, which happens around some tumors, fractures, and infections.
- Digital motion X-ray (DMX) is an X-ray video, an unregulated (and banned-in-Canada) diagnostic technology that is primarily sold to neck pain patients by chiropractors, often for evidence in injury lawsuits. It is eschewed by mainstream medicine because of concern about radiation exposure. Patients should get multiple medical opinions before resorting to this exotic diagnostic method.
Patients are part of excessive imaging problem
One of the best examples of medical incompetence in pain and musculoskeletal medicine is the notoriously excessive imaging for back pain, especially MRI. Why so much imaging?
It seems baffling. This late in history, why would primary care physicians continue to order way too much inappropriate spinal imaging when it’s blatantly at odds with every expert opinion and all the clinical guidelines? When it’s a very well-known problem? Are they feckin' stoopid?! Maybe a few. But mostly it’s this stuff, perfectly summarized by Adam Dobson:
- Patient pressure
- Lack of training
- Defensive medicine
- ‘Fix it’, societal mentality
- Beliefs around ‘reassurograms’
Notice that a few of those fall right in the lap of the patient. 😬
So here’s an ugly truth: “medical incompetence” is often collaborative. Doctor and patient can and do work together to achieve a lousy outcome. We all bring a lot of biases into medical appointments … and often misinformation too. Doctors and patients alike.
- Digital Motion X-Ray: A Dangerous Illusion of Diagnostic Power — What’s the risk from the radiation exposure? Is the diagnostic potential worth it?
- MRI and X-Ray Often Worse than Useless for Back Pain — Medical guidelines “strongly” discourage the use of MRI and X-ray in diagnosing low back pain, because they produce so many false alarms
- 38 Surprising Causes of Pain — Trying to understand pain when there is no obvious explanation
What’s new in this article?
Jun 13, 2023 — Added two new short sections: “Patients are part of the medical incompetence equation,” and “When should you imaging be considered?”
2022 — Publication.
- Ingraham. Pain is Weird: Pain science reveals a volatile, misleading sensation that comes entirely from an overprotective brain, not our tissues. ❐ PainScience.com. 16191 words. Modern pain science shows that pain is as hard to predict or control as the weather, a function of countless chaotic variables, surprisingly disconnected from seemingly “obvious” causes of pain. Pain is jostled by many systemic variables, but especially by the brain’s filters, which thoroughly “tune” pain and often even overprotectively exaggerate it — so much so that sensitization can get more serious and chronic than the original problem. This has complicated all-in-your-head implications: if the brain controls all pain, does that mean that we can think pain away? Probably not, but we do have some neurological leverage — maybe we can influence pain, if we understand it.
- Zanetti M, Pfirrmann CWA, Schmid MR, et al. Patients with suspected meniscal tears: prevalence of abnormalities seen on MRI of 100 symptomatic and 100 contralateral asymptomatic knees. AJR Am J Roentgenol. 2003 Sep;181(3):635–41. PubMed 12933452 ❐
- Akdag T, Guldogan ES, Coskun H, Turan A, Hekimoglu B. Magnetic resonance imaging for diagnosis of bipartite patella: usefulness and relationship with symptoms. Pol J Radiol. 2019;84:e491–e497. PubMed 32082445 ❐ PainSci Bibliography 51992 ❐
- Brinjikji W, Diehn FE, Jarvik JG, et al. MRI Findings of Disc Degeneration are More Prevalent in Adults with Low Back Pain than in Asymptomatic Controls: A Systematic Review and Meta-Analysis. AJNR Am J Neuroradiol. 2015 Dec;36(12):2394–9. PubMed 26359154 ❐
This is one half of a tale of two papers: a pair published by the same researchers, who looked at a whole lot of MRI pictures of spines. The other paper (Brinjikji) presents evidence that signs of spinal degeneration are present in very high percentages of healthy people with no problem at all.
Good to know.
But this paper presents evidence that degenerative features visible on MRI are nevertheless “more prevalent in adults 50 years of age or younger with back pain compared with asymptomatic individuals.”
Also good to know.
Delicious cognitive dissonance? 😜 The take-home message is actually just a nice, reasonable compromise between two well-known viewpoints: degenerative changes matter less than many patients and professionals still assume, and are not an adequate foundation for many popular treatments, but they do still matter. Duh.
- Kasch R, Truthmann J, Hancock MJ, et al. Association of Lumbar MRI Findings with Current and Future Back Pain in a Population-based Cohort Study. Spine (Phila Pa 1976). 2022 Feb;47(3):201–211. PubMed 34405825 ❐
This is a large study of the relationship between back pain and common signs of spinal arthritis, finding mostly that … there wasn’t much of one. The correlation was there, it was just rather puny. MRI findings, on average, “do not have clinically important associations with low back pain.”
The study was a bit unusual, a big “longitudinal” one: just observing the same group of people for a long time. We don’t see a lot of those in back pain research, or of this size/duration: about 3300 people over six years. But it gives us insight into the order of things, producing what I think is probably the most important single result here: pain didn’t develop in people who started out with signs of spinal degeneration. It’s not just that they aren’t strongly correlated, it’s that pain doesn’t follow the signs. More formally stated by the authors:
“We found most MRI findings were not associated with future LBP-severity regardless of the presence or absence of baseline pain.”
And the signs don’t follow the pain either.
Another way to sum this study up: most spinal arthritis isn’t painful, which sounds a bit radical. But none of this is actually news. It’s just great new data that really drives the old point home that most back pain is not caused by spines that are cruddy with arthritis.
- “I was hoping it might be shiny still,” he said in an interview with CBC Radio One’s “As It Happens,” but it was badly corroded — perhaps the reason it finally caused some symptoms, but who knows.
- O’Laughlin SJ, Flynn TW, Westrick RB, Ross MD. Diagnosis and expedited surgical intervention of a complete hamstring avulsion in a military combatives athlete: a case report. Int J Sports Phys Ther. 2014 May;9(3):371–6. PubMed 24944856 ❐ PainSci Bibliography 53845 ❐
- Drew T, Võ MLH, Wolfe JM. The invisible gorilla strikes again: sustained inattentional blindness in expert observers. Psychol Sci. 2013 Sep;24(9):1848–53. PubMed 23863753 ❐ PainSci Bibliography 52552 ❐
“What is it, Doc? What’s wrong with me? Why the sudden banana obsession? The knuckle-walking?”
“Well, the bad news is that you’ve got a little gorilla in your lungs. But we caught it early—only 17% of radiologists can spot it at this stage. Lucky break!“
Researchers have shown that people often miss the occurrence of an unexpected yet salient event if they are engaged in a different task, a phenomenon known as inattentional blindness. However, demonstrations of inattentional blindness have typically involved naive observers engaged in an unfamiliar task. What about expert searchers who have spent years honing their ability to detect small abnormalities in specific types of images? We asked 24 radiologists to perform a familiar lung-nodule detection task. A gorilla, 48 times the size of the average nodule, was inserted in the last case that was presented. Eighty-three percent of the radiologists did not see the gorilla. Eye tracking revealed that the majority of those who missed the gorilla looked directly at its location. Thus, even expert searchers, operating in their domain of expertise, are vulnerable to inattentional blindness.
My wife had a major car accident in 2010 while travelling in Asia. She had extensive titanium hardware installed in her back, and it broke — breakage that I personally confirmed by studying MRI images. The radiologist had missed it! I found it myself, staring at those magical black and white transverse slices of my wife’s back, which clearly revealed cross-sections of a screw (so unlike any anatomy!) floating in the wrong place, the end of one bar well out of its home bracket, and the other on the verge of coming loose as well.
I am proud of making that discovery, even though it is not really as amazing as it sounds. Certainly it’s a minor embarrassment for the radiologist, but mostly his attention was properly on my wife’s bones and spinal canal, not so much her bars. The find was quickly confirmed by a surgeon, who was more amused than shocked (amused in a good, friendly way). “It’s rare. Less than 5% probably,” he explained. “But it does happen, and it’s really not that big a deal.”
Although it wasn’t serious, it’s a very good example of how easy it is to miss something “obvious” when you’re focussing on other things.