I’m sure I’m not the only radiologist with a secret ambition to have something named after them. At this stage of my career, it’s probably not going to be a new disease -- unless it turns out to be the death of me, which would feel like a bit of an own goal. A new radiological sign? Well, I have a few possibilities, but I have never gotten around to publishing them, so it’s unlikely that I’ll ever receive the attribution I think I deserve.
My friend and fellow AuntMinnieEurope contributor Dr. Paul McCoubrie has published two volumes of his “Rules,” which now number up to 100. I couldn’t possibly compete with that, but what I can offer is what I rather grandiosely call “Maskell’s Law of Cancer.” In truth, this is neither a law nor actually mine, and it’s not really about cancer, but I’m hoping that if I repeat this formulation often enough, it might just catch on.
Dr. Giles Maskell. Photo courtesy of European Society of Breast Imaging.
Maskell’s Law states that if the patient doesn’t have cancer, then what you’re looking at probably isn’t a metastasis. The “probably” is important here, and we’ll come back to that in a moment. What it means in practice is that when you’re pondering an unusual appearance on an image in a patient who is, as far as can be seen, entirely fit and well, then metastasis should not be the first thought that comes into your head, or the first suggested diagnosis in your report. This applies to lesions in the liver, lungs, bones, adrenal glands, and most other organs, as well as to all those soft tissue nodules that crop up unexpectedly in odd recesses of the peritoneal cavity.
I should add that in the application of this principle, “having cancer” doesn’t just mean having a biopsy-proven nailed-on diagnosis but also covers pretty much any of the physical or imaging signs of seediness.
I told you it wasn’t really a law, and that’s because I know what you’re thinking. You’re remembering that patient you saw just the other day who turned up out of the blue with disseminated malignancy that came as a total surprise. That’s where the “probably” comes in. Of course, there are exceptions, but that’s exactly what they are -- exceptions, unusual occurrences, something out of the ordinary.
In the ordinary way of things, a solitary liver lesion detected on ultrasound in a young, fit army recruit will not turn out to be a metastasis, no matter how much it looks like one. If it did, radiology would be easy, and we could let the computers do it.
I also mentioned earlier that it wasn’t my law. If it belongs to anyone, it probably belongs to the Reverend Thomas Bayes, who worked it out in the 18th century -- without even having a CT scanner to help.
In my very limited understanding, Bayes’ insight was to do with conditional probability: the likelihood of an event occurring, given that something else had already happened, or the “pretest probability,” as we might call it in our line of work.
As a matter of interest, he didn’t publish anything about what has come to be known as Bayes’ theorem during his lifetime. It was discovered in an essay of his and then publicized by a friend after his death. I’d like to think that my friends will be similarly generous when the time comes, but I’m not totally confident.
So I offer you now Maskell’s Law of Cancer. Not Maskell’s, not a law, and mostly about things that are not cancer. I commend it to you.
Dr. Giles Maskell is a consultant radiologist at Royal Cornwall Hospitals National Health Service (NHS) Trust, Truro, U.K. He is a former president of the U.K. Royal College of Radiologists. Competing interests: None declared.
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