Half of Adults Aged 44 to 48 Have White Matter Hyperintensities
A short read on what a common brain-imaging finding can establish about a collision, and what it cannot. A composite of cases I see repeatedly, with no detail drawn from any actual matter.
Two expert reports land on your desk in one matter, both concerning a 47-year-old man with treated hypertension (high blood pressure) who was rear-ended and reports headache and trouble concentrating. Both read one brain MRI (magnetic resonance imaging, which pictures brain tissue in detail), taken six weeks later, which shows two or three small white matter hyperintensities (bright spots in the brain's wiring, seen on one MRI setting). The plaintiff's expert attributes them to the collision; the defense expert attributes them to age. Both agree the spots are real, and both agree the MRI is the evidence.
Is either report right? Neither is, and both go wrong at the same step: each treats the finding as evidence of its own cause. These spots carry no dating signature. Findings that evolve can be placed in a window; these cannot, so a scan six weeks afterward records that they are there, not when they arrived. Tying them to the collision requires an image of the same brain from before it, and neither report identifies one.
Is choosing between them a close call? It is not, and the base rate that decides it (how often the finding appears anyway) is not in either report. Among 428 adults drawn at random from the community at ages 44 to 48, not screened for vascular risk, 50.9 percent had white matter hyperintensities, and the average across all 428 brains was 1.37 such spots. At 47, spots like these are what half this age band already carries, whether or not anyone was rear-ended.
Consider the mirror image. The defense report looks like the safe one, and it is not. It reaches the conclusion the 50.9 percent supports without ever stating it, and it never asks whether a man of 47 with treated hypertension sits above that figure or below it.
So the question underneath both reports is narrower than which expert is right. Not what these spots mean. What could one scan, with no earlier image to measure it against and no base rate on the page, have settled about where they came from?
Three things follow for a reviewer. A finding with no evolution on imaging cannot be dated by the image that finds it. An opinion that attributes a common finding to a cause should carry the rate for that finding on the page. And amended Federal Rule of Evidence 702(d), effective December 1, 2023, requires that an opinion reflect a reliable application of the principles and methods to the facts of the case. An opinion that names no comparator has not shown the application.
An image is evidence of what it shows. It is not, by itself, evidence of what caused it.
— T.B.K
Tobias B. Kulik, MD, FAAN
CorteXion LLC · Scientia et Veritas
The Primer in this month's Writings
Neuroimaging in Litigation: Reading the Record the Images Came From — cortexion.co/writings/neuroimaging-in-litigation
Primary source
Wen W, Sachdev PS, Li JJ, Chen X, Anstey KJ. White matter hyperintensities in the forties: their prevalence and topography in an epidemiological sample aged 44-48. Hum Brain Mapp. 2009;30(4):1155-1167. doi:10.1002/hbm.20586
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