Leddy “Sport Related Concussion” NEJM Jan 30, 2025, discusses a 17-year-old who struck the back of her head during a soccer game and explains the range of available care post-concussion.
Dr. Leddy provides a good overview of recommended care but his report is surprisingly deficient in any discussion of rotational injuries, the availability of DTI MRI and the salutary role of growth hormones in speeding the recovery of adolescents that practitioners commonly observe. My thoughts on the first two items follow.
Most head injuries involve rotational decelerations. Ji Lan, et al., “How to deform an egg yolk? On the study of soft matter deformation in a liquid environment” Phys. Fluids 33, 011903 (2021); https://doi.org/10.1063/5.0035314 analyzes the significance of rotational force in causing brain injury.
Rotational forces present in most read-end collisions when a driver or passenger is not looking straight ahead, bicycle and motorcycle crashes, slip and fall head strikes, football, soccer, wrestling and boxing.
The chief take-away from Lan’s article is that a soft egg yolk is not sensitive to translational impacts, but is very sensitive to rotation, especially deceleration rotational impacts, during which centrifugal force plays a critical role.
A decelerating rotational impact induces the stretching of neurons and causes damage at a microscopic level, not capable of inspection by visual MRI results but readily analyzed by computerized evaluation in an MRI with deep tensor imagery (DTI) that analyzes data that can only be deciphered by computerized programs.
Individual axons are microscopic and cannot be directly seen on MRI, so there is no way to directly view the axonal shearing. Axonal shearing can only be directly visually confirmed on autopsy when slices of the brain are viewed under a high-powered microscope.
Traditional MRI methodologies are insensitive to damage to white-matter tracts in the brain, so people who have sustained a closed head injury often have normal MRI results using older MRI methodologies despite the damage to white-matter tracts in their brains.
Standard MRIs and CT scans are not capable of the deep dive that DTI MRI provides in analyzing what cannot be seen conventionally.
DTI is based upon the known physics of the flow of water. In an open and unobstructed space, water molecules will diffuse equally in all directions in a manner called isotropic distribution. If there are barriers to flow, such as in intact axonal tracts within the white matter of the brain, water will move unequally in all directions. This is called anisotropic distribution. Because axons are parallel fibers connecting nerve cells in areas of the brain, water between the axons tends to diffuse in a single direction. Water distribution in healthy, intact white-matter tracts tends to be anisotropic; that is, it moves in a single direction. When axons that comprise the white-matter tracts are damaged, torn, or their outer myelin membranes are broken down, water will diffuse in a more isotropic distribution within the axonal/white-matter tracts which can be detected by DTI MRI.
A 2022 article in the Journal of Neurotrauma analyzed the susceptibility of white-matter fiber tracts to concussion and described DTI as follows:
- DTI, a magnetic resonance imaging (MRI) technique, is widely used in studies of mild TBI to detect white matter-related microstructural damage. [citations omitted] DTI provides scalar measures that infer microstructural organization of the tissue and exhibit adequate diagnostic sensitivity to SRC. The scalar metrics include fractional anisotropy (FA) describing the coherence of microstructural organization …. … Most appealingly, DTI also provides directional information for assessing white-matter fiber connectivity via tractography.
- (Mustafi, Yang, Harezlak, et al., Effects of White-Matter Tract Length in Sports-Related Concussion: A Tractography Study from the NCAA-DoD CARE Consortium , Journal of Neurotrauma, Vol. 39, pp. 1495-1506 (Nov. 2022).)
In 2022, the Journal Lancet Neurology published an article by noted clinicians who treat traumatic brain injuries. The article addressed the progress and challenges in prevention, clinical care, and research regarding traumatic brain injuries. With respect to the use of DTI, the authors of the article explained:
- Major advances have resulted from the application of MRI to TBI, with a role for identify injuries that are not visible on CT imaging. Both CENTER-TBI and TRACK-TBI reported structural traumatic abnormalities on MR performed 2-3 weeks after injury, in approximately 30% of patients with mild TBI who had a normal CT on presentation. Advanced MRI techniques, such as diffusion tensor imaging and susceptibility weighted imaging ( both of which are now routinely available on clinical scanners ) are more sensitive at detecting superficial contusion, traumatic axonal injury , and traumatic vascular injury – additionally, traumatic axonal injury and traumatic vascular injury are now recognized as distinct entities with pathophysiology and outcome impact. Quantitative assessments of MRI, such as volumetric analyses, reductions in fractional anisotropy , and increases in mean diffusivity can identify injury not detectable by visual inspection of MR images. Such injuries can be particularly relevant in mild TBI, because fractional anisotropy and diffusivity abnormalities identify patients who are likely to have persistent post-concussional symptoms and long-term disability .
- (Maas, Menon, Manley, et al. Traumatic Brain Injury: progress and challenges in prevention, clinical care, and research. Lancet Neurol 2022, 21:1004-60 (Sept. 2022.), emphasis added.)
In 2023, the Handbook of Clinical Neurology relied upon recent scientific publications to explain:
- A hallmark of concussion is that neurological signs and symptoms are imparted after biomechanical force to the brain in the absence of macroscopic neural damage. In general, this has been interpreted as a result of predominant functional or microstructural injury to neural tissue. … Microstructural injury refers to physical changes not readily evident on routine CT scanning, but detectable through advanced imaging such as diffusion tensor imaging (DTI) to delineate signs of axonal injury and microstructural symmetry -asymmetries particularly of the long white matter tracts , especially the corticospinal tract (CST) and the optic radiations as a result of its vulnerability and variable sensitivity to concussion. Both tracts can be investigated with diffusion tensor tractography (DTT) ( Jang and Kim, 2016 [J. Neurotrauma 33: 1790-1795] ; Jang et al., 2020 [Transl Neurosci 11: 335-340] ; Jang and Seo, 2022 9 Neural Regen Res 17: 978-982]. ) allowing the entire neural tract to be evaluated and reconstructed to indicate abnormalities such as tearing, narrowing, and discontinuation.
- (Younger, Handbook of Clinical Neurology, Vol. 196, Chapter 24, (3RD Series) 2023.)
There is substantial outdated literature concluding that DTI MRI is not worthwhile for diagnosis.
Recent literature recognizes that comparing changes in brain symmetry to a data base has little value in diagnosis, but comparing changes in one side of a patient’s brain with its opposite is a valuable tool to identify and diagnose axonal damage and devise assistive therapy.
