MR imaging findings in mild traumatic brain injury with persistent neurological impairment

Abstract

Traumatic brain injury (TBI) is a widespread cause of neurologic disability, with > 70% of cases being mild in severity. Magnetic resonance imaging provides objective biomarkers in the diagnosis of brain injury by detecting brain lesions resulting from trauma. This paper reports on the detection rates of presumed trauma-related pathology using fluid-attenuated inversion recovery (FLAIR) and susceptibility-weighted imaging (SWI) in TBI patients with chronic, persistent symptoms. Methods: 180 subjects with persistent neurobehavioral symptoms following head trauma referred by personal injury attorneys and 94 asymptomatic, age-matched volunteers were included in the study. 83% of TBI subjects were classified as mild. Results: TBI subjects had a significantly greater number of lesions detected by FLAIR than controls (42% vs. 22%) and more lesions detected by SWI than controls (28% vs. 3%). To reduce the confounding effects of aging, we examined mild TBI subjects < 45 years of age, which reduced the rate of lesions detected by FLAIR (26% vs. 2%) and SWI (15% vs. 0%). This younger group, which contained few age-related lesions, also demonstrated that subcortical lesions on FLAIR are more specific for TBI than deeper lesions. Conclusions: While the presence of litigation in mild TBI cases with incomplete recovery has been associated with greater expression of symptomatology and, by extension, poorer outcomes, this study shows that mild TBI patients in litigation with chronic, persistent symptoms may have associated brain injury underlying their symptoms detectable by MRI biomarkers.

Introduction

Traumatic brain injury (TBI) is responsible for an alarming number of deaths and neurologic disability each year, affecting > 3.5 million people worldwide [1], [2]. > 75% of total TBI cases are mild, and while 80–90% will make a favorable recovery, the remaining 10–20% [3], [4], defined by Ruff et al. [5] as the “miserable minority,” continue to experience persistent cognitive, behavioral or neurological symptoms 6–12 months post trauma. Some symptoms are nonspecific (e.g., anxiety, fatigue, loss of concentration, dizziness, irritability), making it hard to differentiate from other etiologies. Persistence of neurologic impairment may impair quality of life and prevent return to work, leading to lost-wage claims and medical and disability costs [6].

The presence of litigation in cases with incomplete recovery has been associated with greater anxiety, depression, social dysfunction and poorer outcomes in mild TBI (mTBI), suggesting to some the pursuit of monetary compensation may affect the subjective expression of symptoms following mTBI [7]. However, a few studies show an association between imaging findings and post-concussive symptoms. A study looking at depressed mood after concussion found that depression severity correlated with reduced activation in brain areas implicated in major depression, with computerized volume measurements showing gray matter volume loss in these same regions [8]. Liu et al. looked at residual iron deposition as a marker of prior hemorrhaging and found a higher rate of microhemorrhages in patients with persistent post-concussive symptoms compared with those who recovered completely after injury [9]. Wang et al. found that microhemorrhages in the frontal, parietal or temporal lobes predicted presence of depression one year following trauma [10]. These studies suggest imaging may provide a framework to explain residual symptoms and neurologic deficits.

Computed tomography (CT) is used in acute settings to determine the need for surgical intervention. Conventional MRI, however, is known to be superior to CT for the detection of non-hemorrhagic pathology in the brain parenchyma [11], [12]. Gradient echo MRI is more sensitive than conventional MRI in detecting the presence of iron in hemosiderin, which remains after hemorrhaging. Susceptibility-weighted imaging (SWI), which combines both phase and magnitude images, has been shown to be about three times more sensitive than gradient echo MRI. Furthermore, SWI findings have been found to correlate with clinical symptoms and outcome [13], [14].

Fluid-Attenuated Inversion Recovery (FLAIR) is superior to T2-weighted imaging (T2) for detecting traumatic axonal injury [15], [16], [17]. By attenuating the cerebrospinal fluid (CSF) signal, FLAIR allows for better cortical and periventricular lesion detection. Koelfen et al. [18] looked at children one-year post mTBI and found abnormalities in 43% of cases, while Datta et al. [19] showed FLAIR findings in 55% of chronic mTBI cases, and Riedy et al. [20] found findings in 51% of mostly mild blast TBI cases. One issue with FLAIR and T2 is the difficulty distinguishing between trauma-related hyperintensities and hyperintensities associated with aging and microvascular disease. Therefore, young TBI patients would likely be a better population for determination of true sensitivity to trauma, while also providing information regarding the anatomical location and morphology of trauma-related hyperintensities.

The current study addresses the rates and types of trauma-related pathology revealed by FLAIR and SWI in a cohort of mostly mTBI patients who were in litigation at the time of the study. We hypothesize: 1) MR findings generally will increase with clinical severity; 2) SWI will detect microhemorrhages, even in mTBI; 3) lesion detection rates on FLAIR will be higher than SWI, and 4) FLAIR will reveal a propensity for hyperintense lesions in the subcortical white matter at or just deep to the gray-white junction.