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Neuroanatomic Basis of Impaired Self-awareness After Traumatic Brain Injury: Findings From Early Computed Tomography

Sherer, Mark PhD; Hart, Tessa PhD; Whyte, John MD, PhD; Nick, Todd G. PhD; Yablon, Stuart A. MD

Journal of Head Trauma Rehabilitation: July-August 2005 - Volume 20 - Issue 4 - p 287–300
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Background Impaired self-awareness (ISA) is common among patients with severe traumatic brain injury (TBI) and contributes to poorer functional outcome. There is keen interest in improving the understanding of this disorder as the neuroanatomic substrate of posttraumatic ISA is poorly understood.

Objective Determine whether (1) greater number of brain lesions, (2) greater volume of right hemisphere lesions, or (3) greater volume of frontal lesions is associated with greater levels of ISA after TBI.

Design Prospective, observational study.

Participants Ninety-one TBI admissions to one of 2 National Institute on Disability and Rehabilitation Research TBI Model System (TBIMS) programs. Subjects met TBIMS inclusion criteria plus (1) resolution of posttraumatic amnesia (PTA) prior to rehabilitation discharge and (2) initial postinjury computerized tomography (CT) scan available as a hard copy and as an electronic file.

Methods CT scan lesions outlined by a board-certified neuroradiologist were measured using NIH Image, and resulting calculated lesion volumes/scan variables compared against demographic characteristics, TBI severity variables, and ISA variables measured by the Awareness Questionnaire (AQ) at the time of PTA resolution.

Results Most subjects (78%) had at least 1 lesion on emergent CT, and contusion volumes varied in all regions of interest. Patients rated their functioning as more intact on the AQ than ratings of treating clinicians, consistent with ISA. Greater injury severity was associated with a greater degree of ISA. Multivariable linear regression revealed that, after adjustment for other predictors, the number of brain lesions was predictive of degree of ISA. Right hemisphere contusion or frontal lobe contusion volumes, however, were not predictive of degree of ISA.

Conclusions ISA was significantly associated with the number, but not with location or volume of focal lesions early after TBI. Posttraumatic ISA may reflect disruption in the integrated operation of broadly distributed neural networks, with lesion burden in any specific region being less relevant than disruption across multiple regions. Further imaging research is warranted to confirm these findings and to provide insight into the distributed networks required for self-awareness.

Methodist Rehabilitation Center and University of Mississippi Medical Center, Jackson, Miss (Drs Sherer and Yablon); Moss Rehabilitation Research Institute and Department of Rehabilitation Medicine, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pa (Drs Hart and Whyte); and Center for Epidemiology & Biostatistics, Cincinnati Children's Hospital Medical Center and University of Cincinnati College of Medicine, Cincinnati, Ohio (Dr Nick).

Corresponding author: Mark Sherer, PhD, ABPP/Cn, Methodist Rehabilitation Center, 1350 E Woodrow Wilson, Jackson, MS 39216 (e-mail: marks@mmrcrehab.org).

This investigation was supported by funding from the National Institute on Disability and Rehabilitation Research for the Collaborative Study on Impaired Self-awareness After Traumatic Brain Injury (NIDRR grant #H133A980067). We thank Dr Gurmeet Dhillon for his assistance in marking and interpreting CT scans and Sid Dickson, Rob Adams, and Chad Vickery for assistance in measuring lesions on CT scans.

© 2005 Lippincott Williams & Wilkins, Inc.