chapter  5
40 Pages

The Use of Structural and Functional Imaging in the Neuropsychiatric Assessment of Traumatic Brain Injury

It is not possible to provide a comprehensive neuropsychiatric assessment of a person following traumatic brain injury (TBI) without also including at a minimum structural brain imaging. Functional brain imaging may be useful in particular and special circumstances as noted further in this chapter. The use of electroencephalographic evaluation also plays an important role in certain situations following TBI. Table 5.1 is a listing of the common structural and functional procedures available to the neuropsychiatric examiner. Physicians performing a neuropsychiatric examination are not expected to understand neuroimaging at the level of a radiologist or neuroradiologist, nuclear medicine physician or neurologist-electroencephalographer. However, physicians functioning in the neuropsychiatric realm are expected to understand and use neuroimaging where appropriate, particularly in the postacute evaluation of cognitive status following TBI. It is important that the neuropsychiatric examiner develops a professional relationship with radiologists or neuroradiologists, nuclearmedicine physicians and neurologists performing electroencephalograms. Neuroimaging to the neuropsychiatric examiner is no different than any other laboratory examination. The images are obtained using standardized protocols and are interpreted in standardized manners based on the particular standards for the profession involved in the interpretation of the images. The neuropsychiatric examiner then obtains these images and overreads them. Thus, stems the necessity for a good relationship with imaging physicians. It is recommended that the neuropsychiatric examiners, early in their career, overread each image with the imaging physician when it is obtained during a neuropsychiatric TBI examination. Over time, the neuropsychiatric examiner will develop skill in the understanding and detection of TBI lesions identified by functional and structural imaging. This will enhance the skill set of the neuropsychiatric examiner to provide a comprehensive and quality examination of the post-TBI patient. It goes without saying that in a forensic situation, structural and functional imaging is a must for providing the trier of fact with images to establish the integrity of the brain following TBI. This chapter introduces to the examiner performing neuropsychiatric brain injury assessment issues that are primarily related to imaging of acute brain trauma. However, most of the imaging performed in a neuropsychiatric evaluation will be well after the fact of the brain injury and will be used to determine outcomes, damages, and as an adjunct to treatment planning in therapy. It is necessary for the examiner to be aware of imaging obtained either in the emergency department or the acute care setting following TBI. Otherwise, when the examiner reviews medical records, the clinical correlation between the original acute injury and the current findings on neuropsychiatric examination will be poorly understood by the physician. This chapter presents structural and functional imaging figures that correspond to the real life chronic lesions that

may be detected during neuropsychiatric examination. Imaging from acute care settings after TBI will be described and some are figuratively displayed. The reader is referred to expert sources for acute imaging exemplars.1,16,25,27,44,75,78,89,110,121,127

Use in the Acute Care Setting

Computed tomography (CT) is the most common means used for intracranial evaluation following trauma.1 The principles of CT are similar to those of standard planar radiography, except that the former uses stationary detectors rather than radiographic film to capture images. Planar x-ray functions like an ordinary photographic camera, except instead of light striking film, an x-ray beam is attenuated as it passes through tissues before striking the detector. CT also uses an x-ray beam and is counterbalanced with an x-ray detector bank situated within the outer ring of the scan gantry. The degree to which the x-ray beam is absorbed or scattered (attenuated) determines the radiographic density of the structure being scanned. When an x-ray beam enters two separate but contiguous structures, the structure that is composed of the densest material will absorb more of the beam than its neighbor allowing fewer x-ray photons to reach the detectors. A diminished detector signal is translated into a lighter shade of gray on the image gray scale than that of its less dense neighbor. This allows the radiologist to differentiate tissues based on contrast resolution. CT can also be performed with a variety of postacquisition electronic filters. These filters selectively add or remove various frequencies from the raw data and change the limits of the gray scale producing either a smoothing or an accentuation of the edges. Filters are applied to the raw digital data during postacquisition manipulation. If needed, ionic and nonionic forms of contrast media are available for CT. Ionic contrast agents are much less costly than the nonionic forms. However, the nonionic contrast agents have substantially fewer side effects. Contrast is rarely used to detect CT lesions of TBI in the chronic phase. They may be used if there is a question of acute ischemic stroke as a result of mass effects from intracranial traumatic lesions.1