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Article Excerpt
In studies of neurogenic communication disorders, medical records commonly are used to characterize brain lesions, to make decisions regarding participant inclusion, and to draw general conclusions regarding brain-behavior relationships. The validity of using existing medical records has not been directly evaluated. The purpose of this article is to draw attention to the potential problems with relying exclusively on medical records to characterize neurological lesions. Examples from a study of language in adults with right hemisphere brain damage are used to highlight discrepancies between imaging reports taken from existing medical records and structural images obtained at the time of the study. The discussion of factors that may contribute to discrepancies between the imaging reports includes the scanning method and protocol used, interrater reliability for reading neuroradiologic images, the effect of time, and neurological changes associated with normal aging.
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The search for the nature of brain-behavior relationships has been ongoing for nearly two centuries but is still an active search. The description of these relationships can be as broad as comparing right versus left hemisphere functions or as specific as isolating a region of a particular gyrus responsible for specific language functions. The advent of widely used imaging technology has both enhanced our ability to pinpoint such relationships and spawned new questions and problems.
Studies of neurogenic communication disorders frequently rely on reports from participants' medical records to identify site and/or size of lesion. Decisions regarding participant inclusion and group classification are made on the basis of these reports, along with conclusions regarding brain-behavior relationships. In typical studies of neurogenic language disorders, the screening process for potential participants involves a review of medical records. Participants included in a study are those whose medical records provide evidence of a lesion in the hemisphere, lobe, or structure of interest. Many times this information is from a computed tomography (CT) or magnetic resonance imaging (MRI) scan that was obtained within a few hours or days postonset of stroke. In some cases the radiology imaging report is not available, and information is obtained from a neurologist's summary of the CT/MRI scan(s). Some studies include participants who exhibit physical or behavioral signs of unilateral stroke (e.g., hemiparesis) even in the presence of a negative brain scan. Participants may be classified as having anterior versus posterior lesions (in relation to the central sulcus) based on the initial CT/MRI reports. In combination with behavioral data obtained from experimental language tasks or diagnostic tools, conclusions about localization of function may be made from those classifications.
While use of medical records is common in the screening process, the validity of this practice has not been directly addressed. This article draws attention to the potential problems with relying exclusively on medical records to characterize neurological lesions and make assumptions about brain-behavior relationships. Examples are provided from a study of individuals with right hemisphere stroke.
Data for the current discussion were obtained from 12 participants who were recruited for a study of language disorders associated with right hemisphere brain damage. They were included in the study after a review of medical records for each person indicated lesion(s) restricted to the right hemisphere (reports were based on CT and/or structural MRI scans). All participants were at least 1 year postonset of stroke. As part of the research study, a structural MRI scan was completed. Comparisons between the imaging reports from medical records and the recent MRI (see Table 1) indicate more, or more extensive, lesions in each of the 12 participants. Based on the criteria for the original language study (lesions due to stroke restricted to the right hemisphere), 6 of these 12 individuals (Participants 2, 3, 4, 9, 10, & 11) were subsequently excluded. Had the MRIs not been completed, language data from all 12 participants would have been analyzed as a group, thus potentially distorting the conclusions regarding right hemisphere language function.
There are various factors that may contribute to the discrepancies between the imaging reports, including the scanning method and protocol used, interrater reliability for reading CT/MRI scans, the effect of time, and neurological changes associated with normal aging. Each of these factors will be discussed. The focus of the ensuing discussion will be on neurological lesions due to stroke.
SCANNING METHODS AND PROTOCOLS
A stroke is caused by a critical reduction of blood flow (ischemia) to the brain, resulting in insufficient oxygen and glucose delivery to brain tissues (Sweeney, Jager, Walz, & Juurlink, 1995; Vo, Lin, & Lee, 2003). Different imaging methods capture different underlying pathophysiological changes that accompany ischemia. When evaluating brain scan reports, it is essential to know which imaging modality (CT scan or MRI sequence) was used and when, in terms of time postonset, the image was taken. Moreover, it is useful to know the limitations of each of the imaging methods. Specific imaging modalities differ in their capability to depict different tissues and physical properties and in their suitability to capture particular phases of an infarction (Rorden & Karnath, 2004). In the first hours and days after stroke, CT and structural MRIs emphasize different aspects of the underlying pathology as will be detailed below.
Computed Tomography
CT is widely used in clinical practice. The quality of CT images has greatly improved over the past 20 years; nevertheless, they reflect a single property, a tissue's opacity to X-rays (Rorden & Karnath, 2004). To date, unenhanced (or noncontrast) CT imaging remains the gold standard for detecting intracerebral hemorrhage (e.g., Muir, Buchan, von Kummer, Rother, & Baron, 2006). However, CT is less reliable with respect to ischemia. Early changes that result from net water uptake in ischemic brain tissue often are not detected on CT images (although this depends in some part on the experience of the reader, as will be discussed later). Detection rates for early ischemic signs on CT scans increase with time, with images taken 5 to 6 hours or later after symptom onset yielding more reliable detection than images taken earlier (Saur et al., 2003). Apart from duration and severity of ischemia, CT scans have poor sensitivity for small lesion volumes such as lacunar infarcts (Saur et al., 2003) and lesions near the base of the skull such as brain stem lesions. The latter is due to artifacts associated with X-ray beams crossing a high-density structure (von Kummer et al., 2001). Furthermore, if a CT image was taken during the first hours after onset, ischemia confined to white matter often results in a normal CT scan because the initial increase in net water is almost exclusively restricted to gray matter (Saur et al., 2003; von Kummer et al., 2001).
Contrast-enhanced structural CT imaging, in which contrast agents change the opacity of different brain regions, commonly is used to search for tumors or vascular changes. Two additional CT techniques using X-ray contrast agents, intracranial CT angiography and perfusion CT, coupled with unenhanced CT imaging may provide information regarding the presence and site of vascular occlusion (Muir et al., 2006) or perfusion deficits at the capillary level (Aksoy & Lev, 2000; Schramm et al., 2004).
Magnetic Resonance Imaging
Modern MRI can detect vessel occlusion, the presence and extent of infarction, the existence of perilesional hypoperfused regions, and intracerebral hemorrhage or tumor (Fiebach & Schellinger, 2003; see Wardlaw, 2005 for a well-informed discussion of contraindications for examination with MRI). Two types of MR sequences are...
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