Brain Imaging in Multiple Sclerosis _Computed Tomography

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Similar to radiography, computed tomography (CT) scanning has had a limited role in the diagnosis of MS and in the treatment of patients since the advent of MRI. CT scans may be used to exclude other causes of neurologic impairment, but they have a low positive predictive value in the diagnosis of MS; thus, the false-negative rate is high.
Prior to the use of MRI, CT scanning, with the injection of double or triple doses of intravenous contrast material, was used in attempts to identify active MS lesions. However, the scans were insensitive for the detection of chronic lesions. CT scans can help in assessing the degree of cerebral atrophy associated with advanced MS, but given the plethora of additional information provided by MRI, CT is no longer used for this purpose.
An acute MS lesion may enhance and appear simply as an enhancing white matter lesion on CT scans, but the appearance is highly nonspecific. When a highly active MS lesion is observed to enhance and possibly exerts mass effect, it can be termed tumefactive (due to the potential for misidentification as a tumor). Because CT scans typically do not help to identify the more chronic lesions, the tumefactive MS lesion may appear as a solitary enhancing mass, which leads to neurosurgical intervention. Fortunately, this situation is relatively uncommon.
In a cohort of 200 patients, Paty et al found that of the 19 who went on to develop clinically definite MS (CDMS), abnormal CT findings were demonstrated in only 9 (47%). In contrast, abnormal MRI findings were demonstrated in 18 (95%). All of the abnormal CT findings were also demonstrated on MRIs.