Unenhanced CT should be first test for adults with new-onset seizure

For adults with a new-onset seizure, what neuroimaging test, if any, should initially be performed to prevent serious complications or emergency intervention? A new analysis published in the American Journal of Roentgenology recommends unenhanced CT with MRI as a supplementary technique for patients presenting whose CT is negative and those in the non-acute setting.  

Ten percent of adults will experience a seizure during their lifetime, wrote lead author Eric Tranvinh, MD, of the Department of Radiology at Stanford University, and colleagues. For their analysis, the authors reviewed research regarding the role of CT and MRI in the evaluation of adult patients with new-onset seizure between 1977 and 2018, noting that patient history and a physical and neurologic examination are key factors to consider.  

“The presence of a focal neurologic deficit on physical examination is the most consistently reported clinical finding associated with abnormalities at neuroimaging in adults presenting to the emergency department with first seizure,” Tranvinh et al. wrote. “The clinical evaluation of patients with first seizure, however, can be challenging.”  

The authors noted that the main role of neuroimaging in new-onset seizure is to determine whether it was caused by an intracranial legion. 

“In the acute setting, imaging is done to exclude an immediately treatable cause, and this is typically accomplished using CT,” the authors wrote. “A second role of imaging is prognosis, and in some cases, establishment of a diagnosis of epilepsy under the revised practical definition of epilepsy.”  

Overall, Tranvinh and colleagues explained that extensive recent research suggests CT should be used first although the addition of IV contrast material has little benefit in improving CT sensitivity. However, the authors noted that MRI can be used supplementary when the case allows.   

Additionally, the authors reviewed guidelines issued by the American Association of Neurology in 2007, indicating that CT is useful for patients presenting with apparent unprovoked seizure, and the American College of Emergency Physicians in 2004 stating that CT or MRI can be helpful for patients in the emergency department. The American College of Radiology (ACR) appropriateness criteria for new onset seizure, however, recommends MRI as the modality of choice in a non-acute setting.  

Though research on MRI to specifically address new-onset seizure was limited, the authors explained it can provide use in outpatient and inpatient settings for guiding drug therapy and detecting tumors missed on CT.  

“In the inpatient setting, one study showed that MRI detects subtle structural lesions missed at CT that could explain the first seizure presentation,” the authors wrote. “Although MRI results did not acutely affect patient management in this study, it is our opinion that MRI can still potentially achieve the secondary goal of neuroimaging in new-onset seizure of determining prognosis and recurrence risk; more studies are needed to evaluate the value of MRI in this setting.”