American Journal of Neuroradiology 22:1291-1299 (8 2001)
© 2001 American Society of Neuroradiology
ARTICLE
18F-Fluorodeoxyglucose Positron Emission Tomography and MR Imaging Findings in Rasmussen Encephalitis
a From the Department of Radiology (D.J.F., J.M.P, R.E.C., A.A-S.), Duke University Medical Center, Durham, NC, and the Department of Pathology (B.J.C.), The Johns Hopkins University School of Medicine, Baltimore, MD.
BACKGROUND AND PURPOSE: Rasmussen encephalitis is a chronic, progressive encephalitis that manifests as an abrupt-onset, intractable seizure disorder in previously developmentally normal children. The objectives of the current study were to characterize the 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) and MR imaging findings in Rasmussen encephalitis and to test the hypotheses that data from both imaging techniques are required to establish the diagnosis and identify the affected cerebral hemisphere in some cases.
METHODS: Eleven patients with Rasmussen encephalitis were identified from a review of a computer database. The MR (n = 10) and PET (n = 11) imaging data were reviewed retrospectively and conjointly.
RESULTS: On MR images, nine of 10 patients manifested bilateral cerebral atrophy that predominantly involved one hemisphere. One patient had purely unilateral cerebral atrophy. We observed foci of abnormally increased T2 signal intensity in nine of 10 patients. On FDG PET images, all patients showed extensive regions of hypometabolism within the cerebral hemisphere that showed the greatest atrophy. Discrete foci of hypermetabolism, indicative of seizure activity, were observed in six patients. The FDG PET and MR imaging findings were either stable or gradually progressive in patients with multiple imaging studies (MR, n = 5; FDG PET, n = 5).
CONCLUSION: Rasmussen encephalitis is characterized by diffuse, unilateral cerebral hypometabolism on FDG PET images, with corresponding regions of cerebral atrophy on MR images. Although MR imaging data alone are sufficient to suggest a diagnosis of Rasmussen encephalitis in many cases, correlation with FDG PET data increases diagnostic confidence and allows the unequivocal identification of the affected cerebral hemisphere in patients whose MR imaging findings are subtle or distributed bilaterally.
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