An atypical case of two discrete hypermetabolic seizure foci on FDG-PET

Learning Objectives 1. To familiarize the readers with atypical presentations of epileptogenc foci on PET. 2. To emphasize the importance of fusing PET with MR imaging for optimal evaluation.

FDG-PET imaging has become a routine part of a multi-modality approach in patients undergoing pre-operative evaluation for seizure foci. Unlike the sequential ictal and interictal SPECT studies, FDG PET studies are only interictal. The ‘classic’ expected finding is a discrete focus of hypometabolism that should correspond to abnormal MRI findings and/or abnormal EEG findings. We present a case of a patient who had two discreet hypermetabolic foci which were subsequently proven to be the cause of her seizures. The clinical workup including MR imaging as well as the clinical course afterward will also be presented. The brain FDG PET study revealed an atypical finding of two hypermetabolic foci in the left frontal lobe. MRI prior to the PET study was read as normal. However, a software fusion of the PET and MRI images helped elicit a focal cortical abnormality on the MRI. A video EEG also showed corresponding laterality to the left side. The patient underwent surgical resection of these lesions, and continues to have a stable, seizure-free, post-operative clinical course. For referencec purposes, we present a companion case where FDG PET revealed a ‘classic’ hypometabolic focus. There are a few reported cases of patients with hypermetabolic foci as the cause of the seizures. These cases are rare, therefore Nuclear Medicine physicians should remain aware of the atypical presentations of seizure foci in FDG PET. Furthermore, this presentation highlights the value of a contemporaneous MRI as well as fusion of PET and MRI for reporting purposes