Case Author(s): J. Philip Moyers, MD. and Farrokh Dehdashti, M.D. , 7/28/95 . Rating: #D3, #Q4

Diagnosis: epileptic focus left temporal lobe

Brief history:

12-year old boy with history of complex partial seizures, poorly controlled with medications.


transaxial slices through temporal lobe

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Full history/Diagnosis is available below

Diagnosis: epileptic focus left temporal lobe

Full history:

12-year old right-handed boy who is seen with chief complaint of uncontrolled seizures, which first started at the age of approximately 15 monhts. Currently, his seizures are of a complex partial type, described as a blank stare with unresponsiveness, difficulty breathing, and aural/oral automatisms and hand automatisms.


F-18 fluorodeoxyglucose


PET brain study demonstrates a focus of hypometabolism in the left temporal lobe when compared to the right temporal lobe. The remainder of the PET study is within normal limits.


Complex partial seizures with a temporal lobe focus are common among epileptic patients. Imaging can be performed with CT, MRI, or PET. MRI is superior to radiographs and CT in identifying morphologic abnormalities in patients with epilepsy. Small areas of gliosis or small AVMs can be overlooked with CT examination. Also, heterotopic gray matter may also be missed by CT examination. A cause of complex partial seizures is mesial temporal sclerosis. In this pathologic entity, there is prominent hippocampal cell loss with atrophy of the medial aspect of the temporal lobe involved. In some patients with partial seizures, MRI may be normal or demonstrates a smaller temporal lobe without increased signal intensity on the side of the lesion. Therefore, interictal PET studies are helpful to evaluate for interictal cerebral metabolism. Studies of cerebral blood flow, metabolism, and neurotransmitter activity are felt to be more promising than structural imaging in the evaluation of patients with epilepsy who have negative or unequivocal MRI. Clearly, measurement of regional cerebral glucose metabolism has proved the most useful in evaluation of patients for seizure surgery. FDG-PET may avoid unnecessary invasive tests. Most studies demonstrate interictal hypometabolism in approximately 60-90% of patients with complex partial seizures. The degree of hypometabolism on the PET study is not related to the percentage of neuronal loss and, the hypometabolic regions are usually larger than the area of pathologic abnormality. For example in the patient with mesial temporal sclerosis where hippocampal cell loss is a prominent feature, hypometabolism involved the entire temporal lobe rather than just the medial aspect in the region of the hippocampal gyrus. In addition, hypometabolism may be seen in the ipsilateral basal ganglia and thalamus. Both qualitative and quantitative analysis of PET studies can be used to lateralize the abnormal temporal lobe for surgical resections, although it is unclear which approach should be used. In this patient, an MRI was performed which was interpreted as normal. Possibly, the long-standing changes of mesial temporal sclerosis may not have had time in this young patient to form a structural abnormality. This underscores the usefulness of PET studies in the evaluation of seizure foci in patients. with seizure disorder.

References: 1) Mazziotta JC, Gilman S. Clinical brain imaging: principles and applications. Philadelphia, PA: FA Davis Company, 1992. 2) Fisher RS, Frost JJ. Epilepsy. J Nucl Med 1991;32:651-659.


A follow-up EEG suggests a left temporal lobe seizure focus.

Major teaching point(s):

In the absence of an abnormal hippocampus on MRI, FDG-PET may be used to localize the abnormal temporal lobe.

ACR Codes and Keywords:

References and General Discussion of PET Brain (Nontumor) Imaging Studies (Anatomic field:Skull and Contents, Category:Organ specific)

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Case number: pb001

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