Case Author(s): Gregg Schubach\Barry A. Siegel , 8/8/95 . Rating: #D4, #Q4

Diagnosis: Hemimegelencephaly of the brain

Brief history:

3-month old girl who has been seizing approximately 50 times a day since birth.


Axial PET Images

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View second image(mr). MRI through basal ganglia

View third image(mr). Axial MRI image at a higher level

View fourth image(mr). Axial MRI near vertex

Full history/Diagnosis is available below

Diagnosis: Hemimegelencephaly of the brain

Full history:

3-month old girl referred for assessment of right hemimegalencephaly, diagnosed at the time of birth by MRI. The patient has approximately 50 seizures daily, which are characterized by deviation of the eyes to the left with horizontal nystagmus and, on occasion, deviation of the mouth to the left. Abnormal spike EEG changes have been recorded from the hemimegalencephalic and nonhemimegalencephalic hemispheres.


The PET images demonstrate overall decreased activity in the brain compared with the accumulation of FDG in the soft tissues of the face. This overall decrease in cortical activity is further confirmed when compared with the activity in the region of the basal ganglia bilaterally. There is a rind of relatively increased accumulation of FDG in the region of the frontoparietal and inferior frontal lobe on the right side. This corresponds with the abnormally enlarged gyri seen on the MRI study. The patient experienced a seizure within 30 minutes following the administration of FDG. The hypermetabolism seen in the frontal aspect of the hemimegalencephalic right hemisphere is compatible with the increased FDG uptake during the seizure or in close proximity to the recovery phase of this or other seizures noted to have occurred during the day of this study. The MRI, which was performed approximately 2-1/2 weeks prior to the PET study, demonstrates gyri to be abnormal in both number and configuration. Post- gadolinium images show contrast enhancement of the frontal and parietal regions compared with regions of normal parenchyma. The right cerebral hemisphere is enlarged when compared with the left. The frontal horn of the right lateral ventricle is enlarged. Foci of gray matter heterotopia are noted outlining the region of the left lateral ventricle.


Hemimegalencephaly is a developmental brain malformation characterized by congenital hypertrophy of one cerebral hemisphere and ipsilateral ventriculomegaly with associated epilepsy, hemianopsia, and varying degrees of developmental delay. PET is a noninvasive method used to study metabolism of the brain and has proved to be useful in the understanding of many neuropediatric syndromes and epilepsy. As described by Rintahaka, et al., PET can provide unique information that is useful in the management of patients with hemimegalencephaly. There was good correlation between CT/MRI and PET in delineating areas of abnormality on the side of hemimegalencephaly in their study of 8 children. However, PET clearly revealed that many brain regions, particularly on the nonhemimegalencephalic side, which appear to be normal structurally, were functionally abnormal.

Rintahaka P, Chugani H, Messa C, Phelps M. Hemimegalencephaly: evaluation with positron emission tomography. Pediatric Neurology 1993;9:21-8.


The patient subsequently underwent partial right hemispherectomy (fronto- parietal) two days following the PET study with subsequent resolution of all seizure activity.

ACR Codes and Keywords:

References and General Discussion of PET Brain (Nontumor) Imaging Studies (Anatomic field:Skull and Contents, Category:Normal, Technique, Congenital Anomaly)

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Case number: pb002

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