Purpose: Positron emission tomography (PET) has proven useful in epile
psy surgery for its ability to identify unilateral temporal hypometabo
lism (UTH), which is predictive of good surgical outcome. The signific
ance of bilateral temporal hypometabolism (BTH) is not known. Methods:
We identified all patients who had marked bilateral reduction in temp
oral lobe metabolism relative to the cerebellar hemispheres and compar
ed their clinical features and treatment outcomes with those of contro
l patients with UTH. Results: BTH was evident in 10% of PET scans for
epilepsy at our institution. We compared these patients with age-match
ed controls with UTH. The BTH patients had a higher percentage of gene
ralized seizures; were more likely to have bilateral, diffuse or extra
temporal seizure onsets; and had bilateral or diffuse magnetic resonan
ce imaging (MRI) findings. UTH patients were more likely to have unila
teral mesial temporal atrophy on MRI. Even when electrical seizure ons
ets were well localized, surgical outcomes were markedly worse in thes
e patients than in controls. Medical treatment was also less successfu
l. Social and cognitive functioning was worse in the BTH group. The on
ly death occurred in the group with BTH. Conclusions: Patients with BT
H have features distinct from those with UTH and have a worse prognosi
s for seizure remission after surgery.