Typically temporal lobe,subfrontal area,cingulated gyrus and insular cortex
Cerebral convexity,posterior occipital area may be involved.
Typicallly bilateral but asymmetric.
Basal ganglia usually spared.
CT SCAN
Early often normal.
Late acute and subacute patchy or gyriform enhancement of the temporal lobe
Hemorrhage typically late feature
MRI:
Most sensitive for early diagnosis.
T2 WI:Hyperintense signal in bilateral temporal lobes,subcortical white matter ,cingulate gyrus
FLAIR Hyperintense signals ,may see changes earlier than T2WI.
DWI:Restricted diffusion is the most sensitive sequence.
DIFFERENTIAL DIAGNOSIS:
Cerebral ischemia/infarction:
Typical vascular territory( ACA/MCA/PCA)
Acute history
Limbic encephalitides:
Rare paraneoplastic syndrome often primary tumor lung
Limbic system often bilateral ,not hemorrhagic
Onset weeks to mnths vs acute in HSE.
Other Encephalitides:
Limbic system not involved.
Infiltrating neoplasm:
Low grade glioma often involve medial temporal lobe
Gliomatosis cerebri involve frontal and temporal lobe
Onset indolent.