Specific Imaging Findings

Hippocampal sclerosis (HS) is defined by volume loss and T2 hyperintensity of the affected hippocampus. The atrophy may be of a variable degree and is frequently accompanied by more subtle signs: loss of internal architecture; atrophy of the ipsilateral parahippocampal gyrus, fornix, and mammillary body. Dedicated high-resolution FLAIR imaging in the oblique coronal plane perpendicular to the hippocampus is the single best technique to diagnose HS. Heavily T1-weighted inversion recovery images demonstrate the loss of volume and internal architecture. There is no contrast enhancement. Asymmetric bilateral hippocampal atrophy, and even symmetric bilateral involvement may be found in some cases. “Dual pathology”, the coexistence of HS with another epileptogenic focus, is reported in 10–20% of surgical epilepsy patients, prompting search for possible additional foci.

Pertinent Clinical Information

HS, also known as mesial temporal sclerosis (MTS), is the most common abnormality in adults with refractory seizures. Patients have a history of intractable partial complex epilepsy and the treatment is partial temporal lobectomy, typically with open surgery. Resection leads to positive outcome when MRI and EEG findings are concordant, or if both volume loss and T2 hyperintensity are present without EEG correlation. Hyperperfusion in the ipsilateral mesial temporal lobe may be observed with ictal SPECT, while hypometabolism is found on inter-ictal FDGPET; again, concordance with MRI correlates with better surgical outcomes. Lateralization of memory and language is ascertained before surgery, with a Wada test or f-MRI.