MRIs of two patients with mesial (right) and lateral (left) temporal lobe epilepsy due to dysembryoplastic neuroepithelial tumours (DNET).
Left: Coronal FLAIR MRI showing a discrete ring-like lesion in the lateral aspects of the right middle temporal gyrus consistent with a small neoplasm. Pathology revealed a DNET.
Right: Coronal T1-weighted MRI showing a large DNET occupying the left hippocampal areas and adjacent mesial temporal lobe gyri and white matter.

Temporal lobe epilepsies comprise a heterogeneous group of disorders sharing the same topographical seizure onset (the temporal lobe), but often of diverse aetiology, age at onset, prognosis, and response to medical or surgical management. Anatomically they are broadly divided into those originating from the lateral or mesial regions of the temporal lobe (Figures 12.1 and 12.2). Mesial (or medial) is far more common (accounting for two-thirds of cases) than lateral temporal lobe epilepsy (LTLE). The most common of all is hippocampal epilepsy, which probably constitutes a disease with known pathology rather than a syndrome. Other causes of temporal lobe epilepsy, mesial or lateral, are benign or malignant tumours, viral and other infectious and parasitic diseases, cerebrovascular disorders, malformations of cortical development, trauma and other injuries

http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=epi&part=ch12