Mesial temporal sclerosis

Mesial temporals sclerosis (MTS) also commonly referred to as hippocampal sclerosis, is the most common association with intractable temporal lobe epilepsy (TLE) ^2-3. It is seen in up to 65% of autopsy studies, although significantly less on imaging.

Demographics and clinical presentation

Febrile seizures

The relationship, if any, of MTS with febrile seizures is controversial, made all the more difficult due to the relative insensitivity of imaging and the difficulty in establishing whether a particular seizure was truly febrile. Up to a third of patients with established refractory TLE have a history of seizures in childhood at the time of fever ³. Follow up of children with febrile seizures does not demonstrate significant increased incidence of TLE ³.

Pathology

Controversy exists as to the causative mechanism: is MTS a result of TLE or visa versa. In children with newly diagnosed epilepsy, ≈ 1% have evidence of MTS on imaging ³. In adults 10 - 20% are bilateral even though symptoms may be unilateral

The hippocampal formation is not uniformly affected, with the dentate gyrus and the CA1, CA4 and to a lesser degree CA3 sections of the hippocampus being primarily involved ⁴. Histologically there is neuronal cell loss, gliosis and sclerosis. 

Radiographic features

MRI

MRI is the modality of choice to evaluate the hippocampus. Angled coronal sequences at right angles to the longitudinal axis of the hippocampus are required, to minimize volume averaging. Findings include ⁴ :

• reduced hippocampal volume
• increased T2 signal
• abnormal morphology

When severe and long standing, additional associated findings include  ⁴ :

• atrophy of the ipsilateral fornix and mamillary body
• increased signal and or atrophy of the anterior thalamic nucleus
• atrophy of the cingulate gyrus
• increased signal and / or reduction in volume of the amygdala
• reduction in volume of the subiculum
• ipsilateral cerebral hypertrophy
• contralateral cerebellar hemiatrophy

Nuclear medicine

SPECT and PET imaging are also a useful adjuncts, with both ictal and inter-ictal scans demonstrating abnormalities

• ictal scan : hyper perfusion
• inter ictal scan : hypo perfusion

Other causes of temporal lobe epilepsy (TLE) should be considered, especially as small temproal lobe cortical tumours can have similar appearances.

Treatment

TLE is initially managed medically with anti-epileptic agents. In patients who are refractory to medical management temporal lobectomy or selective amygdalohippocampectomy may be performed.