Abstracts

Rationale: The presence of hippocampal sclerosis (HS) on MRI has a great impact on the clinical evaluation and counselling of patients with temporal lobe epilepsy (TLE) and is considered as a key criterion for the decision to recommend epilepsy surgery. However, neuropathological studies describe evidence of HS in up to 10% of non-epileptic individuals, thereby challenging the impact of this MRI finding in patients with TLE. We evaluated the prevalence of HS on 1.5T MRI in the general population. Methods: 100 healthy subjects and 10 patients with TLE due to HS were investigated in a prospective study using a specific protocol for the detection of hippocampal pathology (coronal FLAIR, coronal T2 TSE and a T1 weighted 3D SPGR sequence). Results: None of the healthy subjects had HS on MRI, resulting in a prevalence of 0% - 3.6% in the general population. Hippocampal sclerosis was diagnosed in all patients. Inter-rater agreement was perfect for presence of HS. Thirty-three subjects had a unilaterally enlarged temporal horn as an isolated secondary criterion for HS and inter-rater agreement was slight for this point. Incidental pathological findings were detected in two patients (2%): One had a low grade astrocytoma (1%), one an aneurysm of the posterior communicating artery (1%). Conclusions: HS was not diagnosed in healthy subjects, supporting its impact on the evaluation of patients with temporal lobe epilepsy. A unilateral enlarged temporal horn that occurred in one third of the healthy subjects should not be considered as a pathologic finding or even as a marker for HS.