Evaluation of MRI criteria (1.5 T) for the diagnosis of hippocampal sclerosis in healthy subjects.

PURPOSE: 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, questioning the impact of this MRI finding in patients with TLE. We evaluated the prevalence of HS on 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: HS was detected in none of the healthy subjects (95% confidence interval=0-3.6%), but in all patients. Inter-rater agreement was perfect for presence of HS. Thirty-three subjects had an 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. An 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.