Incidental detection of hippocampal sclerosis on MR images: is it significant?

Abstract

Background and purpose: The prevalence of hippocampal sclerosis in the general nonepileptic patient population is not well described. While reports of its association with partial complex seizures are abundant, its absence in nonafflicted patients is generally presumed but not well documented. To test the hypothesis that hippocampal sclerosis is specific for epilepsy, we reviewed the MR imaging studies of 207 patients referred for hearing loss to determine whether high-resolution MR imaging could detect unsuspected hippocampal sclerosis in nonepileptic patients.

Methods: Our institution screens patients with hearing loss by using high-resolution coronal and axial temporal bone MR imaging that includes the hippocampus within the imaging volume. We retrospectively reviewed 207 studies randomly selected from this database.

Results: The hippocampus was normal in 205 patients; in the remaining two patients we identified one or more primary determinants for hippocampal sclerosis. Subsequent retrospective chart review revealed that both patients had had previously diagnosed seizure disorders.

Conclusion: The imaging determinants of hippocampal sclerosis are not prevalent in nonepileptic patients. Incidental identification of hippocampal sclerosis on MR images is uncommon and significant, and should prompt further clinical investigation to exclude a seizure disorder.

fig 1.

19-year-old nonepileptic patient with hearing loss. T2-weighted FSE (4000/80/3) image shows normal hippocampi bilaterally (arrows). Incidentally noted is a right acoustic schwannoma. fig 2. Case 1: 29-year-old woman with new seizure onset 17 months after AVM hemorrhage. T2-weighted image (4000/80/3) obtained using the screening ear protocol 17 months after initial AVM hemorrhage shows unilateral right hippocampal sclerosis (arrow) with ipsilateral temporal lobe volume loss. No confirmatory high-resolution temporal lobe imaging was performed because the patient was not considered to be a surgical candidate.

fig 3.

Case 2: 46-year-old woman with seizures. A, T2-weighted image (4000/80/3) obtained using the screening ear protocol shows unilateral left hippocampal sclerosis (arrow) with volume loss, poor delineation of internal architecture, and T2 hyperintensity. B and C, Subsequent dedicated high-resolution T1-weighted SPGR image (23/4, 45° flip angle) (B) and T2-weighted FSE image (4860/100/2) (C) confirm hippocampal sclerosis (arrows). There is no forniceal volume loss.