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Advances in MRI for 'cryptogenic' epilepsies

Nature Reviews Neurology volume 7, pages 99–108 (2011)Cite this article

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Abstract

Nearly one-third of patients with focal epilepsy experience disabling seizures that are refractory to pharmacotherapy. Drug-resistant focal epilepsy is, however, potentially curable by surgery. Although lesions associated with the epileptic focus can often be accurately detected by MRI, in many patients conventional imaging based on visual evaluation is unable to pinpoint the surgical target. Patients with so-called cryptogenic epilepsy represent one of the greatest clinical challenges in many tertiary epilepsy centers. In recent years, it has become increasingly clear that epilepsies that are considered cryptogenic are not necessarily nonlesional, the primary histopathological substrate being subtle cortical dysplasia. This Review considers the application of new advances in brain imaging, such as MRI morphometry, computational modeling and diffusion tensor imaging. By revealing dysplastic lesions that previously eluded visual assessments, quantitative structural MRI methods such as these have clearly demonstrated an increased diagnostic yield of epileptic lesions, and have provided successful surgical options to an increasing number of patients with 'cryptogenic' epilepsy.

Key Points

  • In drug-resistant epilepsy, the most important predictor of favorable surgical outcome is complete resection of the lesion detected by MRI

  • Epilepsies that are considered cryptogenic are not necessarily nonlesional

  • The most common histopathological finding in cryptogenic epilepsy is focal cortical dysplasia

  • Quantitative structural image analysis could reveal dysplastic lesions in patients considered to have cryptogenic epilepsy on the basis of visual evaluation by MRI

  • The continued development of new imaging modalities and computational methods aimed at revealing the so-called nonlesional epilepsies will enable surgery in an increasing number of patients

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Figure 1: High-resolution 3T axial sections showing FCD Palmini type IIb in the frontal lobe.
Figure 2: High-resolution 3 T MRI of a 16-year-old patient with drug-resistant cryptogenic frontal lobe epilepsy.
Figure 3: Individual voxel-based morphometry in a 20-year-old patient with cryptogenic epilepsy and a parietotemporal EEG focus.
Figure 4: Computational models of focal cortical dysplasia.

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Authors and Affiliations

  1. Department of Neurology and McConnell Brain Imaging Center, Neuroimaging of Epilepsy Laboratory, Montreal Neurological Institute and Hospital, McGill University, 3801 University Road, Montreal, H3A 2B4, QC, Canada

    Andrea Bernasconi, Neda Bernasconi, Boris C. Bernhardt & Dewi Schrader

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  1. Andrea Bernasconi
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  2. Neda Bernasconi
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  3. Boris C. Bernhardt
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  4. Dewi Schrader
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Contributions

A. Bernasconi and N. Bernasconi wrote the article, and contributed to the editing and reviewing of the article. All the authors provided contributions to discussions of the content, and A. Bernasconi, B. C. Bernhardt and D. Schrader researched data for the article.

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Correspondence to Andrea Bernasconi.

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Bernasconi, A., Bernasconi, N., Bernhardt, B. et al. Advances in MRI for 'cryptogenic' epilepsies. Nat Rev Neurol 7, 99–108 (2011). https://doi.org/10.1038/nrneurol.2010.199

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