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The value of interictal diffusion-weighted imaging in lateralizing temporal lobe epilepsy

From the Epilepsy Center (T.W., P.L., W.B., R.A.P., P.R., B.D.), Brain Tumor Institute (E.L.P.), and Departments of Radiology (J.T., P.R.), Neurosurgery (W.B.), and Pathology (P.R.), Cleveland Clinic, OH. Dr. J. Tkach's current address is Department of Radiology, University Hospitals, Cleveland, OH.

Address correspondence and reprint requests to Dr. T. Wehner, Epilepsy Center–S10, Cleveland Clinic, 9500 Euclid Ave., Cleveland, OH 44195; e-mail: wehnert{at}ccf.org

Background: A subgroup of patients with nonlesional temporal lobe epilepsy (TLE) has no evidence of hippocampal sclerosis on standard temporal lobe protocol MRI.

Objective: To investigate whether interictal diffusion-weighted imaging adds lateralizing information in patients with TLE with and without lateralizing conventional MRI.

Methods: We studied 22 patients (9 right, 13 left TLE) who had undergone temporal lobectomy and 18 control subjects. We measured hippocampal volumes on high- resolution coronal magnetization-prepared rapid gradient echo scans. Apparent diffusion coefficients (ADCs) for the entire hippocampus and three arbitrarily defined areas of interest within the hippocampal head, body, and tail were measured from the coregistered ADC map. Pathology was reviewed and correlated with imaging findings.

Results: Fourteen of 22 patients had hippocampal atrophy on MRI (defined as volume asymmetry greater than 2 SDs compared with asymmetry in the control group). Overall, resected hippocampi (n = 22) were significantly smaller than contralateral hippocampi as well as ipsilateral hippocampi in controls. ADCs were significantly higher in resected hippocampi than contralateral hippocampi as well as ipsilateral hippocampi in controls. These differences were also observed within the three areas of interest. ADCs in the hippocampi contralateral to the epileptogenic zone (n = 22) were also higher than in ipsilateral hippocampi in controls. In the subgroup of eight patients with nonlateralizing conventional MRIs, ADCs of resected hippocampi were not significantly different compared with the contralateral side. Pathology in these patients revealed gliosis only without apparent neuron loss.

Conclusion: Interictal apparent diffusion coefficients confirm lateralization in patients with hippocampal atrophy on standard temporal lobe protocol MRI. However, they do not provide lateralizing information in patients with nonlateralizing conventional MRI.

Additional material related to this article can be found on the Neurology Web site. Go to www.neurology.org and scroll down the Table of Contents to the January 9 issue to find the title link for this article.

Disclosure: The authors report no conflicts of interest.

Received April 26, 2006. Accepted in final form September 18, 2006.

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January 9 Highlights

Neurology 2007 68: 86-87. [Full Text]