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Chapter 21

Neuroimaging of the epilepsies

FERGUS J. RUGG-GUNN

Department of Clinical and Experimental Epilepsy, National Hospital for Neurology and
Neurosurgery, Queen Square, London
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Introduction

Much progress has been made over the last 20 years in the structural and functional imaging
of the brain in epilepsy. The correlation of structure with function is essential in the
understanding of the epilepsies and epileptic seizures, which may have a structural basis.

MAGNETIC RESONANCE IMAGING

The superiority of magnetic resonance imaging (MRI) over X-ray computed tomography
(CT) scanning in terms of sensitivity and specificity for identifying the aetiology of epilepsy
in both adults and children is firmly established. The most common abnormalities identified
are hippocampal sclerosis (HS), malformations of cortical development (MCD), vascular
malformations, tumours, and acquired cortical damage. X-ray CT, however, may be preferred
to MRI if a patient is disturbed or acutely unwell, as the patient is more accessible during the
procedure. An X-ray CT scan is also valuable for the investigation of possible acute
intracranial haematomas and skull fractures, and if there is a contraindication to MRI such as
a cardiac pacemaker or cochlear implants. CT is also useful as a supplement to MRI for
clarification of possible intracranial calcification that is not shown easily by MRI.

The principal clinical applications of MRI are to identify the structural basis of epilepsy and
patients who are suitable for surgical treatment. Rapid advances are being made in MRI
techniques so that patients who were previously regarded as being ‘MRI negative’ may have
relevant abnormalities, which can be identified with contemporary optimal imaging.

MRI epilepsy protocol

Indications for neuroimaging of patients with epilepsy
The Neuroimaging Commission of the International League Against Epilepsy has produced
recommendations for this. The rationale for imaging the brains of patients developing
epilepsy is first to identify underlying pathologies such as vascular lesions, infections and
tumours that require specific therapy; and second to assist the formulation of syndrome and
aetiological diagnoses1. Further recommendations have been made for patients with
refractory seizures2 and for functional neuroimaging3.

In the non-acute situation an MRI scan should include T2-weighted, proton density and fluid
attenuated inversion recovery (FLAIR) sequences to cover the whole brain in at least two
orthogonal planes, with the minimum slice thickness possible. There should also be a T1-
weighted volume acquisition with a partition size of 1.5 mm or less, to allow reformatting in
any orientation and three-dimensional reconstruction of the data set. The FLAIR sequence
produces images in which parenchymal lesions have high signal and CSF gives low signal.
This may help in the differential diagnosis of areas of high signal on T2-weighted images and