Imaging in epilepsy
- The MRI Unit, The National Society for Epilepsy and the Department of Clinical and Experimental Epilepsy, Institute of Neurology, University College London, London, UK
- Correspondence to: Professor John S Duncan Department of Clinical and Experimental Epilepsy, Institute of Neurology, Queen Square, University College London, London WC1N 3BG, UK;
- magnetic resonance imaging
- positron emission tomography
- temporal lobe epilepsy
- seizure focus
- single photon emission tomography
The epilepsies are common serious diseases of the brain, with an age adjusted prevalence of 4–8/1000 and an annual incidence of 20–50/100 000 in developed countries. Modern neuroimaging is central to the assessment of patients with epilepsy and has dramatically modified their management. Magnetic resonance imaging (MRI) can identify substrates underlying epilepsy, and guide clinicians in the determination of treatment and prognosis. The use of x ray computed tomography (CT) has been diminished by the superior sensitivity and specificity of MRI. The results of all imaging studies should be correlated with clinical and neurophysiological data.
Epilepsies and epileptic syndromes are classified into focal and generalised. Seizures of focal origin begin in a specific cerebral area or network, most commonly in the temporal lobes. Focal epilepsies comprise 40–60% of all newly diagnosed cases. Up to 30% of these patients develop intractable epilepsy despite antiepileptic drug treatment. In patients with chronic intractable temporal lobe epilepsy (TLE) surgical treatment with removal of the epileptogenic lesion is vastly superior to medical treatment. Results in extratemporal epilepsy have been less favourable, particularly if there is not a discrete underlying structural abnormality. Therefore, visualisation of lesions that give rise to focal epilepsy and identification of patients who are suitable for surgical treatment are important goals in the imaging of epilepsy.
X RAY COMPUTED TOMOGRAPHY
In the modern imaging of epilepsy CT is supplementary. CT is useful in acute situations when the suspected underlying cause of seizures is a neurological insult such as intracerebral haemorrhage, or abscess, and MRI is not readily available or cannot be acquired. Focal cortical calcifications can be identified with CT, and scanning may provide complementary information for the diagnosis of tuberous sclerosis and Sturge-Weber syndrome. CT is not as sensitive or specific as MRI in identifying common epileptogenic abnormalities, such as small tumours, vascular malformations, malformations …