For any doctor looking after children with epilepsy, an essential skill is interpretation of the MRI. But, even in centers of imaging excellence, accurate clinical and EEG data are required to enable interpretation of an MRI abnormality or, alternatively, to allow a focused search for the common subtle abnormalities that may underlie symptomatic epilepsy. Brain imaging has become an essential part of the evaluation of most children with epilepsy. Yet, MRI has not taken over from the clinical basics. The pillars of a thorough evaluation of a child with seizures still remain; a good clinical assessment (detailed history and physical examination) supplemented by an interictal EEG.
As a consultant dealing with epilepsy, it is clearly a mistake to rely solely on imaging in the absence of good electroclinical data, ideally forming a diagnosis of the child's epilepsy syndrome. If the initial diagnostic question "Does this child have epilepsy?" is answered in the affirmative this should be followed by "what is the epilepsy syndrome?" The answer to the second question is the rational basis to determine which patients require brain imaging (Fig. 5–1).
Decision-tree for neuroimaging based on epilepsy syndrome.
This chapter will focus initially on the rationale, indications, and published clinical guidelines for imaging children with epilepsy. A brief discussion on the broad principles of optimal imaging methods for the epilepsy population will be followed by the application of imaging to more common specific clinical situations.
RATIONALE FOR IMAGING IN CHILDREN WITH EPILEPSY
The rationale for neuroimaging in epilepsy is summarized in a position statement by the Commission on Neuroimaging of the International League Against Epilepsy (ILAE) (1997).1,2 They provided two indications:
Diagnosis of Underlying Aetiology
"To identify underlying abnormalities such as vascular lesions, acute trauma and tumours that require specific treatment."
Syndrome Delineation and Prognosis
"To aid the formulation of syndromic and etiological diagnoses and to give patients, their relatives and physicians an accurate prognosis."
Other reasons for neuroimaging include:
Metabolic diseases diagnosable on MRI can present with focal seizures such as adrenoleukodystrophy or mitochondrial encephalopathy. Other acute, nonepilepsy disorders such as hydrocephalus, trauma, infection, stroke, and acute-disseminated encephalomyelitis can clearly lead to change in management.
Potential Genetic Implications
Apart from the above hereditable metabolic and neurodegenerative conditions that have obvious genetic implications, an important group are the malformations of cortical development. An increasing number of the more common abnormalities such as polymicrogyria now have an underlying genetic diagnosis. Well-characterized recessive and X-linked disorders explain the majority of patients with lissencephaly.