Neuroimaging in the Evaluation of Epilepsy

Naymee J. Velez-Ruiz, MD; Joshua P. Klein, MD, PhD2

Disclosures

Semin Neurol. 2012;32(4):361-373. 

In This Article

Neurocutaneous Disorders

The neurocutaneous syndromes are a group of unrelated disorders characterized by congenital dysplastic abnormalities involving the skin and nervous system. Seizures are encountered most frequently in tuberous sclerosis complex (TSC) and Sturge-Weber syndrome.

TSC is a multisystem, autosomal dominant, genetic disorder with wide phenotypic variability. Brain involvement occurs in 95% of individuals with this condition. Approximately 80–90% of patients develop epilepsy attributable to the neuroanatomic abnormalities associated with TSC, including cortical tubers, subependymal nodules (SN), and subependymal giant cell astrocytomas (SGCA) (Fig. 4).[94] However, the exact pathophysiology of epilepsy in TSC is not well understood.

Figure 4.

Tuberous sclerosis complex in an 8-year-old boy with mental retardation, autism, and epilepsy. Seizure types include infantile spasms, drop attacks with loss of consciousness, and tonic spells. (A,B) Axial T2-fluid attenuated inversion recovery magnetic resonance imaging (FLAIR MRI) shows innumerable hyperintense cortical tubers. (C) Axial T1-magnetization-prepared rapid acquisition gradient echo (MPRAGE) MRI shows subependymal nodules (arrows).

The SN are usually multiple and lie in the lateral ventricles, typically near the body of the caudate or foramen of Monro. They are often less than 1 cm in diameter and do not enhance with contrast. Calcification of SN is common after 18 months of age. On T1WI, SN are isointense to white matter and slightly hyperintense compared with gray matter. They are isointense or hypointense on T2WI, which may show a central area of decreased signal. Overall, SN are better seen on T1WI, whereas cortical tubers are better seen with T2WI.[95] Cortical tubers appear on MRI as multifocal areas of increased T2 signal affecting the cerebral cortex, deep white matter, or most often, both white matter and cortex. SGCA may occur in up to 8% of patients, typically near the foramen of Monro. They are believed to originate from SN, but are differentiated from these by their larger size and contrast enhancement. Patients may also have heterotopic masses of gray matter, consistent with the concept that TSC is a dysplastic process.

In a large number of patients with TSC, epilepsy proves to be refractory to medical treatment. Presurgical evaluation is typically complex due to the presence of multiple intracranial abnormalities with epileptogenic potential. PET scans may reveal hypometabolic cortical lesions corresponding to cortical tubers, and it may also show hypometabolic areas without abnormalities visualized on MRI.[96] In the same fashion SPECT and MEG can be used in the search for the epileptogenic lesion.[97,98]

Sturge-Weber syndrome (encephalotrigeminal angiomatosis) is characterized by a congenital unilateral cutaneous hemangioma (facial port wine stain), hemiplegia, and epilepsy. Neurologic involvement results from the effects of chronic ischemia of the cortex, which is produced by "vascular steal" due to overlying leptomeningeal venous angioma.[99,100] This phenomenon results in cortical atrophy and intracortical calcifications (Fig. 5), which produce the classic tram-track appearance on CT. MRI detects a greater extent of disease than CT, particularly on contrast-enhanced images.[99] In this instance, the pia enhances dramatically, giving a true demonstration of the degree of the vascular abnormality. Cortical enhancement caused by ischemic injury may also be present. Abnormally low signal intensity within the white matter on T2WI is probably related to abnormal myelination from ischemia.[101] Focal perfusion defects are identified on SPECT studies and, PET scan reveals areas of hypometabolism corresponding to the location of the lesions.[99] However, due to the extensive nature of the vascular abnormality, the surgical options for refractory epilepsy are limited, and restricted mostly to hemispherectomy, and in some bilateral cases, corpus callosotomy.

Figure 5.

Sturge-Weber syndrome. A 30-year-old right-handed man with simple partial seizures that began at 7 months of age, involving stiffening and shaking of the left arm without loss of consciousness. (A) Axial T2-fluid attenuated inversion recovery magnetic resonance imaging (FLAIR MRI) shows a large region of right parietal cerebral atrophy. (B) Axial T1-weighted MRI following intravenous administration of gadolinium shows abnormal cortical enhancement, consistent with pial angiomatosis. (C) Axial computer tomography (CT) without contrast shows marked "tram-track" calcification of the cortical gyri.

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