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CLINICAL OVERVIEW

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Tuberous sclerosis complex (TSC) is an inherited neurocutaneous disease of cell differentiation and proliferation affecting multiple organs with hamartomas or abnormal neuronal migration. It was first described by Bourneville in 1880, and the incidence of tuberous sclerosis in the population is reported to be 1/6000 to 1/10,000.1,2 Cortical tubers and subependymal nodules (SEN) are the hallmark pathological findings in children. TSC is caused by aberrant neuronal migration and differentiation. Radial glial fibers guide migration of neurons during development from the 3rd to 5th month of gestation, and if there is a disruption in one tract, hamartomas may develop. This process of abnormal differentiation also explains the occurrence of hamartomas outside the CNS.3

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Tubers and other migrational defects typically arise in the cerebrum rather than the cerebellum or brainstem, although subcortical involvement occurs rarely. It is unknown whether seizures originate from dysplastic neurons or neurons in surrounding cortex. Tubers form during gestation, and all brain tubers do not change in number or location during postnatal life. Pathological examination of cortical tubers reveals sclerotic white patches within the gyri and few neurons. Most neurons are large and bizarrely shaped with 2–3 nuclei located peripherally and prominent nucleoli. Fibrillary astrocytic proliferation and large glial cells are also present.4

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Magnetic resonance imaging (MRI) scans are better in defining tubers than computerized tomography (CT) scans. Tubers occur at the cortical gray white interface and are most frequent in the parietal and frontal lobes. Calcification is less common in tubers than in subependymal nodules (SEN). Myelination helps distinguish tubers from white matter and, tubers therefore become more evident in older children. T2 weighted imaging and fluid attenuation inversion recovery imaging (FLAIR) is more accurate for viewing tubers compared to T1 imaging.5 In children, tubers are hypointense on T1 weighted imaging and hyperintense on T2 weighted imaging and FLAIR. FLAIR also provides better resolution of small subcortical tubers but is not useful for SEN due to CSF flow artifact caused by the inflow of noninverted CSF especially at the foramen of Monroe. White matter radial lines occur in 20–30% of patients and consist of hyperintense linear lesions perpendicular to cortex that extend to the periventricular white matter on T2 weighted imaging.5

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SEN do not cause seizures and are located in the anterior lateral ventricles. They are hamartomas composed of round or oval cells with whorls of fibrillary glial tissue and deposition of amyloid or calcification within the nodule and usually lie around the foramen of Monroe adjacent to the ventricle.6 SENs are less than 1 cm and rarely enhance. On MRI, SENs are better seen on T1 weighted images as the lesions are isointense to white matter and hyperintense to gray matter. SENs calcify with age and are well visualized on CT scans in adults.5,7

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SEN may enlarge over time and may transform into a ...

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