Page 31 - scheppingen

NOVEL HISTOPATHOLOGICAL PATTERNS IN CORTICAL TUBERS IN TSC
Introduction
Tuberous Sclerosis Complex (TSC) is a genetic disease affecting about 1:6,000 live births 1. TSC is characterized by an age-dependent manifestation of primarily non-malignant tumors in many different organ systems 2. In TSC, almost 90% of the affected individu- als will suffer from recurrent seizures 3, and thus most patients are diagnosed after the onset of seizures in infancy or early childhood 2. Only about a third of patients can be treated successfully with anti-epileptic drugs. In the remaining individuals, resective sur- gery of the corresponding epileptogenic zone (EZ) may be considered 4. Defining the EZ is a major challenge in TSC patients since the EZ might not be restricted to one single tuber. Therefore, selected patients often undergo intracranial electroencephalography (EEG) evaluation to localize accurately the EZ and eloquent cortex prior to the deter- mination of the resection area. This procedure is an additional risk factor and burden to patients 5. After epilepsy surgery, 57% of patients achieve seizure freedom and another 18% show a significant reduction in seizure frequency at a minimum of one year fol- low-up 6. In addition to seizure freedom, psychomotor development may also improve 6. However, approximately 25% of patients have unfavorable outcomes after surgery, with ongoing seizures and, in about 3% of cases, major surgical morbidity 7. Therefore, it is urgent to identify those TSC patients who will significantly benefit from epilepsy surgery, and hence, there is a great need for a clear-cut definition of the EZ, based on imaging-, neurophysiological-, and source localization techniques.
TSC is caused by a mutation of either of two genes, TSC1 and TSC2, which encode the proteins TSC1 (hamartin) and TSC2 (tuberin), respectively 3. These proteins are involved in numerous regulatory processes via the regulation of the mTOR signaling pathway including cell growth, proliferation, migration and differentiation. In the first reported case series about 90% had cerebral manifestations, including cortical tubers 8. Histologically, cortical tubers present with a distorted cortical architecture, and contain dysmorphic neurons with aberrant Nissl substance and bright eosinophilic giant cells. It has been proposed that these aberrant cells play an essential role in epileptogenesis 9. However, recent data from intracranial recordings indicate that the perilesional cortex also plays an important role 10.
We examined cortical tubers and perituberal cortex samples using multiple bio- markers from TSC patients who previously underwent epilepsy surgery as a strategy to classify the histological severity of tubers and potentially aid with future evaluation of the EZ in TSC patients. Using quantitative histology and a dedicated imaging program, we assessed a number of cellular features, including mTORC1 activation, amount of neu- rons, dysmorphic neurons, calcification, gliosis, giant cells, vessels, inflammatory markers, myelin content and amount of oligodendroglial cells. The results were cross-referenced to clinical data, and analysed statistically.
Materials and methods
Subjects
We critically evaluated 28 tubers from whom we received anatomically well preserved, en bloc resected neocortical tissue and sufficient clinical data (Department of Pediatric Neurology, Brain Center Rudolf Magnus, University Medical Center Utrecht; Department of Pediatric Neurology, Charles University, 2nd Medical School, Motol University Hospital,
29
two