Abstracts

Rationale: Focal Cortical Dysplasias (FCDs) are frequently associated with intractable epilepsy and according to the current classification three different subtypes can be histopatologically distinguished (Blumcke et al, 2010). While FCD Type I and III are characterized by cortical dyslamination only, the histological hallmarks of FCD Type II consist in severe cortical laminar disorganization and the presence of abnormal cell types: dysmorphic neurons (DNs) and balloons cells (BCs). FCDs are assumed to be "epileptogenic" due to intrinsic structural disorganization but despite numerous neuropathologic reports, the modifications of circuital network remain to be unraveled. Aim of this study is to investigate and characterize dendritic abnormalities and neuronal morphology in surgical samples from drug-resistant epileptic patients presenting distinct histopathologic patterns. Methods: We examined specimens from patients presenting different types of FCDs (Type I/III and II) and from cryptogenic patients, in which imaging and neuropathological investigation did not reveal structural lesion. We performed immunohistochemistry (ICC) on paraffin sections using neuronal markers (NeuN, SMI) and glial/immature markers (GFAP, VIM). Tissue slabs adjacent to those processed for ICC, were processed for Golgi-Cox method (Zaqout and Kaindl, 2016). We evaluated: 1) the dendritic number, morphology, branching and orientation of neurons, 2) spine density and morphology. Results: In samples from cryptogenetic patients, pyramidal neurons appeared regularly oriented, with normal morphology and with recognizable basal and apical dendrites that can be traced for long distance. Conversely, neurons in FCD I/III had a disorganized appearance, exhibiting occasionally inversion or partial rotation. The organization of the apical/basal dendrites was normal but, despite the thickness of the sections (200 µm), the apical dendrites were followed only for short distance from the cell body suggesting a more tortuous course. In FCD II, neurons were deeply disarranged. DNs were clearly recognized by their bizarre morphology with increased dendritic branching complexity, number and thickness and complete disruption of the normal apical/basal dendrite organization. A dramatic reduction of spine density, both involving normal-appearing neurons and DNs, were observed in comparison to neurons in cryptogenic and FCD I/III samples. BCs were also recognized, characterized by enlarged soma and enormous branching of processes. Conclusions: Golgi method allows to visualize different neuronal cortical organization in tissues from cryptogenic patients or with different subtypes of FCDs suggesting possible circuital abnormalities involved in seizure generation and maintenance. In FCD II, the dendritic changes and the dramatic reduction of spines are particularly evident in comparison to the others groups. These data suggest that abnormalities in spine distribution and morphology might be an intrinsic aspect of this dysplasia and not a consequence of seizures.  Funding: Supported by: European Union grant FP7 (DESIRE) No. 602531, Italian Ministry of Health grant RF-2011-02350578, and the Associazione ‘‘Paolo Zorzi’’ per le Neuroscienze.