Abstracts

Rationale: Hypothalamic hamartomas (HH) are benign, congenital tumors that arise in the ventral hypothalamus, associated with treatment-resistant epilepsy. HH are usually symptomatic in early childhood with gelastic epilepsy, and at later ages, with multiple seizure types. Surgical resection is effective for controlling seizures in many patients. The HH lesions are intrinsically epileptogenic, although the mechanisms responsible for generating seizures are unknown. HH tissue is known to contain both small (8-12μm) and large (20-30μm) neurons, often occurring in clusters (Coons SW, et al, J Neuropathol Exp Neurol, 2007). Our aim is to further define the microanatomy of human HH by quantifying total nucleated cell and total neuron densities with the use of design-based stereology on surgically-resected tissue. Methods: We studied HH tissue from 3 patients (2 females; age range 1.8 - 11.3 years). HH tissue was formalin-fixed and frozen. Tissue blocks were cut into 50μm sections with random orientation. At least 3 sections were counted for each subject for each stain. Counting grids of 250μm x 250μm with dissectors of 50μm x 50μm were used. For all dissectors, the depth was 25μm with a 2.5μm guard height. The total counting volume for each box was 5 x 10^4μm3. Total nucleated cell counts were determined on sections stained with hematoxylin and eosin (HE), and total neuron cell counts were determined on sections immunostained with anti-neuronal nuclei (NeuN) antibody. Results: Results illustrated in table below. Conclusions: These initial results suggest that individual HH cases differ slightly in cellular density, but may have a more consistent relationship between total neuron and total cell number (16% of all HH cells are neurons). Accordingly, quantitative technique suggests that neurons may be less abundant than previously thought (Coons SW, et al, J Neuropathol Exp Neurol, 2007). Further studies will differentiate and quantify HH neurons on the basis of cell size and expression of phenotypic markers relating to cell lineage, maturity, and neurochemistry. Stereology provides a quantitative analysis of the constituent cells of HH tissue, a prerequisite to the development of a comprehensive model for intrinsic epileptogenicity.