An assessment of the proliferative potential of ‘balloon cells’ in focal cortical resections performed for childhood epilepsy

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Abstract
Cerebral cortical dysplasia is an uncommon pathological substrate of severe intractable childhood epilepsy, sometimes treated by hemispherectomy. Neuropathological findings include abnormal gyrus formation, loss of cortical lamination, unusual giant neurons and 'balloon cells' of indeterminate histogenesis similar in appearance to neoplastic gemistocytic astrocytes. In order to investigate the proliferative potential of 'balloon cells', we used Crocker's silver impregnation technique to demonstrate nucleolar organizer regions (AgNORs) involved in cellular proliferation, together with immunohistochemical evaluation of proliferating cell nuclear antigen (PCNA) expression. Balloon cells (5.56 +/- 0.24) had significantly (P < 0.001) greater AgNOR numbers than reactive astrocytes (3.89 +/- 0.15), neurons (2.30 +/- 0.13) or giant neurons (4.26 +/- 0.20). However, when corrected for nuclear size, results showed that 'balloon cells' (0.093 +/- 0.006) had significantly (P < 0.001) fewer AgNORs/square micrometre of nuclear area than reactive astrocytes (0.225 +/- 0.016) and had significantly (P < 0.001) more AgNORs/square micrometre of nuclear area than normal (0.048 +/- 0.003) or giant neurons (0.054 +/- 0.003). On the assumption that astrocytes are typical interphase cells and that normal neurons are post-mitotic, the results suggest that 'balloon cells' are unlikely to be undergoing proliferative activity and, when adjusted for nuclear size, the number of AgNORs/unit of nuclear area is more reflective of cellular ploidy than of proliferative activity in non-neoplastic neural tissues. The virtual absence of PCNA expression by 'balloon cell' nuclei supports such an interpretation of the AgNOR results.