Delicate longitudinal nuclear grooves in childhood ependymomas

Nuclei of ependymal tumor cells have a pattern of delicate uniform, linear, longitudinal, excentric grooves or clefts, usually single, involving the nuclear membrane and extending at least half the nuclear diameter, producing a notched mitten-shaped nuclear outline, forming a pattern not seen in other neural tumors. Histologically, 13 of 14 childhood ependymal tumors had nuclear clefts. Using these clefts with other histologic criteria, ependymal tumors were identified at the time of surgery 11 of 11 times, with no false-positive results. Cytologically, eight of 10 ependymal and seven of 32 other brain tumors had clefts. These seven other tumors had either additional nonuniform convolutions or folds (n = 5) or had only rare clefts (n = 2). This uniform pattern of nuclear clefts may help identify poorly differentiated ependymal tumors on permanent sections and may help recognize ependymal tumors at surgery, guiding the surgeons' resection.