Dysembryoplastic neuroepithelial tumor (DNT): an ultrastructural study of six cases

We report six cases od DNT with a detailed ultrastructural characteristics. The patient age ranged from 7 to 16 years (mean 12), the location was temporal in three cases and frontal, temporooccipital and parietooccipital in each of one remaining cases. The predominant clinical feature in each case was history of episodes of intractable seizures. Histopathologically, the neoplasms were multinodular, each nodule was well-circumscribed and was composed of glioneuronal elements embedded in the variable amount of myxoid matrix. The oligodendroglial-like cells (OLC) predominated in the nodules with some accompanying mature neurons. The nodules were frequently surrounded by small calcifications which could be found also within the tumors. OLCs were immunoreactive for S-100 protein and neurons had the expression of synaptophysin and neurofilament proteins. Ultrastructurally, each tumor consisted of three major elements: neoplastic cells (OLC), elongated processes forming neuropil-like structure and expanded "mucoid" extracellular space: the latter gave an impression of cellular elements floating within it. Neoplastic cells had round, oval or elongated nuclei, no discernible nucleoli and a relatively narrow rim of the cytoplasm. Some nuclei were irregular and invaginated and pseudoinclusions were observed; a part of cytoplasm sequestered within pseudoinclusions often appeared degenerated with large blabs and electron-lucent vesicles, some of these contained in turn semicircular profiles of unknown significance. The second element consisted of innumerable cellular processes. Some of these were elongated and formed stacks connected by symmetrical symmetric or asymmetric adhesive plaque junctions. The others had shorter "neck" containing microtubules, these extended into bullous extensions. Dense-cored vesicles were occasionally observed, in both cytoplasm of neoplastic cells and within processes. In one cell, cross-sectioned annulate lamellae were found. In cytoplasm of a few cells, unusual inclusions reminiscent ribosome-lamellae complexes were observed. These were cylindrical resembling "laboratory tubes" with a cone-like endings. At higher power, walls of the "tubes" resolved into layered structures composed of several laminae; between laminae, ribosome-like structures were visible.