Histological heterogeneity of dysembryoplastic neuroepithelial tumour: identification and differential diagnosis in a series of 74 cases

Aims: In a retrospective study of resected specimens from 416 patients bein g treated for long-standing epilepsy 74 cases of dysembryoplastic neuroepit helial tumour (DNT) were encountered that were all characteristically compo sed of small round oligodendroglia-like cells (OLC), astrocytes and mature neurones in varying proportions. The architectural patterns, histological, immunohistochemical and ultrastructural features and results of cell prolif eration studies and postoperative follow-up are described to facilitate the identification of DNT and to differentiate it from other intrinsic neoplas ms that commonly present with seizures, Methods and results: The tumours presented with early onset of seizures, at a median age of 7 years, without the signs of raised intracranial pressure . A majority of the lesions were located in the temporal lobe (n = 59), wit h fewer cases in the frontal (n = 8), parietal (II = 6) and occipital lobes (n = 1), and ranged in size from 10 to 70 mm; 33 were cystic, Histological ly three types could be distinguished, multinodular, solitary nodular and d iffuse, The first type (37.8%) had the features of a typical DNT with multi nodular architecture and mixed cellular composition. The second type (33.8% ) consisted of a solitary nodule, while the third (28.4%) was a diffuse tum our, both composed of a similar mixture of cells as the multinodular DNT. T he lesions were seen in the neocortex and white matter and tumours in the t emporal lobe often involved the amygdala and hippocampus, The presence of m yxoid matrix, microcystic change, calcification and leptomeningeal involvem ent were common, Dysplastic neurones at the periphery of the tumour and abn ormalities in cortical lamination in the adjacent neocortex were found in a bout one-third of the resections. Rare mitotic figures were encountered in eight of the tumours and necrosis was found in two. Immunocytochemistry for glial fibrillary acidic protein (GFAP) and neuronal markers neuron-specifi c enolase, synaptophysin and neurofilament (RT 97) assists in establishing the diagnosis, highlighting the astrocytic and neuronal components, and the OLC, by the absence of expression of GFAP, Electron microscopy showed that in some cases OLC show neuronal differentiation. Although the proliferatin g cell nuclear antigen labelling index varied between 0 and 45.5%, 20 of th e 51 tumours stained failed to express the antigen, in keeping with the ind olent nature of this neoplasm. The response to surgery was excellent: none of the tumours have recurred, and the control of seizures remained good, Conclusions: Despite some histological heterogeneity, the clinical and path ological features and indolent biological behaviour indicate that these tum ours constitute a single distinct entity. The spectrum of morphological app earances of DNT is broader than has been previously reported, the recogniti on of which is needed to avoid unnecessary neoadjuvant therapy.