NQ-135: (A) These tumors are usually seen in older adults (over 40 years old)

Diagnosis: Dysembryoplastic neuroepithelial tumor (DNET), WHO grade I

Pathology of the case: There are 3 salient features in this image. First, it is composed of two populations of cells with the smaller ones suggestive of glial cells and the larger one suggestive of ganglionic neurons (white arrows). Second, the background is rather mucoid and microscopic mucoid cysts are common. Third, many of the ganglionic neurons seems to be floating in the mucoid materials. On immunohistochemistry, the ganglionic cells are positive for neurofilament proteins and their long cytoplasmic processes are well illustrated here. 

DNET is typically seen in infant and children and the most common presentation is intractable seizure. These tumors are often found in the mesial temporal lobe and tend to be cortical based. Due to its high mucoid content, they are often solitary, hyperintense well-circumscribed mass on T2-weighted images.

There are three major cell types. The  oligodendroglia-like cells: They are small cells with round to oval hyperchromatic nuclei with perinuclear halo and small inconspicuous nucleoli and scanty cytoplasm. These cells are S100 positive and GFAP negative. Large ganglion cells are often found in the lesion and in the adjacent cortex. It is very common to see these ganglionic cells floating in the mucoid background. Astrocytes are present and may present as nodules resembling fibrillary astrocytoma and pilocytic astrocytomas. Specific glioneuronal element is the histological hallmark of DNETs. Specific glioneuronal elements are columns that are perpendicular to the cortical surface. They are formed by bundles of axons lined by small oligodendroglia-like cells. In between these columns are pools of mucoid material that are alcian blue positive. Large ganglion cells often float within these muoid pools. Dysplastic cortex are sometimes found in the surrounding brain.