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    Dysembryoplastic neuroepithelial tumor
     Key features:
 
Clinical: child or young adult with long standing refractory seizures
Location: classic cases are located in the medial temporal lobe
Imaging: single or multiple, limited to cortex (no white matter involvement) without mass effect or surrounding edema.
Histopathology: oligodendroglial-like cells arranged loosely in columns perpendicular to the cortex with microcystic spaces containing 'floating neurons;' often associated dysplasia in the adjacent cortex


Differential diagnosis:
Oligodendroglioma
Central neurocytoma

Etiology:  
Likely malformative lesion

Clinical:  
Typically occurs in the setting of long standing, drug resistant, partial seizures beginning in childhood

Radiology:  
Well demarcated 'bubbly' lesion in the medial temporal lobe, limited to the cortex, and sometimes multiple foci
Usually non-enhancing; 20% of cases may show faint patchy enhancement
No or minimal mass effect (unless cystic)
No or minimal edema
Deformation of overlying calvarium in some cases supports the diagnosis

Histopathology:  
Specific glioneuronal element consists of columns of oligodendroglial-like cells oriented perpendicular to the cortex along axons. Scattered well-formed neurons, so called floating neurons, are present in the intersitial spaces.
Typically multiple tumor foci that by strict definition are limited to the cortex without involvement of underlying white matter
Microcysts and dysplasia in the cortex adjacent to the tumor are common.
Marked nuclear atypia of the degenerative type may be present

Immunohistochemistry:  
Astroglial, oligodendroglial and neuronal elements may be present with corresponding variable staining patterns
Mib-1 proliferative rate less than 5%.

Prognosis:  
Recurrence is rare, even in partially excised cases.
Seizures may recur.
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Dysembryoplastic neuroepithelial tumor
Dysembryoplastic neuroepithelial tumor
Dysembryoplastic neuroepithelial tumor: two separate nodules
Dysembryoplastic neuroepithelial tumor: encorporated neuron
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