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Dysembryoplastic neuroepithelial tumour

Dr Yuranga Weerakkody and Dr Frank Gaillard et al.

Dysembryoplastic neuroepithelial tumours (DNET) are benign (WHO Grade I) slow growing tumours arising from either cortical or deep grey matter. The vast majority are centered in cortical grey matter, arise from secondary germinal layers and are frequently associated with cortical dysplasia (up to 80% of cases). They characteristically cause of intractable partial seizures (see temporal lobe epilepsy). 

Pathology

It is a mixed glial-neural neoplasm a multi-nodular architecture and a heterogenous cellular composition.

Location

The temporal lobe is the most common location, but all parts of the CNS containing grey matter are potential locations. 

Radiographic Features

CT
  • if cortical may scallop the inner table of of the skull vault (44-60%) but no erosion.
  • the cranial fossa can be minimally enlarged at times
  • calcification in 20 - 40% (more common histologically) 
  • low density
  • no enhancement
MRI

Typically seen as a cortical lesion with hardly any surrounding vasogenic oedema 

  • T1 - generally low signal
  • T2 - generally high signal with high signal 'bubbly appearance'
  • FLAIR - mixed signal intensity with bright rim sign. (see case 2) . This sequence is helpful in identifying the small peripheral lesions with simila
  • r intensity to CSF.
  • DWI - no restricted diffusion
  • GE (gradient echo) - haemosiderin staining uncommon as bleeding into DNETs is only occasional ; calcification is not infrequent
  • SWI -  areas of signal drop out may be seen. 
  • T1 C+ (Gd)
    • may show enhancement in ~ 20-30% of cases 5
    • enhancement may be heterogeneous or a mural nodule
  • MR spectroscopy - non-specific although lactate may be present

Treatment and prognosis

They demonstrate essentially no growth over time, although very gradual increase in size has been described. As expected prognosis is excellent and even though these lesions are often incompletely resected, tumour progression is uncommon. Additionally even in cases of incomplete resection, seizures frequently cease. 

Differential diagnosis

The differential diagnosis will depend on the location of the tumour. 

If in the mesial temporal lobe consider

See also temporal lobe tumours

If cortical consider

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