Dysembryoplastic neuroepithelial tumor
Dysembryoplastic neuroepithelial tumors (DNET) are benign (WHO Grade I) slow growing tumors 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 intractable partial seizures (see temporal lobe epilepsy).
Typically these tumors are diagnosed in children or young adults, as a result of the investigation of seizures.
Patients with DNETs typically present with longstanding treatment resistant partial seizures without associated or progressive neurological deficit 5.
It is a mixed glial-neural neoplasm a multinodular architecture and a heterogeneous cellular composition. Three histological forms are recognized 5:
- specific glioneuronal element (SGNE) only
- same clinical and neuroimaging features as complex DNET, but...
- no specific glioneuronal element (SGNE)
The temporal lobe is the most common location, but all parts of the CNS containing grey matter are potential locations.
- temporal lobe: over 60% of cases
- frontal lobe: 30% of cases
- caudate nucleus
- cerebellum: presentation is then more commonly with ataxia rather than seizures
DNETs are typically predominantly cortical and well-circumscribed tumors.
- if cortical may scallop the inner table of the skull vault (44-60%), but no erosion
- the cranial fossa can be minimally enlarged at times
- calcification in ~30% (more common histologically)
- low density
- no enhancement
Typically seen as a cortical lesion with hardly any surrounding vasogenic edema.
- generally hypointense c.f adjacent brain
T1 C+ (Gd)
- may show enhancement in ~20-30% of cases 5
- enhancement may be heterogeneous or a mural nodule
- generally high signal
- high signal 'bubbly appearance'
- mixed signal intensity with bright rim sign
- partial suppression of some of the "bubbles"
- FLAIR is helpful in identifying the small peripheral lesions with similar intensity to CSF
- calcification relatively frequent
- hemosiderin staining uncommon as bleeding into DNETs is only occasional
- no restricted diffusion
- 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. Only one case of malignant transformation has been reported 5.
Prognosis is excellent, however due to the difficulty in managing seizure medically, patients usually undergo resection and even in cases of incomplete resection, seizures frequently cease.
Main differential diagnosis is that of other cortical tumors, with helpful distinguishing features including 1-6:
- contrast enhancement more common
- calcification in ~50% of cases
- no 'bubbly' appearance
pleomorphic xanthoastrocytoma (PXA)
- contrast enhancement prominent
- dural tail sign often seen
- calcifications common
desmoplastic infantile ganglioglioma
- young children
- dural involvement prominent
- large often multiple lesions
Importantly the 'bubbly' appearance can be seen also in multinodular and vacuolating neuronal tumors (MVNT) which are however in the juxtacortical white matter, rather than in the cortex 7.
The differential diagnosis also depends on the location of the tumor.
If in the temporal lobe consider:
- tumors (in order of decreasing frequency)
See also: temporal lobe tumors
If cortical elsewhere consider: