Dysembryoplastic neuroepithelial tumor (DNET)
Benign mixed glial-neuronal neoplasm
Frequently associated with cortical dysplasia
May occur in any region of supratentorial cortex
Mesial temporal lobe most common
Mass frequently "points" towards ventricle
Sharply demarcated, wedge-shaped
Cystic ("bubbly ") intracortical mass
Minimal/no mass effect
No surrounding edema
Slow growth over years
Usually does not enhance
Faint focal punctate or ring enhancement in 20-30%
Higher rate of recurrence if enhancement
Taylor dysplasia
Neuroepithelial cyst
Ganglioglioma
Pleomorphic xanthoastrocytoma (PXA)
Angiocentric glioma (a.k.a. ANET)
WHO grade I
Hallmark = "specific glioneuronal element" (SGNE)
Longstanding drug-resistant partial complex seizures in child/young adult
Surgical resection usually curative
Histology usually remains benign even if tumor recurs, enhances
TERMINOLOGY
Dysembryoplastic neuroepithelial tumor (DNET)
Mixed glial-neuronal neoplasm
Benign tumor frequently associated with cortical dysplasia
IMAGING
Best diagnostic clue: Demarcated, wedge-shaped cystic cortical mass in young patient with longstanding partial complex seizures
Location
May occur in any region of supratentorial cortex
Mesial temporal lobe most common (68%)
Caudate nucleus, septum pellucidum less frequent sites
Cortical mass frequently "points" towards ventricle
Size
Variable: Small (involving part of gyrus)
Large (several cm lesions involving large portion of lobe have been reported)
Morphology
Circumscribed, wedge-shaped, cystic
Minimal or no mass effect relative to size of lesion
No associated surrounding edema
Slow growth over many years
May remodel overlying bone
NECT
Wedge-shaped
Cortical/subcortical
Scalloped inner table in 44-60%
Low density
May resemble stroke on initial CT
Calcification in 20-36%
CECT
Usually nonenhancing
Faint nodular or patchy enhancement in 20%
Higher incidence of recurrence if enhancement
CTA: Avascular CTA, MRA, conventional angiography
T1WI
Multilobular, hypointense "bubbly" mass
Cortex ± extension into subcortical WM
T2WI
Multilobular or septated appearance
Very hyperintense on T2
"Pseudocystic" or multicystic appearance
True cysts uncommon
PD/intermediate: Hyperintense rim
FLAIR
Variable
Mixed hypo/isointense signal
Well-defined, complete or incomplete, hyperintense ring(s) surrounding mass
No peritumoral edema
T2* GRE
Bleeding into DNET uncommon but does occur
Possibly in association with microvascular abnormalities
May simulate cavernoma
DWI: Usually lacks restricted diffusion
T1WI C+
Usually does not enhance
Focal punctate or ring enhancement in up to 30%
MRS
Nonspecific, but lactate present in some
Often spectroscopy normal
PET
18F-FDG PET demonstrates glucose hypometabolism
Lower 11C-methionine (MET) uptake in DNET than in ganglioglioma or gliomas
Tc-99m-HMPAO SPECT
Ictal may show hyperperfusion
Interictal hypoperfusion typical
Best imaging tool: MR with T1WI C+, FLAIR ± MRS
DIFFERENTIAL DIAGNOSIS
Taylor Dysplasia
Single tuberous sclerosis lesion
Expands single gyrus
Looks like tuber, nonenhancing
Neuroepithelial Cyst
Nonenhancing single or complex cystic structure
No bright rim on FLAIR
Ganglioglioma
Ca++ common
Frequently solid and cystic components
Solid components avidly enhance
Pleomorphic Xanthoastrocytoma (PXA)
Enhancing nodule abuts pia
May have pial enhancement
Look for dural "tail"
Angiocentric Glioma
a.k.a. "angiocentric neuroepithelial tumor" (ANET)
Rare superficial cortical lesion, usually frontoparietal
Child/young adult with longstanding epilepsy
PATHOLOGY
Etiology
Embryology: Dysplastic cells in germinal matrix
Extend along migratory path of neurons towards cortex
Associated with cortical dysplasia
Ring-like, slightly hyperintense rim on T1WI
Genetics
Sporadic
Nonneoplastic focal cortical dysplasias may be syndrome related
Reported cases with NF1
WHO grade I
Neocortical lesion
Thick gyrus
Glioneuronal component of tumor is viscous in consistency
Firm nodules represent more stromal components
Hallmark = "specific glioneuronal element" (SGNE)
Characterized by columns of bundled axons oriented perpendicular to cortex
Columns lined by oligodendroglia-like cells
Other cells show astrocytic, neuronal differentiation
Several histological types
Complex form
Multinodular architecture
Mixed cellular composition
Foci of cortical disorganization
SGNE
Simple form with SGNE only
3rd "nonspecific" form has no SGNE
But has same neuroimaging characteristics as complex form
Microcystic degeneration
Neurons "float" in pale, eosinophilic mucoid matrix
Calcification and leptomeningeal involvement common
Adjacent cortical dysplasia common
Low proliferative potential with variable MIB-1 index
CLINICAL ISSUES
Most common signs/symptoms: Partial complex seizures
Clinical profile: Longstanding frequently drug-resistant partial complex seizures in child or young adult
Age
Children and young adults
2nd to 3rd decades
Majority present by 20 years
Gender: Slight male predominance
Epidemiology
< 1% of all primary brain tumors
Approximately 1% of primary neuroepithelial brain tumors in patients < 20 years
Represents 0.2% of neuroepithelial tumors in patients > 20 years
Reported in 5-80% of epilepsy specimens
Benign lesions
No or very slow increase in size over time
Rare recurrence
Beware of atypical features (enhancement) on preoperative imaging
Malignant transformation extremely rare
Imaging may look alarming (e.g., new ring-enhancing mass)
Histology usually remains benign
Seizures may become intractable
Glutamate receptors shown within tumor and margins may explain typical difficult-to-control seizures
Surgical resection of epileptogenic foci (may include cortical dysplasia)
Surgical resection usually curative
DIAGNOSTIC CHECKLIST
DNET if "bubbly" cortical mass in child/young adult with longstanding epilepsy
Beware of enhancing lesions; they may represent more ominous lesion than DNET