= benign tumor of neuroepithelial origin arising from cortical / deep gray matter

Origin: derived from secondary germinal layers; originally diagnosed as low-grade astrocytoma

Histo: specific glioneuronal element in a columnar pattern oriented perpendicular to cortical surface; admixture of astrocytes + oligodendroglial elements in association with “floating neurons” and mucinous degeneration; ± multinodular architecture

Age: usually <20 years; M >F

• medically refractory partial seizures; neurologic deficits (rare)

Location: temporal (62%) / frontal (31%) lobe; caudate nucleus; cerebellum; pons

CT:

• hypoattenuating mass ± calcifications
• remodeling of inner table of skull

MR:

• cortical mass without surrounding vasogenic edema:
  • hypointense on T1WI + hyperintense on T2WI
  • “soap bubble” / megagyrus appearance at cortical margin = enlargement of cortical surface
  • contrast enhancement (in 33%)

Prognosis: partial resection stops seizure activity; rarely recurs

DDx: diffuse astrocytoma, ganglioglioma, oligodendroglioma