Hemimegalencephaly

  • Etiology: Partial or complete hamartomatous overgrowth of entire or a portion of a cerebral hemisphere due to defective stem cells with abnormal proliferation and migration and organization
  • Imaging:
    — Unilateral generalized or focal enlargement of cerebral hemisphere and ventricle
    — Dysmyelination
    — Thick cortical ribbon
    — Cortical dysplasia
    — Pachygyria
    — Polymicrogyria
    — Heterotopia
    — Ipsilateral advanced myelination
  • DDX:
  • Complications:
  • Treatment:
  • Clinical:
    — Often have hemihypertrophy of ipsilateral body
    — Associated with neurofibromatosis Type 1 and tuberous sclerosis and epidermal nevus syndrome and Proteus syndrome and Klippel-Trenauny syndrome and hypomelanosis of Ito

Radiology Cases of Hemimegalencephaly

MRI of hemimegalencephaly
Axial T2 MRI of the brain shows the left cerebral hemisphere to have diffusely thickening of the cortical ribbon and a decreased amount of white matter.
MRI of pediatric hemimegalencephaly
Axial (above left) and coronal (above right) T1 MRI without contrast and axial (below left) and coronal (below right) T2 MRI of the brain show an enlarged left cerebral hemisphere and left cerebellum. There is left hemispheric gyral thickening and pachygyria and polymicrogyria and dysmyelination. The left lateral ventricle is enlarged as are the left extra axial spaces. The left cerebellum is dysplastic in appearance.