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Hemimegalencephaly

Hamartomatous overgrowth of hemisphere

Brain can be affected in isolation or can be associated with hemihypertrophy of part or all of the body

Macrocephaly at birth; seizures, hemiplegia, and severe developmental delay at very early age (usu before age 1)

Associations

Epidermal nevus syndrome

Proteus syndrome

Unilateral hypomelanosis of Ito

NF I

Tuberous sclerosis

Imaging

FDG-PET features

MR features

Enlarged cerebral hemisphere

Enlarged ipsilateral lateral ventricle (classic)

Cortical dysgenesis

Enlarged hemisphere

Diffuse hypermetabolism of affected hemisphere due to ongoing seizure activity

Treatment

Anatomic hemisherectomy

Must carefully screen contralateral side

Functional hemisherectomy

Hemidecortication

Intravascular hemisherectomy (no long term follow-up)