title: Hemispheric dysplasia and hemimegalencephaly: imaging definitions.
abstract: OBJECTIVE
  Hemispheric dysplasia (HD) and hemimegalencephaly (HME) are both brain malformations with early clinical manifestation including developmental delay and intractable epilepsy. Sometimes the differentiation of these conditions is not simple. HME is an anomaly of cortical development caused by a combination of neural proliferation and cell migration dysfunction, showing lobar or hemispheric enlargement. On the other hand, HD shows no brain hypertrophy, and even brain atrophy, eventually.
  
  
  METHODS
  To compare both conditions, we reviewed clinical, MRI, and histopathology of 23 patients with developmental delay and refractory epilepsy treated with hemispheric surgery.
  
  
  RESULTS
  Histologically, both groups presented polymicrogyria, focal cortical dysplasia, gray matter (GM) heterotopia, pachygyria, and agyria. The white matter (WM) showed different degrees of gliosis and myelin impairment. Even though with no specificity in histopathology, the degree of lesion was more impressive on HME. The combination of WM dysmyelination and hypertrophy leads to the so called hamartomatous appearing. Although not all HME showed brain enlargement and some HD might show no size changes or atrophy, the size of affected hemisphere and the hamartomatous appearance of the WM were the more relevant signs to differentiate both conditions.
  
  
  CONCLUSIONS
  Brain MRI was the best diagnostic tolls because it allowed together high contrast resolution, whole brain coverage and spatial distribution analysis. HD and HMD showed brain asymmetry tendency, but in opposite directions. The size of affected hemisphere and the hamartomatous appearance of the WM were the more relevant signs to differentiate both conditions.
authors.affiliation: Radiology Division-Internal Medicine Department, Ribeirão Preto School of Medicine, University of São Paulo, Ribeirão Preto, São Paulo, Brazil, acsantos@fmrp.usp.br.
authors.forename: Antonio Carlos
authors.initials: AC
authors.lastname: Santos
authors.forename: Sara
authors.initials: S
authors.lastname: Escorsi-Rosset
authors.forename: Gustavo N
authors.initials: GN
authors.lastname: Simao
authors.forename: Vera C
authors.initials: VC
authors.lastname: Terra
authors.forename: Tonicarlo
authors.initials: T
authors.lastname: Velasco
authors.forename: Luciano
authors.initials: L
authors.lastname: Neder
authors.forename: Americo C
authors.initials: AC
authors.lastname: Sakamoto
authors.forename: Helio R
authors.initials: HR
authors.lastname: Machado
mesh_terms: D001037:Aphasia / Q000175:diagnosis*; D007839:Functional Laterality; D006801:Humans; D058627:Megalencephaly / Q000150:complications*; D059906:Neuroimaging / Q000379:methods*