Encyclopedia of Clinical Neuropsychology

2018 Edition
| Editors: Jeffrey S. Kreutzer, John DeLuca, Bruce Caplan


  • Erin D. BiglerEmail author
  • Jo Ann Petrie
Reference work entry
DOI: https://doi.org/10.1007/978-3-319-57111-9_1565


Brain with excessive weight; Large brain; Large occipito-frontal head circumference; Macrocephaly; Macroencephaly; Overgrowth, hemimegalencephaly; P13K-AKT-mTOR pathogenesis; Ras/MAPK pathway

Short Description or Definition

Megalencephaly means that a brain is larger than normal and is usually defined when brain size is greater than two standard deviations above normal (Almgren et al. 2008; Gooskens et al. 1988; Olney 2007; Petersson et al. 1999). The term is a derivative of the Greek words encephalon, referring to the brain, and mega, referring to large.


Typically with megalencephaly, there is also a large head size, sometimes referred to as macrocephaly (see Dubois et al. 2014; Lainhart et al. 2006) as there is an intimate relationship between brain growth and head size in infancy (Tate et al. 2007). However, large head size or macrocephaly does not always mean that the brain inside is large or megalencephalic (DeMeyer 1972; Homem et al. 2015; van der Knaap...

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Authors and Affiliations

  1. 1.Department of Psychology and the Neuroscience CenterBrigham Young UniversityProvoUSA