Megalencephaly UMLS:C0221355 Enlarged brain HP:0001355 Diffuse enlargement of the entire cerebral hemispheres leading to macrocephaly (with or without overlying cortical dysplasia). SNOMEDCT_US:19410003 Megalencephaly is defined as fronto-occipital diameter above two standard deviations of the mean for the patient's age because of an oversized brain parenchyma. This is different from macrocephaly, which is defined by an enlarged head circumference and therefore accounts also for the size of the extra-axial spaces. Macrencephaly Abnormal cerebral morphology