The Collaborative International Dictionary of English v.0.48:

macrocephaly \macrocephaly\ n.
   THe condition of having an unusually large head; it differs
   from hydrocephalus because there is no increase
   intracranial pressure and the overgrowth is symmetrical.

   Syn: megacephaly, megalocephaly.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

macrocephaly
    n 1: an abnormally large head; differs from hydrocephalus
         because there is no increased intracranial pressure and the
         overgrowth is symmetrical [syn: macrocephaly,
         megacephaly, megalocephaly]