macrocephaly vs macrocephalic

macrocephaly is a noun but macrocephalic is not a noun.

Word	Noun	Adjective	Verb	Adverb
macrocephaly	Yes	No	No	No
macrocephalic	No	Yes	No	No

macrocephaly (noun)	macrocephalic (noun)
an abnormally large head; differs from hydrocephalus because there is no increased intracranial pressure and the overgrowth is symmetrical

macrocephaly (adjective)	macrocephalic (adjective)
	having an exceptionally large head and brain