The Collaborative International Dictionary of English v.0.48:

Malformation \Mal`for*ma"tion\, n. [Mal- + formation.]
   Ill formation; irregular or anomalous formation; abnormal or
   wrong conformation or structure; -- often used of body parts
   such as limbs which do not develop properly during fetal
   maturation.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

malformation
    n 1: an affliction in which some part of the body is misshapen
         or malformed [syn: deformity, malformation,
         misshapenness]
    2: something abnormal or anomalous [syn: malformation,
       miscreation]