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]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "malformation":
   absurdity, anticness, bizarreness, bizarrerie, bowlegs, camelback,
   cleft palate, clubfoot, crookback, curiousness, defacement,
   deformation, deformity, disfigurement, distortion, fantasticality,
   flatfoot, freakishness, grotesqueness, grotesquerie, harelip,
   humpback, hunchback, knock-knee, kyphosis, lordosis,
   malconformation, misproportion, misshape, monstrosity,
   monstrousness, mutilation, oddity, outlandishness, peculiarity,
   quaintness, queerness, singularity, splayfoot, strangeness,
   swayback, talipes, teratism, teratology, torticollis, truncation,
   valgus, weirdness, wryneck