Microcephaly occurs in many
Smith’s book on recognizable patterns of human malformation lists microcephaly
as a frequent finding in 42 syndromes and as an occasional finding in
The differential diagnosis of congenital microcephaly can be approached
by categorizing each patient in one of the following groups: (1) neonates
with dysmorphic facial features and normal karyotype; (2) neonates with
dysmorphic facial features and abnormal karyotype; (3) neonates with normal
facial features and elevated serum IgM; and (4) neonates with normal facial
features and normal serum IgM.
WITH DYSMORPHIC FACIAL FEATURES AND NORMAL KARYOTYPE
with dysmorphic facial features and normal karyotype include those exposed
to teratogenic physical or chemical agents during pregnancy and those
with genetic abnormalities that are not detected by chromosomal studies.
due to teratogenic physical or chemical agents results from exposure of
the fetus to a noxious agent at a vulnerable period of brain development.
Physical agents include radiation. Microcephaly due to radiation is very
rare since the introduction of low-dose ionizing radiation for diagnostic
radiological evaluations, the shielding of the pelvis for chest radiographs,
and the avoidance of pelvic radiographs if pregnancy is remotely suspected.
Hyperthermia was once considered a significant factor in the production
of microcephaly based on experimental animal studies and an initial medical
report. However, hyperthermia is no longer considered a significant factor
in the production of microcephaly.
Chemical agents that may cause microcephaly include phenylalanine, alcohol,
and anticonvulsant drugs.