BRAIN
Trisomy
13 Syndrome
Trisomy
13 syndrome is characterized by microcephaly, posterior scalp lesions,
microphthalmia, cleft lip (Figure 157.1 [A]), coloboma of the iris, low-set
dysplastic ears, deafness, cleft palate, polydactyly, typical trisomy
18 hands (Figure 157.1 [B]), prominent heels, cryptorchidism, and abnormal
scrotum.
Figure 157.1.— Trisomy 13 syndrome. [A] Typical facial features
of trysomy 13 syndrome and [B] typical positions hands position of distal
athrogryposis.
The
most frequent central nervous system anomaly is holoprosencephaly. Holoprosencephaly
can be diagnosed by brain ultrasound but MRI is the study of choice (Figure
157.2). Holoprosencephaly may be alobar, semilobar and lobar.
This distinction may at times be difficult since they often overlap.
Figure 157.2.— Brain ultrasound demonstarting Holoprosencephaly.
[A] Coronal anterior view. [B] Coronal posterior view.
Alobar
holoprosencephaly is characterized by fused thalami, no third ventricle,
no interhemispheric fissure, no corpus callosum, an anteriorly displaced
pancake-like mass of tissue, and a cresent-shaped holoventricle continuous
with a large dorsal cyst.
Semilobar
holoprosencephaly is characterized by partially separated thalami, small
third ventricle, an interhemispheric fissure that is only present posteriorly,
a corpus callosum that is only present posteriorly, normal occipital or
temporal lobes, and a telencephalic ventricle that is continuous with
a dorsal cyst (Figure 157.3).
A |
B |
C |
 |
|
 |
Figure 157.3.— MRI studies demostrating semilobar holoprosencephaly.
Lobar
holoprosencephaly is characterized by hypoplastic anterior falx, hypoplastic
frontal lobes, absence of the anterior regions of the corpus callosum,
absence of the septum pellucidum but separated thalami, and a normal third
ventricle and interhemispheric fissure (Figure 157.4).
Figure 157.5.— CT
scan of the brain demonstrates holoprosencephaly. Partially fused frontal
lobes, partially formed interhemispheric fissure.
Full
trisomy 13 occurs more often in neonates born to older mothers. Translocation
of chromosome 13 material produces a similar phenotype. The parents of
an infant with translocation should have chromosomal studies because they
may be asymptomatic carriers of a balance translocation. The chance of
recurrence is higher if either parent is a carrier of a balance translocation.
|