 |
This
image view shows elongated, turned out feet with pointed heels (called "rocker
bottom feet") This abnormal pattern is associated with chromosome problems,
most often trisomy (extra chromosome) 13. Frequently associated findings
are referred to as "Syndromes". Some findings are always there,
others may occur in a per centage of cases. For example, congenital
heart disease is present in about 25% of cases of trisomy 21, absent
in the remainder. |
Trisomies (extra chromosome) 13, 18, 21 and monosomy (one chromosome) X are the most commonly encountered major chromosome problems in fetuses and babies. Malformations represent the 'phenotypic' expression of a disorder. Trisomy 13 usually, but not always, has multiple malformations, while Trisomy 18 has few major structural problems, but a wide range of functional issues. Both of these problems are lethal. Down's syndrome is intermediate. Phenotypic expression varies between different forms of aneuploidy and within each individual syndrome. |
 |
Only an amniocentesis identifies or excludes a chromosomal disorder.
 |
We pay special attention to the brain, which is not part of the routine ultrasound procedure. Most of the trisomies have a component of delayed neuronal development of the cerebral hemispheres, particularly between 15 and 22 weeks GA. This is super-resolution endovaginal view of the left occipital lobe of the brain in a case of trisomy 13: the cortex is thin, and the neurons remain in the periventricular zone (producing a narrow white band), instead of streaming into and expanding the cortex. When the cortex is thin, the head is small. Extreme retardation of brain and head growth is referred to as"microcephaly". |
