Brain Development I//Choroid Plexus Cysts

Ultrasound may provide clues to possible chromosomal problems about 80% of the time, depending upon the stage of the pregnancy, the equipment that is used, and the skill and expertise of the examiner.   A common finding that is associated with chromosome problems are one or more fluid pockets in the choroid glomi, shown as a central void in one of the blue colored structures within the head, visible here, because the front part of the skull of this 12 week fetus has been erased digitally, letting us look within.

The choroid glomi are paired structures that produce cerebro-spinal fluid, which is a sugar rich material that bathes the brain and spinal cord, nourishing and supporting nerve cell growth. Both choroid glomi ('glomus' is singular, 'plexus' is an equivalent term) are the first structures to be identified ultrasonically within the head, being visible 5 to 6 weeks after conception. Seeing paired and equal sized choroid glomi confirms that the brain is developing in two halves. (A single chamber kind of brain is one of the worst developmental malformations, and goes by the term, "holoprosencephaly").

The brain develops around the choroid glomi. Fluid exudes from the surface of the choroid. Fairly often, little pockets of fluid are trapped within a glomus, forming "cysts". These cysts are NOT important. They always go away. BUT, choroid cysts (big enough to be seen ultrasonically) are associated with an small but definitely increased chance of chromosome problems (especially, but not only, extra chromosome or trisomy #18). Trisomy 18 is a lethal dosorder which often has few structural findings, so that any clue that it might be present is an indication for amniocentesis. In most cases of choroid plexus cysts, the amnio will be normal, emphasizing the primary role of genetic testing as a wellness procedure.

Fetal Behavior