Dandy Walker Syndrome pic
    spectrum of abnormal cerebellum and 4th ventricle
    vermian dysgenesis with expanded 4th ventricle shifts tentorium upward
    normal size of the posterior fossa
    detected at 20 wks, with associated hydrocephalus and corpus callosal dysgenesis
    the wider the cerebellar spread, the worse the prognosis
    Dandy-Walker Variant has normal posterior fossa size, lesser dilation of the 4th ventricle, and less cerebellar hypoplasia with no mass effect
 Ddx   unlike an arachnoid cyst which displaces the cerebellum, a DW spreads it apart
          may also have a mega cisterna magna (>11mm) with cerebellar hypoplasia and communicating hydrocephalus

Arnold Chiari Malformation
   
    There are 3 types of Arnold-Chiari malformation
     Type 1,  a lip of cerebellum is downwardly displaced with the tonsils, but the fourth ventricle remains in the posterior fossa. This is mainly an incidental CT discovery.
    Type 2 Arnold-Chiari malformation is the one usually involved in prenatal cases and is a congenital deformity characterized by displacement of cerebellar tonsils parts of the cerebellum, fourth ventricle, pons and medulla oblongata through the foramen magnum into the spinal canal. This is usually associated with hydrocephalus and meningomyelocele
    Type 3 is a more severe form with large herniation of the posterior fossa content and myelomeningocle and hydrocephalus, small posterior fossa with cerebellum squeezed upwards against the tentorium, downward through the forament magnum and anteriorly around the brainstem

    the "banana sign" of the cerebellar hemispheres as they are compressed and pushed downward toward the cisterna magna is pathognomonic. Ideally look for obliteration of fluid in cisterna magna
    hydrocephaly is seen 80% of the time which is mild in second trimester and worsens in 3rd trimester from obstruction of the foramen of magendie
    corpus callosum is completely or partially absent
    associated with myelomenigocele (>90%)
    the "lemon sign" usually disappears by 34 weeks as the skull ossifies more
    Tx: termination, or if legs are moving, possibly experimental IU repair at 24-30wks, genetic counselling
   

Trisomy 21 (Down's syndrome)
    dysmorphic features not seen by US in 50%
    Nuchal Skin Folds - redundant & thickened in 80%
        direct at suboccipital-bregmatic trans axial plane
        skull to outer skin >6mm abnormal at 15-20wks
    Femur & Humerus Length - below 10th %ile at 15-20wks
    Heart Defects - 20% die in 1st year due to heart failure & luekemia
        VSD, ECD & ostium primum ASD freq
    Duodenal Atresia - 10% only seen after 22wks, 30% of babies with "double bubble"
    Hydrops - frequent in 2nd trimester as with all cytogenetic disorders
    Widely spaced 1st & 2nd toes
    Hard signs: duodenal atresia, congenital heart disease (atrioventricular canal/VSD)
    Soft signs: echogenic focus in cardia ventricle (increases risk by 4X), mild renal pyelectasis (>24mm at 15-20 wks), choroid plexus cysts, echogenic bowel

Trisomy 13 (Patau Syndrome)
    profound MR, only 18% survive 1st year
    CNS disorders - holoprosenceph #1, agenesis of CC also
    Craniofacial disorders - micrognathia, cleft, sloped forehead
    Congen heart defects - Dextrocardia, VSD & ASD
    2nd tri IUGR, polyhydramnios, hypotonia, GI & renal abn also
    Omphalocele should be Karyotyped

Trisomy 18 (Edward Syndrome)
    similar presentation to Patau syndrome
    Limb malformations also included - clubfoot, clenched hand
    Micrognathia, dolichocephaly & prom occiput characteristic
    Choroid Plexus cyst also common, often large & bilat

Turner Syndrome
     missing X chrom, most miscarry 1st or 2nd trimester
    Corarctation of aorta accounts for 70% of deaths
    R ventricle enlarged due to shunting across ductus to dist aorta
    Cystic Hygromas, Nuchal Edema & freq Hydrops

Triploidy Syndrome
     2 sperm fertilize egg, 20% of miscarriages
    live birth rare, severe IUGR, disproportionate large head
    multi system & amnion abn ormalities

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