Module 11 : Fetal Neural Tube Pathology Flashcards
What produces CSF
Choroid plexus
Where are the choroid plexus located
- body of lat ventricle
- roof of third vent
- superior lateral walls of fourth vent
Flow of CSF through the brain
Choroid plexus»_space; lat vents»_space; interventricular foramen»_space; 3rd vent»_space; cerebral aqueduct»_space; fourth vent»_space; megendie ( spinal cord) and Lushka ( brain)
Normal fourth vent location
- anterior and inferior edge of cerebellum
Hydrocephalus
- increase in CSF that results in enlargement of ventricular system
- usually due to obstruction along the pathway to CSF
- MOST COMMON CRANIAL ANOMALY
- dangling choroid
Intraventricular obstruction hydrocephalus - aqueduct stenosis
- csf can’t flow from 3rd vent to 4th vent
- lat and 3rd bent enlarged but 4th vent normal
Extraventricular obstruction hydrocephalus - spine bifida
- CSF can’t flow normally through the spinal canal and back up in ventricle of brain
- ALL ventricles effects s
Extraventricukar obstruction hydrocephalus - excess CSF
- less common
- excess secretion from a choroid plexus papilloma (tumor)
Types of extraventricular obstruction hydrocephalus
- spina bifida
- excess CSF
- dandy walker malformation
Evaluating ventricular size
- measure ATRIAL diameter \+ size doesn’t change much 15 - 35 \+ normal size 7mm \+ 10 mm upper limit of normal - < 3mm from medial vent wall to choroid
Dangling choroid
- always rests in a gravitationally dependent position
- sign of hydrocephalus
True hydrocephalus
- either from CSF obstruction OR ventriculomegaly resulting from brain atrophy
Causes of true hydrocephalus
- neural tube defect NTD
- aqueductal stenosis
- dandy walker malformation
Ventriculomegalyt
- brain atrophy result in a smaller brain allowing ventricles more room to expand
Where to look when hydrocephalus is suspected
- additional anomalies tend to occur with hydrocephalus
- posterior fossa views
+ cisterna magna and cerebellum
= obliterated cisterna magna
= deformed cerebellum (banana)
= lemon sign
Banana sign
- indicates obliterated cisterna magna
- ## often ARNOLD CHIARI
Lemon sign
- resulting when cranial contents are pulled toward spine with Arnold Chiari II malformation
+ associated with spina bifida - frontal bones caved in
- seen in second trimester
- lemon sign disappears in 3rd trimester due to resulting in hydrocephalus from enlarging ventricles of blocked CSF
Dandy walker malformation DWM
- enlarged cisterna magna and defect in the cerebellar VERMIS
- the cisterna magna communicates with the 4th vent through a defect in cerebellum
- ventricles can be enlarged due to pressure in the post fossa
Dandy walker variant
- partial agenisis of the vermis with a smaller cisterna magna and minimal dilation of the ventricles
- associated with many syndromes
DWM associated with
- intellectual impairment and fetal steam
- AGENISIS OF CORPUS CALLOSUM
- heart defects
- genitourinary
- polydactyly
- increase risk
+ maternal viral infection
+ alcohol consumption
+ maternal diabetes
Assessing DWM
- cisterna magna > 1cm abnormal
- cerebellar view must include
+ caveman septi pellucidi
+ peduncles
+ cerebellum - measure
What to prove for DWM
- cisterna magna communicates with 4th vent
- cerebbellaR VERMIS absent or partially absent
- enlarged ventricles
- DDx = arachnoid cyst in posterior fossa
Arachnoid cysts in post fossa
- fluid collections in the layers of teh arachnoid membrane
- cysts can occur anywhere in the brain
Choroid plexus cysts CPC
- cysts in choroid plexus
- usually disappear in 2nd trimester
- associated with trisomy 18
+ 1 / 200 are associate with T18 - HAVE TO BE > 3MM
Nuchal fold
- 80% of infants with T21 have redundant skin in the posterior part of the neck
- can only be assessed between 16 and 20 weeks because of gestational diabetes
Gestational diabetes mellitus
- mothers with GDM the fetus can be LGA
- baby will have more fat in general making nuchal fold thick
- occurs after 20 weeks
- continuing to measure nuchal fold with make lots of false positives
Assessing nuchal fold
- greater than or equal to 6 mm abnormal
- measure from outer skull to outer skin surface
Acrania
- absent skull / cal aria
Anencephaly
- no or distorted cerebral cortex
Exenceohaly
- some cerebral cortex but abnormal
- early stage of anencephaly
- brain tissue exposed to amniotic fluid gets damages
- brain tissue in beginning (excencephaly) then by time fetus is imaged there is minimal tissue left so diagnosed anencephaly
Sonographic features of anencephaly
- facial structures present and orbits
- no calvaria (skull) above orbits
- image through face would resemble a frog
- polyhydroamnios (no swallowing)
- very active fetus
- can not be reliable diagnoses before 12-13 weeks
