NTDs & Foetal Surgery Flashcards
What is neurulation?
What are the major stages in this process that lead to neural tube formation?
- The process by which the neural plate forms the neural tube*
- the neural plate lengthens and its lateral edges elevate to form neural folds
- the depressed midregion forms the neural groove
- the neural folds elevate and approach the midline
- the neural folds fuse in the midline at the cervical region, and fusion continues both cranially and caudally to form the neural tube
- this leaves only the anterior and posterior neuropores open to the external environment
How is open foetal surgery performed?
When during the pregnancy is this performed and why?
- it involves a potentially large hysterectomy to expose the foetus
- the contents of the uterus are removed for a small period of time before being returned
- it occurs around 20 weeks (halfway through development)
- the later the foetal surgery is left, the greater the risk to the mother
- but the foetus has to be developed to a certain extent before surgery can be performed
What is it important not to do during open foetal surgery?
When is this method typically used?
- it is important not to rupture any placental membranes during the procedure as this can result in preterm birth
- it is often performed for prenatal repair of myelomeningocele
How is foetoscopy performed?
For which conditions is this an appropriate method of surgery?
- it is performed using endoscopes and requires a much smaller hysterectomy
- it can be used in:
- urinary tract obstruction
- congenital diaphragmatic hernia repair (poor outcomes)
- TTTs and TRAP
- experimental use in amniotic band syndrome
How is foetal surgery planned?
What is the associated risk?
- CT and MRI can be used to plan treatment
- there is no incidence of a radiating scan leading to a congenital malformation, but there is a well-established link between radiation and chromosomal abnormalities
How can foetoscopy be used in TTTS and TRAP?
Are the outcomes good?
Twin-to-twin transfusion syndrome (TTTS):
- the twins share a placenta and abnormal anastomoses between blood vessels leads to one receiving a greater blood supply than the other
- foetoscopy is used to ablate larger vessels and leave an equal distribution of maternal blood
Twin reverse arterial perfusion (TRAP):
- one foetus is pumping oxygenated blood over towards the other one
- TRAP has poor outcomes regardless of surgical intervention
What medication is given prior to open foetal surgery and how does it work?
Tocolytics
- given to prevent premature labour
- typically involves giving a calcium channel blocker, such as nifedipine
- calcium channel blockers will also relax the uterus
- procedure is performed under general anaesthetic
How is open foetal surgery performed?
What must be pumped into the uterine cavity and why?
- hysterectomy is performed to expose the foetus
- this involves an incision of the anterior abdominal wall and removal of the contents of the uterus
- fluid is continually pumped into the uterine cavity to maintain the pressure and prevent placental separation
- the fluid is similar to saline but has different sodium levels as it is important not to modify the pH of the amniotic sac/fluid
- this can cause problems with development later on
What is the importance of medical imaging during open foetal surgery?
- medical imaging is used to assess the position of the placenta to ensure it is avoided during incision
- if the placental linings attached to the walls of the uterus are accidentally incised, this can lead to placental separation and preterm birth
What injection can be given during open foetal surgery?
How is the surgery concluded and what precaution must be taken in the future?
- a foetal narcotic injection can be given for pain relief
- the defect is repaired and amniotic fluid is replaced before closing the surgical site
- following open surgery, all babies must be born via C-section
What are the limitations on when open foetal surgery can be performed?
Why must all future pregnancies be delivered by C-section?
- it can only be performed after 18 weeks due to the size and fragility of the foetus
- it is usually performed at 20 weeks
- this pregnancy and all future ones must be delivered via C-section to avoid uterine rupture at the scar site
What are the complications associated with open foetal surgery?
- uterine rupture
- maternal bleeding
- premature delivery
- respiratory distress syndrome (RDS)
- foetal death
What is myelomeningocele and why does it occur?
- it is the most severe form of spina bifida
- failure of the posterior neuropore to close leads to protrusion of the meninges and neural tissue through the vertebral arch
- it is not a defect of neurulation as the neural tube has formed
- it occurs due to splitting of the vertebral arches
When do the edges of the neural plate begin to elevate?
What are the processes that occur following this?
- the edges of the neural plate elevate to form neural folds on day 23
- the neural folds fuse in the midline to form the neural tube
- the neural tube separates from the surface ectoderm
- the surface ectoderm will form the epidermis of the skin
- a subset of cells from the neural folds (NCCs) will go on to migrate all around the body
Why do neural tube defects occur?
- NTDs result when neural tube closure fails to occur
What is craniorachischisis and why does it occur?
- there is a completely open brain and spinal cord
- it is a combination of anencephaly (absence of brain & cranial vault) with a continguous bony defect of the spine (rachisisis - no meninges covering neural tissue)
- occurs due to failure of the neural folds to fuse
- the surface ectoderm becomes continuous with part of the nervous system
- it is rachischisis if it only involves the spinal cord
What is anencephaly and why does it occur?
- there is an open brain and lack of skull vault** due to **failure of the anterior neuropore to close
- after a certain point in development, amniotic fluid becomes damaging to the nervous tissue
- if the anterior neuropore does not close, the amniotic fluid damages the cranial structures and prevents development of the brain
- only the brainstem can develop and death occurs in utero or shortly after birth
What is encephalocele and why does it occur?
- there is herniation of the meninges (and brain) through an opening in the skull
- it occurs due to incomplete closure of the neural tube
- any area of the skull can be affected and the protruding sac can be covered with skin or just a thin membrane
What is meant by iniencephaly?
- this describes occipital skull and spine defects with extreme retroflexion of the head
- the neural tube is not always involved
- extreme retroflexion is often combined with occipital encephalocele and rachischisis of the cervical or thoracic spine
- often results in stillbirth and live birth is rare