NTDs & Foetal Surgery Flashcards

1
Q

What is neurulation?

What are the major stages in this process that lead to neural tube formation?

A
  • 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 well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How is open foetal surgery performed?

When during the pregnancy is this performed and why?

A
  • 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is it important not to do during open foetal surgery?

When is this method typically used?

A
  • 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 well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How is foetoscopy performed?

For which conditions is this an appropriate method of surgery?

A
  • it is performed using endoscopes and requires a much smaller hysterectomy
  • it can be used in:
  1. urinary tract obstruction
  2. congenital diaphragmatic hernia repair (poor outcomes)
  3. TTTs and TRAP
  4. experimental use in amniotic band syndrome
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How is foetal surgery planned?

What is the associated risk?

A
  • 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 well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How can foetoscopy be used in TTTS and TRAP?

Are the outcomes good?

A

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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What medication is given prior to open foetal surgery and how does it work?

A

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 well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How is open foetal surgery performed?

What must be pumped into the uterine cavity and why?

A
  • 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the importance of medical imaging during open foetal surgery?

A
  • 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What injection can be given during open foetal surgery?

How is the surgery concluded and what precaution must be taken in the future?

A
  • 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the limitations on when open foetal surgery can be performed?

Why must all future pregnancies be delivered by C-section?

A
  • 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are the complications associated with open foetal surgery?

A
  1. uterine rupture
  2. maternal bleeding
  3. premature delivery
  4. respiratory distress syndrome (RDS)
  5. foetal death
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is myelomeningocele and why does it occur?

A
  • 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

When do the edges of the neural plate begin to elevate?

What are the processes that occur following this?

A
  • 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Why do neural tube defects occur?

A
  • NTDs result when neural tube closure fails to occur
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is craniorachischisis and why does it occur?

A
  • 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is anencephaly and why does it occur?

A
  • 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is encephalocele and why does it occur?

A
  • 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is meant by iniencephaly?

A
  • 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Why does spina bifida occur?

A
  • it results from failure / abnormal formation of the vertebral arches
  • the neural tube and spinal cord form normally, but there is protrusion through an incomplete vertebral arch
21
Q

What is meant by spina bifida occulta and how can it be recognised?

What symptoms does it present with and why is intervention needed?

A
  • it is the least severe form of spina bifida and is often asymptomatic
  • some of the vertebrae are not completely closed
    • it usually affects the caudal region of the spinal cord
  • it is called “blind” as it cannot be seen except for a tuft of hair being present on the overlying skin
  • intervention is needed as the only thing covering and protecting the spinal cord is subcutaneous fat
22
Q
A
23
Q

What is meant by meningocele?

A
  • there is protrusion of the meninges through a defect in the skull or spine
  • as the meninges are filled with CSF, this produces a CSF-filled cyst
  • there is no neural tissue protruding through the spinal cord
24
Q

What is meant by myelomeningocele?

What may this be accompanied by?

A
  • this occurs when both the meninges and neural tissue protrude through a defect in the skull or spine
  • the spinal cord is open to the external environment and at risk of damage
  • it can be accompanied by severe neurological defects
25
Q

How can spina bifida be detected prenatally?

Why is it important to recognise this condition?

A
  • both myelomeningocele and meningocele can be detected in utero via USS as part of the foetal anomaly scan
  • both of these conditons require closure of the defect
  • plans are made for foetal surgery or C-section as you do not want to disturb exposed nervous tissue by squeezing it through the vaginal canal
26
Q

What are the 4 primary functional deficits associated with myelomeningocele?

A
  1. paralysis and sensory loss of the lower limb
  2. frequent UTIs
  3. bladder / bowel dysfunction (due to compression of pudendal nerve)
  4. cognitive dysfunction & hydrocephalus
  • in lumbosacral lesions, only 3-15% retain the ability to walk
27
Q

What is the most common way to repair a myelomeningocele?

A
  • it is detected on prenatal scans and in utero foetal surgery can be performed, but postnatal repair is more common
  • closure occurs in the first few hours / days of life after a planned C-section
  • a C-section is required to prevent compression of nervous tissue through a vaginal birth
28
Q

What are the possible complications associated with postnatal repair of a myelomeningocele?

A
  1. blood loss
  2. infection
  3. leakage of CSF
  4. problems with wound healing
  5. hydrocephalus
  6. tethered spinal cord
  • all of these complications lead to functional deficits
  • 15-20% will develop a tethered spinal cord at some point in their lifetime as a result of adhesions following surgery
    • this will require further surgery to repair
29
Q

What structure often herniates alongside myelomeningocele and why?

A
  • herniation of the cerebellum into the spinal cord can occur alongside myelomeningocele
  • CSF leaks into the defect and reduces the hydrostatic pressure
  • this draws the hindbrain through the foramen magnum
30
Q

What is the benefit of performing in utero surgery for myelomeningocele?

A
  • operating as early as possible in development leads to better outcomes in terms of functional deficits
  • there is more time for the nervous system to develop and repair itself, reducing the severity of functional deficits
31
Q

How did a study using rats look at the use of stem cell therapy to repair congenital defects (including NTDs)?

A
  • mesenchymal stem cells were derived from the amniotic fluid of rat foetuses and concentrated
  • NTDs induced in pregnant rats by giving retinoic acid
  • concentrated stem cells injected into the amniotic cavities of some mothers, whilst controls were given saline injections
  • NTDs were partially or fully covered by skin in the group receiving stem cells
32
Q

Why is food impregnated with folic acid?

A
  • to ensure that effective neurulation** occurs and to **reduce the incidence of NTDs
  • folic acid is important in neurulation
  • a mother needs sufficient levels of folic acid 4-6 weeks before fertilisation and 50% of pregnancies are unplanned
33
Q

What is congenital diaphragmatic hernia?

Who is more commonly affected and how can it be detected?

A
  • there is herniation of the gut / gut structures into the thorax
  • it more commonly affects the left side (unknown why)
  • it affects 2x more males than females
  • it can be detected via prenatal screening but is sometimes missed, resulting in the baby going into respiratory compromise immediately after birth
34
Q

What other malformations is congenital diaphragmatic hernia associated with?

A
  • NTDs are present in 50% of cases
  • trisomy 18
  • various other syndromes
35
Q

What is the septum transversum and what is it derived from?

A
  • a thick plate of mesodermal tissue occupying the space between the thoracic cavity and stalk of the yolk sac
  • it is derived from splanchnic mesoderm surrounding the heart
  • it assumes its position between the primitive thoracic and abdominal cavities when the cranial end of the embryo grows and curves into the foetal position
36
Q

How does the septum transversum separate the primitive thoracic and abdominal cavities?

A
  • the septum transversum does NOT fully separate the thoracic and abdominal cavities
  • it leaves large openings on either side of the foregut - the pericardioperitoneal canals
37
Q

How is the connection between the pleural cavities and peritoneal cavity sealed off during development?

A
  • the pleural cavities are in open communication with the peritoneal cavity via the pericardioperitoneal canals
  • the opening between the prospective pleural and peritoneal cavities is sealed off by crescent-shaped pleuroperitoneal folds
  • by week 7 the pleuroperitoneal folds have fused with the septum transversum and the mesentery of the oesophagus to separate the peritoneal and pleural cavities
38
Q

Why does congenital diaphragmatic hernia occur?

A
  • it results from failure of one or both of the pleuroperitoneal membranes to close the pericardioperitoneal canals
  • this leads to the pleural and peritoneal cavities being continuous with each other at the posterior body wall
39
Q

Why does failure of the pleuroperitoneal membranes to close the pericardioperitoneal canals result in CDH?

A
  • the pleuroperitoneal folds come towards the midline and fuse with the septum transversum to form the diaphragm
  • the septum transversum forms the central part of the muscular diaphragm
  • the pleuroperitoneal membranes form the domes of the diaphragm
  • if the pleuroperitoneal membranes fail to form sufficiently in size or fail to fuse with the septum transversum, there is a space in the diaphragm
  • abdominal contents protrude through the opening in the diaphragm as the pressure in the abdomen is higher than in the thorax
40
Q

How can CDH affect the developing lungs?

A
  • as the abdominal contents occupy the space of the developing lungs, this results in hypoplasia of one of the lungs
41
Q

What are the signs and symptoms of congenital diaphragmatic hernia?

A
  1. respiratory distress
  2. difficult resuscitation at birth
  3. cyanosis
  4. bowel sounds over one hemithorax (usually left)
  5. displaced heart sounds
42
Q

Why are there displaced heart sounds in CDH?

A
  • the presence of the intestines within the thorax leads to mediastinal shift
  • the heart is pushed over to the opposite side of the thorax (usually right)
43
Q

What 2 types of tubes must be inserted immediately after birth in CDH?

A
  • an endotracheal tube is inserted for mechanical ventilation
  • a nasogastric tube is inserted and an X-ray taken to confirm correct placement
  • the tube is seen passing through the oesophagus and curling back into the thorax as the stomach is situated within the thorax
44
Q

How can the lungs be affected by CDH?

A
  • a defect in the diaphragm results in herniation of bowel loops into the left (usually) side of the thorax
  • this results in hypoplasia of the left lung as it lacks space to develop properly
  • sometimes the right lung can become larger to compensate and protrude onto the left side (better prognosis)
45
Q

What are the 2 aims of prenatal foetal surgery for CDH?

A
  1. restore the gastrointestinal tract to the abdomen
  2. promote normal lung development
46
Q

How is prenatal foetal surgery performed in CDH?

A

FETO - foetal endoscopic tracheal occlusion

  • the intestinal contents are returned to the abdomen
  • a balloon is inserted towards the left bronchus and inflated
  • this causes fluid and pressure to build up within the left lung, forcing tissue to expand and promoting development of the hypoplastic lung
47
Q

What happens in twin-twin transfusion syndrome (TTTS)?

A
  • there is development of abnormal blood vessels between twins that share a placenta
  • this results in one twin receiving a greater share of the circulation compared to the other
48
Q

What problems can occur in the 2 twins involved in TTTS?

A
  • the twin receiving the larger share of the circulation is the “recipient twin”

they become overloaded, resulting in oedema** and **heart failure

  • the twin that is deprived of the circulation is the “donor twin”

they become dehydrated, resulting in renal failure

  • in the majority of cases, the prognosis is poor for both twins and neither will survive
49
Q

How can in utero foetal surgery be performed for TTTS?

A
  • laser ablation of vessels is associated with a good chance of survival for at least one twin
  • it is minimally invasive and requires only a small incision to insert a scope into the uterus
  • this allows for visualisation of abnormal vessels, which can be targeted with a laser