ABDOMINAL WALL DEFECTS

(EXOMPHALOS & GASTROSCHISIS)

JOHN LOADSMAN

12/10/94 (RAHC)

Types of Abdominal Wall Defects

1. Omphalocele/Exomphalos: Congenital herniation of abdominal contents at the umbilicus (i.e. into the umbilical cord). Occasionally divided into:
   • <4cm - umbilical cord hernia
   • >4cm - omphalocele.

Rarely occurs above or below umbilicus (see below). N.B. Amniotic sac (amnion & peritoneum) is always present but it may have ruptured at or before birth exposing the contents.

1. Gastroschisis: Full thickness abdominal wall defect situated almost always to the right of the umbilicus without a covering membrane. A bridge of skin separates it from the umbilicus.
   
   
2. Prune Belly Syndrome: Congenital deficiency of abdominal musculature, urinary tract dilatation and cryptorchidism. There are three grades:
   • I. Severe renal and pulmonary disease incompatible with life.
   • II. Severe uropathy requiring extensive reconstruction.
   • III. Healthy neonates requiring little or no surgery.
     
     
3. Others: e.g. Bladder extrophy.
   

Incidence

Omphalocele: 1:6,000
Gastroschisis: 1:20,000 - 30,000
Prune Belly: 1:50,000

Associations

1. Omphalocele: 30% have associated congenital defects (? up to 50%).
   • 20% have congenital heart disease, most commonly tetralogy.
   • G.I.T.
   • G.U.T., most commonly bladder extrophy.
   • C.N.S.
   • Beckwith-Wiedmann syndrome:
     • Omphalocele
     • Macroglossia (gigantism)
     • Visceromegaly
     • In 50% pancreatic hyperplasia leads to hypoglycaemia.
     • Polycythemia with hyperviscosity is also common.
       
       
2. Gastroschisis: Congenital associations are uncommon (?5 - 25%) but 22% are premature. The gut may be infarcted or perforated.
   
   
3. Prune Belly: >90% have associated defects:
   • G.U.T.
     • Cryptorchidism
     • Phimosis/meatal stenosis
     • Megaureter (85%)
     • Oligohydramnios
   • Respiratory
     • Pulmonary hypoplasia (?due to mechanical effect of oligohydramnios)
   • G.I.T.
   • Cardiac
   • Dislocated hips
   • Club feet
     

Embryology

Abdominal wall and bowel develop conjointly over the 3rd to 12th weeks in utero, final bowel fixation occurring after birth.

Week 3: the embryo has cephalic, caudal and lateral folds:

• Cephalic
  • Anterior
  • Contains:
    • foregut
    • stomach
    • mediastinal/thoracic contents
  • Somatic layer defect causes the rare epigastric omphalocele associated with diaphragmatic, thoracic wall and cardiac/pericardial defects.
• Caudal:
  • Posterior
  • Contains:
    • colon
    • rectum
    • bladder
    • hypogastric abdominal wall
  • Defects cause bladder extrophy or the rare hypogastric type of omphalocele.
• Lateral:
  • Forms:
    • lateral abdominal wall
    • future umbilical ring
  • Defects cause umbilical hernia or periumbilical omphalocele.

Weeks 4 - 10: Gut growth is faster than abdominal wall growth forcing the gut into the cord.

Weeks 10 - 12: Gut returns to the abdomen with counterclockwise rotation.

Gastroschisis has been blamed on intrauterine disruption of the right omphalomesenteric artery but it may be just a different expression of the same defect that causes omphalocele.

The embryology of Prune Belly Syndrome is unknown.

Initial Management

The Problems:

• Heat loss from exposed abdominal contents.
• Fluid loss into & from exposed bowel (greater with gastroschisis).
• Infection.
• Gastric distension.
• Associated malformations.

1. Fluid management:
   • excellent i.v. access mandatory.
   • ?choice of fluid:
     • loss is mainly isotonic with some protein
     • logically Hartmanns + NSA best.
   • may need 10 - 15ml/kg/hr + boluses.
     
2. Heat management:
   • usual problems of heat loss in neonates apply.
   • Additional loss from bowel may be reduced by covering with sterile wrap and towels or bowel bag (also helps to reduce fluid loss).
     
3. Infection control:
   • risk is reduced by covering bowel, prompt surgery and broad spectrum antibiotics.
     
4. Gastric Distension:
   • relieve with nasogastric tube.
     
5. Associations:
   • All need cardiac and respiratory review with appropriate investigations and treatment of associated defects/diseases.
   • All children with omphaloceles need repeated BSL's to exclude Beckwith-Wiedemann syndrome and hypoglycaemia. Treatment is with glucose infusion 6 - 8mg/kg/min. Boluses may cause severe rebound hypoglycaemia.
     

Surgical Management

• First decision:
  • Is the child fit for surgery at all?
  • Depends on associated defect.
  • If not then conservative management (used to be with mercurochrome to promote eschar formation!).
    
• Second decision:
  • Primary or staged closure?
  • Staged closure used a silon pouch which is gradually reduced in size ("reefed") then removed under G.A.
  • Depends on whether or not exposed contents will fit back into the abdomen.
  • Decision may have to wait till during surgery.
  • Based on:
    1. Size of defect:
       • extremes are obvious
         • small ones --> primary
         • very big ones --> staged
       • marginal ones more difficult, then based on:
    2. Surgical "preference":
       • some prefer to attempt primary closure since the prosthetic sac may dehiss and predispose to infection and ileus.
       • others prefer staged since there is less risk of dehiscence, marginal infarction, bowel ischaemia/infarction, i.v.c. obstruction with hepatic and renal ischaemia, and respiratory failure (primary closure usually requires 24 - 48hrs ventilation).
       • there doesn't seem to be much difference in outcome between the two in truly marginal situations.
    3. Intra-op indications: --> all suggest changing to a staged approach.
       • difficulty with ventilation after closure
       • measured gastric or bladder pressure > 20mmHg
       • lower body swelling/oedema
       • dusky wound margins
         

Anaesthetic Considerations

1. Usual problems of neonatal anaesthesia:
   • "warm"
   • "wet"
   • "sweet"
   • "pink"
     
2. Compounded by:

   • problems of prematurity when present - R.D.S.
   • associated cardiac defects
   • associated pulmonary hypoplasia
   • increased heat and fluid loss
   • hypoglycaemia in Beckwith-Weidemann

   • require
     • ongoing fluid/protein/red cell resuscitation
     • strict attention to heat preservation
     • BSL monitoring when appropriate
     • careful attention to respiratory function especially at time of closure and afterwards. Should be hand ventilated during closure. ?advisability of arterial line for sampling.
     • watch for impaired cardiac function after closure due to obstructed i.v.c. ?advisability of art line again.
       
3. Additional problems:
   • full stomach
     • NG tube
     • aspirate before induction
     • awake intubation or rapid sequence.
   • lower body congestion
     • lines in upper body
     • BP & SpO₂ on upper limbs
     • watch renal/hepatic function (may have reduced drug clearance).
   • controversy over muscle relaxation, most arguing its necessity but some saying it may make a marginal call a wrong one (i.e. gets too tight when NDMR wears off).
   • N₂O not a good idea:
     • use Air/O₂/Volatile.
   • question of post-op ventilation:
     • no
       • small ones
     • yes
       • bigger ones with primary closure
       • premature
       • associated defects
       • Prune Belly with poor musculature
     • ???
       • marginals (probably yes)
       • Big ones with pouch may be able to breath spontaneously since the abdominal pressure is low. Some suggest spont. resp. for final closure to assess if it's OK.
     • macroglossia/gigantism in Beckwith-Wiedemann may lead to difficulty with airway/intubation.
       
4. Analgesia:
   • epidural has been suggested as best:
     • good analgesia
     • reduced abdominal and vascular pressures
     • better respiratory function.