Congenital Abdominal Defects

Congenital Abdominal defects

Embryology  Abdominal wall and bowel develop conjointly over the 3rd to 12th weeks in utero, final bowel fixation occurring after birth.  Week 3: The abdominal wall is formed by four separate embryologic folds 1) Cephalic  Anterior  Contains: i. foregut ii. stomach iii. mediastinal/thoracic contents  Somatic layer defect causes the rare epigastric omphalocele associated with diaphragmatic, thoracic wall and cardiac/pericardial defect 2) Caudal  Posterior  Contains i. Colon ii. Rectum iii. Bladder iv. Hypogastric abdominal wall  Defects cause bladder extrophy or the rare hypogastric type of omphalocele. 3) right and left lateral folds  forms: i. lateral abdominal wall ii. 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.

Pathogenesis  result from failure of the mesoderm to replace the body stalk, which persists in a region the somatopleure normally occupies.  Embryonic dysplasia, decreased apoptotic cell death, and inadequate mesodermal development cause insufficient growth at the umbilical ring and enlargement of its diameter. Rather than investing the yolk sac and body stalk centrally at the umbilicus, the amnion remains attached to the margins of the body wall defect, creating a persistent communication between the intraembryonic body cavity and the extraembryonic coelom.  Gastroschisis has been blamed on ischemic insult to the developing body wall with intrauterine disruption of the right omphalomesenteric artery but it may be just a different expression of the same defect that causes omphalocele.  Prune belly occurs as a result of increased apoptotic cell death in the body-wall placode, which leads to insufficient deposition of mesodermal cells. Retention of an abnormally large amount of yolk sac causes attenuation of the abdominal musculature. Muscle fibers are absent and replaced by a thick collagenous aponeurosis. I

Classification

Majority of defects belong to one of four categories 1. diaphragmatic hernias 2. umbilical hernia 3. omphaloceles 4. gastroschisis 5. Prune Belly Syndrome

Congential Diaphragmatic hernia  3 basic types of CDH: 1. posterolateral Bochdalek hernia (90%) i. occurring at approximately 6 weeks' gestation ii. left-sided Bochdalek hernia occurs in approximately 90% of cases. Left- sided hernias allow herniation of both small and large bowel as well as intra-abdominal solid organs into the thoracic cavity. iii. right-sided hernias, only the liver and a portion of the large bowel tend to herniate. iv. Bilateral hernias are uncommon and usually fatal. 2. anterior Morgagni hernia (5-10%) i. occurs in the anterior midline through the sternocostal hiatus of the diaphragm, with 90% of cases occurring on the right side. 3. hiatus hernia. i. very rare in neonates. In this form, hernia of stomach occurs through the esophageal hiatus  characterized by a variable degree of pulmonary hypoplasia associated with a decrease in cross-sectional area of the pulmonary vasculature and dysfunction of the surfactant system.  With the use of extracorporeal membrane oxygenation a vast majority of infants survive with partial or complete agenesis  50% of children will need surgery  Reconstruction options 1. direct repair of diaphragm 2. prosthetic patches (Surgisis, Goretex) i. 50% will show reherniation and require revision within 3 years ii. have no growth potential and can cause restriction on the chest wall growth 3. muscle flaps i. difficult in the initial stages as they have high complication rate and increased risk of bleeding ii. Reversed latissimus dorsi . Based on lumbar perforating vessels . pleural cavity entered through the eighth intercostal space, . Muscle fixed to the bed of the tenth rib and sutured in place over a Vicryl mesh scaffold . thoracodorsal nerve was anastomosed to the phrenic nerve  recommendations are to use an absorbable mesh in the initial instant and then as the child grows , then use a muscle flap

Umbilical hernia  Failure of timely closure of the abdominal ring leaves a central defect in the linea alba. Relation of the amnion to the yolk sac and connecting stalk is normal.  Small hernias (<1 cm at the time of birth) usually close spontaneously by 1-2yrs  Larger defects can be surgically closed at 2ys  Curved infraumbilical incision used and the defect closed with permanent sutures

Omphalocele/ exomphalos

 Congenital herniation of abdominal contents at the umbilicus (i.e. into the umbilical cord).  <4cm considered an umbilical hernia, >4cm omphalocele  Rarely occurs above or below umbilicus  50-70% have associated congenital defects . 30% have chromosomal anomalies . 30-50% have congenital heart disease, most commonly tetralogy. . Pentalogy of Cantrell i. Omphalocele ii. Diaphragmatic hernia iii. Sternal cleft iv. Ectopia cordis v. Intracardiac anomaly . Associated feature in Beckwith-Wiedemann syndrome (10%)  A perpetuation of the existing intrauterine defect connecting the midgut and the yolk sac  usually larger than 4cm and contain liver and mid gut and a hernial sac  Amniotic sac (amnion & peritoneum) is always present but it may have ruptured at or before birth exposing the contents. Management  Emergency treatment involve resuscitation and stabilization and IV hyperalimentation when stable  if the covering sac is intact, then there is no urgency to perform operative closure.  Options 1. conservative a. squeezing the sac to reduce the herniated viscera or painting the sac with escharotic agents to promote epithelisation b. When the sac is epithelialized or otherwise sturdy enough to withstand external pressure, compression is done with elastic bandages and serially increased until the abdominal contents are reduced. When the abdominal contents are reduced, the membrane is epithelialized, and the baby is well, a ventral hernia repair is done. 2. Shuster technique . circumferential incision is made along the skin-omphalocele junction . omphalocele membrane is left intact . rectus fascia is exposed from xiphoid to pubis . Teflon sheets are sutured along the edge of the fascia and approximated over the omphalocele sac . As reduction is effected, the rectus muscles are elevated over the anterior aspect of the liver and gradually approximated. . At second stage, the Teflon sheets are removed; the omphalocele sac is excised, and a DualMesh patch (Gore-Tex), is sutured circumferentially to the rectus fascia. . Alloderm patch has been used instead of GoreTex o Alloderm may be left exposed and dressed with topical antimicrobials; like a partial thickness burn wound, is eventually epithelialized. o Disadvantage: as it is not rigid, leads to development of a huge ventral hernia, which ultimately requires repair with a rigid patch   Horbar uses tissue expander is placed between the IO and TA with tissue expansion of the outer (200%) and inner layers(50%)

Gastroschisis  Congenital defect of the abdominal wall to the right of the normal location of the umbilical cord that permits the escape of the intestine from the abdominal cavity  Contents not covered with amnion  Less often associated with other abnormalities (10-20%), usually GIT anomalies  The intestines are oedematous and mattered indicating the loops have been floating freely in the amnionic fluid  baby should be placed under a radiant heater, and the exposed intestines should be wrapped with a prefabricated, spring-loaded Silastic silo is placed in the defect to cover the exposed bowel  After the placement of the spring-loaded silo, the baby is evaluated further and cared for in the ICU.  With spontaneous diuresis, gastrointestinal tract decompression from above and below, and resolution of bowel wall edema, the volume of the exposed bowel in the bag markedly decreases in a short period of time.  When the baby is otherwise stable and the spontaneous reduction of bowel into the abdomen has reached a plateau, the baby is taken to the operating room for an attempt at delayed primary closure.  amount of inflammation and edema and turgor of the intestines determines whether reduction of the extruded intestine and closure of the abdominal wall can be accomplished.  Intestinal dysfunction takes 6 weeks to several months to normalize.  Same treatment principles as omphalocele but prompt return of contents to the abdominal cavity is indicated  Modification of Schuster technique used 1. Silastic sheets are sutured to the full thickness of the enlarged abdominal wall defect and closed over the eviscerated intestine by stretching the abdominal musculature, emptying the stomach and bladder, and manually evacuating the colon. 2. Too tight a closure of the abdominal wall must be avoided, keep Peak Inspiratory Pressures <25mmHg

Prune belly syndrome

 Congenital hypoplasia or aplasia of the abdominal musculature with marked wrinkling of the skin over the lower abdo  ncidence is 1 case in 30,000-50,000 births  thin, flaccid abdominal wall and hypertrophy of the bladder wall with dilatation of the bladder, ureters, and renal collecting system, which may be associated with obstruction of the prostate urethra at its junction with the bladder neck. \  Patients are infertile because absence of the prostate and seminal fluid precludes normal sperm development.  Rare, Mainly males (95%)  >90% have associated defects: Associated with hypoplastic kidneys, tortuous ureters, dilated bladder and cryptorchidism Management  Urinary diversion followed by staged reconstruction  Dissection of fascial remnant to the mid axillary line followed by medial advancement and closure in double breasted fashion  Bilateral orchidopexy and GU recon

Management of exposed viscera

Problems: i. Heat loss from exposed abdominal contents. ii. Fluid loss into & from exposed bowel (greater with gastroschisis). iii. Infection. iv. Gastric distension. v. Associated malformations.

1. Fluid management: a. excellent i.v. access mandatory- umbilical artery and vein may be cannulated if needed during resuscitation b. choice of fluid: i. loss is mainly isotonic with some protein ii. logically Hartmanns + NSA best. iii. may need 10 - 15ml/kg/hr + boluses. c. bladder catheter is useful to closely monitor urine output and guide the resuscitation 2. Heat management: a. usual problems of heat loss in neonates apply. b. 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: a. risk is reduced by covering bowel, prompt surgery and broad spectrum antibiotics. 4. Gastric Distension: a. May lead to aspiration b. relieve with nasogastric tube. 5. Associations: a. All need cardiac and respiratory review with appropriate investigations and treatment of associated defects/diseases. b. 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.