Flashcards in Paediatrics Deck (59)
The thyroid gland begins as an outgrowth from the
midline of the tongue in the primitive pharynx, which
moves caudally into the neck, looping around or
through the hyoid bone and moving caudally further
to its final site in the lower neck.
The thyroid may fail to descend, and remain as a
small gland in the tongue at the site where it started
its outgrowth (the foramen caecum, in the midline at
the junction of the anterior two-thirds and posterior
third of the tongue), or it may partially descend and
be mistaken for a thyroglossal cyst.
This ‘ectopic’ or incompletely descended thyroid tissue is invariably hypoplastic, and should be removed, as it may suffer from all the pathological problems of a normally sited thyroid. The patient should be investigated to see if they have any normally sited thyroid, which most of them do not. The patient will usually become hypothyroid, as this gland is hypoplastic, and if it is their only thyroid tissue, and it is removed, the patient will certainly become hypothyroid, but without
potential problems from the gland.
The thyroid may keep its connection to the tongue as the thyroglossal duct, and a cyst can develop anywhere along the line of this duct, the commonest site being at the level of the body of the hyoid bone. This thyroglossal cyst can present at any age, as a midline swelling in the upper neck, which moves upward when the tongue is protruded. Excision is advised, along with the whole
thyroglossal tract (and consequently the midportion
of the hyoid bone), in order to stop infection, following which excision is so much more difficult.
Dermoid cysts develop at an area where fusion of
sections of the embryo has occurred, and are most
common in the midline of the neck, at the external
angle of the eye, and behind the pinna. They should be removed to prevent secondary infection.
Cleft lip and palate
This is one of the more common congenital anomalies, occurring in 1 in 600 live births.
The face forms during the fifth to the eighth week,
from the maxillary and mandibular prominences of
the first branchial arch.
They grow and fuse together, and if this fusion is incomplete, unilateral or bilateral cleft lip may arise.
The palate develops after the eighth week, and
fusion occurs between the primary palate (the anterior section of the premaxilla and attached four front teeth) and the secondary palate (the hard and soft palate).
The palate may be cleft posteriorly only, a cleft soft palate, or it may extend anteriorly to include the hard palate, cleft palate only, and more commonly it extends further anteriorly to join up with either a unilateral or bilateral cleft lip.
Surgical correction of cleft lip and palate needs to
take the embryological origins and in particular the
blood supply into consideration, in order to allow an
optimum repair and subsequent growth.
The primitive lymph sacs develop in the mesenchyme in the sixth week, and the largest is in the neck, and should resolve, but persistence and sequestration produces a multicystic swelling within the neck which is a lymphangioma, a benign hamartoma (overgrowth of normal tissue), which is also called a cystic hygroma when it occurs in the neck.
Occasionally this is very large and causes respiratory distress in the neonatal age group, but more usually is just a soft swelling in the neck which may extend into the axilla, or even the chest.
A degree of spontaneous resolution can be
hoped for, but often it comes to surgical debulking – a difficult prospect because of the multicystic nature, which makes it difficult to be sure that every bit of the abnormal tissue is removed. If there is a haemangiomatous element as well as the lymphangiomatous part, spontaneous resolution is unlikely.
An MRI scan is recommended to delineate the full extent and nature of the lesion, and the normal structures which are involved, to help plan surgical excision.
Congenital diaphragmatic hernia
The diaphragm develops between the thoracic and
abdominal cavity, and this is a complex process which is finished before the end of the eighth week.
As the embryo folds and carries the primitive heart
and septum transversum caudally and ventrally, it
carries part of the yolk sac dorsally to develop as the foregut. The lateral mesenchyme develops into the pericardioperitoneal canals, from which the pericardial cavity and the lungs develop, and is separated from the peritoneal cavity by the closure of the diaphragm.
The motor nerve supply travels with the diaphragm as it descends, and so comes from a more cranial region than may be expected: C3–5. This explains the clinical observation that diaphragmatic infl ammation/irritation, e.g. due to intraperitoneal blood, can demonstrate referred pain and can cause shoulder tip pain (which area is also supplied by C4).
Diaphragm develops from the fusion of four
The diaphragm develops from the fusion of four
• The septum transversum (the fi brous central
• The mesentery of the foregut (the area adjacent
to the vertebral column becomes the crura and
• Ingrowth from the body wall (the peripheral
muscular portion); and
• The pleuroperitoneal membrane (a small dorsal
Types of congenital diaphragmatic hernia
There are different types of congenital diaphragmatic hernia, depending on which section has failed to close.
The most common defect is the posterolateral
Bochdalek hernia (through the pleuroperitoneal canal) which is more common on the left, as that side closes last. Absence of the diaphragm can also occur, or absence of the central tendon.
These three hernias tend to present early with respiratory distress soon after birth. The presence of the intestines within the pleural cavity antenatally prevents the normal development of
the lung on the ipsilateral side, and mediastinal shift
also prevents normal development of the contralateral lung.
If the lung hypoplasia is severe, it is not compatible with life. Urgent supportive ventilation is required, and nasogastric aspiration of the gut, to decrease direct pressure on the lungs.
Treatment of diaphragmatic hernias
These diaphragmatic hernias must be dealt with
surgically, after resuscitation of the patient (this is
sometimes not possible in a neonate because of the severity of the lung hypoplasia) – up to 50% of babies born with congenital diaphragmatic hernias will die even today with all the modern management possibilities of oscillatory and jet ventilation, or extracorporeal membrane oxygenation (bypass).
Morgagni hernias are small defects in the anterior
diaphragm close to the sternum, and are rarely associated with lung hypoplasia. They may be a coincidental fi nding on a chest x-ray taken for another reason.
These hernias also require surgical repair.
GI tract development
The foregut develops from the yolk sac which folds in to the embryo at its cephalad end during the fourth week.
From this foregut is derived the:
• pharynx (and from the floor of that the thyroid)
• airways and lungs
• duodenum (proximal to the opening of the bile
• liver, biliary system and pancreas.
The foregut starts to divide into the oesophagus and
the laryngotracheal tube during the fourth week. If it
fails to do so correctly, there can be pure oesophageal atresia (in 8% of cases), or atresia associated with tracheo-oesophageal fistula – the commonest (in 80% of cases), being a fi stula between the lower trachea and the distal oesophagus.
The baby presents soon after birth, unable to swallow saliva, and an attempt to pass a tube into the stomach fails. An x-ray taken then will show the tube in the proximal oesophagus, and either no gas below the diaphragm (in pure oesophageal atresia) or gas below the diaphragm (in patients with oesophageal atresia and tracheo-oesophageal fistula).
There is a high incidence (50% of babies) of associated anomalies described by the acronym
• Vertebral anomalies (e.g. hemivertebrae);
• Anorectal anomalies (e.g. imperforate anus);
• Cardiac anomalies;
• Tracheal anomalies (e.g. fi stula, tracheomalacia);
• Esophageal anomalies (the American version!);
• Renal anomalies; and
• Limb anomalies (e.g. radial aplasia).
Management of oesophageal atresia
Management involves protection of the lungs from
aspiration of saliva prior to surgical repair. This is
usually by a right thoracotomy to ligate the fi stula,
freeing the distal oesophagus which is then anastomosed primarily to the upper oesophageal pouch.
If primary repair is not possible, a feeding gastrostomy is performed to feed the baby until it has grown enough to perform a delayed primary anastomosis or oesophageal substitution, e.g. with stomach, colon, or small bowel.
The stomach develops from a simple tubular part
of the foregut by localised dilatation. The stomach
rotates clockwise so that the vagus which followed the left side of the oesophagus supplies the anterior stomach.
The mesentery which suspends the stomach from
the posterior abdominal wall enlarges and becomes
the greater omentum. The exit of the stomach into the duodenum is the pyloric canal.
All of the gastrointestinal tract has two layers of
muscle: circular and longitudinal. The circular muscle only of the pylorus can become hypertrophied in some babies. This is often called ‘congenital’ hypertrophic pyloric stenosis, but does not actually exist at birth.
Pyloric stenosis presentation
The baby usually presents after 10–50 days (most commonly 3–5 weeks), as the pyloric canal is narrowed by the hypertrophied muscle, and milk is prevented from leaving the stomach. The stomach becomes full and peristalses vigorously to try to empty. This peristalsis may be visible on the baby’s abdomen. The baby will then vomit forcefully, which is described as projectile.
As the baby vomits fluid and gastric hydrochloric
acid, the baby becomes dehydrated, hypochloraemic and alkalotic. This is reflected in the baby’s electrolytes and blood gases at presentation.
Diagnosis and treatment
The diagnosis is made by feeding the baby, to relax the baby. The visible peristalsis may be seen, and the abdomen is palpated to feel for the pylorus, which can be felt as a lump in the right upper quadrant, about the size and shape of an olive.
After rehydration and correction of
the acid-base balance, the baby is taken to theatre for a laparotomy, and the hypertrophied muscle is split, without opening the mucosa – a pyloromyotomy. This is a curative operation, and the baby will be fully fed within 24–36 h postoperatively and discharged home.
The duodenum develops from both the fore and the
midgut. The caudal part of the foregut, which is supplied by the coeliac artery, develops into the fi rst and second parts of the duodenum, up to the ampulla of Vater – where the bile and pancreatic ducts enter. The cephalad part of the midgut, supplied by the superior mesenteric artery, develops into the second part of the duodenum after the entry of the bile and pancreatic ducts, and the third and fourth parts.
Embryology of duodenal anomaly
The embryology of duodenal obstruction is different
to that of atresias lower in the intestine, and has
a greater number of associated other anomalies. During the fi fth and sixth week, the duodenum becomes occluded by proliferation of its endodermal lining. It then recanalises by the end of the eighth week, but if this recanalisation is incomplete, either atresia (complete occlusion) or stenosis (narrowing) of the duodenum occurs. 30% of babies with duodenal atresia have Down’s syndrome.
The pancreas develops from two outgrowths of the foregut, one ventral and one dorsal.
Due to rotation, the ventral bud and the adjacent
gallbladder and common bile duct rotates so that the ventral and dorsal buds lie adjacent to each other and fuse. The two ducts also usually fuse, and the main pancreatic duct enters the duodenum adjacent to the entry of the common bile duct at the ampulla of Vater.
The proximal part of the dorsal bud duct may persist as the accessory duct, which opens proximally into the duodenum. Occasionally the pancreas appears to encircle the duodenum – annular pancreas – and appears to be causing duodenal obstruction. This annular pancreas is invariably associated with an abnormality
of the development of the duodenum, which makes
it appear to be causing the obstruction, but is in fact an apparent effect rather than the true cause. This is supported by the fact that annular pancreas has also been recorded without associated obstruction.
Duodenal atresia presentation
Babies with duodenal atresia present in the fi rst
few days of life, vomiting every feed. Babies with duodenal stenosis present later – how much later depends on the degree of the stenosis.
The most common part of the duodenum to be obstructed is just distal to the ampulla of Vater, and so the vomit is most likely to be bilestained. Plain abdominal x-ray in duodenal atresia reveals a ‘double bubble’ – the first bubble being air in the distended stomach, and the second bubble being air in the distended duodenum.
The diagnosis may have been made antenatally, as the mother may have had ultra-sound scans. This reveals a double cystic structure – similar to the double bubble, but the appearance is not due to swallowed air but to swallowed amniotic fluid which is prevented from passing through the gastrointestinal tract by the obstructed duodenum. This can lead to polyhydramnios.
Due to the common association of duodenal atresia
and stenosis with other congenital anomalies, the
baby must be checked thoroughly, e.g. for Down’s syndrome, for cardiac and renal anomalies, etc.
Duodenal atresia treatment
After rehydration, the baby undergoes laparotomy,
and a duodenoduodenostomy – which is the most
physiological operative correction.
Duodenojejunostomy might bypass the obstruction, but leaves a blind part of the duodenum, which often fails to work and
causes later problems.
The midgut is supplied by the superior mesenteric
artery, and develops into the duodenum distal to the
entry of the bile/pancreatic duct, all of the small bowel, and the colon from the caecum to two-thirds of the way along the transverse colon.
Between the sixth and eleventh week, the midgut
develops and rotates. As the midgut lengthens, it
forms a loop which projects and herniates into the
base of the umbilical cord.
While the midgut is within the cord, it rotates through 90 degrees, counterclockwise
around the superior mesenteric artery. This brings
the third and fourth part of the duodenum across to
the left of the midline, behind the superior mesenteric artery, and this duodenum is fixed retroperitoneally.
The midgut returns to the abdomen during the tenth
week, and during this time it continues to rotate
counterclockwise through a further 180 degrees, which brings the ascending colon to the right side of the abdomen, with the caecum and appendix to the right iliac fossa.
The ascending colon also becomes retroperitoneal.
The mesentery of the small bowel stretches from the duodenojejunal fl exure in the left upper quadrant to the right iliac fossa.
Malrotation occurs when the normal rotation
sequence described above does not occur, or is incomplete. This results in the duodenojejunal fl exure not becoming fixed retroperitoneally in the left upper quadrant, but hanging freely from the foregut, and tending to lie on the right of the abdomen.
The caecum is also free, and may obstruct the
second part of the duodenum because of fi brous bands which stretch across the duodenum from the caecum. The base of the mesentery of the midgut is then very narrow, as it is not fi xed at either end, and the whole of this midgut can undergo twisting around its own blood supply, with resultant ischaemia.
This is malrotation volvulus, a true surgical emergency. These patients classically present in the firrst week or two of life with bilious vomiting. In neonates and infants, bilious vomiting has a surgical diagnosis in origin until proved otherwise.
Plain abdominal x-ray may show the small bowel on the right of the abdomen, and the large bowel on the left, suggesting malrotation.
This requires urgent resuscitation, and then laparotomy and correction, before a volvulus occurs. Even more worrying is an x-ray with no gas distal to the stomach – suggestive of a volvulus of the midgut.
This is potentially fatal if the whole of the midgut is
ischaemic, and again requires emergency laparotomy after urgent resuscitation. If the plain x-ray cannot confirm the diagnosis, a contrast meal will demonstrate the position of the duodenojejunal flexure and subsequent lie of the jejunum.
The diagnosis and management of malrotation of the midgut is one of the very few causes for true emergency neonatal laparotomy for a congenital anomaly.
Small and large bowel atresia
Duodenal atresia is thought to be due to a defect in
recanalisation during the eighth week of embryonic
Atresia of the small and large bowel is thought to occur later during fetal life, in the second
trimester (fourth to sixth months of pregnancy), and to be due to an ischaemic vascular accident of the
This is confirmed by the presence of bile (first produced in the eleventh week) and squames which have been swallowed (swallowing fi rst occurs after the third month) being found in the bowel distal to an atresia.
Jejunal atresia is twice as common as ileal atresia,
and both present in the first few postnatal days with increasing bilious vomiting and abdominal distension.
Small and large bowel atresia treatment
The atresias may be multiple, and apart from surgical correction, the main problem is any associated dysmotility of the bowel proximal to the atresia, short bowel syndrome, and complications of the total parenteral nutrition required to maintain the baby whilst the intestines function normally, if ever. Colonic atresia is very rare, and presentation and treatment is similar to that of small bowel atresia.
Meconium ileus is the term given to ileal obstruction
due to inspissated meconium in the terminal ileum in neonates. In 95% of cases, this is found to be due to cystic fibrosis. The intestinal secretions in babies with cystic fi brosis are abnormal, producing very thick and viscid meconium. In combination with abnormal pancreatic enzymes, this produces meconium which produces an intraluminal obstruction in the terminal ileum. The obstruction may be simple, and presents at birth with failure to pass meconium, abdominal distension, and bilious vomiting.
In some cases the obstruction is complex, with intrauterine perforation, volvulus, or atresias. Management includes treatment of the obstruction, and then investigation and treatment of the baby for cystic fibrosis. Cystic fibrosis is the most commonly inherited gene of a potentially lethal congenital disorder. It has an autosomal recessive inheritance, meaning that one in four pregnancies will be affected in a family. The genetics are now more fully identified, and the diagnosis
is made by DNA testing, looking for the delta F508
mutation on gene 7.