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.
Anterior abdominal wall defects
These comprise exomphalos and gastroschisis. The embryology of these two defects is not understood, and various theories have been postulated but with no definitive outcome, except that they are separate clinical entities. The closure of the anterior abdominal wall muscles occurs between the fourth and seventh week, and failure of this could explain exomphalos,but not gastroschisis where the anterior abdominal wall
muscles are in complete existence but with a defect.
Exomphalos is the herniation of a variable amount
of the intra-abdominal contents through the open
umbilical ring into the base of the umbilical cord. It
differs from an umbilical hernia, which is skin covered, as it is covered by a thin double membrane of peritoneum on the inside, and an outer layer of amniotic membrane. The size of the exomphalos varies from a single loop of bowel within it (minor exomphalos) to a giant exomphalos containing stomach, all of the small and large intestine, liver, spleen, pancreas and urinary
bladder, leaving the peritoneal cavity almost empty.
Gastroschisis babies have a full thickness defect in
the abdominal wall, usually adjacent to the right side of the umbilical cord. The intestines may be outside the defect to a varying degree, and the stomach, but never the liver. There is no sac or membrane covering the defect, and the intestines have been exposed to the amniotic fluid during pregnancy, and this often produces a very thickened and dysmotile bowel wall, from
which the baby may not recover. The defect is much narrower in gastroschisis, and there may be vascular ischaemic insults to the exteriorised bowel, causing atresias, or even complete absence.
Babies with exomphalos may have other associated
congenital malformations, some of which may
be incompatible with life, for instance major lethal
cardiac or chromosomal anomalies. Gastroschisis is rarely associated with other anomalies, although there may be gastrointestinal atresias or bowel malfunction.
Treatment of anterior abdominal wall defects
The principle of management of both anterior
abdominal wall abnormalities is to replace the exteriorised bowel/organs into the abdominal cavity, and then to feed the baby intravenously until his/her own guts tolerate enteral nutrition. If there is no other gross congenital abnormality in an exomphalos baby, the problem is closure of the abdominal wall defect. Once this is complete, the guts usually function well. In a gastroschisis baby, the problem is that even though it is usually easier to get the guts back into the peritoneal cavity, the bowel may be slow to, or may never, function.
Antenatal diagnosis of both these anomalies is very
common these days, and, if there is an exomphalos, chromosomal analysis will be recommended, with scanning for other major anomalies. A baby with gastroschisis rarely has other anomalies, but regular scanning is carried out during pregnancy to watch for intestinal catastrophes.
Umbilical remnant: Meckel’s diverticulum
The vitello-intestinal duct is the remnant of the yolk
sac which is attached to the primitive midgut in the
first few weeks of embryonic development. It should
completely obliterate during the sixth week, but may persist completely or in part. If it persists
completely, there is a diverticulum, the Meckel’s diverticulum, which arises from the terminal ileum.
The classical description in adults is that it is present in 2% of the population, is 2 inches (5 cm) long, and 2 feet (60 cm) from the ileocaecal valve. A persistent vitellointestinal duct can present at birth, as a swelling at the base of the umbilical cord, or as a fi stulous connection to the umbilicus, or as an umbilical polyp, which does not respond like simple granulation tissue to cautery, because it has a mucosal surface.
Meckel's diverticulum treatment
Surgical excision is required. It may be lined by ileal mucosa, or contain ectopic gastric mucosa, which may undergo peptic ulceration with subsequent bleeding. It may present with diverticulitis (like appendicitis), or with adhesion/
band obstruction and volvulus because of its persistent attachment to the umbilical cord.
Management is by excision after the diagnosis
has been made – which is often only at laparotomy,
although it may be suspected beforehand. There is no definitive scan or investigation to confi rm the existence of a Meckel’s diverticulum. A radiolabelled technetium scan looking for ectopic gastric mucosa (that is, outside the stomach) is only positive in about 70% of patients with a Meckel’s diverticulum who present with rectal bleeding.
Umbilical remnant: Urachus
The urachus is the embryonic remnant of the connection between the urinary bladder and the allantois at the umbilicus (Fig. 16.9). It can also persist, either in part – as a cyst or fi ne cord, or completely – as a mucosa-covered structure at the umbilicus, from which urine comes. Treatment is by surgical excision after accurate diagnosis.
The structures of the rectum, anus and genitourinary tracts are created by the end of the ninth week of gestation, by separation of these structures within the cloaca. The exact mechanism of these events has never been clear, and there is still no consensus.
The cloaca contains the hindgut and the urogenital
passage (Fig. 16.9). The cloacal membrane should
extend from the genital tubercle anteriorly to the tail
dorsally and initially separates the future gut and urinary passages from the amniotic cavity. The urorectal septum is a mass of mesenchymal tissue between these two passages. As the cloacal membrane thins dorsally and the tail regresses, the hindgut and urogenital passages open into the amniotic cavity. The distance between these passages increases as the urorectal septum
broadens, with the urogenital passage maintaining close proximity to the genital tubercle anteriorly, and the gut passage moving relatively dorsally.
The mesenchyme of the urorectal septum develops into the muscles of the pelvic fl oor and sphincter mechanisms. If the cloacal membrane does not reach the tail groove, abnormalities of the anorectum occur – with the many types of anorectal anomalies which exist.
Anorectal anomalies types
The varieties of anorectal anomalies can be broadly
divided into low, intermediate and high, in males and females. The high lesions commonly have a fistula, which goes anteriorly – to the urinary system in a boy, or to the vagina in a girl.
The division into high or low is dependent on the
amount of mesenchymal tissue which existed in the
urorectal septum, from which the sphincter mechanisms developed. If most or all the sphincter muscles develop it is a low lesion; or, if very little, a high lesion.
Anorectal anomaly high and low lesions I
A high lesion is associated with poor continence, even after surgical reconstruction, but even the low lesions often have problems of continence; and both types have associated problems with the urinary system.
After birth, all babies must be examined for the
presence of a normally sited anus. If the anus is imperforate, assessment and investigations may help identify the lesion to be high or low. In the former case, a fistula is looked for, and the parents are warned about the long term difficulties in achieving normal continence.
Anorectal anomaly high and low lesions II
The baby may have a colostomy formed, and a definitive pull through operation at the age of a few months; or it is becoming more common for that definitive procedure to be done at the first operation if the baby is healthy, and the surgeon experienced.
A low imperforate anus is dealt with by a local procedure, and longterm followup still needs to be maintained until the child has developed continence.
Although Hirschsprung described two patients with
this disease in 1887, it was not until 1948 that the histopathological abnormality of aganglionosis was identifed.
The aganglionosis is in the colonic wall, always
involving the distal rectosigmoid, and extending proximally for a variable length (total colonic aganglionosis occurs, as does total gastrointestinal aganglionosis).
The aganglionosis does not allow normal gut peristalsis, and is non-propulsive, thereby producing a functional intestinal obstruction.
Histology of Hirschsprungs disease
Proximal to the abnormal section is a transitional zone which is hypoganglionic, and then the normally ganglionic bowel is chronically distended – a megacolon – because of the functional
obstruction. As well as aganglionosis, the other
histological abnormality is hypertrophied nerve trunks in the bowel wall, which stain densely for acetylcholinesterase.
The combination of these two histological
techniques – cholinesterase staining and routine histology for ganglion cells – enables the diagnosis of Hirschsprung’s disease to be made on a suction rectal biopsy on a newborn baby who classically presents at the age of 36 h with abdominal distension, bilious vomiting, and failure to pass meconium (they should pass meconium within 24 h of delivery).
Treatment of Hirschsprungs disease
Treatment is aimed at decompression of the bowel,
either with a stoma in ganglionic bowel just proximal to the transitional zone, or by regular washouts, until a defi nitive operation is performed.
On this occasion, the aganglionic bowel is excised and normal ganglionic bowel brought down to the anus, to prevent the functional obstruction. The operative procedures available are many and variable, indicating as ever that the perfect procedure is still elusive.
Most cases are sporadic, but occasional cases are
familial. In these cases, the affected segment tends to be longer, and increases in length as the number of affected children increases. There is still no gene probe available to test antenatally.
Renal and ureteric and urethral: Normal development I
The development of the kidneys, ureters and reproductive system is an overlapping process which consists of the development and degeneration of various organs and ducts. It starts in very early fetal life (the third week) with the first ‘kidney’ – the pronephros, which does not function.
The second ‘kidney’ appears in the fourth week, as the pronephros is degenerating, and is the mesonephros with its mesonephric duct. This
mesonephros also degenerates, but the mesonephric duct persists (the Wolffian duct), which in males persists and develops into the epididymis, vas deferens,ejaculatory ducts and seminal vesicles.
Renal and ureteric and urethral: Normal development II
In females, this Wolffian duct degenerates, but the paramesonephric ducts (Mullerian ducts) grow and develop into the female genital tract. The Mullerian ducts do not persist in the male (due to the secretion of Mullerian inhibiting substance), apart from the most cranial end which persists as the appendix testis (hydatid of Morgagni) on the upper pole of the testis – which may undergo torsion
and present the patient with acute scrotal pain.
The third and final kidney starts development in
the fifth week, as metanephric mesoderm in both
sides of the pelvis is invaginated by the metanephric
duct on that side – which is the ureteric bud,
or diverticulum growing from the caudal end of the
mesonephric duct. The ureter continues to grow into
the renal tissue, and undergoes repeated branching
until it has developed into the full collecting
system of ureter, renal pelvis, calyces and collecting tubules. These collecting tubules fuse with the nephrons, the renal tubules of the metanephric tissue, to form the defi nitive kidney and collecting system.
Renal and ureteric and urethral: Normal development III
Abnormalities of the collecting tubules can lead to
polycystic disease of the autosomal recessive variety, which can be lethal (usually within a year or so of birth), or the autosomal dominant variety, which is more likely to present in the third decade of life
These definitive kidneys are initially close together
in the pelvis, but then, as the abdomen grows, the two kidneys separate and move cranially until they lie in their final position in the lumbar region. As the kidney moves cranially, its blood supply also moves cranially. The artery comes from more and more cranially, initially from the iliac artery and then from the aorta. The venous drainage also goes into the inferior vena cava in a more cranial position. Although each kidney may have only one artery and vein, their blood supply is very variable, especially to the lower pole if the previous vessels have not degenerated.
Renal and ureteric and urethral anomalies I
This complex developmental process explains the various congenital anomalies of the renal tract which are seen. If the kidney fails to ascend to its normal position, it can be ectopic, anywhere along the normal line, although pelvic is most common (Fig. 16.14).
If the kidneys fuse whilst they are close together in
the pelvis, they can remain fused by a bridge of tissue connecting each lower pole – a horseshoe kidney (Fig.16.14). Abnormalities of reflux and urinary drainage are more common in these abnormal kidneys. Division of the ureteric bud at an early stage leads to a divided, or duplex kidney.
Renal and ureteric and urethral anomalies II
This duplex kidney itself is not necessarily associated with abnormalities of reflux
or obstruction. If the ureters draining the two parts of the kidney are completely separate, the cranial part of the kidney invariably drains more caudally, either lower into the bladder, or even into the urethra in a boy or the urethra or vagina in a girl, causing problems of continence due to this ectopic ureter if it drains outside the urethral sphincter (Fig. 16.14).
The existence of urinary tract anomalies is commonly detected during routine antenatal scanning. It has not been found helpful to intervene antenatally, as the renal damage from anatomical changes has occurred before the date of the early antenatal scans in the 14th–20th week.
Renal and ureteric and urethral anomalies III
It is essential however to accurately investigate the
baby postnatally, especially if bladder outfl ow obstruction is possible, which may lead to bilaterally damaged kidneys. The usual initial investigations include a urine for culture, an ultrasound of the urinary tract, and close monitoring. The urea, electrolytes and creatinine
may be measured if poor renal function is suspected, remembering that the fi gures in the fi rst 24 h of life only refl ect the mother’s renal function, due to placental clearance of the baby’s waste products.
The commonest abnormalities of the urinary tract
of paediatric surgical relevance are vesico-ureteric
reflux, or obstruction.
Vesico-ureteric reflux (VUR)
Vesico-ureteric reflux (VUR) is the retrograde fl ow
of urine from the bladder into the ureters. If the child
gets a urinary tract infection (UTI), there is a chance of infected urine refl uxing into the kidneys, risking renal cortical damage and scarring. Refl ux is treated energetically with prophylactic antibiotics to prevent UTIs and thus to prevent renal damage.
Surgery is rarely performed for simple reflux these days. If it is required, the surgical principle is to reimplant the ureter with a long submucosal tunnel, to prevent the reflux. Unilateral obstruction is most commonly seen at the junction between the renal pelvis and the upper ureter – pelvi-ureteric junction (PUJ) obstruction – or less commonly at the junction between the lower ureter and
the bladder, vesico-ureteric junction (VUJ) obstruction, the causes of which are unknown.
Vesico-ureteric reflux (VUR) II
Bilateral PUJ or VUJ obstruction does occur, but less commonly. PUJ obstruction may be due to a ureteric kink, a high ureteric insertion, a narrow area of ureter, extrinsic bands, or an aberrant blood vessel. Surgical treatment, if required, consists of a pyeloplasty, where the narrow upper end of the ureter is excised, along with the distended renal
pelvis. The remaining collecting system is anastomosed to the ureter, with a wide drainage channel.
Unilateral obstruction to urine drainage can cause
deteriorating renal function on that side, and operative intervention is undertaken if that is happening.
Vesico-ureteric reflux (VUR) III
Commonly, however, the obstruction is incomplete
and the renal function is maintained. Many children
will ‘grow out’ of the obstruction over the fi rst few
years of life, and surgery can be avoided.
Bladder outflow obstruction can occur in boys,
but rarely, due to posterior urethral valves, which are
membraneous mucosal folds in the posterior urethra
distal to the veru montanum.
This serious anomaly can be lethal if the valves cause severe obstruction leading to renal failure. If there is only mild obstruction, they may only be detected in childhood during investigations of a boy with a urinary tract infection, or with difficulty in becoming dry. Surgical treatment involves endoscopic ablation of the valves.
Some patients can have a combination of refl ux and obstruction.
This is one of the commonest congenital anomalies, affecting 3 per 1000 boys. It occurs as a result of failure of complete fusion of the urogenital folds on the penis. Eighty-five percent will have minor degrees of hypospadias
only (i.e. glandular). This leaves 15% having moderate (urethral opening on the penile shaft) or severe (urethral opening at the base of the penis or perineal) hypospadias. The degree of severity dictates the type of surgical correction performed, but it is expected that, eventually, most boys will pass urine from a near terminal meatus. In severe cases, especially if the testes are impalpable, intersex must be considered and excluded, and also congenital adrenal hyperplasia syndrome.
Surgical correction involves construction of a
neo-urethra, and is a complicated process, especially in the more proximal hypospadias. The urethral meatus should end on the glans, and should enable the boy to stand and pass urine normally in a good stream.
This is very rare, the urethral opening being on the
dorsal surface of the penis. It is usually associated with more complex penile anomalies, which may require very complex surgical correction.
Hernia, hydrocele and imperfect descent of the testis
The gonads in both sexes develop from the urogenital ridges. Up to the seventh week of the embryo, it is not possible to differentiate between the sexes, but then the Y chromosome in the male leads to testosterone production and to the differentiation of the gonad into a testis.
The mesonephric duct (Wolffian duct)
becomes the epididymis, vas deferens and ejaculatory duct. Males also release Mullerian-inhibiting substance, which inhibits the development of the paramesonephric
ducts (Mullerian ducts) – which become
the reproductive organs in female embryos.
At the time the second kidneys – the mesonephric
kidneys – are degenerating, the gonads descend from the abdomen into the pelvis. A peritoneal diverticulum protrudes through the internal ring of the anterior abdominal wall, as the processus vaginalis. This occurs by the 15th week. After the 28th week, the gubernaculum with its adjacent patent processus vaginalis (PPV) migrates into the scrotum, with the testis posterior to the PPV. Once complete testicular descent has occurred, the PPV should obliterate.
If the PPV remains patent, a congenital hydrocele is found clinically (Fig.16.15). Fluid migrates up and down the PPV to and from the peritoneal cavity, allowing the size of the hydrocele to alter. The PPV can obliterate in part, leaving an encysted hydrocele of the cord (Fig. 16.15).
If the PPV is large enough, it allows abdominal contents to prolapse into the scrotum – an inguinal hernia. Surgical correction of congenital inguinal hernia and PPV ligation are two of the commonest paediatric surgical procedures. The principle is to explore the inguinal region, to locate the hernial sac or PPV either within or as it leaves the inguinal canal, to separate that sac from the spermatic cord in a boy, and to ligate the sac.
Failure of the testis to descend fully is known as an
undescended testis. This can lead to the testis being located anywhere along the line of normal descent, down the posterior abdominal wall, in the inguinal canal or in the upper scrotum.
If the testis descends, but to an abnormal position, it is called ectopic.
Ectopic testes are very uncommon, but can be found in the perineum, in the upper part of the femoral triangle in the thigh, at the base of the penis, or in the anterior abdominal wall. An undescended testis usually has a patent processus vaginalis associated with it.