By MRCSA in MRCS Part A — 04 Jul 2026

57 PAEDIATRIC GENERAL SURGERY

PAEDIATRIC GENERAL SURGERY

Paediatric surgical emergencies are an MRCS Part A favourite because each condition has a tight age window, a pathognomonic clinical sign, and a single best investigation. Master those three columns for each disease and you will answer most SBAs on sight.

The master table — group by age and presentation

The fastest way to revise this topic is by age at presentation. If you remember nothing else, remember the row.

Age	Condition	Cardinal feature	First-line investigation	Treatment
Day 1 (newborn)	Oesophageal atresia + TOF	Can't pass NG tube; antenatal polyhydramnios	CXR (NG coiled in upper pouch; air in stomach if distal TOF)	Surgical repair
Day 1 (newborn)	Congenital diaphragmatic hernia	Respiratory distress, scaphoid abdomen, bowel sounds in chest	CXR	Stabilise then surgical repair
Day 1 (newborn)	Malrotation + volvulus	Bilious vomiting in a neonate	Upper GI contrast — corkscrew sign	Ladd's procedure
Day 1–2	Duodenal atresia	Bilious vomiting; Down's syndrome	AXR — double bubble	Duodenoduodenostomy
Day 1–2	Meconium ileus	Failure to pass meconium <48h; cystic fibrosis	Contrast enema (microcolon)	Gastrografin enema ± surgery
Day 2+	Hirschsprung's disease	Delayed meconium >48h, abdo distension, bilious vomit	Rectal suction biopsy (absent ganglia)	Pull-through (Soave/Duhamel)
Day 7–14 (preterm)	Necrotising enterocolitis	Bloody stools, distension, bile aspirates	AXR — pneumatosis intestinalis, portal venous gas	NBM + abx; surgery if perforation
4–6 weeks	Pyloric stenosis	Non-bilious projectile vomit, olive RUQ	USS (pylorus >3 mm thick, >15 mm long)	Ramstedt's pyloromyotomy
6 m – 2 y	Intussusception	Colicky pain, redcurrant jelly stool, sausage mass	USS — target/donut sign	Air enema first; surgery if fails
1–2 y	Meckel's diverticulum	Painless melaena from ectopic gastric mucosa	Technetium-99m pertechnetate (Meckel's) scan	Surgical resection
2–6 y	Juvenile polyp	Painless fresh PR bleed, prolapsing mass	Colonoscopy	Polypectomy
<2 y	Neuroblastoma	Abdominal mass, raccoon eyes, bone mets	Urinary catecholamines (VMA/HVA), MIBG scan	Chemo + surgery
3–4 y	Wilms' tumour	Painless flank mass, haematuria	USS abdomen then CT	Nephrectomy + chemo

Pyloric stenosis

Hypertrophy of the pyloric circular muscle progressively narrows the gastric outlet. The classic candidate is a first-born male, 4–6 weeks old, presenting with non-bilious projectile vomiting shortly after every feed, ravenous hunger afterwards, and failure to thrive. The vomit is non-bilious because the obstruction is proximal to the ampulla of Vater.

The pathognomonic sign is an olive-shaped mass in the right upper quadrant, best felt during a test feed when the abdominal wall relaxes. Visible gastric peristalsis may be seen rolling left-to-right across the epigastrium.

👩‍⚕️ Biochemistry is the favourite exam stem: hypochloraemic, hypokalaemic metabolic alkalosis. Loss of HCl in vomit drops chloride and raises bicarbonate; the kidneys retain Na⁺/H₂O at the expense of K⁺ and H⁺ (paradoxical aciduria).

Diagnosis: ultrasound — pyloric muscle thickness >3 mm and channel length >15 mm.

Management: correct fluids and electrolytes FIRST, then Ramstedt's pyloromyotomy. Operating on an alkalotic baby risks post-anaesthetic apnoea — this is a classic exam trap.

Intussusception

Telescoping of one segment of bowel into the next, most commonly ileocolic (terminal ileum into caecum). Peak age 6 months to 2 years. Often follows a viral illness (Peyer's patch hypertrophy acts as the lead point); in older children look for a pathological lead point (Meckel's, polyp, lymphoma, Henoch-Schönlein purpura).

The triad is colicky abdominal pain (child draws up knees, screams, then settles between episodes), redcurrant jelly stool (late sign — sloughed mucosa and blood), and a sausage-shaped mass in the right upper quadrant.

Investigation: ultrasound shows the target / doughnut sign (transverse) or pseudokidney sign (longitudinal).

Treatment: air (or contrast) enema reduction is both diagnostic and therapeutic and succeeds in ~80%. Surgery is reserved for failed reduction, peritonitis, or perforation.

Malrotation and midgut volvulus

Failure of normal 270° anticlockwise rotation of the midgut around the SMA during week 10 leaves the caecum high and the small bowel mesentery on a narrow pedicle. The bowel can then twist around the SMA — a midgut volvulus.

👩‍⚕️ Bilious vomiting in a neonate is malrotation with volvulus until proven otherwise. This is a true surgical emergency — delay leads to infarction of the entire midgut.

Investigation: upper GI contrast study — the duodeno-jejunal flexure lies on the wrong side of the midline and the contrast shows a corkscrew pattern.

Treatment: Ladd's procedure — division of Ladd's bands, broadening of the mesentery, placement of small bowel on the right and colon on the left, and appendicectomy.

Hirschsprung's disease

Failure of neural crest cells to migrate to the distal hindgut leaves a segment of colon devoid of ganglion cells in the myenteric (Auerbach) and submucosal (Meissner) plexuses. The aganglionic segment is tonically contracted and functionally obstructed; the proximal bowel dilates.

Classic stem: a term infant with delayed passage of meconium (>48 hours), abdominal distension and bilious vomiting. M:F ~4:1. Associated with Down's syndrome. The rectosigmoid is the most commonly affected segment.

Diagnosis: rectal suction biopsy showing absent ganglion cells and hypertrophied acetylcholinesterase-positive nerve fibres.

Treatment: rectal washouts then a pull-through procedure (Soave / Duhamel / Swenson).

Meconium ileus

Thick, inspissated meconium obstructs the distal ileum. ~90% of cases occur in babies with cystic fibrosis — pancreatic insufficiency and abnormal mucus glycoproteins produce abnormally viscid meconium. Presents in the first 24–48 hours with bilious vomiting, distension and palpable bowel loops.

Investigation: contrast enema shows a microcolon (unused, narrow distal colon).

Treatment: gastrografin (hyperosmolar) enema — both diagnostic and therapeutic. Surgery if enema fails or there is meconium peritonitis (antenatal perforation → intra-abdominal calcifications).

Necrotising enterocolitis (NEC)

A devastating ischaemic-inflammatory disease of the neonatal bowel. Risk factors: prematurity, low birth weight, formula feeding, hypoxia, sepsis. Terminal ileum and proximal colon are most affected. Presents around day 7–14 with feed intolerance, bile-stained NG aspirates, abdominal distension, bloody stools and systemic deterioration.

Investigation: AXR shows pneumatosis intestinalis (intramural gas — pathognomonic), portal venous gas and, if perforated, Rigler's sign or free air.

👩‍⚕️ Bell's staging guides management. Stage I–II: NBM, NG decompression, IV antibiotics, TPN. Stage III (perforation, full-thickness necrosis, clinical deterioration): laparotomy with resection of necrotic bowel and stoma formation.

Oesophageal atresia and tracheo-oesophageal fistula (TOF)

Failure of the tracheo-oesophageal septum to divide the foregut. Five anatomical variants exist; Type C (proximal oesophageal blind pouch with distal TOF) is by far the most common (~85%).

Antenatal clue: polyhydramnios (foetus cannot swallow amniotic fluid). At birth: drooling, frothy oral secretions, choking with feeds, cyanosis. Failure to pass an NG tube past ~10 cm is the cardinal sign. CXR shows the NG tube coiled in the upper pouch; air in the stomach indicates a distal TOF (without TOF, the abdomen is gasless).

👩‍⚕️ Look for VACTERL associations: Vertebral, Anorectal, Cardiac, Tracheo-oesophageal, oesophagEal, Renal, Limb.

Treatment: surgical ligation of fistula and primary oesophageal anastomosis.

Congenital diaphragmatic hernia

Failure of fusion of the pleuroperitoneal membrane → abdominal viscera herniate into the thorax → pulmonary hypoplasia.

- Bochdalek: Back and to the left, Big. Posterolateral defect; left-sided in ~85%; commonest type.

- Morgagni: anterior (retrosternal), right-sided, smaller, often asymptomatic.

Presentation: respiratory distress at birth, scaphoid abdomen (gut is in the chest), displaced apex beat, bowel sounds in the thorax.

Treatment: stabilise (intubate, NG decompression — do NOT bag-mask ventilate as it inflates herniated bowel), then surgical reduction and diaphragmatic repair. Outcome depends on the degree of pulmonary hypoplasia, not the hernia itself.

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Paediatric inguinal hernia

Persistence of a patent processus vaginalis allows abdominal contents to enter the inguinal canal — always indirect. M>>F. Higher incidence in premature infants. Right side commoner (later closure of the right processus).

👩‍⚕️ Unlike adults, paediatric inguinal hernias are repaired promptly because the risk of incarceration is high (and the contents can include ovary in girls). Repair is a simple herniotomy (high ligation of the sac) — no mesh.

Undescended testis (cryptorchidism)

The testis fails to complete its descent from the abdominal wall to the scrotum. Found in ~3% of term and ~30% of preterm boys; most descend spontaneously by 3 months. If still undescended at 6 months, refer for orchidopexy by 12–18 months.

Why operate? Two reasons examiners want you to know:

- ↑ Risk of seminoma (the risk persists even after orchidopexy, but earlier surgery allows palpable surveillance).

- Impaired fertility (higher scrotal temperature is needed for normal spermatogenesis).

Also higher rates of torsion and inguinal hernia.

Wilms' tumour (nephroblastoma)

The commonest renal malignancy of childhood. Peak age 3–4 years. Presents with a painless, smooth, unilateral flank mass (doesn't cross the midline), haematuria and hypertension (renin secretion).

Associations: WAGR syndrome (Wilms, Aniridia, Genitourinary anomalies, Retardation — WT1 deletion), Beckwith-Wiedemann, Denys-Drash.

Investigation: abdominal ultrasound first, then CT for staging.

Treatment: nephrectomy plus chemotherapy ± radiotherapy. Prognosis is excellent (>90% survival).

Neuroblastoma

A malignancy of neural crest origin arising in the adrenal medulla or sympathetic chain. Commonest extracranial solid tumour of childhood. Median age <2 years.

Presents with an irregular, midline-crossing abdominal mass, systemic upset (weight loss, fevers), and signs of widespread metastases — bone pain, lytic lesions, periorbital ecchymoses ("raccoon eyes") from skull metastases, and opsoclonus-myoclonus ("dancing eyes, dancing feet").

Investigation: urinary catecholamine metabolites (VMA, HVA), MIBG scan, biopsy.

👩‍⚕️ Wilms vs neuroblastoma is a classic SBA pair. Wilms = older child (3–4), smooth, doesn't cross the midline, haematuria. Neuroblastoma = younger (<2), irregular, crosses midline, raccoon eyes, raised catecholamines.

Comparison: the bilious-vomit differential

Feature	Malrotation/volvulus	Duodenal atresia	NEC	Hirschsprung's
Age	Day 1 (any age really)	Day 1	Day 7–14, preterm	Day 2+
Vomit	Bilious	Bilious	Bilious aspirate	Bilious
Abdomen	Initially scaphoid	Scaphoid	Distended, tender	Distended
Meconium	Passed	Passed	Passed	Delayed >48h
AXR	Distal gasless	Double bubble	Pneumatosis	Distended loops
Key test	Upper GI contrast	AXR	AXR	Rectal biopsy
Down's link	–	✔	–	✔

[Image: MCQs banner]

Test yourself

A 5-week-old first-born boy has projectile non-bilious vomiting and an olive-shaped mass in the RUQ. What is the most likely diagnosis?

((Hypertrophic pyloric stenosis::☑️ Classic age 4–6 weeks; non-bilious projectile vomit; palpable pyloric "olive".))
((Duodenal atresia::Presents day 1 with bilious vomit and double-bubble on AXR.))
((Gastro-oesophageal reflux::Non-projectile, weight gain preserved, normal electrolytes.))
((Malrotation with volvulus::Vomit is bilious; surgical emergency at any age.))

👩‍⚕️ Non-bilious = obstruction proximal to ampulla of Vater.

Which ABG pattern is expected in pyloric stenosis?

((Hypochloraemic, hypokalaemic metabolic alkalosis::☑️ Loss of HCl in vomit; renal K⁺ wasting causes paradoxical aciduria.))
((Metabolic acidosis with raised lactate::Suggests ischaemic bowel (e.g. volvulus, NEC).))
((Respiratory alkalosis::Tachypnoea; not the primary metabolic disturbance here.))
((Hyperchloraemic acidosis::Pattern of diarrhoea or RTA, not gastric outlet obstruction.))

A baby with pyloric stenosis is admitted. What is the first step in management?

((IV fluid and electrolyte resuscitation::☑️ Correct alkalosis and hypokalaemia BEFORE anaesthesia to avoid post-op apnoea.))
((Immediate Ramstedt's pyloromyotomy::Definitive but not until biochemistry is corrected.))
((Endoscopic balloon dilatation::Not used; hypertrophy is muscular, not a stricture.))
((Trial of thickened feeds::Appropriate for GORD, not pyloric stenosis.))

An 8-month-old has colicky pain, a sausage-shaped RUQ mass and redcurrant jelly stool. Best initial investigation?

((Abdominal ultrasound::☑️ Target/doughnut sign confirms intussusception quickly and without radiation.))
((Air enema::This is the first-line TREATMENT once diagnosed.))
((CT abdomen::Avoided in children where USS is diagnostic.))
((Plain AXR::May show paucity of gas in RLQ but is not diagnostic.))

Air enema fails to reduce an intussusception. What is the next step?

((Surgical reduction::☑️ Indicated for failed enema, peritonitis, or perforation.))
((Repeat enema after 24 hours::Risk of perforation and bowel ischaemia rises.))
((Observation::Inappropriate — ongoing risk of ischaemic bowel.))
((Oral rehydration and discharge::Unsafe; intussusception is a surgical emergency.))

A neonate vomits bile on day 1 of life. Which diagnosis must be excluded first?

((Malrotation with midgut volvulus::☑️ Bilious vomiting in a neonate is volvulus until proven otherwise.))
((Pyloric stenosis::Non-bilious; presents at 4–6 weeks, not day 1.))
((Necrotising enterocolitis::Typically preterm, day 7–14, with pneumatosis on AXR.))
((GORD::Does not cause bilious vomiting.))

What investigation confirms malrotation with volvulus?

((Upper GI contrast study::☑️ Corkscrew duodenum and abnormal position of duodeno-jejunal flexure.))
((Abdominal ultrasound::Can show SMA/SMV inversion but is operator-dependent and not first line.))
((Barium enema::Useful in Hirschsprung's, not volvulus.))
((MRI abdomen::Not used acutely; too slow.))

A term baby fails to pass meconium for 72 hours and develops abdominal distension. Rectal biopsy is awaited. Diagnosis?

((Hirschsprung's disease::☑️ Failed neural crest migration; aganglionosis of distal colon.))
((Meconium ileus::Associated with cystic fibrosis; obstruction is at terminal ileum.))
((Anorectal malformation::Clinically apparent on perineal inspection at birth.))
((NEC::Preterm baby with pneumatosis intestinalis, not delayed meconium.))

Which feature is most characteristic of meconium ileus?

((Cystic fibrosis association::☑️ ~90% of meconium ileus babies have CF.))
((Pneumatosis intestinalis::Feature of NEC.))
((Aganglionosis on rectal biopsy::That defines Hirschsprung's.))
((Double bubble on AXR::Feature of duodenal atresia.))

A preterm 10-day-old has bile-stained aspirates, distension and bloody stools. AXR shows intramural gas. Diagnosis?

((Necrotising enterocolitis::☑️ Pneumatosis intestinalis is pathognomonic; preterm formula-fed neonate.))
((Hirschsprung's disease::Distension but no pneumatosis; bloody stools are not classic.))
((Intussusception::Older infants; sausage mass, target sign on USS.))
((Volvulus::Earlier, with corkscrew on contrast; no pneumatosis.))

An NG tube cannot be passed in a newborn with frothy oral secretions. CXR shows gas in the stomach. Most likely diagnosis?

((Oesophageal atresia with distal TOF (Type C)::☑️ Atresia blocks NG; gas in stomach proves a distal fistula. Commonest variant (~85%).))
((Pure oesophageal atresia (Type A)::NG blocked but abdomen is gasless on CXR.))
((Congenital diaphragmatic hernia::Respiratory distress with bowel in chest, NG passes.))
((Duodenal atresia::NG passes; AXR shows double bubble.))

Polyhydramnios in pregnancy is most associated with which neonatal condition?

((Oesophageal atresia::☑️ Foetus cannot swallow amniotic fluid, so it accumulates.))
((Renal agenesis::Causes oligohydramnios (Potter sequence).))
((Pyloric stenosis::Presents postnatally at 4–6 weeks, no antenatal sign.))
((Hirschsprung's disease::No antenatal hydramnios association.))

A newborn has severe respiratory distress, scaphoid abdomen and bowel sounds in the left chest. What embryological defect explains this?

((Failure of the left pleuroperitoneal membrane::☑️ Bochdalek hernia; posterolateral, left >> right.))
((Failure of the septum transversum::Forms central tendon; defects rare and central.))
((Failure of urorectal septum::Causes anorectal malformations, not diaphragmatic.))
((Persistence of pleuropericardial fold::Causes pericardial defects, not diaphragmatic hernias.))

👩‍⚕️ Bochdalek = Back (posterolateral), Big, Left. Morgagni = Mid (anterior, retrosternal), Minor, Right.

A 3-year-old has a painless, smooth right flank mass and microscopic haematuria. Best initial investigation?

((Abdominal ultrasound::☑️ First-line for a paediatric abdominal mass; identifies Wilms' tumour.))
((CT abdomen with contrast::Used after USS for staging and surgical planning.))
((Plain AXR::Low yield; will not characterise the mass.))
((MRI abdomen::Reserved for problem-solving; not first-line.))

A 2-year-old has bone pain, lytic skeletal lesions and periorbital bruising. Most likely diagnosis?

((Neuroblastoma::☑️ Neural crest tumour with skull mets — "raccoon eyes"; raised urinary VMA/HVA.))
((Wilms' tumour::Older child (3–4y); flank mass + haematuria, does NOT cross midline.))
((Acute lymphoblastic leukaemia::Bone pain possible but raccoon eyes are not classic.))
((Rhabdomyosarcoma::Soft-tissue mass, head/neck or GU; not classic periorbital bruising.))

Which condition is most strongly associated with WAGR syndrome?

((Wilms' tumour::☑️ WT1 deletion: Wilms, Aniridia, GU anomalies, Retardation.))
((Neuroblastoma::Linked to MYCN amplification, not WAGR.))
((Hepatoblastoma::Associated with Beckwith-Wiedemann and FAP.))
((Retinoblastoma::RB1 gene mutation; not part of WAGR.))

A 6-month-old boy has an undescended right testis. When should orchidopexy be performed?

((By 12–18 months::☑️ Reduces fertility impairment; allows palpable surveillance for seminoma.))
((At 5 years::Too late — irreversible germ cell damage and cancer risk are higher.))
((Immediately at diagnosis::Most testes descend spontaneously by 3 months; wait until 6 months.))
((After puberty::Far too late; orchidectomy may be considered if found post-pubertally.))

Why are paediatric inguinal hernias repaired promptly rather than electively?

((High risk of incarceration::☑️ Narrow internal ring + abundant viscera; ovary may be in sac in girls.))
((Risk of malignant transformation::Hernia sacs do not undergo malignant change.))
((Cosmetic concerns::Not the driver in young children.))
((To prevent recurrence::Recurrence rates are low regardless of timing.))

👩‍⚕️ Paediatric inguinal hernia = patent processus vaginalis = always indirect; repair = herniotomy (no mesh).

Revision summary

- Pyloric stenosis: 4–6 weeks, first-born boy, non-bilious projectile vomit, olive RUQ, hypochloraemic hypokalaemic metabolic alkalosis, USS, Ramstedt's pyloromyotomy after fluid resus.

- Intussusception: 6 m – 2 y, colicky pain, redcurrant jelly stool, sausage mass, USS target sign, air enema first, surgery if fails.

- Malrotation + volvulus: bilious vomiting in a neonate = surgical emergency; upper GI contrast corkscrew; Ladd's procedure.

- Hirschsprung's: failed neural crest migration → aganglionic distal colon; delayed meconium >48 h, distension; rectal biopsy; pull-through. Down's link.

- Meconium ileus: thick meconium, cystic fibrosis in 90%; gastrografin enema.

- NEC: preterm, formula fed, day 7–14; bloody stools; pneumatosis intestinalis and portal venous gas; NBM + abx; surgery if perforation.

- Oesophageal atresia + TOF: antenatal polyhydramnios; can't pass NG; Type C (proximal atresia + distal TOF) most common; VACTERL.

- Diaphragmatic hernia: Bochdalek (posterolateral, Left, Big — common) vs Morgagni (anterior, Right, smaller); scaphoid abdomen, bowel sounds in chest; don't bag-mask.

- Paediatric inguinal hernia: patent processus vaginalis → always indirect; herniotomy, no mesh; repair promptly.

- Undescended testis: orchidopexy by 12–18 months; ↑ seminoma, ↓ fertility.

- Wilms' tumour: 3–4 y, painless flank mass + haematuria; WAGR; USS first.

- Neuroblastoma: <2 y, neural crest, raccoon eyes, lytic bone mets; urinary VMA/HVA.