Necrotising enterocolitis and spontaneous intestinal perforation — formative SAQs

SAQ 1 — The deteriorating preterm with established NEC (10 marks)

A 26-week, 780 g infant is day 9 of life, established on formula feeds. Over 12 hours the gastric residuals have increased and become bilious, the abdomen is distended and tender, and the infant has had three apnoeic spells requiring stimulation. Abdominal radiograph shows bubbly lucency in the bowel wall of the terminal ileum and branching lucency over the liver. The platelet count has fallen from 220 to 90 × 10⁹/L and the capillary gas shows a base excess of −8. [3]

a) Give the diagnosis, the radiological stage, and two signs that mark this as severe disease. (3 marks) [1]

The diagnosis is necrotising enterocolitis (NEC). The bubbly bowel-wall lucency is pneumatosis intestinalis and the branching liver lucency is portal venous gas, which places this at modified Bell Stage IIB (definite NEC, moderate). Two signs of severity are the portal venous gas itself (a marker of advanced, often pan-intestinal disease) and the falling platelet count with metabolic acidosis, indicating systemic deterioration towards Stage III. [1] [3]

b) Outline the immediate medical bundle, including the antibiotic principle and the planned duration of gut rest. (4 marks) [3]

Make the infant nil by mouth for 7 to 14 days depending on the course, and pass a large-bore nasogastric tube for free drainage and decompression. Take blood, urine and CSF cultures. Start broad-spectrum antibiotics with anaerobic cover — a gram-negative agent plus metronidazole or clindamycin, adjusted to local resistance and to any positive cultures — for a duration of 7 to 14 days for established NEC, prolonged if perforation or ongoing sepsis occurs. [3]

c) State three surgical triggers that would prompt urgent operative intervention, and describe the operative options for a perforated infant. (3 marks) [4]

Three surgical triggers are: a new pneumoperitoneum; a fixed and persistent loop with clinical deterioration; and abdominal wall discolouration with shock, or a positive diagnostic paracentesis (brown or bile-stained fluid, bacteria on Gram stain). The operative options for perforation are primary peritoneal drainage (a bedside right-lower-quadrant catheter draining gas and meconium, used for ELBW or unstable infants, as bridge or sole therapy) and laparotomy (resection of necrotic bowel with stoma or, in selected cases, primary anastomosis). The NET trial found PD did not improve survival versus laparotomy, so the choice is individualised. [4] [13]

SAQ 2 — A well infant with an incidental pneumoperitoneum (10 marks)

A 24-week, 560 g infant is day 6 of life. He is on minimal ventilatory support and tolerating small expressed breast-milk feeds. Early postnatal indomethacin was given for a patent ductus arteriosus, with a 7-day course of dexamethasone for lung disease. A routine abdominal radiograph shows free air outlining the liver edge; there is no pneumatosis and no portal gas. The infant is afebrile, haemodynamically stable, with a soft but slightly distended abdomen and a normal capillary gas. [7]

a) What is the most likely diagnosis, and which three features discriminate it from necrotising enterocolitis? (3 marks) [7]

The most likely diagnosis is spontaneous intestinal perforation (SIP), also called focal intestinal perforation. The three discriminating features are: the infant is haemodynamically stable and well (unlike the toxic NEC infant); there is no pneumatosis intestinalis and no portal venous gas (the radiological hallmarks of NEC are absent); and the risk profile fits — an ELBW infant exposed to early postnatal indomethacin and glucocorticoid, which is the modifiable association for SIP. [7] [11]

b) Explain the pathophysiology of SIP, and correct the common misconception about antenatal steroids. (2 marks) [11]

SIP arises from a focal thinning or defect of the muscularis propria at the terminal ileum, compounded by early postnatal indomethacin (impaired mucosal restitution and mesenteric vasoconstriction) and postnatal glucocorticoid. A proposed eosinophilic muscularis reaction is described in a subset. The result is a single, clean, isolated perforation rather than necrosis. The misconception is that antenatal steroids contribute — a national dataset found antenatal corticosteroids have no adverse association with SIP; the signal is for postnatal indomethacin combined with postnatal steroid. [11]

c) How does the immediate management of SIP differ from that of established NEC, and what surgical option is often definitive? (3 marks) [4]

SIP management is usually lighter because the infant is stable: maintain gut rest and gastric decompression, give targeted antibiotics (often including anaerobic cover but with less of the profound sepsis resuscitation NEC demands), and drain the pneumoperitoneum. Primary peritoneal drainage is often definitive for SIP — a bedside right-lower-quadrant catheter that evacuates the free air and seals the single perforation — sparing the infant a laparotomy. Laparotomy is reserved for the infant who fails drainage or in whom the diagnosis is in doubt. [4] [12]

d) Contrast the prognosis of SIP with perforated NEC, and state two prevention measures that reduce NEC incidence. (2 marks) [6]

SIP carries a markedly better prognosis than perforated NEC, with mortality around 10 to 15% versus 20 to 30% for NEC, because SIP lacks the septic, inflammatory, multi-segment burden. Two prevention measures that reduce NEC incidence are own mother's milk (dose-dependent protection; donor human milk also reduces NEC versus formula per the Cochrane review) and standardised feeding protocols, supplemented by antenatal steroids and strain-specific probiotics where local policy permits. [6] [9]