Necrotizing enterocolitis

Necrotising enterocolitis (NEC) is the most common gastrointestinal condition in premature neonates, and continues to have significant mortality and morbidity.

Epidemiology

NEC usually develops 2-3 days following birth, with 90% developing within the first 10 days of life ⁴. The incidence is inversely proportional to gestational age, with 90% occurring in premature infants. Its overall incidence is ~1 in 1000 births but is as high as 20% in low birth weight infants (<1500g) ⁵.

Clinical presentation

Presentation is often non-specific, and includes:

• poor feeding 
• bile-stained vomitus
• abdominal distension
• blood-stained stools +/-  explosive diarrhoea
• respiratory distress with acidosis
• features of generalised sepsis

Risk factors

• prematurity (50-80%) ⁴
• congenital heart disease
• perinatal asphyxia
• decreased umbilical flow in utero

Pathology

NEC is usually idiopathic and multi-factorial. A combination of ischaemic and infective aetiology with added contributive factors such as immature immunity have been proposed ¹.  Although a partially infective aetiology has also been proposed, no causitive organism has been isolated. Translocation of intestinal flora though immature mucosa has been postulated ⁵.

Inflammation starts from the mucosal surface and progresses to haemorrhagic and coagulative necrosis with the ensuing loss of mucosal integrity, transmural necrosis and perforation.

Although NEC can affect any part of the large or small bowel, the most common location is the terminal ileum. Other sites include caecum, right colon as well as less common areas such as stomach.

Radiographic features

Plain film

Supine abdominal x-rays are the mainstay of diagnosis. If NEC is suspected clinically, or there is concern on supine films, then an additional cross-table lateral  or left-lateral decubitus film should be obtained ⁵:

• dilated bowel loops (often asymmetrical in distribution)
• loss of the normal polygynal gas shape
• bowel wall oedema with thumb printing
• pneumatosis intestinalis (intramural gas)
• portal venous gas
• pneumoperitoneum secondary to perforation
  • air on both sides of the bowel (Rigler sign)
  • air outlining the falciform ligament (football sign)
  • it is important to note that only 50-75% of patients with proven perforation will have visible free gas ⁵

Ultrasound

• bowel wall thickening free fluid 
• alteration of vascular state
  • hypervascular (viable but engorged in early stage)
  • hypovascular (infarcted in later stage)
• intramural gas manifesting as high echohyperechoic foci within the bowel wall
• free fluid especially with echogenic debris is suspicious for perforation ⁵

Treatment and prognosis

NEC can be managed both medically and surgically and appropriate patient selection is essential in optimising outcome. A clinical staging system has been developed (see necrotising enterocolitis staging), with stage I and II receiving medical therapy and stage III undergoing surgery ⁸.

Medical management consists of supportive measures and cessation of oral feeding, along with broad spectrum antibiotics and gasticgastric aspiration ⁷. 

Surgery is usually reserved for patients with evidence of perforation, and entails resection of clearly necrotic bowel and the creation of a proximal enterostomy ^5-6. Other relative indications for surgery include portal venous gas, a fixed dilated loop on serial x-rays and abdominal wall erythema ⁷. Re-anastomosis is usually delayed until the infant has completely recovered.

Despite therapy, mortality remains significant, ranging between 9 and 28% ⁵. Furthermore ~20% of surviving patients will go on to develop stricture. These are more commonly in the large bowel (80%) and may result in bowel obstruction weeks andto months later ^{5, 8}.

Differential diagnosis

In the correct clinical scenario the presence of gas within bowel wall has little differential.Conditions worth keeping in mind include ⁸:

• pneumatosis coli
• neonatal appendicitis
• meconium ileus
• Hirschsprung disease
• infectious enterocolitis