Small bowel obstruction

Small bowel obstruction (SBO) accounts for 80% all mechanical intestinal obstruction; the remaining 20% result from large bowel obstruction. It has a mortality rate of 5.5%.

Pathology

Causes

Causes can be divided into congenital and acquired. Acquired causes may be extrinsic causing compression, intrinsic or luminal.

Congenital

• jejunal atresia
• ileal atresia or stenosis
• enteric duplication
• midgut volvulus
• mesenteric cyst
• Meckel diverticulum

Extrinsic bowel lesion

• fibrous adhesions
• abdominal hernia
• volvulus
• masses
  • extrinsic neoplasm
  • intra-abdominal abscess
  • aneurysm
  • haematoma
  • endometriosis

Intrinsic bowel wall lesion

• intussusception
• tumour (rare), e.g. lipoma
• strictures, e.g. surgical, irradiation

Luminal occlusion

• neoplasm, e.g. adenocarcinoma, carcinoid, lymphoma
• inflammation, e.g. Crohn's, Tuberculosis
• intestinal ischaemia
• intramural haemorrhage, e.g. trauma, Henoch-Schonlein purpura, over-anticoagulation
• swallowed, e.g. foreign body, bezoar
• gallstone - gallstone ileus
• meconium ileus (or meconium ileus equivalent)

Radiographic features

Plain film

In most cases, the abdominal radiograph will have the following features:

• dilated loops of small bowel proximal to the obstruction
• predominantly central dilated loops
• three instances of dilatation over 3cm
• valvulae conniventes are visible
• fluid levels if the study is errect (non-standard technique)

However, obstruction (which may be high grade mechanical obstruction) may also present with the following features:

• a gasless abdomen: gas within the small bowel is a function of vomiting, NG tube placement and level of obstruction
• the string-of-beads sign : small pockets of gas within a fluid-filled small bowel

See also

• closed loop obstruction