Intestinal Obstruction
On this page
Direct answer
Intestinal obstruction presents with the four cardinal features — colicky abdominal pain, vomiting, distension and absolute constipation — and the pattern of these features localises the level. Plain radiographs in the erect and supine positions remain the first investigation, showing central dilated small bowel loops with valvulae connivente in small bowel obstruction and peripheral dilated colon with haustra in large bowel obstruction. Initial management is resuscitation and nasogastric decompression ("drip and suck"), with emergency surgery for strangulation or failure to settle.
What you must remember
- Small bowel obstruction: central colicky pain, early bilious vomiting, distension appearing later and absolute constipation late; the erect film shows central loops over 3 cm with valvulae connivente crossing the full breadth and a ladder pattern.
- Large bowel obstruction: gross distension and absolute constipation early, vomiting late; the film shows peripheral shadows with incomplete haustra, and a caecum over 9 cm warns of impending perforation.
- Causes: post-operative adhesions are the commonest overall cause of small bowel obstruction, with external hernias important wherever they go untreated; carcinoma is the commonest cause of large bowel obstruction, followed by volvulus.
- Strangulation danger signs — constant severe pain, fever, tachycardia, peritonism, a tender irreducible hernia, shock and rising lactate — demand emergency surgery.
- Sigmoid volvulus, typically in the elderly, gives the coffee-bean sign and is decompressed by sigmoidoscopy and rectal tube first, with elective colectomy considered to prevent recurrence; caecal volvulus needs surgery.
- Gallstone ileus causes recurrent subacute obstruction in the elderly with Rigler triad — dilated loops, pneumobilia and an ectopic gallstone — and is treated by enterolithotomy.
- Baseline management of adhesive or partial obstruction is nasogastric decompression, intravenous fluid with potassium correction and serial examination, with surgery for non-resolution or strangulation.
Common confusion
Mechanical obstruction must be separated from paralytic ileus: ileus produces painless, diffuse distension with absent bowel sounds and no colic, treated by treating the cause and gastric decompression rather than laparotomy. Candidates also mix up the mucosal fingerprints — valvulae connivente are complete, haustra incomplete — and forget that the caecal diameter decides the perforation risk in a closed loop.
Exam-focused takeaway
FMGE stems on obstruction reward three recognitions: the cardinal features naming the level from their order of appearance; the radiograph description naming valvulae versus haustra; and any strangulation cue — constant pain, tender hernia, rising lactate — switching the answer to emergency laparotomy. The elderly patient with a coffee-bean shadow is sigmoid volvulus, decompressed endoscopically first; the elderly woman with pneumobilia and small bowel loops has gallstone ileus treated by enterolithotomy. Always check the hernial orifices; a tender irreducible femoral hernia is how this exam hides an emergency.
Frequently asked questions
What are the four cardinal features of intestinal obstruction?
Colicky abdominal pain, vomiting, abdominal distension and absolute constipation — the absence of both flatus and stool.
How do small and large bowel obstruction differ on X-ray?
Small bowel shows central loops with complete valvulae connivente; large bowel shows peripheral shadow with incomplete haustra, and a caecal diameter over 9 cm signals perforation risk.
What is the commonest cause of small bowel obstruction?
Post-operative adhesions overall, with external hernias an important cause wherever hernias remain untreated — always examine the hernial orifices.
How is sigmoid volvulus managed initially?
By sigmoidoscopy and rectal tube decompression in a stable patient, followed by consideration of elective sigmoid colectomy to prevent recurrence.
What is Rigler triad?
The imaging triad of gallstone ileus — small bowel obstruction, pneumobilia and an ectopic gallstone — treated by enterolithotomy.
Which features indicate strangulation?
Constant severe pain, fever, tachycardia, peritonism, a tender irreducible swelling, shock and a rising serum lactate; all are indications for emergency surgery.