Surgery chapters
Small intestine: obstruction, Meckel diverticulum, tumours and mesenteric ischaemia
Causes, features, X-ray signs and treatment of small bowel obstruction, plus Meckel diverticulum, gallstone ileus, small bowel tumours, typhoid and TB of the ileum, and acute and chronic mesenteric ischaemia.
- Adhesions are the commonest cause of small bowel obstruction where surgery is common; hernias must always be checked. Treat with drip and suck unless there are signs of strangulation (constant pain, tenderness, fever, tachycardia, rising lactate).
- Meckel diverticulum: rule of 2s, antimesenteric ileum, true diverticulum; bleeds from ectopic gastric mucosa (technetium-99m scan).
- Acute mesenteric ischaemia: severe pain out of proportion to signs, often with AF; embolus lodges just beyond the middle colic origin.
On this page
Overview
The small intestine runs from the duodenojejunal flexure to the ileocaecal valve. In surgery it matters mainly because it obstructs, loses its blood supply and occasionally grows tumours.
- Small bowel obstruction (SBO) is one of the commonest surgical emergencies.
- Meckel diverticulum is the classic congenital anomaly, tested through its "rule of 2s" and its complications.
- Acute mesenteric ischaemia is rare but lethal and easily missed.
- In Pakistan, typhoid perforation, ileocaecal tuberculosis and worm obstruction are still common.
Intestinal obstruction: classification
| Type | Meaning | Examples |
|---|---|---|
| Dynamic (mechanical) | Peristalsis works against a block | Adhesions, hernia, tumour, volvulus |
| Adynamic | No block; peristalsis absent or weak | Paralytic ileus, pseudo-obstruction |
Mechanical causes by site:
| Site | Causes |
|---|---|
| In the lumen | Faecal impaction, gallstone, bezoar, foreign body, worms (Ascaris) |
| In the wall | Stricture (Crohn, TB), tumour, intussusception |
| Outside the wall | Adhesions and bands, hernias, volvulus |
Where abdominal operations are common, adhesions cause most small bowel obstruction; obstructed hernia comes next. In a "virgin" abdomen (no previous surgery), think hernia, tumour, TB or Crohn. Large bowel obstruction is usually due to carcinoma.
Pathophysiology in brief
- Bowel above the block dilates; bowel below keeps working until it empties and collapses.
- Distension comes from gas (mostly swallowed nitrogen, plus bacterial gas) and fluid (several litres of digestive juice made each day).
- Fluid is lost by vomiting, poor absorption, pooling in the lumen and leakage into the peritoneum → dehydration, raised urea and haematocrit.
- Strangulation = the blood supply is cut off. Venous outflow fails first, the wall swells, then arterial inflow stops and the bowel infarcts. Bacteria and toxins then cross the wall.
- Closed-loop obstruction: the segment is blocked at both ends (volvulus, a band, or a colonic cancer with a competent ileocaecal valve). Pressure rises fast, so strangulation or perforation comes early.
Causes of strangulation: a tight hernial neck, a band, a volvulus or intussusception twisting the mesentery, and high pressure in a closed loop. Richter hernia traps only part of the bowel wall, so the wall can necrose without full obstruction.
Clinical features
| Feature | High SBO | Low SBO | Large bowel obstruction |
|---|---|---|---|
| Vomiting | Early, profuse | Later; may become faeculent | Late |
| Distension | Little | Central, marked | Early, marked, flanks |
| Pain | Colicky, around the umbilicus | Colicky, central | Less severe, lower abdomen |
| Dehydration | Rapid | Moderate | Late |
- Absolute constipation (no faeces or flatus) is typical of complete obstruction.
- Bowel sounds are often high-pitched and tinkling; they may later go quiet.
- Always examine the hernial orifices (including femoral and port-site scars).
Absolute constipation may be absent in Richter hernia, gallstone ileus, mesenteric vascular occlusion, pelvic abscess and any partial obstruction (diarrhoea can even occur).
Signs of strangulation
- Pain that becomes constant and severe, not relieved by strong analgesia.
- Localised tenderness, guarding, rigidity, peritonism.
- Fever, tachycardia, shock not corrected by fluids.
- Raised white count, rising lactate.
- An external hernia that is tense, tender, irreducible with no cough impulse, with red or dusky skin over it.
Strangulation is mainly a clinical diagnosis. Any of these signs during conservative treatment means urgent surgery.
Investigations
- Bloods: FBC, urea and electrolytes, lactate, amylase, group and save. Look for dehydration and hypokalaemia.
- Plain abdominal X-ray (supine): dilated loops. Erect film shows fluid levels.
- CT with contrast: now the main test. Shows the level, the cause and signs of ischaemia (poor wall enhancement, mesenteric fluid).
- Water-soluble contrast (Gastrografin) in adhesive SBO: if it reaches the colon within about a day, the obstruction will usually settle; it also helps it settle.
| X-ray clue | Jejunum | Ileum | Colon |
|---|---|---|---|
| Position | Central, transverse loops | Central, lower | Around the periphery |
| Mucosal pattern | Valvulae conniventes cross the whole width ("concertina" or ladder) | Featureless | Haustra do not cross the full width, irregularly spaced |
Never give barium by mouth in suspected acute obstruction. Fluid levels alone are not specific; they also occur in ileus, gastroenteritis and pancreatitis.
Management of small bowel obstruction
Drip and suck is the start for everyone:
- Nasogastric tube on drainage (decompresses and protects the airway at induction).
- IV fluids: Hartmann's or 0.9% saline with potassium as needed; urinary catheter and fluid chart.
- Analgesia, antiemetic, monitor closely.
Conservative management suits adhesive obstruction with no sign of strangulation. Most settle; it should rarely go on beyond 72 hours.
Surgery is indicated for:
- Any sign of strangulation or closed-loop obstruction.
- Obstructed external hernia.
- Obstruction in a virgin abdomen.
- Failure to settle with conservative treatment.
At laparotomy, find the collapsed bowel and follow it back to the block. Divide only the band or adhesion causing the problem.
Is the bowel viable?
| Feature | Viable | Dead |
|---|---|---|
| Colour after release and warm packs | Pinker | Stays dark |
| Mesenteric pulsation | Present | Absent |
| Surface | Shiny | Dull |
| Wall | Firm | Thin, flabby, friable |
| Peristalsis | Seen | None |
Wrap doubtful bowel in warm packs for about 10 minutes, then look again. Resect if still doubtful. Record the length of bowel removed and left.
Special mechanical causes
- Gallstone ileus: elderly woman; a large stone erodes from the gallbladder into the duodenum and impacts in the terminal ileum. Rigler triad: SBO, air in the biliary tree and an atypical calcified shadow. Treatment: enterotomy above the stone and remove it; do not disturb the gallbladder at the same operation.
- Bezoars: trichobezoar (hair) in girls with hair-pulling or chewing; phytobezoar (plant fibre) after gastric surgery.
- Ascaris lumbricoides: children in tropical areas; may follow starting deworming. Start with drip and suck; deworm after the obstruction settles.
- Internal hernia: through mesenteric defects or paraduodenal fossae. Do not cut the ring where major vessels run in its edge.
Rigler triad = "3 Ps": Pneumobilia, a Pebble in the right iliac fossa, and the Picture of SBO.
Paralytic ileus
- No mechanical block; peristalsis stops. Usual after laparotomy for 24–72 hours.
- Causes: abdominal surgery, sepsis, hypokalaemia, uraemia, spinal or rib fractures, retroperitoneal haematoma.
- Distension without colic; bowel sounds absent; effortless vomiting.
- Treat the cause, nasogastric tube, correct K+ and Mg2+. CT if prolonged.
After a laparotomy, colicky pain with loud bowel sounds that come back and then stop suggests early mechanical obstruction, not ileus.
Meckel diverticulum
A remnant of the vitellointestinal (omphalomesenteric) duct.
| Feature | Fact |
|---|---|
| Frequency | About 2% of people |
| Length | About 2 inches (5 cm) |
| Site | Antimesenteric border of the ileum, roughly 60 cm (2 feet) proximal to the caecal valve |
| Wall | All three coats → a true (congenital) diverticulum, with its own blood supply |
| Ectopic tissue | In about 20%: gastric (commonest), pancreatic or colonic |
Rule of 2s: 2% of people, 2 inches long, 2 feet from the ileocaecal valve, 2 types of ectopic tissue (gastric and pancreatic), symptoms often before age 2.
Presentations
- Painless rectal bleeding (dark red or melaena) in a child: acid from ectopic gastric mucosa ulcerates the nearby ileum. Diagnose with a technetium-99m pertechnetate scan.
- Meckel diverticulitis: mimics appendicitis; perforation can mimic a perforated duodenal ulcer.
- Intussusception: acts as the lead point.
- Obstruction: a band from the tip to the umbilicus causes obstruction or volvulus.
- Found in a hernial sac = Littre hernia.
If the appendix is normal at surgery for suspected appendicitis, examine the terminal ileum for a Meckel diverticulum.
Treatment
- Symptomatic: excise the diverticulum (stapled or sutured), or resect a short segment of ileum if the base is thickened or there is ulcer in the adjacent ileum.
- Incidental, wide-mouthed and soft: can be left alone.
- Do not amputate and invaginate it like an appendix; this risks stricture and leaves ectopic tissue.
Infections of the small bowel relevant to surgery
- Typhoid perforation: usually in the third week; a single ulcer in the distal ileum over Peyer's patches, lying along the long axis of the bowel. Resuscitate, then close the ulcer and wash out; exteriorise in the very unwell. Resistant (XDR) typhoid is common in Pakistan; follow current national antibiotic guidance.
- Ileocaecal tuberculosis: right iliac fossa mass, weight loss, subacute obstruction. Ulcerative TB gives transverse (girdle) ulcers; hyperplastic TB gives a thick, narrow ileocaecal segment with a pulled-up contracted caecum on barium. Treat with antituberculous drugs; operate for obstruction (strictureplasty or limited ileocaecal resection) or perforation. M. bovis from unboiled milk is a classic source.
Typhoid ulcers lie along the bowel (longitudinal); TB ulcers lie across it (transverse). TB strictures cause obstruction; typhoid ulcers perforate.
- Crohn disease: surgery treats complications only (obstruction, fistula, abscess, bleeding, perforation, failed medical therapy). Preserve bowel; use strictureplasty for short multiple strictures.
Small bowel tumours
Small bowel tumours are rare (under 10% of gut tumours). Most are benign. They present with anaemia, bleeding, intussusception or obstruction. Capsule endoscopy or CT enterography helps find them.
| Tumour | Key points |
|---|---|
| Adenocarcinoma | Commoner in jejunum; risk with Crohn, coeliac disease, FAP, Lynch, Peutz–Jeghers; presents late; wide resection with mesentery |
| Carcinoid (neuroendocrine) | From Kulchitsky (enterochromaffin) cells; sites in order: appendix, ileum, rectum; often multiple in ileum; causes mesenteric fibrosis |
| Lymphoma | Usually B-cell non-Hodgkin; T-cell lymphoma in long-standing coeliac disease; Burkitt at the ileocaecal region in children; treated with chemotherapy, surgery for complications |
| GIST | From interstitial cells of Cajal in the muscle layer; commonest in stomach; c-KIT (CD117) positive; surgery first; imatinib for advanced or high-risk disease |
| Peutz–Jeghers syndrome | Autosomal dominant (STK11); pigmented spots on lips and mouth; hamartomatous polyps → intussusception and bleeding |
Carcinoid syndrome
- Gut carcinoid makes serotonin (5-HT), which the liver breaks down. Symptoms appear only when liver metastases release it straight into the systemic veins.
- Features: flushing (often set off by alcohol), diarrhoea, bronchospasm, palpitations, and right heart valve disease (tricuspid regurgitation, pulmonary stenosis).
- Tests: raised urinary 5-HIAA; plasma chromogranin A; somatostatin-receptor (octreotide) scan.
- Treatment: resect primary and liver deposits where possible; octreotide controls symptoms and covers surgery to prevent a carcinoid crisis.
- Pellagra-like dermatitis can occur because tryptophan is used up making serotonin (niacin deficiency).
Carcinoid of the gut causes the syndrome only after liver metastases (bronchial and ovarian carcinoids drain straight into systemic veins and can cause it without).
Mesenteric ischaemia
Acute mesenteric ischaemia
| Cause | Typical patient | Key point |
|---|---|---|
| Arterial embolus (commonest) | Atrial fibrillation, recent MI, endocarditis | Lodges just beyond the middle colic origin, sparing proximal jejunum |
| Arterial thrombosis | Atherosclerosis, older smoker, prior mesenteric angina | At the SMA origin; whole midgut affected |
| Venous thrombosis | Thrombophilia, oral contraceptive pill, portal hypertension, pancreatitis | Swollen, congested bowel; bloody fluid; treat with heparin |
| Non-occlusive | Shock, heart failure, vasopressors, critical illness | Low flow, patent vessels |
Clinical: sudden, severe central abdominal pain out of proportion to the findings; early vomiting and bowel emptying, later blood per rectum; soft abdomen at first, then peritonism and shock.
Investigations: high white count, raised lactate, metabolic acidosis. CT angiography is the test of choice. Late signs: gas in the bowel wall and portal vein.
Treatment: resuscitation, heparin, laparotomy with embolectomy or bypass/stenting, and resection of dead bowel; second-look laparotomy at 24–48 hours. Mortality is high. Infarction of the whole midgut (from just beyond the DJ flexure to mid-transverse colon) is often unsalvageable in the elderly; survivors of massive resection may need long-term parenteral nutrition.
A soft abdomen with severe pain and a high lactate in a patient with AF is mesenteric ischaemia until proved otherwise. Do not be reassured by the lack of signs.
Chronic mesenteric ischaemia (mesenteric angina)
- Atherosclerosis of the SMA and coeliac origins.
- Central abdominal pain 30–60 minutes after eating, fear of food and weight loss.
- Treat with angioplasty and stenting, or bypass; stop smoking.
Expect: commonest cause of SBO (adhesions) and LBO (carcinoma); features that mean strangulation and urgent surgery; X-ray difference between small and large bowel (valvulae conniventes vs haustra); Rigler triad of gallstone ileus; the rule of 2s of Meckel diverticulum, its bleeding from ectopic gastric mucosa and the technetium scan; Littre and Richter hernias; typhoid perforation in week three in the distal ileum; ileocaecal TB; carcinoid syndrome needing liver metastases, 5-HIAA and octreotide; GIST and CD117; Peutz–Jeghers; acute mesenteric ischaemia with pain out of proportion in AF, and mesenteric angina after meals.
Quick revision
- SBO: adhesions most common; examine hernial orifices every time.
- Drip and suck; operate for strangulation, closed loop, hernia, virgin abdomen or failure by 72 hours.
- Jejunum: valvulae conniventes cross the full width; colon: haustra do not.
- Gallstone ileus: SBO + pneumobilia + gallstone in the ileum.
- Meckel: 2%, 5 cm, 60 cm from the ileocaecal valve, antimesenteric, true diverticulum; bleeds from gastric mucosa; Tc-99m scan.
- Typhoid: week 3, distal ileum, longitudinal ulcer. TB: transverse ulcers, contracted caecum.
- Carcinoid: appendix commonest; syndrome needs liver metastases; 5-HIAA; octreotide.
- Acute mesenteric ischaemia: AF, pain out of proportion, lactate high, CT angiography.
Written by The House Job from standard references (Bailey & Love).
FAQ
What is the commonest cause of small bowel obstruction?
Adhesions from previous abdominal surgery, followed by obstructed hernias. In someone with no previous surgery, a hernia or tumour is more likely.
How long can adhesive obstruction be managed without surgery?
Usually up to about 72 hours, as long as there are no signs of strangulation. Any constant pain, tenderness, fever, tachycardia or rising lactate means operating sooner.
Why does a Meckel diverticulum bleed?
It may contain ectopic gastric mucosa that secretes acid and ulcerates the nearby ileum. A technetium-99m pertechnetate scan picks up this gastric tissue.
Why is acute mesenteric ischaemia easy to miss?
Early on the abdomen is soft and the pain is far worse than the signs. A high lactate and CT angiography make the diagnosis.
When does carcinoid syndrome occur?
With a gut carcinoid, only when there are liver metastases, because the liver normally breaks down the serotonin before it reaches the systemic circulation.