Adult intussusception is a rare but important cause of bowel obstruction. Unlike in children-where most cases are idiopathic-adults nearly always have an underlying pathology such as a tumour, polyp, or adhesion acting as a “lead point.” Prompt recognition is vital because delays can lead to ischaemia, necrosis, and perforation.

ℹ️ About

Definition: Invagination of a proximal bowel segment into a distal segment, leading to obstruction and vascular compromise.
Terminology: From Latin intus (“within”) and suscipere (“to receive”).
Mechanism: A mass or irritant alters peristalsis, causing telescoping and progressive compromise of blood supply.

Epidemiology

Rare: ~5% of all intussusceptions.
Accounts for ~1% of adult bowel obstructions.
Peak incidence: middle-aged to older adults.

🧬 Aetiology

Tumours: Adenocarcinoma, lymphoma, metastases, gastrointestinal stromal tumour (GIST).
Benign lesions: Polyps, lipomas, Meckel’s diverticulum.
Postsurgical changes: Adhesions, bariatric (gastric bypass) or bowel surgery.
Inflammatory conditions: Crohn’s disease or infection causing mucosal thickening.

Sites of Involvement

Small bowel (52%):
- Enteroenteric – 39%
- Ileocolic – 13%
Large bowel (38%):
- Ileocecal – 17%
- Colocolic – 17%
- Appendiceal – 4%

🩺 Clinical Features

Often subacute or chronic – symptoms may last weeks to months before diagnosis.
Colicky abdominal pain ± palpable mass.
Obstructive features: Nausea, vomiting, constipation, distension.
Red flag signs: Melaena, weight loss, systemic symptoms (may indicate malignancy).
Some present acutely with peritonitis if perforation occurs.

🔎 Investigations

Blood tests: FBC (↑WCC), U&Es (dehydration, electrolyte imbalance).
X-ray: Dilated loops, air-fluid levels – non-specific.
Ultrasound: “Target” or “doughnut” sign.
CT scan (gold standard): Sausage-shaped or target mass, identifies lead point.
Colonoscopy: May detect intraluminal masses but not first-line in acute obstruction.

💊 Management

Stabilisation: IV fluids, NG tube, analgesia, antibiotics if sepsis suspected.
Definitive treatment:
- Surgical resection (preferred) – avoids reducing a malignant lesion and missing pathology.
- Exploratory laparotomy or laparoscopy to inspect the entire bowel (from ligament of Treitz to terminal ileum).
- Endoscopic reduction considered in select benign cases, but uncommon in adults.

Prognosis

Outcome depends on the underlying cause. Benign lesions carry an excellent prognosis post-resection. Malignant causes account for the majority of large-bowel intussusceptions in adults, and prognosis depends on stage of disease at resection. Early recognition prevents catastrophic complications such as infarction and perforation.

References

Adult Intussusception – AJR Review

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Intussusception in Adults