Intussusception — ileocolic, air enema reduction, operative management, lead points

Definition / Overview

The small bowel encompasses the duodenum, jejunum, and ileum, approximately 6-7 metres of bowel responsible for digestion and nutrient absorption. Small bowel pathology spans a wide spectrum including obstruction, ischaemia, inflammatory disease, neoplasia, diverticular disease, and motility disorders. Timely diagnosis is challenging because symptoms are often nonspecific and the small bowel is not readily accessible by standard endoscopy. The consultant surgeon must systematically approach each condition through targeted investigation, appropriate operative or non-operative management, and anticipation of complications.

Anatomy and Surgical Exposure

Relevant Anatomy

• Duodenum: C-shaped, retroperitoneal (D2-D4), adjacent to the head of pancreas, CBD, and superior mesenteric vessels; D1 is intraperitoneal
• Jejunum: Left upper quadrant; thick wall, prominent plicae circulares, short fat-laden mesentery; major site of absorption
• Ileum: Right lower quadrant; thinner wall, longer mesentery, Peyer patches; terminal ileum reabsorbs bile salts and vitamin B12
• Blood supply: Superior mesenteric artery (SMA) via jejunal and ileal branches forming arcades; venous drainage via SMV → portal system
• Lymphatics: Drain to mesenteric lymph nodes and then to para-aortic nodes, critical in oncological resection

Operative Exposure

• Midline laparotomy: Workhorse for emergencies; provides full access
• Laparoscopy: Favoured for adhesiolysis, diagnostic exploration, and elective resection in stable patients
• Kocherisation of duodenum: Mandatory for D2/D3 pathology; mobilise peritoneum lateral to duodenum and rotate medially
• Running the bowel: Systematic hand-over-hand technique from Treitz ligament to terminal ileum; critical in trauma and ischaemia assessment

Pathophysiology and Classification

Clinical Features and Diagnosis

History

• Obstruction: Colicky central abdominal pain, vomiting (bilious early vs faeculent late), absolute constipation, abdominal distension
• Ischaemia: Severe constant pain disproportionate to examination findings; atrial fibrillation, peripheral vascular disease, recent cardiovascular event; post-prandial angina suggests chronic mesenteric ischaemia
• Inflammatory (Crohn's): Chronic diarrhoea, weight loss, RIF pain, perianal disease; extra-intestinal manifestations (uveitis, arthropathy, erythema nodosum)
• Neoplasm: Insidious weight loss, anaemia, occult GI bleeding, obstruction or intussusception in adults (malignancy until proven otherwise)
• Bleeding: Haematochezia or melaena; Meckel's typically presents as painless rectal bleeding in children/young adults

Predisposing Conditions

• Prior abdominal surgery (adhesions), hernias
• FAP, HNPCC/Lynch syndrome, Peutz-Jeghers syndrome, predispose to small bowel neoplasia
• Crohn's disease, coeliac disease, chronic inflammation increases malignancy risk
• Atrial fibrillation, hypercoagulable states, mesenteric ischaemia
• Cystic fibrosis, distal intestinal obstruction syndrome; markedly elevated baseline SB malignancy risk

Physical Examination

• Distension, high-pitched tinkling bowel sounds (mechanical SBO) vs absent sounds (ileus/ischaemia)
• Localised tenderness or peritonism, suggests strangulation or perforation
• Hernia orifices must be examined in every patient presenting with SBO
• Palpable mass, consider neoplasm, abscess, or intussusception
• Haemodynamic compromise, indicates strangulation, ischaemia, or perforation with sepsis

Investigations

Bloods

• FBC: Anaemia (chronic blood loss, Crohn's); leucocytosis (infection, ischaemia, strangulation)
• U&E, creatinine: Dehydration from obstruction; renal function before contrast imaging
• Lactate: Elevated in ischaemia; a late and prognostically poor sign in mesenteric ischaemia, a normal lactate does NOT exclude ischaemia early
• CRP, albumin: Inflammatory burden and nutritional status
• Coagulation: Septic coagulopathy; pre-operative assessment
• Tumour markers (CEA, CA19-9, CgA): Adjunct only; chromogranin A elevated in neuroendocrine tumours

Imaging

Management

Small Bowel Obstruction (SBO)

Non-operative (First-line for Partial/Adhesive SBO)

1. IV fluid resuscitation, crystalloid; correct electrolyte derangements
2. Nasogastric decompression, large-bore NGT; free drainage
3. Strict nil-by-mouth
4. DVT prophylaxis, LMWH + compression stockings once haemorrhage excluded
5. Serial clinical assessment, 4-6 hourly; escalate if peritonism develops or no resolution at 48-72 hours
6. Water-soluble contrast (Gastrografin) challenge, 100 mL orally/via NGT; appearance in colon on AXR at 24 hours predicts resolution AND has a therapeutic effect; reduces need for surgery and length of stay

Operative Indications

• Immediate: Signs of strangulation (fever, tachycardia, peritonism, leucocytosis, raised lactate), closed-loop obstruction on CT, non-reducible hernia, complete obstruction not resolving
• Elective: Recurrent SBO from adhesions, specific anatomical cause (tumour, stricture, internal hernia)

Operative Approach

• Laparoscopy, appropriate for selected cases (single adhesive band, stable patient, non-distended abdomen); conversion rate higher with matted adhesions
• Open adhesiolysis, sharp dissection preferred; avoid enterotomy; assess bowel viability after release (colour, peristalsis, Doppler, fluorescein)
• Bowel resection: Mandatory for ischaemic or non-viable segments; stapled anastomosis or hand-sewn; primary anastomosis generally safe if no faecal contamination and well-perfused ends
• Damage control: In haemodynamically unstable patients, resect, leave bowel in discontinuity, temporary abdominal closure, return to ICU for resuscitation, relook at 24-48 hours for anastomosis

Mesenteric Ischaemia

Acute (Surgical Emergency)

1. Resuscitation: Large-bore IV access, fluid resuscitation, anticoagulation with UFH (bolus 5000 units then infusion)
2. Antibiotics: Broad-spectrum (e.g. piperacillin-tazobactam 4.5 g 8-hourly) for bacterial translocation and peritonitis
3. CT angiography to delineate occlusion pattern
4. Embolectomy / thrombectomy / thrombolysis, SMA embolus: operative embolectomy via transverse arteriotomy; consider endovascular approach in selected stable patients
5. Bowel resection of non-viable segments; second-look laparotomy at 24-48 hours mandatory to assess anastomotic viability and residual ischaemia
6. NOMI: Intra-arterial papaverine infusion (30-60 mg/hr) via angiography catheter; correct precipitating cause (cardiac failure, sepsis, vasopressors)
7. Venous thrombosis: Anticoagulation first-line; resection if peritonism

Chronic Mesenteric Ischaemia

• Post-prandial pain, weight loss ("food fear"), vascular risk factors
• Revascularisation: endovascular angioplasty ± stenting preferred (lower morbidity); open bypass (aortomesenteric or iliac-mesenteric) for complex anatomy or endovascular failure

Crohn's Disease

Medical Management First

• Induction: corticosteroids (prednisolone 40-60 mg/day), budesonide for ileocaecal disease
• Maintenance: thiopurines (azathioprine 2-2.5 mg/kg/day), methotrexate; biologics (infliximab, adalimumab) for steroid-dependent/refractory disease
• Nutritional support: enteral preferred; TPN for high-output fistulae or pre-operative optimisation

Surgical Indications

• Failed medical therapy, obstruction, fistula/abscess, perforation, haemorrhage, or dysplasia/malignancy
• Principle: bowel-sparing surgery, resect only macroscopically diseased bowel; microscopic margins do not affect recurrence; avoid short gut syndrome
• Strictureplasty, preferred over resection for short strictures (\<10 cm) in the absence of active sepsis or malignancy; Heineke-Mikulicz for short, Finney or Michelassi for longer segments
• Complete obstruction from Crohn's: trial of NGT decompression, IV steroids, and hydration before operative intervention, most resolve and can proceed to elective surgery under safer conditions
• Post-operative recurrence: Endoscopic monitoring at 6-12 months; early reintroduction of biologics reduces recurrence

Small Bowel Neoplasms

Work-up

• CT chest/abdomen/pelvis with contrast for staging
• MRI for liver lesions (hepatic metastases from NETs)
• Octreotide scan / $^{68}$Ga-DOTATATE PET for NETs
• Staging laparoscopy for locally advanced disease

Management by Histology

Meckel's Diverticulum

• Symptomatic: Always resect, diverticulectomy (stapled or wedge) if base is narrow and uninvolved; segmental ileal resection if base is wide, inflamed, or contains ectopic mucosa
• Incidental: Resection debated; generally indicated in children, patients <40 years, symptomatic history, or anatomically at high-risk features (wide base, heterotopic mucosa suspected)
• Laparoscopic approach appropriate for elective resection

Motility Disorders and Ileus

• Post-operative ileus: Multimodal analgesia (minimise opioids), early enteral feeding, gum chewing, alvimopan (mu-opioid antagonist, 12 mg pre-operatively then 12 mg BD for up to 7 days; evidence-based reduction in ileus duration); early mobilisation; correct electrolytes
• Adynamic ileus (generalised): Address systemic cause (sepsis, metabolic derangement); NGT decompression; neostigmine not indicated (colonic pseudo-obstruction agent); avoid pharmacologic agents until mechanical obstruction excluded
• Chronic intestinal pseudo-obstruction: MDT approach; nutritional support; prokinetics; exclude mechanical cause; surgical decompression rarely required

Complications and Special Considerations

Anastomotic Leak

• Risk factors: Tension, ischaemia, malnutrition, immunosuppression, distal obstruction, steroids
• Clinical: Day 3-7 fever, tachycardia, rising CRP, ileus, drain output change, abdominal pain
• Diagnosis: CT with oral ± rectal contrast
• Management: Small contained leak, IV antibiotics, radiological drain; large uncontained or peritonitis, return to theatre; proximal diversion (defunctioning stoma) or resection with end stoma

Post-operative Haemorrhage

• Early return to theatre if haemodynamically unstable despite resuscitation; identify source (mesenteric vessel, anastomosis); angioembolisation for non-operative candidates

Short Bowel Syndrome

• Occurs when functional intestinal length $< 100-150$ cm; common after extensive resection for ischaemia, Crohn's, or trauma
• Management: TPN initially, intestinal rehabilitation (glutamine, GLP-2 agonist teduglutide), enteral adaptation, and ultimately intestinal transplantation in select cases

DVT Prophylaxis

• Pharmacological: LMWH (e.g. enoxaparin 40 mg SC daily) commenced 12-24 hours post-operatively; extended course 28 days for oncological resections
• Mechanical: Graduated compression stockings + intermittent pneumatic compression devices intraoperatively and post-operatively
• High-risk (cancer, prolonged bed rest): Combined pharmacological and mechanical; consider pre-operative insertion of IVC filter only in exceptional circumstances

Perioperative Management and MDT Considerations

Pre-operative Optimisation

• Correct nutritional deficits: albumin $< 30$ g/L warrants pre-operative enteral or parenteral nutritional support for at least 7-10 days in elective cases
• Optimise immunosuppression: withhold biologics (infliximab, adalimumab) 4-6 weeks pre-operatively where possible; steroids, do not abruptly stop; consider stress dosing
• Bowel preparation: not routinely required for small bowel surgery
• Consent: stoma possibility, short bowel risk, anastomotic leak, re-operation

MDT Decision-Making

• All small bowel malignancies discussed at a multidisciplinary tumour board including surgical oncology, medical oncology, gastroenterology, radiology, pathology, and clinical nurse specialist
• Neoadjuvant therapy (e.g. imatinib in GIST) considered to facilitate R0 resection of borderline-resectable disease
• Palliation vs curative intent established early to guide operative planning

Enhanced Recovery

• Carbohydrate loading pre-operatively, multimodal analgesia (minimise opioid), early mobilisation, early enteral feeding (day 1 post-operative), targeted IV fluid strategy
• Aim for early transition from IV to oral medications

Key viva point: In any patient presenting with SBO, always examine hernia orifices, assess CT for a transition point and signs of strangulation, and apply a water-soluble contrast challenge for partial adhesive obstruction, this has both diagnostic and therapeutic value and is supported by level I evidence.

Sources

• RACS position statements & curriculum (Royal Australasian College of Surgeons)
• NCCN clinical practice guidelines in oncology
• ASCO clinical practice guidelines (American Society of Clinical Oncology)