Quick Answer
Intestinal obstruction yields 2 to 3 NEET PG questions per paper and is heavily weighted in INI-CET surgery stems. Lock these:
- SBO vs LBO — SBO ladder pattern, central; LBO peripheral, haustrations.
- Adults SBO — adhesions, hernias, malignancy (top three).
- Indian context — abdominal TB, sigmoid volvulus, neglected hernias.
- Strangulation — fever, tachycardia, peritonitis, raised lactate.
- Imaging — CT contrast first-line; plain X-ray for triage.
- Conservative — NPO, NG decompression, IV fluids, electrolytes (drip and suck).
- Surgery — strangulation, peritonitis, complete obstruction failing 48 to 72 hours.
Intestinal obstruction is one of the most testable emergency-surgery topics for NEET PG and INI-CET — it integrates anatomy, plain-film and CT pattern recognition, fluid resuscitation, and operative decision-making in a single vignette. India-specific stems on abdominal tuberculosis, sigmoid volvulus in elderly bedridden patients, and neglected groin hernias appear repeatedly.
This NEETPGAI deep dive walks through mechanical vs paralytic obstruction, SBO vs LBO, closed-loop and strangulation, common causes by region, imaging signs, conservative management, surgical indications, special scenarios, and high-yield MCQ traps. Pair it with the acute abdomen guide for a complete surgical-emergency map.
Classification
Mechanical vs paralytic
- Mechanical obstruction — physical blockage of the bowel lumen. Active peristalsis above the obstruction, audible bowel sounds, colicky pain.
- Paralytic ileus — failure of peristalsis without a mechanical block. Silent abdomen, continuous distension, no colicky pain. Causes — post-operative (commonest), electrolyte disturbance (low K, low Mg), drugs (opioids, anticholinergics), retroperitoneal pathology (haematoma, pancreatitis), spinal trauma.
Small bowel obstruction (SBO) vs large bowel obstruction (LBO)
| Feature | SBO | LBO |
|---|
| Vomiting | Early, bilious | Late, feculent |
| Distension | Central, mild | Peripheral, marked |
| Pain | Colicky, periumbilical | Colicky, lower abdominal |
| Constipation | Late | Early |
| Plain X-ray | Central ladder pattern, valvulae conniventes | Peripheral, haustrations |
| Bowel loop diameter | Greater than 3 cm dilated | Greater than 6 cm colon, 9 cm caecum |
Simple vs strangulated
- Simple — luminal blockage with viable bowel wall.
- Strangulated — compromised mesenteric blood supply → ischemia → infarction → perforation. Surgical emergency.
Closed-loop obstruction
Both ends of a bowel segment are obstructed (e.g., volvulus, incarcerated hernia, adhesive band with secondary twist). The trapped segment distends rapidly, compromising perfusion. High strangulation risk — mandates urgent surgery.
Causes by location
Small bowel
- Adhesions — 60 to 70 percent. Post-operative (especially after pelvic and lower-abdominal surgery). Inflammatory (Crohn's, TB).
- Hernias — 10 to 20 percent. Inguinal, femoral, incisional, umbilical, obturator. Femoral hernia is the commonest hernia to strangulate (women, narrow neck).
- Malignancy — 10 to 15 percent. Primary small bowel tumours rare; commoner is metastatic disease (peritoneal carcinomatosis) or extrinsic compression.
- Crohn's disease — strictures, often terminal ileum.
- Intussusception — pediatric predominant; adult intussusception suggests a lead point (polyp, tumour).
- Abdominal tuberculosis — Indian classic. Ileocaecal strictures, lymphadenopathy, peritoneal involvement.
- Gallstone ileus — large gallstone erodes into duodenum (cholecystoduodenal fistula) and impacts in the terminal ileum. Rigler's triad — pneumobilia, SBO, ectopic gallstone on plain X-ray.
- Bezoars, foreign bodies — psychiatric patients, children.
Large bowel
- Colorectal carcinoma — 60 percent of LBO; commonest at sigmoid (narrow lumen, solid stool).
- Volvulus — sigmoid (80 percent) and caecal (15 percent).
- Diverticular stricture — chronic recurrent diverticulitis.
- Fecal impaction — elderly, bedridden, opioid users.
- Hirschsprung disease — pediatric; aganglionic distal segment.
- Anorectal malformation — neonatal.
Indian-specific causes
- Abdominal tuberculosis — ileocaecal or jejunoileal strictures; pulmonary TB history in 30 percent; ASCITES, doughy abdomen, weight loss.
- Neglected groin hernia — late presentation with strangulation; femoral hernia in elderly women.
- Sigmoid volvulus — high-fibre Indian diet, elongated redundant sigmoid, elderly bedridden.
- Roundworm bolus (Ascaris lumbricoides) — pediatric; severe infestation forms bolus in ileum.
Clinical features
Cardinal symptoms — abdominal pain, vomiting, distension, absolute constipation (no flatus or stool).
- Pain pattern — colicky in mechanical, continuous in strangulation, absent in paralytic ileus.
- Vomiting — early bilious in proximal SBO, late feculent in distal SBO or LBO.
- Distension — central in SBO, peripheral in LBO, massive in volvulus and chronic LBO.
- Bowel sounds — high-pitched tinkling in mechanical, absent in paralytic ileus.
- Tachycardia, fever, peritonism — strangulation flags.
Signs of dehydration — dry mucous membranes, low urine output, hypotension, tachycardia. Fluid sequestration into the obstructed bowel ("third space") causes severe deficit.
Abdominal exam — distension, tenderness, hernial orifices (always examine all sites in obstruction — easily missed obturator and femoral hernias), DRE for impaction, blood, or mass.
Investigations
Laboratory
- CBC — leukocytosis suggests strangulation.
- U&E — dehydration, hypochloraemic hypokalaemic metabolic alkalosis (proximal SBO vomiting), metabolic acidosis (strangulation, lactate).
- Lactate — raised in strangulation.
- LFT, amylase — exclude other causes.
- Group and save — pre-operative.
Plain abdominal X-ray (erect and supine)
- SBO — central dilated loops greater than 3 cm, valvulae conniventes crossing the full lumen, multiple air-fluid levels (over three on erect film), ladder pattern.
- LBO — peripheral loops, haustrations not crossing full lumen, caecum greater than 9 cm at risk of perforation.
- Sigmoid volvulus — coffee-bean or omega-loop sign in LUQ pointing to RLQ.
- Caecal volvulus — comma sign, embryo-shaped distended caecum in LUQ.
- Rigler's triad — gallstone ileus.
- Pneumoperitoneum — perforation.
Sensitivity only 60 to 80 percent; misses many strangulations.
CT abdomen with IV contrast
Modality of choice. Sensitivity over 90 percent. Identifies:
- Level (transition point).
- Cause (adhesion is diagnosis of exclusion; hernia, malignancy, volvulus visible).
- Strangulation signs — mesenteric oedema, mesenteric haziness, free fluid, pneumatosis intestinalis, portal venous gas, reduced bowel-wall enhancement.
- Closed-loop — C-shape or U-shape of dilated bowel with mesenteric whirl sign.
Other modalities
- Water-soluble contrast study (Gastrografin) — both diagnostic (failure to reach colon at 24 h predicts surgical SBO) and therapeutic (osmotic effect reduces wall oedema; reduces operative rate in adhesive SBO).
- USG — pediatric intussusception (target sign, pseudokidney sign).
- MRI — Crohn's mapping, pregnancy.
Management
Initial resuscitation ("drip and suck")
- NPO — nothing by mouth.
- Nasogastric decompression — relieves vomiting, reduces aspiration risk, decompresses dilated bowel.
- IV fluids — isotonic crystalloid; replace deficit plus maintenance plus ongoing losses. Average deficit 4 to 6 L.
- Electrolyte correction — particularly K+ in proximal SBO.
- Urinary catheter — monitor output (target greater than 0.5 mL/kg/h).
- Analgesia — IV opioid (but cautious — can mask peritonism).
- Antibiotics — broad-spectrum (amoxicillin-clavulanate or piperacillin-tazobactam plus metronidazole) if strangulation suspected or pre-operative.
- DVT prophylaxis — LMWH unless bleeding risk.
Adhesive SBO — trial of conservative management
- Most adhesive SBO resolves in 48 to 72 hours without surgery.
- Water-soluble contrast study (Gastrografin) shortens hospital stay and increases non-operative resolution.
- Indications to abandon conservative management — failure to improve at 48 to 72 hours, signs of strangulation, complete obstruction (no contrast through to colon).
Surgical management — indications
- Strangulation suspected — urgent surgery.
- Peritonitis — urgent surgery.
- Complete obstruction failing conservative trial at 48 to 72 hours.
- Hernia obstruction — early surgery (high strangulation risk).
- Closed-loop obstruction — urgent surgery.
- Malignant LBO — surgery, stent as bridge, or palliative diversion depending on stage.
- Volvulus — sigmoidectomy after endoscopic detorsion or emergency if detorsion fails.
Operative approach
- Adhesiolysis — sharp dissection; minimise enterotomy risk.
- Resection — for non-viable bowel; assess viability (colour, peristalsis, pulse, fluorescein, Doppler) after warm-saline pack and 100 percent oxygen for 10 minutes.
- Primary anastomosis vs stoma — depends on contamination, patient stability, blood supply.
- Damage control — in unstable patient — resect, leave open, return after 24 to 48 hours for anastomosis.
Special scenarios
Sigmoid volvulus
- Endoscopic detorsion plus rectal-tube placement → success 70 to 90 percent.
- Elective sigmoidectomy after bowel preparation — recurrence 50 to 90 percent without surgery.
- Emergency sigmoidectomy if detorsion fails, peritonitis, or gangrenous bowel on scope.
Caecal volvulus
- Detorsion usually unsuccessful.
- Right hemicolectomy or caecopexy (in selected fit patients).
Pediatric intussusception
- Peak age 6 months to 2 years; ileocolic in 90 percent.
- Presentation — paroxysmal screaming, drawing up of legs, currant-jelly stool (late), sausage-shaped mass.
- USG — target or doughnut sign.
- Treatment — air or hydrostatic enema reduction (success 80 to 90 percent). Surgery if failure, perforation, peritonitis, recurrence (more than 3), or pathological lead point in older child.
Gallstone ileus
- Rigler's triad — pneumobilia, SBO, ectopic gallstone.
- Treatment — enterolithotomy at obstruction site; cholecystectomy and fistula closure can be staged.
Acute mesenteric ischemia (a mimic)
- Pain out of proportion to physical signs.
- Atrial fibrillation history → embolism (SMA most affected).
- Lactate, CT angiography, urgent embolectomy or revascularisation.
Ogilvie syndrome (acute colonic pseudo-obstruction)
- Massive colonic dilatation without mechanical cause.
- Elderly, post-op, severe illness, electrolyte disturbance.
- Treat — correct electrolytes, stop offending drugs, decompress (NG, rectal tube, neostigmine, colonoscopic decompression). Surgery if caecal diameter over 12 cm or perforation.
NEET PG MCQ traps
- Adhesions are the commonest cause of SBO in adults.
- Hernias are the commonest cause of SBO in children and in patients without prior surgery.
- Colorectal cancer is the commonest cause of LBO.
- Sigmoid volvulus — coffee-bean sign on plain X-ray; treat with endoscopic detorsion then elective sigmoidectomy.
- Caecal volvulus — comma sign, treat with right hemicolectomy (detorsion usually fails).
- Femoral hernia is the commonest hernia to strangulate.
- Rigler's triad — gallstone ileus.
- Strangulation flags — fever, tachycardia, peritonitis, raised lactate, leukocytosis, continuous pain.
- Closed-loop obstruction — urgent surgery; do not delay for conservative trial.
- Gastrografin study — both diagnostic and therapeutic in adhesive SBO.
- Caecum greater than 9 cm in LBO is at risk of perforation per Laplace law.
- Pediatric intussusception — first-line is air or hydrostatic enema reduction.
- Abdominal TB — Indian classic; ileocaecal strictures plus ascites plus weight loss.
- Currant-jelly stool — late sign of intussusception, indicates mucosal slough.
- Ogilvie syndrome — colonic pseudo-obstruction; treat with neostigmine and colonoscopic decompression.
Recent updates and Indian context
- NMC CBME 2024 — surgical emergency teaching emphasises ATLS-style resuscitation and CT-led decision-making in obstruction.
- WSES 2021 ASBO guidelines — formalise the Gastrografin protocol; non-operative trial up to 72 hours unless strangulation or closed-loop.
- Self-expanding metallic stents (SEMS) for malignant LBO — bridge to surgery in operable patients, palliation in unresectable disease.
- ERAS in colorectal surgery — reduces post-operative ileus rates; recovery from emergency obstruction surgery also benefits from structured protocols.
- Indian epidemiology — abdominal TB remains a major NEET PG vignette; obstructed inguinal and femoral hernias common in rural elderly; sigmoid volvulus prevalent in northern and central India.
- NEXT — expect integrated stems pairing CT findings with management decisions; recent INI-CET trends favour image-based diagnosis of volvulus, gallstone ileus, and closed-loop obstruction.
Frequently asked questions
What are the commonest causes of small bowel obstruction?
In adults, the three commonest causes of small bowel obstruction worldwide are adhesions (60 to 70 percent, usually post-operative), hernias (10 to 20 percent — inguinal, femoral, incisional), and malignancy (10 to 15 percent). In India, abdominal tuberculosis remains a top differential, especially for ileocaecal strictures, and is a frequent NEET PG vignette.
How do you distinguish strangulation from simple obstruction?
Strangulation suggests bowel ischemia. Red flags — fever, tachycardia disproportionate to dehydration, peritonitis (rebound, guarding), continuous (non-colicky) pain, leukocytosis, raised lactate, and CT signs of closed-loop or pneumatosis. Simple obstruction has colicky pain, normal vitals, and no peritoneal signs. Strangulation mandates urgent operative exploration.
What is the management of sigmoid volvulus?
Sigmoid volvulus on plain X-ray shows a coffee-bean or omega-loop sign in the LUQ. Initial management is endoscopic detorsion (sigmoidoscopic or colonoscopic) with rectal-tube placement — successful in 70 to 90 percent. Elective sigmoidectomy follows after bowel preparation because the recurrence rate without surgery is 50 to 90 percent. Emergency sigmoidectomy is needed if detorsion fails, signs of strangulation are present, or peritonitis develops.
What is the first-line imaging for suspected bowel obstruction?
CT abdomen with IV contrast is the modality of choice — sensitivity over 90 percent, identifies the level (small vs large bowel), transition point, cause (adhesion, hernia, malignancy, volvulus, intussusception), and signs of strangulation (mesenteric oedema, pneumatosis, portal venous gas). Plain X-ray (erect, supine) is still useful for initial triage but misses 20 to 30 percent of cases and most strangulations.
How is pediatric intussusception managed?
Air or hydrostatic (saline or barium) enema reduction under fluoroscopic or ultrasound guidance is the first-line management for ileocolic intussusception in children if there are no signs of perforation, peritonitis, or shock. Success rate is 80 to 90 percent. Surgical reduction is reserved for failed enema, perforation, or recurrent intussusception. A pathological lead point (Meckel diverticulum, lymphoma) raises the threshold for surgery.
This content is for educational purposes for NEET PG exam preparation. It is not a substitute for professional medical advice, diagnosis, or treatment. Clinical information has been reviewed by qualified medical professionals.
Written by: NEETPGAI Editorial Team
Reviewed by: Pending SME Review
Last reviewed: May 2026
