# Large Bowel Obstruction and Volvulus
## Overview
Large bowel obstruction (LBO) accounts for approximately 25% of all intestinal obstructions. Unlike small bowel obstruction, LBO is more frequently caused by malignancy and carries a higher risk of perforation, particularly when the ileocecal valve is competent, creating a closed-loop obstruction. The general surgeon must distinguish mechanical obstruction from pseudo-obstruction and understand the management of volvulus, the second most common cause of LBO.
## Etiology
| Cause | Frequency | Key Features |
|-------|-----------|-------------|
| Colorectal carcinoma | 50–60% | Left-sided tumors most common |
| Volvulus | 10–15% | Sigmoid 60–75%, cecal 25–40% |
| Diverticular disease | ~10% | Stricture from recurrent diverticulitis |
| Pseudo-obstruction (Ogilvie) | Variable | Non-mechanical colonic dilation |
| Other (adhesions, fecal impaction, intussusception) | <10% | Extrinsic compression, lead points |
**Colorectal carcinoma** is the most common cause of LBO, responsible for 50 to 60% of cases, with left-sided tumors more commonly causing obstruction. **Volvulus** accounts for 10 to 15% and involves sigmoid volvulus (60 to 75% of colonic volvulus), cecal volvulus (25 to 40%), and rarely transverse colon volvulus. **Diverticular disease** causes approximately 10% of cases through stricture formation from recurrent diverticulitis. **Pseudo-obstruction (Ogilvie syndrome)** produces non-mechanical colonic dilation. Other causes include extrinsic compression from pelvic tumors, endometriosis, or adhesions; fecal impaction in elderly, debilitated, or psychiatric patients; intussusception (usually with a lead point such as a tumor in adults); and inflammatory strictures from Crohn disease, radiation, or ischemia.
## Pathophysiology
A closed-loop obstruction occurs when the ileocecal valve is competent, which is the case in approximately 50 to 75% of patients. Progressive colonic dilation develops proximal to the obstruction, and the risk of **cecal perforation** becomes critical when the cecal diameter exceeds 12 to 14 cm. The cecum is the most common site of perforation due to the **Law of Laplace** -- at the largest diameter, wall tension is greatest. Bowel wall ischemia leads to bacterial translocation, sepsis, and peritonitis. When the ileocecal valve is incompetent, retrograde decompression into the small bowel reduces the perforation risk.
## Clinical Presentation
LBO presents with a more gradual onset of symptoms compared to SBO. Progressive abdominal distension is the most prominent feature, accompanied by crampy abdominal pain, obstipation (absolute constipation with no passage of flatus or stool), and late feculent vomiting -- a much later finding compared to SBO. A change in bowel habits preceding the obstruction suggests underlying malignancy. On examination, the abdomen is tender and distended, tympanic to percussion. Digital rectal exam reveals an empty rectum unless a rectal tumor or fecal impaction is present. Peritoneal signs indicate perforation or ischemia.
## Diagnostic Workup
### Laboratory Studies
Standard workup includes CBC, BMP, lactate, and blood gas. A type and crossmatch is obtained if surgery is anticipated, and a CEA level is drawn if malignancy is suspected.
### Imaging
**Abdominal radiographs** show dilated colon (greater than 6 cm for the transverse colon, greater than 9 cm for the cecum) with visible haustral markings and air-fluid levels. Sigmoid volvulus produces the classic "coffee bean sign" or "omega sign" -- a massively dilated sigmoid loop pointing toward the right upper quadrant. Cecal volvulus shows a dilated cecum displaced to the left upper quadrant, creating a "kidney bean" appearance.
**CT abdomen/pelvis with IV contrast** is the study of choice for LBO evaluation. It identifies the site, cause, and complications (perforation, ischemia), distinguishes mechanical obstruction from pseudo-obstruction, and demonstrates the transition point with decompressed distal colon. Malignant strictures show an "apple-core" lesion with shouldering and irregular wall thickening. Volvulus produces the "whirl sign" of twisted mesentery and vessels. Cecal wall pneumatosis or free air indicates imminent or completed perforation.
**Water-soluble contrast enema** is useful when CT is equivocal or unavailable and confirms the level of obstruction, but it is contraindicated if perforation is suspected.
## Malignant Large Bowel Obstruction
### Left-Sided Obstruction
Left-sided obstruction is the most common presentation. **Emergency surgery** is required for perforation, peritonitis, or cecal ischemia. The **Hartmann procedure** -- resection of the obstructing tumor with end colostomy and rectal stump closure -- is the safest option in unstable patients, peritonitis, or fecal contamination, though the reversal rate has historically been only 30 to 60%. **Resection with primary anastomosis**, with or without a diverting ileostomy, is increasingly performed in stable patients with adequate bowel prep or on-table lavage. **Subtotal or total colectomy with ileorectal anastomosis** is appropriate when synchronous proximal pathology or cecal compromise is present.
**Self-expanding metallic stents (SEMS)** as a bridge to surgery allow decompression, bowel preparation, optimization, and staging before an elective single-stage resection. Technical success rates are 90 to 95% with clinical success of 70 to 90%, converting emergency surgery to elective surgery with a higher primary anastomosis rate. However, concerns include tumor perforation (5 to 10%), stent migration, re-obstruction, and potentially adverse oncologic outcomes including tumor seeding and worse disease-free survival in some studies. Stenting is contraindicated in peritonitis, perforation, or distal rectal lesions and is most appropriate for patients with incurable disease (palliation) or high surgical risk.
### Right-Sided Obstruction
Right-sided obstruction is managed with right hemicolectomy with primary ileocolic anastomosis, which is typically safe even in the emergency setting.
### Obstructing Rectal Cancer
Obstructing rectal cancer is managed with diverting loop colostomy or transverse colostomy for decompression, followed by neoadjuvant chemoradiation and definitive resection. Stenting may be considered but carries a higher complication rate in low rectal lesions.
## Sigmoid Volvulus
### Epidemiology and Risk Factors
Sigmoid volvulus is the most common colonic volvulus (60 to 75%) and typically affects elderly, institutionalized, or psychiatric patients with neurologic conditions. Risk factors include chronic constipation, high-fiber diet, megacolon, and Chagas disease. It is endemic in the "volvulus belt" spanning Africa, South America, Eastern Europe, and the Middle East.
### Pathophysiology
A redundant sigmoid colon with a narrow-based mesentery twists on its axis, creating a closed-loop obstruction with risk of ischemia and gangrene.
### Diagnosis
The abdominal X-ray shows the characteristic "coffee bean sign" -- a massively dilated sigmoid loop usually extending above the transverse colon. CT demonstrates the "whirl sign" at the point of torsion with massively dilated sigmoid.
### Management
In the absence of peritonitis or perforation, initial management is **endoscopic decompression** via flexible sigmoidoscopy or rigid proctoscopy, with a success rate of 80 to 90%. A rectal tube is placed after decompression to prevent early recurrence. However, the recurrence rate without surgery is 40 to 60%, so **elective sigmoid colectomy** should be performed during the same admission or within 2 to 3 days to prevent recurrence.
When peritonitis, perforation, or gangrenous bowel is present, **emergent laparotomy** is required. The Hartmann procedure is the most commonly performed operation, though resection with primary anastomosis is an alternative. Endoscopic decompression should never be attempted if gangrene is suspected.
## Cecal Volvulus
### Epidemiology and Types
Cecal volvulus is the second most common colonic volvulus (25 to 40%) and tends to affect younger patients (30 to 60 years) compared to sigmoid volvulus. It requires a mobile cecum resulting from incomplete fixation during embryologic development. Two types exist: **axial (true cecal volvulus)**, in which the cecum twists clockwise on its mesentery, and **cecal bascule**, in which the cecum folds anteriorly and superiorly without torsion.
### Diagnosis
Abdominal X-ray shows a dilated cecum displaced to the left upper quadrant or central abdomen. CT confirms an ectopic dilated cecum with the "whirl sign" at the point of torsion and a small bowel obstruction pattern.
### Management
A critical distinction from sigmoid volvulus is that **endoscopic decompression is not effective and not recommended** for cecal volvulus -- surgery is required. Without gangrene, right hemicolectomy with primary ileocolonic anastomosis is preferred; cecopexy has a high recurrence rate and is generally not recommended. With gangrene, right hemicolectomy is performed with primary anastomosis versus ileostomy depending on patient stability and contamination.
## Ogilvie Syndrome (Acute Colonic Pseudo-Obstruction)
### Definition and Risk Factors
Ogilvie syndrome is massive colonic dilation in the absence of mechanical obstruction, typically involving the cecum and ascending colon. Risk factors include postoperative states (especially after orthopedic, cardiac, or pelvic surgery), critical illness, sepsis, electrolyte imbalances (hypokalemia, hypomagnesemia, hypocalcemia), opioid or anticholinergic medication use, and neurologic conditions (spinal cord injury, stroke).
### Diagnosis
The clinical picture features massive abdominal distension without peritoneal signs. Abdominal X-ray or CT shows diffuse colonic dilation (especially of the cecum and ascending colon) without a mechanical transition point. It is essential to **exclude mechanical obstruction** with a water-soluble contrast enema or CT before diagnosing Ogilvie syndrome.
### Management
The stepwise management of Ogilvie syndrome is summarized below:
| Step | Intervention | Details |
|------|-------------|---------|
| 1 | Conservative measures (24–48 h) | NPO, NGT, rectal tube, correct electrolytes, stop offending meds, ambulation |
| 2 | Neostigmine | 2 mg IV over 3–5 min; success 80–90%; requires cardiac monitoring + atropine at bedside |
| 3 | Colonoscopic decompression | Success 60–80%; risk of perforation |
| 4 | Surgery | Cecostomy or subtotal colectomy for refractory cases or perforation |
**Conservative measures** are the initial management for 24 to 48 hours and include NPO status, nasogastric decompression, rectal tube placement, correction of electrolyte abnormalities, discontinuation of offending medications (opioids, anticholinergics), and ambulation with position changes (knee-chest, prone).
If conservative management fails after 24 to 48 hours and the cecal diameter exceeds 12 cm, **neostigmine** (an acetylcholinesterase inhibitor) is indicated. It is given at 2 mg IV over 3 to 5 minutes with a success rate of 80 to 90%. Cardiac monitoring is mandatory, and atropine must be at the bedside because bradycardia is a significant risk. Neostigmine is contraindicated in mechanical obstruction, recent myocardial infarction, and active bronchospasm.
If neostigmine fails, **colonoscopic decompression** is attempted with a success rate of 60 to 80%, though it carries a risk of perforation. **Surgery** -- cecostomy or subtotal colectomy -- is reserved for cases where all other measures fail or if peritoneal signs or perforation develop.
Abdominal radiograph showing the classic coffee bean sign of sigmoid volvulus with a massively dilated sigmoid loop extending above the transverse colon, pointing toward the right upper quadrant. Include comparison panels showing cecal volvulus with the dilated cecum displaced to the left upper quadrant and normal colonic gas pattern for reference.
CT scan findings in large bowel obstruction showing three panels: (1) malignant obstruction with apple-core lesion and proximal colonic dilation, (2) sigmoid volvulus with whirl sign of twisted mesentery and vessels, and (3) Ogilvie syndrome with diffuse colonic dilation without a transition point. Label key diagnostic features in each panel.
Surgical decision-making algorithm for malignant large bowel obstruction showing pathways based on patient stability, presence of perforation/peritonitis, tumor location (right vs. left sided), and options including Hartmann procedure, resection with primary anastomosis, subtotal colectomy, and colonic stenting as bridge to surgery. Include decision points for palliative vs. curative intent.
## Clinical Pearls
The cecum is the most common site of perforation in LBO due to the Law of Laplace, and risk increases significantly when cecal diameter exceeds 12 cm. Mechanical obstruction must always be excluded before diagnosing Ogilvie syndrome, requiring a water-soluble contrast enema or CT. Sigmoid volvulus can be decompressed endoscopically, but cecal volvulus cannot -- cecal volvulus requires surgery. After successful endoscopic decompression of sigmoid volvulus, semi-elective sigmoid colectomy should be performed during the same admission to prevent recurrence, which occurs in 40 to 60% of cases without surgery. Neostigmine for Ogilvie syndrome is highly effective at 80 to 90% but requires cardiac monitoring and atropine at the bedside for potential bradycardia. Self-expanding metallic stents for malignant LBO are best used for palliation in patients with incurable disease, as oncologic concerns limit their use as a bridge to curative surgery. A competent ileocecal valve creates a closed-loop obstruction in LBO, significantly increasing the risk of cecal perforation. Feculent vomiting in LBO is a late finding indicating severe, prolonged obstruction.
## References
- Vogel JD, Feingold DL, Stewart DB, et al. Clinical practice guidelines for colon volvulus and acute colonic pseudo-obstruction. *Dis Colon Rectum*. 2016;59(7):589-600.
- Frago R, Ramirez E, Millan M, et al. Current management of acute malignant large bowel obstruction: a systematic review. *Am J Surg*. 2014;207(1):127-138.
- Vanek VW, Al-Salti M. Acute pseudo-obstruction of the colon (Ogilvie's syndrome): an analysis of 400 cases. *Dis Colon Rectum*. 1986;29(3):203-210.
- Alavi K, Poylin V, Davids JS, et al. The American Society of Colon and Rectal Surgeons clinical practice guidelines for the management of colonic volvulus and acute colonic pseudo-obstruction. *Dis Colon Rectum*. 2021;64(9):1046-1057.