Volvulus: Sigmoid, Caecal and Gastric

Introduction

A volvulus is torsion of a loop of bowel around the axis of its own mesentery. Two things happen at once: the lumen is obstructed at both ends of the twisted segment, creating a closed loop, and the mesenteric vessels running to the segment are kinked, threatening its blood supply. This combination is what makes volvulus dangerous out of proportion to how well the patient may initially look.

Colonic volvulus accounts for roughly 5% of large bowel obstruction in the UK and Western Europe, ranking third behind colorectal cancer and diverticular stricture. Its incidence is far higher in parts of Africa, the Middle East, South America and South Asia, an area sometimes called the volvulus belt, where a high-residue diet produces a long, loaded, redundant sigmoid colon and volvulus becomes the leading cause of large bowel obstruction.¹

Pathophysiology and predisposing factors

A segment of bowel can only twist if it is both mobile and long, and if its mesentery has a narrow base. The narrow base acts as a pivot; the long loop provides the leverage.

Sigmoid volvulus

Chronic constipation and a high-residue diet produce a chronically loaded, elongated sigmoid. Over years the sigmoid mesocolon lengthens while its attachment to the pelvic brim narrows, producing a dolichosigmoid on a stalk. The loop then twists, most often anticlockwise, through 180 to 360 degrees or more.

• Advanced age and institutional care - by far the strongest associations in UK practice
• Chronic constipation and laxative dependence
• Neurological and psychiatric disease - Parkinson disease, multiple sclerosis, dementia, learning disability, and spinal cord injury
• Drugs - antipsychotics, anticholinergics and opioids, all of which slow colonic transit
• High-residue diet, which explains the geographical distribution
• Previous episodes - the single strongest predictor of a further volvulus is having had one
• Chagas disease, through destruction of the myenteric plexus and consequent megacolon

Caecal volvulus

This is embryological rather than acquired. Normally the ascending colon and caecum fuse to the posterior abdominal wall during development. In around 10 to 20% of people this fixation is incomplete, leaving a mobile caecum on a mesentery. Only a small proportion of these will ever twist, but they are the population at risk, which is why caecal volvulus presents at a younger age than sigmoid volvulus.

Two patterns occur. Axial torsion is a true volvulus in which the caecum twists around its mesentery. Caecal bascule is upward folding of a mobile caecum onto the ascending colon without torsion, which obstructs but does not initially compromise the blood supply.

Clinical features

Sigmoid volvulus

• Gross abdominal distension, often described by relatives as sudden and dramatic, and frequently tympanic to percussion
• Absolute constipation to faeces and flatus, present early because the obstruction is distal
• Colicky lower abdominal pain, though pain may be surprisingly modest
• Little or no vomiting until late, because the competent ileocaecal valve holds back the colonic contents
• A history of previous similar episodes that settled, which is common and highly suggestive
• An empty rectum on digital examination

Caecal volvulus

The obstruction is proximal, so the picture is that of small bowel obstruction: colicky central abdominal pain, earlier and more prominent vomiting, and less distension. Distension may be asymmetrical with a tympanic mass in the left upper quadrant, where the twisted caecum has migrated.

Gastric volvulus

The Borchardt triad is severe, sudden epigastric or lower chest pain, violent retching that produces nothing, and inability to pass a nasogastric tube. It is a genuine emergency because gastric necrosis follows quickly, and it should be suspected in any patient with a known large paraoesophageal hernia who develops severe upper abdominal pain.

Investigations

Blood tests

FBC, U&Es, CRP, clotting and group and save, and a venous blood gas for lactate. Bloods do not make the diagnosis, but a raised lactate or a leucocytosis with a left shift raises the probability of ischaemia and should be acted upon rather than repeated.

Abdominal radiograph

• Coffee bean sign - a massively dilated, gas-filled loop, with the two apposed medial walls forming a dense midline line that resembles the cleft of a coffee bean
• Inverted U or bent inner tube - the loop arises from the pelvis and points towards the right upper quadrant in sigmoid volvulus
• Northern exposure sign - the apex of the sigmoid loop lies above the level of the transverse colon
• Absent rectal gas, with proximal large bowel dilatation
• In caecal volvulus the dilated caecum is displaced to the left upper quadrant, with small bowel dilatation and a relatively gasless distal colon
• Free subdiaphragmatic gas or Rigler sign indicates perforation

CT

Contrast-enhanced CT is now obtained in almost every case and has largely replaced the contrast enema. It confirms the diagnosis, identifies the level and direction of the twist, excludes an obstructing tumour as an alternative explanation, and, most importantly, assesses viability.²

• Whirl sign - the twisted mesentery and its vessels spiralling around the point of torsion, which is essentially pathognomonic
• Bird beak sign - tapering of the bowel to the point of the twist, also seen on contrast enema
• X marks the spot - two transition points crossing at the site of torsion
• Signs of ischaemia - reduced or absent bowel wall enhancement, wall thickening, mesenteric fluid, pneumatosis intestinalis and portal venous gas

Management of sigmoid volvulus

Management divides sharply on whether the bowel is viable. Resuscitate every patient first: intravenous fluid, correction of electrolytes, analgesia, nil by mouth, a nasogastric tube if vomiting, catheterisation and venous thromboembolism prophylaxis.

Viable bowel: endoscopic decompression

The initial treatment is endoscopic decompression using a flexible sigmoidoscope, passed to the point of torsion under direct vision, allowing the loop to untwist and deflate. A soft flatus tube is left in place for 24 to 48 hours to prevent immediate retorsion. This succeeds in around 80% of patients and converts an emergency into a semi-elective situation.³

• The endoscopist must inspect the mucosa. Dusky, ulcerated or necrotic mucosa means the loop is not viable and the patient goes to theatre rather than back to the ward.
• A gush of gas and liquid faeces with immediate relief of distension marks successful decompression
• Rigid sigmoidoscopy with a flatus tube is an older alternative, still used where flexible endoscopy is not available out of hours, but it does not permit mucosal assessment above the rectosigmoid
• Repeat plain radiography or clinical reassessment confirms resolution
• Perforation is the main procedural risk, and is more likely in ischaemic bowel

The recurrence problem

Decompression relieves the obstruction but does nothing about the redundant sigmoid that caused it. Recurrence rates after decompression alone are 50 to 90%, and each recurrence carries a further risk of ischaemia and a higher mortality than an elective operation.³

For this reason, patients fit for surgery should be offered elective sigmoid colectomy with primary anastomosis during the same admission, once they have been resuscitated and the bowel prepared. In frail patients where the operative risk is prohibitive, decompression alone with attention to bowel habit is a reasonable and often appropriate palliative strategy, and this decision should be documented as a considered one rather than a default.

Non-viable bowel or failed decompression

• Emergency laparotomy with resection of the affected segment
• Hartmann procedure - sigmoid resection with an end colostomy and closure of the rectal stump - is the usual operation in an unstable or contaminated patient
• Resection with primary anastomosis, with or without a defunctioning stoma, in a stable, well-resuscitated patient with healthy bowel ends
• Detorsion alone without resection is not appropriate, because recurrence is near universal

Management of caecal and gastric volvulus

Caecal volvulus

Endoscopic decompression is rarely successful, because the colonoscope must traverse the entire colon to reach the twist, and the reported success rate is low. Caecal volvulus is therefore a surgical diagnosis.

• Right hemicolectomy with primary ileocolic anastomosis is the definitive operation, and the ileocolic anastomosis heals reliably even in the emergency setting
• Ileocolic resection with end ileostomy where the patient is unstable or the peritoneal contamination is significant
• Caecopexy - fixing the caecum to the parietal peritoneum - avoids a resection but has a higher recurrence rate and is reserved for patients unfit for resection
• Caecostomy decompresses and fixes the caecum but has a high rate of wound and stomal complications

Gastric volvulus

Acute gastric volvulus is an emergency. Attempt nasogastric decompression, which is often impossible, and arrange urgent CT and surgical intervention. Treatment is untwisting of the stomach with repair of the underlying diaphragmatic defect or hiatus hernia, and gastropexy or gastrostomy to prevent recurrence. Gastric necrosis requires resection and carries a high mortality.

Complications

• Bowel ischaemia, gangrene and perforation with faecal peritonitis and septic shock, the principal cause of death
• Recurrence after decompression alone, which is the expected outcome rather than a complication in the usual sense
• Perforation during endoscopic decompression, particularly where the bowel is already compromised
• Anastomotic leak after emergency resection, which is why a Hartmann procedure is preferred in unfavourable conditions
• Stoma complications - retraction, prolapse, parastomal hernia and skin excoriation - and the substantial number of Hartmann procedures that are never reversed
• Abdominal compartment syndrome from massive distension
• Aspiration pneumonia and deconditioning in frail patients, who make up most of the sigmoid volvulus population

Red flags

Prognosis

Outcome depends almost entirely on whether the bowel is viable at the time of treatment. Successful endoscopic decompression of a viable sigmoid volvulus carries a low immediate mortality, but where gangrene has already developed, mortality after emergency resection is high, commonly reported between 20 and 40%, reflecting both the septic insult and the frailty of the typical patient.

The other determinant is recurrence. Because more than half of patients managed by decompression alone will have a further volvulus, and because emergency surgery carries several times the mortality of an elective operation, the decision about definitive surgery is really a decision about how a patient's remaining risk is distributed rather than whether they carry any.

That framing is the useful exam point. Endoscopic decompression is not the treatment of sigmoid volvulus; it is the treatment of this episode of sigmoid volvulus, and every patient in whom it succeeds needs an explicit plan for what happens next.