Sigmoid colon is characterized by torsion of the sigmoid loops of the colon, causing mechanical obstruction of the passage leading to the rectum and restriction of blood supply.
The classical clinical symptoms of acute SV include abdominal pain and constipation. Most of the acute episodes of SV are sudden in onset and present with additional symptoms of vomiting, nausea, anorexia and hematemesis.
Physical examination of the abdomen reveals a distended, soft and palpable abdomen along with abnormal bowel sounds and noticeable peristalsis. Retention of feces in the sigmoid colon is manifested by an empty rectum and presence of fecal odor on the patient's breath.
Obvious signs of sustained, long-term SV are colonic gangrene and peritonitis. Morphological changes consist of a hypertrophied colonic wall and a narrowed mesentery resulting from a distended colon and visibly clear vasculature.
Several imaging tests coupled with typical clinical findings of SV aid in establishing an accurate diagnosis.
Computed tomography (CT) scan and magnetic resonance imaging (MRI) serve as important diagnostic tools for SV. Both CT scan and MRI show twisted sigmoid mesentery and dilated loops, which are the characteristic features of SV.
The X-ray of the abdomen has proven as successful diagnostic aid for SV in 57%-90% of the patients. An abdominal X-ray shows a dilated sigmoid colon and several intestinal air fluid levels. Laboratory tests are of no value in diagnosing SV.
Endoscopic evaluation of the sigmoid colon shows characteristic spiral sphincter twist in the mucosa of the obstructed sigmoid colon.
In the absence of serious complications such as gangrene, peritonitis and perforation, barium contrast enemas are used to observe obstruction. Barium enemas have been found to be useful in about 20%-30% of the cases.
Treatment options depend on the severeness of the disease. The treatment of choice for SV is flexible endoscopic detorsion which has proven to be successful in about 33%-91% of the cases. In emergency situations such as bowel gangrene, peritonitis and bowel perforation, surgical intervention is required. Common surgical procedures employed in SV include sigmoidopexy, mesosigmoidoplasty, anastamosis and sigmoid resection. Resection of the gangrenous site of the bowel is followed by Hartmann's procedure specifically in unstable patients. Alternative surgical procedures that may be applied comprise percutaneous endoscopic colostomy, tube sigmoidostomy and extraperitonealization of the sigmoid colon.
The mortality rate of treated cases of SV has been reported to be 12%-15% with an increase in figures to approximately 24% in emergency cases. The mortality range for elective procedures has been reported to be 6%.
Moreover, SV shows a high risk of morbidity and mortality when diagnosis and treatment are delayed. In the absence of prompt diagnosis and early management, mortality rate reaches up to 40%.
Several etiologic factors have been recognized that may predispose an individual to develop SV. Variation in the normal anatomy of the colon such as redundancy of the sigmoid colon, presence of a mesentery that is wider in appearance and a tapered base of sigmoid mesentery may lead to SV  . Several factors are correlated with redundant sigmoid colon and narrow pelvis, some of which are discussed below.
Typically, narrow pelvic inlet is common in males and sigmoid colon redundancy has been shown to occur in elderly patients. Therefore, the risk of SV is proposed to be slightly higher in males and among the elderly . In some cases, twisting of the sigmoid colon has been reported to occur during pregnancy . The incidence of developing a redundancy of the sigmoid colon is also thought to be associated with high altitudes and an intake of a high-fiber vegetable diet. Therefore, individuals living at elevated heights and consuming a vegetarian diet show an increased risk of SV . Another extremely common cause of SV is long-term constipation. In the presence of chronic constipation, the sigmoid colon lengthens which increases the risk for SV to a large extent. Less common etiologies for SV include internal herniations, postsurgical adhesions, congenital megacolon, malrotations, appendicitis and malignancies.
SV is predominant among males between 40-80 years of age . The disease is more common among Eastern countries and accounts for 20%-50% cases of colonic obstructions. However, SV is responsible for about 2%-5% of colonic obstruction cases in the Western world . In the United States, the annual incidence of SV has been reported to be 1.67 in 100,000 persons .
The twisting of the sigmoid colon in SV causes mechanical obstruction. Persistent obstruction results in bacterial infiltration and fermentation inside the colon, causing distention of the sigmoid colon and the proximal colon. This leads to an increased pressure build up within the colon coupled with decreased capillary perfusion due to occlusion of the blood vessels supplying the colon. This is ultimately followed by ischemia of the intestinal mucosa. Sustained ischemic damage causes increased bacterial infiltration inside the sigmoid colon, leading to colonic gangrene.
Based on disease severeness and pathophysiologic events presenting overtime in the sigmoid colon, SV can be categorized into five distinct classes. Class I is characterized by the presence of SV alone with no coexisting morbidity. In Class II, comorbidities may present but bowel gangrene and shock do not develop. In class III, patients will present with both shock and associated disease. Class IV patients usually suffer from bowel gangrene, shock as well as other illnesses. The last and more severe stage of Class V comprises all findings described above.
Sigmoid volvulus (SV) is referred to as twisting of the sigmoid colon which results in large bowel obstruction  . Volvulus can develop in any segment of the alimentary canal although the most common affected areas include the sigmoid colon and cecum    .
Colonic obstruction resulting from sigmoid volvulus can be either acute, subacute or chronic   and one of the leading causes is chronic constipation. In severe cases of SV related to constipation, the sigmoid segment distends with retained feces and gas and twists, resulting in a closed loop obstruction. The site also becomes devoid of blood supply. Consequently, venous infarction occurs in the sigmoid colon which ultimately leads to fecal peritonitis and perforation.
Based on etiology, SV has been classified as primary or secondary. Anatomical variations in SV can be congenital or acquired . Primary SV mainly occurs due to a congenital anatomic variation of the sigmoid loop. SV as consequence of an existing disease condition such as internal herniations or postoperative conditions is termed secondary SV.
SV is commonly found in middle aged and elderly males, although rare cases among children have also been reported. Endemic regions for SV include Asian, Eastern and Middle Eastern and Northern European countries.
Typical symptoms of SV comprise constipation, abdominal pain, nausea, vomiting, hematemesis and anorexia. The physical examination of patients reveals abdominal distension, abnormal bowel sounds and increased peristalsis. Complications arising from retention of feces include colonic gangrene and peritonitis which leads to a fecal odor of the patient's breath.
Definite clinical findings along with X-ray and imaging studies help develop precise diagnosis of SV. Abdominal X-ray detects SV in the majority of the cases although computed tomography (CT) scan and magnetic resonance imaging (MRI) may be conducted to confirm a suspected diagnosis. In advanced cases, endoscopic evaluation can be performed to identify potential complications of the disease.
Treatment requires employment of surgical intervention and often includes resection of the sigmoid colon. SV does not necessarily have a good prognosis and mortality even after surgery lies around 25%-30% whereas the probability of disease recurrence is around 40%-50%.
Sigmoid volvulus (SV) is a disease of the lower S-shaped portion of the large intestine. In SV, the sigmoid colon becomes twisted, causing obstruction in the pathway leading to the rectum. The disease is more common among elderly persons and extremely rare among infants and children. SV is typically found in African, Asian, South American, Middle Eastern and Northern European countries. About 50% of the colon obstruction cases reported in Asian countries result from SV whereas in North America, SV is the third leading cause of bowel obstruction.
The exact cause of SV remains unknown. In most cases, SV results from elongation and twisting of the sigmoid segment (known as redundant colon). Sigmoid redundancy can be present since birth or may develop late in life. Long term constipation is one of the factors that lead to the development of redundant colon which ultimately causes bowel obstruction. Abdominal pain and constipation are the common symptoms of SV. Findings on physical examination comprise abdominal distension and abnormal bowel sounds. Diagnosis is based on X-ray radiographs while CT scan and MRI can be used for confirmation.
The most accurate therapy of SV requires surgical intervention. Common surgical procedures include sigmoid resection and primary anastamosis. Other procedures that may be applied to treat SV are still under clinical trials to prove their effectiveness. The mortality rate in SV is reported to be 14%-45%.