Sigmoid Colon: Where It Is, How It Works and What Can Go Wrong

Where is the sigmoid colon, and what is the colon?

The sigmoid colon is the S-shaped section of the colon between the descending colon and the rectum. It lies low in the abdomen, mostly on the left and in the pelvis, and has its own mesentery, so it is fairly mobile. Because of this its position varies noticeably from person to person^[7].

The large intestine is usually described as the cecum, the colon with its four sections (ascending, transverse, descending and sigmoid), then the rectum and anal canal^[6]. So the sigmoid colon is part of the colon, and the colon is part of the large intestine.

Why does the “sigmoid hurt”?

People often link lower left abdominal pain to the sigmoid colon, but it has many possible causes. These include functional bowel disorders or constipation, inflammation of diverticula, and tumors. Pain in this area can also come from the urinary tract and, in women, from the gynecological organs. Because the sigmoid colon is mobile, the location of the pain does not point to it reliably^[7].

The cause is determined after an examination and tests. Some signs should not be put off: blood in the stool, a persistent change in bowel habit, unexplained weight loss, iron-deficiency anemia. With these, see a doctor; a colonoscopy is often needed to find the cause. How cancer shows up in this section is described on the sigmoid colon cancer page.

Diverticula and diverticulitis

Diverticula are small pouch-like bulges in the bowel wall, and they become more common with age. In data from more than 271,000 colonoscopies, the prevalence of diverticula increased with age in both men and women^[1]. On their own, diverticula usually cause no symptoms.

When a diverticulum becomes inflamed, this is called diverticulitis. If the diagnosis is uncertain, an abdominal CT is recommended. Most patients with uncomplicated diverticulitis are treated as outpatients, and some selected patients are initially managed without antibiotics^[2]. This decision is made by a doctor after examination, not by the patient.

Occasionally, cancer is mistaken for diverticulitis^[8]. So after an episode of complicated diverticulitis, for example with an abscess, a colonoscopy is advised if one has not been done recently^[3]. It is usually scheduled not straight away but 6–8 weeks later or after the acute symptoms have fully resolved, whichever comes later^[8].

When a surgeon is needed. Elective surgery, removal of the affected part of the sigmoid colon, is discussed when uncomplicated diverticulitis persists or keeps recurring, and after complicated diverticulitis. The decision is individual, weighing the severity of the disease, quality of life, benefits, risks and the patient’s preferences^[3]. Mesalamine is not recommended to prevent recurrences^[3].

Polyps of the sigmoid colon

Most polyps are removed during colonoscopy, without incisions, and the method depends on the size and type of polyp. According to the European guideline, small polyps up to 9 mm are removed with a cold snare, non-pedunculated adenomatous polyps of 10–19 mm with a hot snare, and large non-pedunculated adenomatous lesions of 20 mm or more by endoscopic mucosal resection. For serrated lesions without dysplasia, cold techniques are recommended regardless of size. If superficially invasive cancer is suspected, the lesion is removed in one piece where possible, while signs of deeper invasion call for a different approach and discussion at a tumor board^[4].

A surgeon is needed for a minority of patients: when a lesion cannot be removed safely endoscopically, or when a polyp already removed is found to contain cancer with unfavorable features. Surgery to remove the segment of bowel together with lymph nodes may then be needed. More on the polyps and precancerous bowel conditions page.

Sigmoid volvulus

This is an emergency in which a loop of the sigmoid colon twists around its mesentery. It causes bloating, pain and no passage of stool or gas. If the patient is stable and there are no signs of peritonitis, perforation or compromised blood supply, the volvulus is usually first untwisted endoscopically, and elective surgery is then discussed during the same admission, because without it volvulus often recurs. If such signs are present or untwisting fails, emergency surgery is needed^[5].

Sigmoid colon cancer

Most tumors of the large intestine develop from polyps over years, so a timely colonoscopy can change not only the outlook but also the extent of treatment. If a tumor is found electively, the treatment plan is decided after a full workup and a tumor board review. With obstruction, bleeding or perforation, the threat to life is dealt with first and the full workup comes afterwards. How the operation is done and when a stoma can be avoided is described on the sigmoid colon cancer page. I perform colon surgery laparoscopically when the tumor’s location and the extent of resection allow it.

What to do if your report mentions the “sigmoid colon”

1. Find out exactly what was foundDiverticula, a polyp, inflammation or a tumor: this decides who to see next, a gastroenterologist, an endoscopist or a surgeon.
2. Do not put off testsIf you have blood in the stool, a persistent change in bowel habit or iron-deficiency anemia, see a doctor. After complicated diverticulitis, colonoscopy is usually scheduled 6–8 weeks later and not before full recovery.
3. Know the emergency signsSudden severe pain, bloating with no gas or stool, especially with vomiting: call 103. Pain with fever: see a doctor without delay.
4. Show the results to a surgeon if surgery is neededSend your colonoscopy report, histology and CT: the online consultation is free. We discuss the treatment plan after a full workup.

Sources

1. Peery AF, Keku TO, Galanko JA, Sandler RS. Sex and Race Disparities in Diverticulosis Prevalence. Clin Gastroenterol Hepatol. 2020;18(9):1980–1986. PMID 31634580
2. Qaseem A, Etxeandia-Ikobaltzeta I, Lin JS, et al. Diagnosis and Management of Acute Left-Sided Colonic Diverticulitis: A Clinical Guideline From the American College of Physicians. Ann Intern Med. 2022;175(3):399–415. PMID 35038273
3. Qaseem A, Etxeandia-Ikobaltzeta I, Lin JS, et al. Colonoscopy for Diagnostic Evaluation and Interventions to Prevent Recurrence After Acute Left-Sided Colonic Diverticulitis: A Clinical Guideline From the American College of Physicians. Ann Intern Med. 2022;175(3):416–431. PMID 35038270
4. Ferlitsch M, Hassan C, Bisschops R, et al. Colorectal polypectomy and endoscopic mucosal resection: European Society of Gastrointestinal Endoscopy (ESGE) Guideline — Update 2024. Endoscopy. 2024;56(7):516–545. PMID 38670139
5. 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. PMID 34016826
6. Omole AE, Mandiga P, Kahai P, Lobo S. Anatomy, Abdomen and Pelvis: Large Intestine. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2025. PMID 29261962
7. Harkins JM, Sajjad H. Anatomy, Abdomen and Pelvis, Sigmoid Colon. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2023. PMID 31751014
8. Peery AF, Shaukat A, Strate LL. AGA Clinical Practice Update on Medical Management of Colonic Diverticulitis: Expert Review. Gastroenterology. 2021;160(3):906–911.e1. PMID 33279517

This article is for general information and does not replace a consultation: the cause of symptoms is determined after examination and tests.