An anastomosis is the surgical connection created between two sections of bowel after part of the intestine has been removed. One complication that can occur after colorectal anastomosis is anastomotic leak, in which a defect develops at the connection between the bowel ends.
Anastomotic leakage is an important complication of colorectal surgery. Its causes are complex, and the likelihood of a leak can be influenced by patient characteristics, disease and previous treatment, the location of the anastomosis and factors related to the operation itself.
Understanding these factors is important not only when planning surgery, but also when recognising and managing a leak if one occurs.
What Is an Anastomotic Leak?
The International Study Group of Rectal Cancer defines an anastomotic leak as a defect in the intestinal wall at the site of the anastomosis that creates an opening between the inside of the bowel and the surrounding tissues or spaces.
The way a leak presents can vary considerably. Some leaks remain relatively contained, while others can result in a pelvic or abdominal collection, peritonitis or sepsis. This variation also affects treatment. Some patients can be managed without surgery, while more extensive leaks or those associated with clinical instability may require operative intervention. Both the condition of the patient and the circumstances surrounding the anastomosis need to be considered.
Why Does an Anastomotic Leak Matter?
Reported rates of anastomotic leakage vary according to the type of surgery, location of the anastomosis, patient population and definition used.
The risk is particularly relevant in rectal surgery. A systematic review and meta-analysis of 18 studies involving 18,039 patients who underwent curative rectal cancer surgery reported an overall anastomotic leak rate of 9.8%.
The effects of a leak can extend beyond the immediate postoperative period. Depending on its severity, an anastomotic leak may require antibiotics, drainage, additional surgery or a longer period of recovery.
Longer-term effects have also been studied. A 2025 systematic review of 13 studies involving 4,618 patients after colorectal cancer surgery found that anastomotic leakage was associated with impaired quality of life, with the greatest overall impact observed during the first postoperative year. The studies varied substantially in how and when quality of life was assessed, so the findings should be interpreted in that context.
What Factors Are Associated With Anastomotic Leak?
Anastomotic leakage does not usually result from a single factor. Research has shown that it is influenced by a combination of patient-, disease- and procedure-related factors.
Patient-Related Factors
Systematic reviews have reported associations with factors including smoking, obesity, poor nutritional status, certain comorbidities and overall health status.
These are risk factors rather than direct causes. Their presence does not mean that an individual patient will develop an anastomotic leak.
Disease and Treatment Factors
The location of the disease and previous treatment can also be relevant.
Lower rectal anastomoses are associated with a higher risk of leakage than anastomoses located further along the bowel. Previous pelvic radiotherapy and emergency surgery have also been identified as risk factors in colorectal surgery studies. Read More
Surgical Factors
Several factors are considered when the bowel is reconnected. These include the condition of the tissue, blood supply to the bowel, tension at the anastomosis and the level at which the connection is created.
Adequate tissue perfusion is important for healing, although it is only one factor involved. Operative circumstances such as substantial blood loss, transfusion and longer operating times have also been associated with anastomotic leakage in systematic reviews.
The technique used to join the bowel depends on the operation and location of the anastomosis. Anastomoses may be created using sutures or staplers. In many left-sided colorectal and rectal procedures, a circular stapler is used to join the two ends of the bowel after the affected section has been removed.
Different circular stapler sizes and designs are available, with selection depending on factors including the anatomy, tissue characteristics, location of the anastomosis and surgical approach.
Find out more about Circular stapler
Other aspects of surgical stapling, including tissue compression and staple formation, are discussed separately in our educational content on surgical stapling.
What Are the Signs of an Anastomotic Leak?
The presentation of an anastomotic leak varies according to its location and extent and the patient’s clinical condition.
Possible signs can include:
- Fever
- Increasing abdominal or pelvic pain
- Tachycardia
- Abdominal tenderness
- Persistent or recurrent ileus
- Abnormal or enteric discharge from a surgical drain or wound
- Unexplained deterioration during postoperative recovery
Some patients may initially not have specific signs, particularly early after surgery.
More extensive leakage can be associated with abdominal or pelvic infection, peritonitis or sepsis. A change from the expected course of postoperative recovery may therefore prompt further clinical assessment.
How Is an Anastomotic Leak Diagnosed?
Diagnosis is based on a combination of the patient’s clinical presentation, examination, laboratory findings and imaging rather than on a single test.
Blood tests may show evidence of inflammation or infection. Inflammatory markers such as C-reactive protein can contribute to postoperative assessment but are not specific for anastomotic leakage.
When a colorectal anastomotic leak is suspected, computed tomography (CT) is commonly used to evaluate the abdomen and pelvis. Findings can include fluid collections, abscesses, extraluminal gas or contrast leakage outside the bowel.
The imaging approach depends on the clinical circumstances and location of the anastomosis. A 2023 meta-analysis examining investigations after colorectal or coloanal anastomosis found that CT performed with contrast administered through the rectum had higher diagnostic sensitivity than water-soluble contrast enema alone.
Imaging findings still need to be interpreted alongside the patient’s clinical condition. When suspicion remains despite inconclusive imaging, further assessment may be required.
How Is an Anastomotic Leak Managed?
Management depends on the patient’s clinical condition, the location and extent of the leak, the presence of infection or collections and the response to initial treatment.
Selected clinically stable patients with a contained leak may be managed without immediate surgery. Treatment can include antibiotics and, where an accessible collection is present, image-guided drainage.
Other patients require operative intervention, particularly when there is clinical instability, diffuse peritonitis, uncontrolled sepsis or failure of non-operative management.
Endoscopic approaches have also been described for selected colorectal leaks, depending on the location and characteristics of the defect and the expertise available.
There is therefore no single treatment approach for all anastomotic leaks. Management is determined by the individual clinical circumstances.
Understanding Anastomotic Leak Risk in Colorectal Surgery
Anastomotic leakage is an important complication of colorectal surgery with multiple contributing factors. Patient characteristics, previous treatment, the location of the anastomosis, tissue condition, perfusion and operative circumstances can all be relevant.
Early recognition and appropriate management are important when a leak occurs. At the time of surgery, careful assessment of the bowel and the conditions in which the anastomosis is created remain part of reducing avoidable risk, regardless of whether the connection is created using sutures or a stapling device.
References
- Rahbari NN, Weitz J, Hohenberger W, et al. Definition and grading of anastomotic leakage following anterior resection of the rectum: a proposal by the International Study Group of Rectal Cancer. Surgery. 2010;147(3):339–351.
- McDermott FD, Heeney A, Kelly ME, et al. Systematic review of preoperative, intraoperative and postoperative risk factors for colorectal anastomotic leaks. British Journal of Surgery. 2015;102(5):462–479.
- Ha GW, Kim JH, Lee MR. Anastomotic leak and cancer-specific outcomes after curative rectal cancer surgery: a systematic review and meta-analysis. Colorectal Disease. 2020. The analysis included 18 studies and 18,039 patients and reported an overall anastomotic leak rate of 9.8%.
- Gielen AHCG, Heuvelings DJI, Sylla P, et al. Impact of Anastomotic Leakage After Colorectal Cancer Surgery on Quality of Life: A Systematic Review. Diseases of the Colon & Rectum. 2025;68(2):154–170. The review included 13 studies and 4,618 patients and found that published evidence suggests an association between anastomotic leakage and impaired quality of life, particularly during the first postoperative year.
- Chierici A, Granieri S, Frontali A. Diagnostic accuracy of water-soluble contrast enema, contrast-enema computed tomography and endoscopy in detecting anastomotic leakage after (colo)proctectomy: a meta-analysis. Colorectal Disease. 2023;25(7):1371–1380.
- Hedrick TL, Kane W. Management of Acute Anastomotic Leaks. Clinics in Colon and Rectal Surgery. 2021;34(6):400–405.
This article is intended for general educational purposes and does not replace individual medical advice, diagnosis or treatment from a qualified healthcare professional.