Low anterior resection syndrome is a collection of ongoing bowel function changes that can affect people who have undergone surgical treatment for rectal cancer. These symptoms can significantly impact daily life and quality of living, even though the surgery itself may have successfully removed the cancer.

Understanding Low Anterior Resection Syndrome

Low anterior resection syndrome, often called LARS, describes a group of persistent symptoms that develop after a specific type of surgery for rectal cancer. This surgery, known as a low anterior resection, involves removing the part of the rectum that contains cancer along with some healthy tissue around it, and then reconnecting the remaining parts of the bowel so it can still function. The surgery aims to cure rectal cancer while preserving the anus, meaning patients do not need a permanent colostomy bag to collect waste^[1].

During a low anterior resection, surgeons perform what is called an anastomosis, which means sewing or stapling the two remaining ends of the large intestine and rectum back together. This creates a shorter colon, which leads to the various symptoms that together make up LARS^[10]. While the surgery is successful in removing cancer and allowing the bowel to remain connected, the resulting changes to the digestive system can create a “new normal” for bowel function^[7].

Epidemiology

Low anterior resection syndrome is remarkably common among people who undergo sphincter-preserving surgery for rectal cancer. Research suggests that a very large majority of patients experience some degree of these symptoms. According to multiple studies, it is estimated that as much as 80 percent of patients develop one or more symptoms of LARS following surgery for rectal cancer^[9]. Some research indicates that up to 90 percent of patients experience long-term changes in quality of life from symptoms following this type of surgery^[2].

The widespread nature of this condition has led experts to recommend that all patients receiving a low anterior resection should be routinely screened for LARS. Given that LARS is such a common problem that often leads to poor quality of life, systematic recording of bowel function levels after sphincter-preserving surgery has been called for by medical researchers^[9].

The prevalence of LARS has increased over time as medical advances have allowed more patients to avoid permanent colostomies. Outcomes for rectal cancer surgery have improved significantly over the past 20 years with increasing rates of survival and decreasing local recurrence. These gains have occurred during a period when there has been an increasing emphasis on sphincter preservation, meaning surgeons have become increasingly aggressive in avoiding resection of the anus^[2].

Causes

Low anterior resection syndrome develops as a direct result of surgical treatment for rectal cancer. The condition occurs after the removal of part or all of the rectum during a low anterior resection procedure. The rectum is a segment of the large intestine at the lower end, about six inches long, that connects the colon above with the anus below. Under normal circumstances, the rectum stores stool until a person is ready to release it^[1].

The surgery removes the cancerous section of the intestine, and sometimes this means removing part of the colon as well. After this removal, the surgeon reconnects the remaining parts of the bowel so it can still work. However, this creates a shorter colon and altered anatomy, which disrupts normal bowel function^[4][10].

In many cases, patients also receive radiation therapy or chemotherapy before or after surgery to help shrink the tumor or prevent cancer recurrence. These additional treatments can contribute to the development of LARS symptoms. The combination of surgical changes to the digestive tract and the effects of cancer treatments creates the conditions that lead to this syndrome^[1].

Risk Factors

Several factors can increase the likelihood and severity of developing low anterior resection syndrome after rectal cancer surgery. The location of the tumor plays a crucial role. When the cancer is lower in the rectum, the surgery must be performed very close to the anus, which increases the risk of bowel function problems afterward. The tumor must be high enough in the rectum for the surgeon to safely remove it without damaging the anus for a low anterior resection to be an option^[1].

Preoperative radiation therapy is a significant risk factor for LARS. Patients who receive radiation treatment before surgery are more likely to develop symptoms and may experience more severe dysfunction. Radiation can cause changes to the tissues of the rectum and surrounding structures that contribute to bowel problems even after the surgical healing is complete^[6].

The extent of the surgery also matters. When surgeons need to remove more of the rectum or include portions of the colon, this creates a shorter remaining bowel and reduces the capacity for stool storage, which can worsen symptoms. Additionally, any damage to the nerves that control bowel function during surgery can increase the risk of developing LARS^[5].

Symptoms

Low anterior resection syndrome encompasses a wide range of bowel-related symptoms that can vary significantly from person to person. The most commonly reported symptoms include increased frequency of bowel movements, often needing to go to the bathroom many more times per day than before surgery. Many patients experience urgency, which means feeling a sudden and immediate need to have a bowel movement that is difficult to delay^[3].

A particularly challenging symptom is called clustering. This occurs when a person feels the need to go to the bathroom, has a small bowel movement, and then needs to return again within minutes or hours. Patients may find themselves going in and out of the bathroom repeatedly over several hours, which can be exhausting and disruptive to daily activities^[7][9].

Incontinence is another common problem, which can involve accidental leakage of gas, liquid stool, or sometimes solid stool. This loss of control over bowel movements can be distressing and affects a person’s confidence in social situations. Some people also experience soiling, which is minor leakage that stains undergarments^[3][9].

Changes in stool consistency are frequent, with many patients experiencing diarrhea or loose stools. Conversely, some people develop constipation and feelings of incomplete bowel emptying, where they feel like they have not fully evacuated even after using the bathroom. This can be accompanied by difficulty actually getting the stool out during a bowel movement^[3].

Additional symptoms that are sometimes overlooked but are part of LARS include bowel function that is variable or unpredictable from day to day, making it hard to plan activities. Some patients experience rectal pain, particularly near the site where the bowel was reconnected or in areas that received radiation treatment. Food sensitivities often develop, with extreme reactions to foods high in certain types of fiber^[7][9].

Researchers have noted that patients typically fall into two main categories based on their symptoms. The first group develops incontinence, urgency, and increased frequency of bowel movements. The second group experiences constipation, a sensation of incomplete evacuation, and issues with emptying the bowels. Some patients report features of both categories, either occurring at the same time or alternating between these two patterns of symptoms^[3].

In a recent study, researchers found that the symptom most strongly associated with low quality of life was diarrhea. The correlation between decreasing quality of life scores and high LARS symptom scores was clear, demonstrating how significantly these symptoms can affect a person’s daily functioning and overall well-being^[2].

Prevention

Because low anterior resection syndrome is a direct consequence of the surgical treatment needed for rectal cancer, it cannot be entirely prevented. However, patients and healthcare teams can take steps to potentially minimize the severity of symptoms and prepare for managing them after surgery. Understanding what to expect is an important first step in prevention planning.

Before surgery, healthcare teams should discuss with patients the possibility of developing LARS symptoms. This allows patients to prepare mentally and practically for changes in bowel function. Some patients may need to make arrangements for time off work, ensure bathroom access in their living and working environments, and arrange for support from family members or friends during the recovery period^[1].

The surgical technique and approach can influence outcomes. Surgeons consider whether to perform minimally invasive surgery or open surgery, as these different approaches may have varying effects on subsequent bowel function. Additionally, the decision about whether chemotherapy or radiation therapy should be given before or after surgery is carefully planned, as these treatments can affect the likelihood and severity of LARS^[1].

In some cases, surgeons create a temporary ostomy, which is an opening that allows stool to be diverted into a bag outside the body. This temporary measure gives the reconnected bowel time to heal properly before it needs to function again. While this requires an additional surgery later to reverse it, it may help reduce complications and potentially lessen long-term symptoms^[1].

Early evaluation and initiation of appropriate treatment after surgery are crucial for managing LARS effectively. Healthcare providers should routinely screen patients for LARS symptoms during follow-up appointments after sphincter-preserving surgery. This allows for early intervention when symptoms first appear, which may prevent them from becoming more severe or chronic^[5].

Pathophysiology

The pathophysiology of low anterior resection syndrome involves multiple complex factors that affect how the bowel functions after surgery. Understanding these underlying mechanisms helps explain why patients experience such a wide range of symptoms. LARS is believed to be caused by several factors working together, rather than a single cause^[5].

Direct structural damage to the anal sphincter can occur during surgery. The anal sphincter is a group of muscles that control the opening and closing of the anus. Even though low anterior resection is designed to preserve these muscles, the surgical process and the reconnection of the bowel can affect their function. This can lead to problems with controlling bowel movements and maintaining continence^[5].

Damage to the nerves that control bowel function is another important factor. The rectum and surrounding pelvic area contain many nerves that send signals between the brain and the bowel, helping coordinate the storage and release of stool. Surgery in this area, as well as radiation therapy, can damage these nerves. This disrupts the normal communication system that allows people to sense when they need to have a bowel movement and to control when it happens^[5].

The loss of the rectoanal inhibitory reflex is a key pathophysiological change. This reflex normally helps the rectum relax and accommodate stool, allowing gradual filling without triggering an immediate urge to defecate. When this reflex is disrupted by surgery, patients may feel urgent needs to use the bathroom even with small amounts of stool present^[5].

The surgery creates a significant decrease in rectal volume and compliance. The rectum normally acts as a storage reservoir for stool, gradually stretching to accommodate waste until it is convenient to have a bowel movement. After removing part or all of the rectum, the remaining bowel has much less capacity to store stool. This reduced storage ability means that even small amounts of stool trigger the urge to defecate, leading to increased frequency of bowel movements^[5][10].

Changes in how the colon moves stool along also contribute to symptoms. The wavelike muscle contractions that normally move waste through the intestines, called peristalsis, can be altered after surgery. The shortened bowel may move stool more quickly than before, giving less time for water absorption. This can result in loose or liquid stools and contribute to urgency problems^[6].

Radiation therapy, when used as part of cancer treatment, causes additional changes at the cellular and tissue level. Radiation can damage the blood vessels that supply the bowel, affect the muscle layers of the intestinal wall, and cause inflammation and scarring. These changes reduce the flexibility and function of the remaining rectum and can lead to problems with sensation and coordination of bowel movements. The effects of radiation may continue to develop over time, which explains why some patients experience worsening symptoms months or even years after treatment^[6].