A fistula is an abnormal connection that forms between two organs, creating a passage where none should exist. A colovesical fistula connects the large intestine (colon) directly to the urinary bladder. This condition allows the contents of the colon, including gas, bacteria, and fecal matter, to pass into the bladder, which is normally a sterile environment. This abnormal communication can lead to significant discomfort and recurrent, complicated infections.
Understanding the Anatomy and Mechanism
The sigmoid colon and the bladder lie in close proximity within the pelvis. The sigmoid colon is the S-shaped last section of the large intestine before the rectum, and it is the site where most colovesical fistulas originate, typically forming between the sigmoid colon and the dome of the bladder.
The mechanism of formation begins with an inflammatory process or a tumor causing a breach in the wall of the colon. As the inflammation or abscess progresses, it adheres to the adjacent bladder wall, eventually eroding through the tissue barrier to create a tunnel. Because the pressure inside the colon is generally higher than the pressure inside the bladder, material naturally flows from the colon into the bladder.
The abnormal passage allows bacteria, gas, and particulate fecal matter to enter the bladder. These contaminants immediately trigger a severe inflammatory response and recurrent infections within the urinary system. In women, the uterus and other pelvic structures generally separate the colon and bladder, which is why colovesical fistulas occur less frequently in females than in males.
Common Causes and Risk Factors
The vast majority of colovesical fistulas are a complication of a pre-existing disease process, with complicated diverticulitis being the most frequent cause. Diverticulitis involves the inflammation or infection of small pouches (diverticula) that form in the lining of the colon. In over two-thirds of all cases, an abscess or inflammation from a ruptured diverticulum near the bladder erodes through the tissue to create the fistula.
Malignancy is the second most common underlying cause, accounting for approximately 10 to 20 percent of cases. This typically involves advanced colorectal cancer that directly invades the adjacent bladder wall. Cancers originating in the bladder or other pelvic organs can similarly lead to fistula formation.
Inflammatory Bowel Disease (IBD), particularly Crohn’s disease, represents another significant cause, contributing to about five to seven percent of cases. Crohn’s disease is characterized by chronic inflammation that affects the entire thickness of the bowel wall, making it prone to forming fistulas to nearby organs. Prior abdominal or pelvic surgery, as well as radiation therapy for pelvic cancers, can also damage tissues and increase the risk of developing a fistula years later.
Recognizing the Signs
The symptoms of a colovesical fistula are often unique and help doctors distinguish the condition from a simple urinary tract infection. The most pathognomonic sign is pneumaturia, which is the passage of gas in the urine. This occurs because gas produced by intestinal bacteria enters the bladder through the fistula and is expelled during urination, often described as bubbles or fizzing.
Another telling symptom is fecaluria, the presence of fecal matter or stool fragments in the urine. This may manifest as cloudy, brownish, or dark urine containing obvious particulate material, and it affects over half of patients with the condition. The constant contamination leads to recurrent and persistent urinary tract infections (UTIs) that are often resistant to standard antibiotic treatment.
Patients frequently experience painful urination, known as dysuria, due to the bladder irritation and infection. While less common, some individuals may also notice hematuria (blood in the urine) or experience generalized lower abdominal pain. These collective symptoms usually prompt an investigation into the possibility of an abnormal connection.
Diagnosis and Management
The process of diagnosing a colovesical fistula begins with a detailed review of the patient’s symptoms, especially the presence of pneumaturia and fecaluria. A computed tomography (CT) scan of the abdomen and pelvis is typically the first and most useful imaging study. This scan is highly effective at identifying air within the bladder, a strong indicator of a fistula, and can also help pinpoint the underlying cause like diverticular disease or a tumor.
Specialized internal examinations are also utilized to confirm the diagnosis and determine the cause. A cystoscopy involves inserting a thin, flexible tube with a camera into the bladder to visualize the inner lining. This procedure can reveal inflammation, bubbles of gas, or the actual opening of the fistula tract within the bladder wall. A colonoscopy may also be performed to examine the colon lining and rule out malignancy.
Management of a colovesical fistula is primarily surgical, as the abnormal tract must be physically removed and the affected organs repaired. Before surgery, patients are often stabilized with intravenous antibiotics to treat the severe urinary infection and manage any associated abscesses. The definitive operation involves a bowel resection to remove the diseased section of the colon containing the fistula, followed by a primary anastomosis to reconnect the healthy ends of the colon. The defect in the bladder wall is then closed, and in most cases, the surgical approach offers a complete resolution of the condition.