What Are the Symptoms of a Fistula Between Bowel and Bladder?

A fistula between the bowel and bladder, medically called an enterovesical fistula, produces a distinctive cluster of urinary symptoms that often catches people off guard. The most recognizable sign is air bubbles in the urine, which occurs in roughly half to three-quarters of cases, sometimes accompanied by visible fecal material in the urine. These symptoms sound alarming because they are: a channel has formed between two organs that should never communicate, and the contents of the intestine are leaking into the bladder. But beyond those two hallmark signs, the condition also triggers a range of urinary and sometimes gastrointestinal complaints that can delay diagnosis if a doctor isn’t specifically looking for a fistula.

Air in the Urine Is Usually the First Clue

The single most reported symptom is pneumaturia, which simply means passing gas through the urethra when you urinate. People often describe a bubbling or fizzing sensation during urination, or they notice air rising in the toilet bowl. This happens because intestinal gas travels through the abnormal channel into the bladder and escapes when you void. One review found pneumaturia present in up to 70% of cases, while another series of patients with surgically confirmed fistulas recorded it in 95% of cases.¹² The variation likely depends on fistula size and location, but pneumaturia is so distinctive that many clinicians consider it nearly diagnostic on its own.

The experience can be intermittent. Some people notice it every time they urinate; others only occasionally, depending on body position, how full the bowel is, or whether a meal has recently produced intestinal gas. Because passing air during urination is so unusual, people who experience it tend to recognize something is wrong fairly quickly, though they may struggle to describe it or feel embarrassed bringing it up to a doctor.

Fecal Material in the Urine

The second hallmark symptom is fecaluria, meaning visible stool particles or brownish, cloudy discoloration in the urine. This occurs when liquid or solid intestinal contents cross through the fistula into the bladder. Reported rates vary: one case series placed it at about 82.5% of patients, while other reviews describe it appearing in roughly half of cases.²³ The discrepancy probably reflects differences in fistula size: a very small channel may allow gas to pass but not much solid material.

Fecaluria is even more unsettling to experience than pneumaturia. It can present as particles floating in the urine, a persistently foul smell, or urine that looks murky or dark. Some patients initially mistake it for a severe urinary tract infection because the urine looks abnormal and smells offensive. The combination of pneumaturia and fecaluria together is considered so characteristic that one diagnostic study found 87.5% of patients with a confirmed bowel-bladder fistula presented with one or both of these symptoms.¹

Recurrent Urinary Tract Infections

Many people with a bowel-bladder fistula first come to medical attention not because they notice air or stool in their urine, but because they keep getting urinary tract infections. Bacteria from the intestine have a direct route into the bladder, so infections recur even after antibiotics clear them. Patients typically present with irritative urinary symptoms and repeated UTIs that don’t stay gone.⁴ A veteran affairs medical center review spanning 28 years listed UTI among the most common presenting complaints, alongside pneumaturia, fecaluria, painful urination, and blood in the urine.⁵

This pattern of infections that keep coming back is one reason fistulas sometimes go undiagnosed for months. If your doctor treats each UTI as an isolated event and the more dramatic symptoms like pneumaturia are mild or intermittent, the underlying fistula can be missed. In one reported case, a patient had recurrent UTIs for six months before a CT scan revealed the fistula.⁶ If you are experiencing UTIs that respond to antibiotics but keep returning, especially if you’ve also noticed anything unusual about how your urine looks or smells, it’s worth raising the possibility of a fistula with your doctor.

Other Urinary Complaints

Beyond infections, a bowel-bladder fistula can produce a cluster of lower urinary tract symptoms that overlap with many other conditions. Painful urination (dysuria) is common, as is urinary frequency and urgency. Blood in the urine, or hematuria, also shows up in some patients. One case report described a fistula that presented primarily with hematuria and rectal bleeding, initially mimicking other conditions entirely.⁷ Lower abdominal pain, sometimes described as suprapubic discomfort, rounds out the picture for some patients.³

These nonspecific urinary symptoms are tricky because they mimic straightforward conditions like an overactive bladder, prostatitis in men, or interstitial cystitis. The key differentiator is usually context: if you have urinary complaints alongside any hint of pneumaturia, fecaluria, or a history of bowel disease, the combination should raise suspicion for a fistula.

Gastrointestinal Symptoms That Sometimes Appear

Because the fistula connects to the bowel, some patients also have gastrointestinal symptoms, though these are often overshadowed by the more dramatic urinary findings. In patients with Crohn’s disease, abdominal pain, diarrhea, an abdominal mass, and abscesses are commonly found alongside the fistula.³ For fistulas caused by diverticulitis, the bowel symptoms may have preceded the fistula by weeks or months, presenting as episodic left-sided abdominal pain or changes in bowel habits.

The relationship between bowel and bladder symptoms depends partly on which direction material flows. Gas and stool tend to pass from the higher-pressure bowel into the lower-pressure bladder, which is why urinary symptoms usually dominate. Urine flowing the other direction into the bowel is less common and harder to detect. Related but distinct conditions include fistulas between the colon and the vagina, which present with stool passing through the vagina, and fistulas between different loops of bowel, which primarily cause diarrhea.⁷

What Causes These Fistulas to Form

Understanding what leads to a bowel-bladder fistula helps explain who is at risk and why symptoms sometimes develop gradually. The most common cause by a wide margin is diverticular disease of the colon. When a diverticulum (a small pouch in the colon wall) becomes inflamed and infected, the resulting abscess can erode through surrounding tissue and eventually breach the bladder wall. This complication can occur even during a first episode of acute diverticulitis.⁸

Crohn’s disease is the second most common culprit. The transmural inflammation that characterizes Crohn’s, meaning it penetrates the full thickness of the bowel wall, can create fistulous tracts to the bladder, skin, or other organs. Enterovesical fistula is considered a rare but recognized complication of Crohn’s, with pneumaturia, fecaluria, and recurrent UTIs as its characteristic presentation.⁹ Cancer, particularly colorectal or bladder tumors, can also erode the tissue separating the two organs.

Less common causes include prior radiation therapy and surgical or catheter-related injuries. Radiation to the pelvis for cervical, prostate, or rectal cancer can damage the tissue between the bowel and bladder years or even decades after treatment. One case involved a woman who developed a bladder fistula 20 years after radiotherapy for cervical cancer.¹⁰ Iatrogenic fistulas from surgical procedures or long-term indwelling catheters are also documented, and they present with the same urinary symptoms as those caused by disease.¹¹

How the Fistula Is Diagnosed

One of the frustrations patients encounter is that diagnosing a bowel-bladder fistula can be genuinely difficult, even when the symptoms strongly suggest one. The diagnosis often requires a combination of imaging and endoscopy, and no single test catches every case.¹²

A CT scan of the abdomen and pelvis is typically the first-line imaging test. It can show air inside the bladder, thickening of the bladder and bowel walls near the fistula, or an inflammatory mass bridging the two organs. However, sensitivity varies considerably. Some reports place CT accuracy between 60% and 100%, while others describe a narrower range of 61% to 90%.¹³¹⁴ In practical terms, a CT scan can confirm a fistula when the findings are clear, but a negative scan doesn’t rule one out. One important caveat is that air inside the bladder on a CT scan is not automatically proof of a fistula. It can also result from recent catheterization, bladder procedures, or certain bladder infections.¹⁵

Cystoscopy, where a camera is inserted into the bladder through the urethra, can sometimes visualize the fistula opening or show localized inflammation and edema on the bladder wall. Colonoscopy can help identify the bowel-side source of the problem, such as an area of diverticulitis or a Crohn’s-related lesion. But even together, these tests occasionally miss the fistula, particularly when it is small or partially sealed by inflammation.

The Poppy Seed Test

An unexpectedly low-tech test has proven remarkably effective at confirming a bowel-bladder fistula. In the poppy seed test, you swallow a measured amount of poppy seeds (or sometimes a dye like charcoal), and then your urine is collected over the next 24 to 48 hours. If seeds or dye appear in the urine, the fistula is confirmed.

A study comparing the poppy seed test against CT scans and a nuclear medicine study found striking results. CT was positive in 70% of patients with surgically confirmed fistulas, the nuclear medicine study caught 80%, but the poppy seed test was positive in all 20 patients, a 100% detection rate, at a cost of about five dollars per test compared to over six hundred dollars for the CT.¹⁶ The poppy seed test doesn’t show you where the fistula is or what caused it, so imaging is still needed for surgical planning. But as a confirmation tool, especially when a CT scan comes back negative despite convincing symptoms, it fills an important gap.

When to Suspect a Fistula Over a More Common Condition

Because the urinary symptoms of a bowel-bladder fistula overlap with many more common problems, it helps to know which red flags should shift your thinking. Isolated painful urination or a single UTI doesn’t warrant concern about a fistula. But the following combination of features should prompt further investigation:

Pneumaturia: Air bubbles during urination are almost never caused by anything other than a fistula or recent bladder instrumentation. If you haven’t had a catheter or cystoscopy recently and you’re passing gas when you urinate, bring it up immediately.
Recurrent UTIs in someone with bowel disease: If you have known diverticulitis, Crohn’s disease, or a history of pelvic cancer or radiation, and you keep getting infections that clear with antibiotics but return weeks later, a fistula deserves consideration.
Foul-smelling or visibly particulate urine: Fecaluria is distinctive and doesn’t have many mimics. Cloudy urine from a standard infection looks different from urine containing actual fecal material.
Mixed bowel and bladder symptoms: Concurrent changes in bowel habits (new diarrhea, abdominal pain, or rectal bleeding) alongside urinary complaints can suggest a process involving both organ systems.

The combination of even two of these features, especially in someone with a relevant medical history, is a strong signal. Mentioning your bowel history to a urologist or your urinary symptoms to a gastroenterologist can help bridge the gap between specialties, because fistulas sit at the intersection of two different medical fields and can fall through the cracks if each specialist only looks at their own organ.

Treatment and What to Expect

Surgery is the definitive treatment for most bowel-bladder fistulas. The standard approach involves removing the diseased segment of bowel, taking down the fistula tract, and allowing the bladder to heal. This can be done through open surgery or minimally invasive techniques. Laparoscopic and robotic-assisted procedures have both been used successfully, with patients remaining symptom-free at follow-up.¹⁷

One question that comes up in surgical planning is whether the bladder defect needs to be formally repaired or whether it can be left to heal on its own after the fistula is disconnected. A systematic review and meta-analysis found no significant difference in urinary leak rates between patients who received bladder repair and those who did not, suggesting that a selective approach to bladder repair is reasonable for appropriately chosen patients.¹⁸

Not everyone is a good surgical candidate, however. Older patients with significant other medical problems may face high surgical risk. For these individuals, conservative management with antibiotics, urinary drainage, and dietary modifications can be considered. Some benign fistulas have resolved without surgery, though this is not reliably predictable and requires close follow-up. No randomized controlled trials have compared conservative to surgical management, so the decision remains individualized.¹⁹

Fistulas That Form After Cancer Treatment

Radiation-related fistulas deserve a separate mention because they can appear years or even decades after treatment, long after a patient has stopped thinking about their cancer therapy. Pelvic radiation for cervical, rectal, bladder, or prostate cancer damages blood vessels in surrounding tissues, leading to progressive fibrosis and weakening of the tissue between the bowel and bladder. This process can eventually create a fistula well after the radiation course has ended.¹⁰

The symptoms are the same as fistulas from other causes: pneumaturia, fecaluria, recurrent UTIs, and abdominal discomfort. But the delayed onset can make diagnosis harder, because neither the patient nor their current doctors may connect new urinary symptoms to radiation that happened a decade or two earlier. Radiation-related fistulas can also be complicated by the fact that the surrounding tissue is already compromised, which may make surgical repair more challenging and affect healing. If you have a history of pelvic radiation and develop persistent or recurrent urinary symptoms, making sure your physician knows about that radiation history can speed up diagnosis considerably.¹¹

1
PubMed Central. Pneumaturia and faecaluria: Symptoms leading to a life-saving diagnosis – Section: Discussion
2
ScienceDirect (International Journal of Surgery). Surgical protocol and outcome for sigmoidovesical fistula secondary to diverticular disease of the left colon
3
PubMed Central. Enterovesical Fistula Revealing Crohn’s Disease: A Case Report – Section: Discussion
4
PubMed Central. First Case of Enterovesical Fistula Caused by Ischaemic Enteritis
5
Surgery in Practice and Science. Colovesical Fistula: A 28 year experience at a major United States Department of Veterans Affairs Medical Center – Section: Results
6
Hindawi / PubMed Central. Colovesical Fistula due to Sigmoid Diverticulitis – Section: INTRODUCTION
7
PubMed Central. Colovesical Fistula: An Uncommon Cause of Hematuria and Rectal Bleeding – Section: Discussion
8
PubMed Central. Colovesical Fistula Complicating the First Symptomatic Episode of Acute Diverticulitis in a Young Adult – Section: Abstract
9
PubMed Central. Management of Enterovesical Fistula in a Patient with Crohn’s Disease: A Case Report and Literature Review – Section: Abstract
10
PubMed Central. Peritoneal bladder fistula following radiotherapy for cervical cancer: A case report – Section: Abstract
11
American Journal of Case Reports. Radiotherapy-Related Bladder Fistula: A Hidden Cause of Recurrent Abdominal Symptoms – Section: Discussion
12
PubMed Central. Reviving the poppy seed test for the diagnosis of colovesical fistula: A case report from a single rural center experience – Section: Abstract
13
PubMed Central. Four cases of enterovesical fistula and the importance of CT in the diagnosis – Section: Discussion
14
PubMed Central. Colovesical Fistula Surgically Managed With Delayed Computed Tomography Detection – Section: Discussion
15
PubMed Central. Villous adenoma of the urinary bladder with imaging findings suggestive of enterovesical fistula: A case report – Section: Discussion
16
PubMed. The poppy seed test for colovesical fistula: big bang, little bucks!
17
PubMed Central. Comparison of Open Versus Minimally Invasive Repair of Colovesical Fistula: A Case Report and Propensity-Matched National Database Analysis – Section: Results
18
F1000Research. Impact of bladder repair on postoperative outcomes in the surgical management of colovesical fistula: a systematic review and meta-analysis – Section: Abstract
19
PubMed Central. Colo-vesical fistula: Complete healing without surgical intervention – Section: Conclusion