Diverticulitis can cause blood in urine, though it does so through an indirect and relatively uncommon pathway rather than by directly affecting the urinary tract. The most frequent mechanism involves a colovesical fistula, an abnormal tunnel that forms between the inflamed colon and the bladder. Because the sigmoid colon sits close to the bladder in the lower abdomen, severe or repeated bouts of diverticulitis can erode through the tissue separating the two organs, allowing intestinal contents to leak into the urinary system. Hematuria (blood in the urine) is one of several urinary symptoms that can result, and it often catches people off guard because they have no reason to connect a bowel condition with what looks like a urinary problem.
How Diverticulitis Reaches the Bladder
The sigmoid colon, where diverticula most commonly form, is draped directly over the dome of the bladder. When a diverticulum ruptures or a diverticular abscess builds up, the inflammation can spread to adjacent structures. A colovesical fistula forms when a ruptured diverticulum extends directly into the bladder wall or when a diverticular abscess slowly erodes through it.1Annals of Coloproctology. A Case of Colovesical Fistula Induced by Sigmoid Diverticulitis Once that channel exists, gas, stool particles, bacteria, and sometimes blood can travel from the colon into the bladder. Diverticulitis is the single most common cause of colovesical fistulas, ahead of Crohn’s disease, radiation injury, and cancer.2PubMed Central. Colovesical Fistula: An Uncommon Cause of Hematuria and Rectal Bleeding
Only a small fraction of people with diverticulitis ever develop a fistula.3PubMed Central. Pneumaturia and faecaluria: Symptoms leading to a life-saving diagnosis Most episodes of diverticulitis resolve with antibiotics or rest and never come close to breaching the bladder. But when an episode is severe, when an abscess forms and is not drained, or when someone has repeated flare-ups in the same spot, the risk of a fistula goes up. The process usually happens over weeks to months, not overnight.
What the Urinary Symptoms Actually Look Like
Blood in the urine is only one piece of a broader symptom picture when a colovesical fistula develops. Other hallmark signs include pneumaturia (passing gas through the urethra during urination) and fecaluria (seeing small particles of stool in the urine). These two symptoms are far more specific to a fistula than hematuria alone, and they tend to appear earlier. Dysuria, a burning or painful sensation while urinating, is also common, along with frequent urinary tract infections that keep coming back despite treatment.2PubMed Central. Colovesical Fistula: An Uncommon Cause of Hematuria and Rectal Bleeding
The blood in urine caused by a fistula tends to be different from what you would see with, say, a kidney stone or a bladder tumor. It is often mixed with cloudy, foul-smelling urine because of the bacterial contamination from the colon. If you notice air bubbles when you urinate, or if your urine smells distinctly like stool, those are strong clues that the problem is not originating in the urinary tract itself. Many people, understandably, go to a urologist first and get treated for a urinary tract infection before anyone thinks to look at the colon.
Why This Gets Misdiagnosed So Often
One of the more frustrating aspects of colovesical fistula is how frequently it masquerades as a simple urinary problem. The urinary symptoms tend to dominate the clinical picture. A patient walks in with burning urination, blood in the urine, and a positive urine culture. The obvious diagnosis is a UTI, and antibiotics clear it up temporarily. But the fistula is still there, and the infection returns weeks later. One case report documented a misdiagnosis rate of about 68% for colovesical fistulas, partly because clinicians may not consider that a colorectal condition can present primarily as urinary symptoms.4PubMed Central. Challenges in the initial diagnosis of colon carcinoma from symptoms of a bladder and colon fistula: a case report In that particular case, it took six months from symptom onset to a correct diagnosis.
The delay matters. Chronic fistulas expose the urinary tract to a constant stream of gut bacteria, which can lead to recurrent kidney infections and, in extreme cases, kidney damage. One reported case involved a patient whose long-standing colovesical fistula led to chronic pyelonephritis, persistent air in the collecting system, and eventually end-stage renal disease requiring dialysis.5PubMed Central. Chronic Colovesical Fistula Leading to Chronic Urinary Tract Infection Resulting in End-Stage Renal Disease in a Chronic Granulomatous Disease Patient That is an extreme outcome in a patient with an underlying immune disorder, but it illustrates where a missed fistula can lead over time.
Ureteral Compression Without a Fistula
A colovesical fistula is not the only way diverticulitis can affect the urinary system. A large diverticular abscess can press on the ureter, the tube that carries urine from the kidney to the bladder, without actually forming a hole into the urinary tract. When the ureter gets squeezed shut or narrowed, urine backs up into the kidney and causes hydronephrosis, a swelling of the kidney that can produce flank pain and sometimes blood in the urine.
One documented case involved a patient whose CT scan revealed a diverticular abscess measuring roughly 6 by 2.6 centimeters that was compressing the left ureter, causing moderate hydronephrosis.6PubMed Central. Hydronephrosis: An Unusual Complication of a Diverticular Abscess In these situations, the hematuria is a consequence of pressure and obstruction rather than a direct connection between the colon and urinary tract. Treating the abscess, whether by drainage or surgery, typically relieves the compression and allows the kidney to recover.
Who Is More Likely to Develop a Fistula
Men develop colovesical fistulas from diverticulitis far more often than women. The reason is anatomical: in women, the uterus sits between the sigmoid colon and the bladder, acting as a physical buffer. The uterus is a sturdy, muscular organ that is difficult for inflammation to penetrate.7Egyptian Journal of Radiology and Nuclear Medicine. A case report of colouterine fistula due to colonic diverticulitis: a rare complication As long as the uterus is in place, it shields the bladder from direct contact with an inflamed colon.
This protective effect disappears after a hysterectomy. A large study found that women who had undergone a hysterectomy and also had diverticulitis faced a roughly 25-fold increase in the risk of needing fistula surgery compared to women with neither condition. Even hysterectomy alone, without diverticulitis, quadrupled the risk. Women with diverticulitis but an intact uterus had a sevenfold increase, a substantially lower risk than the hysterectomy-plus-diverticulitis group.8PubMed. Influence of hysterectomy on fistula formation in women with diverticulitis If you are a woman with a history of both hysterectomy and diverticulitis, the odds that urinary symptoms could be fistula-related are higher than average.
How a Colovesical Fistula Is Found
CT scanning is the most reliable non-invasive tool for detecting a colovesical fistula. It can show air inside the bladder (a telltale sign when the patient has not had a catheter), thickening of the bladder wall adjacent to the colon, soft-tissue changes forming a bridge between the two organs, and any nearby abscess or diverticular inflammation.9PubMed Central. Four cases of enterovesical fistula and the importance of CT in the diagnosis One study found CT accurately predicted the presence and location of the fistula in nearly all patients evaluated.10Journal of Urology. Accuracy of Computerized Tomography in the Diagnosis of Colovesical Fistula Secondary to Diverticular Disease
Other tests fare surprisingly poorly. In one review, barium enema identified the fistula in only about 20% of cases, and cystography (filling the bladder with contrast dye) picked it up in roughly 11%. Cystoscopy, colonoscopy, and intravenous pyelograms were essentially non-diagnostic for the fistula itself, though cystoscopy can show localized inflammation on the bladder wall that raises suspicion.11PubMed. The spectrum of colovesical fistula and diagnostic paradigm This means that if a doctor suspects a fistula, a CT scan with contrast is the study to request. Standard urological workups alone are likely to miss it.
That said, CT is not infallible. In at least one reported case, a colovesical fistula in a young adult with sigmoid diverticulitis went undetected on CT, and the fistula was only confirmed during surgery.12Annals of Medicine and Surgery. Colovesical fistula in a young adult due to sigmoid colon diverticulitis undetected in computed tomography: Case report and review of literature When the clinical picture strongly suggests a fistula but imaging comes back negative, further investigation is still warranted.
Other Causes of Blood in Urine to Rule Out
Hematuria has a long list of possible causes, and diverticulitis-related fistula is relatively low on that list in terms of frequency. If you see blood in your urine, the more common explanations include kidney stones, urinary tract infections unrelated to the bowel, kidney infections, bladder or kidney tumors, and prostate enlargement in men.13American Journal of Case Reports. A Rare Case of Acute Urinary Bladder Diverticulitis Mimicking Acute Appendicitis Vigorous exercise, certain medications (blood thinners in particular), and even some foods can temporarily cause pink or red urine.
What should make you suspect a diverticulitis connection specifically is the combination of urinary symptoms with a history of diverticular disease or recent bowel symptoms. If you are passing gas through your urethra, seeing debris in your urine, or dealing with UTIs that keep returning despite appropriate antibiotics, and you have a known history of diverticulitis, those pieces together are a strong signal to investigate for a fistula. Hematuria alone, without those other features, is unlikely to be caused by diverticulitis.
What Happens Once a Fistula Is Confirmed
Most colovesical fistulas caused by diverticulitis are treated surgically. The standard approach involves removing the segment of colon responsible for the fistula (typically the sigmoid colon), separating it from the bladder, and reconnecting the remaining healthy bowel. The bladder defect usually heals on its own once the diseased colon segment is taken out.14PubMed Central. Colovesical Fistula due to Sigmoid Diverticulitis In some cases, surgeons can perform this as a single-stage operation; in others, particularly when there is significant infection or abscess, a temporary colostomy is created to divert stool while everything heals, followed by a second surgery to reverse it.
Conservative management with antibiotics and bowel rest can control symptoms temporarily, and it is sometimes used as a bridge to surgery or in patients who are not fit for an operation. But antibiotics alone do not close the fistula. As long as the abnormal connection persists, the cycle of urinary infections and contamination continues. For most patients who are reasonable surgical candidates, definitive repair offers the best chance of resolving the urinary symptoms permanently.
When to Bring Up Diverticulitis With Your Doctor
If you have a known history of diverticulitis or diverticular disease and you start experiencing unexplained urinary symptoms, mention your bowel history even if the visit is with a urologist. Recurrent UTIs in someone with diverticulitis should trigger at least a conversation about whether a fistula might be present. The same applies if you notice air in your urine or your urine has an unusual fecal odor. These are not subtle symptoms, but they are easy to dismiss or attribute to something else if no one connects them to the colon.
Conversely, if you have no history of diverticular disease and you see blood in your urine, a fistula from diverticulitis is very unlikely to be the explanation. Hematuria on its own is common and usually points to urological causes. The crossover into diverticulitis territory happens when bowel and bladder symptoms overlap, when infections refuse to stay treated, or when imaging reveals changes in the tissue between the colon and bladder. Keeping your doctors informed about your full medical history, digestive issues included, gives them the context to catch a fistula before it causes lasting damage.
Bladder Diverticulitis as a Separate Entity
Adding a layer of confusion, the bladder itself can develop diverticula, small outpouchings of the bladder wall that have nothing to do with the colon. Bladder diverticula are more common in older men with prostate enlargement, which creates back-pressure in the bladder. These bladder diverticula can occasionally become inflamed on their own, a condition sometimes called bladder diverticulitis, and this can cause hematuria and pain that mimics other abdominal conditions.13American Journal of Case Reports. A Rare Case of Acute Urinary Bladder Diverticulitis Mimicking Acute Appendicitis
This is a completely separate condition from colonic diverticulitis, despite the confusingly similar name. Bladder diverticulitis involves the urinary tract from the start, not the colon. It does not involve a fistula and is managed differently. If you are reading about diverticulitis and blood in urine, it is worth knowing that not every diverticulum lives in the colon, and not every case of “diverticulitis” with urinary symptoms involves a colon-to-bladder connection. Your doctor can usually sort this out quickly with imaging.