What Is Hydrodistention and How Is It Performed?

Hydrodistention is a procedure in which a doctor fills your bladder with sterile fluid under controlled pressure while you are under anesthesia, stretching the bladder wall to its capacity. It serves a dual purpose for people with interstitial cystitis/bladder pain syndrome (IC/BPS): it helps the doctor see characteristic signs of the condition on the bladder lining, and for many patients it temporarily relieves symptoms like pain, urgency, and frequent urination. Though it has been part of the urologist’s toolkit for decades, its role has evolved considerably, and there is more nuance to the procedure, its results, and its limitations than most patients hear about before being wheeled into the operating room.

How the Procedure Works Step by Step

Hydrodistention is performed in an operating room or procedure suite, almost always under general or spinal anesthesia. You need to be fully anesthetized for two reasons: a conscious patient would find the degree of bladder stretching intolerably painful, and involuntary muscle guarding would prevent the bladder from expanding enough for the procedure to be useful. Research comparing anesthesia types suggests that spinal anesthesia may do a better job of blocking the body’s automatic stress responses during the distention than general anesthesia does.¹

Once anesthesia takes effect, the urologist inserts a cystoscope, a thin instrument with a camera and a light, through the urethra and into the bladder. Sterile saline or water is then infused through the scope, gradually filling the bladder under a specific, measured pressure. This is not a casual fill; the pressure is set using a column of water at a defined height above the patient, typically around 80 centimeters of water (cm H₂O) for a therapeutic distention. The bladder is held at that pressure for a set period, then slowly drained so the doctor can inspect the lining.

There is no universal agreement on exactly how long the bladder should stay distended. A systematic review examining published trials found a wide range, from as little as 2 minutes up to 2 hours in older studies. Nine trials looked at distention times of 15 minutes or less, and five older trials pushed the duration to between 30 minutes and 2 hours.² Most urologists today use shorter durations, and many centers employ a two-stage approach within the same session: a brief low-pressure distention first (around 40 cm H₂O for 2 minutes) for diagnosis, followed by a higher-pressure distention (80 cm H₂O for 8 to 10 minutes) intended to provide therapeutic benefit.³

What Doctors See When the Bladder Is Drained

The diagnostic value of hydrodistention lies in what happens after the fluid comes out. As the bladder empties, the urologist watches the lining through the cystoscope, looking for specific patterns of bleeding and tissue changes that suggest IC/BPS. The most commonly observed feature is glomerulations: tiny pinpoint hemorrhages scattered across the bladder wall. They look like small red spots or petechiae, and their severity is graded on a scale from 0 (none visible) to 3 (severe “waterfall” bleeding).⁴ Beyond glomerulations, the doctor also looks for splotch hemorrhage, mucosal fissures (cracks in the lining), and a more distinctive finding called Hunner’s lesions.

Hunner’s lesions are reddened, inflamed patches on the bladder wall that are considered the hallmark of a specific subtype of interstitial cystitis. Unlike glomerulations, which only become visible after distention, Hunner’s lesions can often be spotted through a standard office cystoscopy without anesthesia.⁵ Patients with Hunner’s lesions tend to have more severe symptoms and are classified differently from those who have only glomerulations or no visible findings at all. Modern clinical thinking recognizes at least three phenotypes based on what the cystoscope reveals after hydrodistention: no glomerulations, characteristic glomerulations, and Hunner’s lesions.⁶

One detail that matters more than many patients realize: the maximum bladder capacity measured during the distention, sometimes called anesthetic bladder capacity (ABC). This is simply how much fluid the bladder holds when it is fully distended under anesthesia. This number turns out to be clinically meaningful for both prognosis and treatment planning.

Does It Actually Relieve Symptoms?

For a procedure that has been around for decades, the evidence on how well hydrodistention works is surprisingly messy. The short answer is that it helps some people, usually temporarily, and the benefit varies widely depending on the patient’s subtype of IC/BPS and possibly on how the procedure is performed.

Among the shorter-duration studies (15 minutes or less), the results are mixed. Out of nine trials examined in one systematic review, four found no meaningful difference in symptoms before and after the procedure at follow-ups between one and six months. Four others did find significant improvement in patient symptom scores. One study that compared two different distention durations found that patients improved in both groups, and a separate study reported that the average time before symptoms returned after a 3-minute distention was about 25 months.²

The older, longer-duration studies (30 minutes to 2 hours), which were performed under spinal or local anesthesia, reported that roughly a third to two-thirds of patients had sustained improvement, with follow-up periods running from 7 months to over 3 years. A study specifically looking at prolonged distention found that about 38% of patients responded at 6 months and 22% at 1 year in one patient series, while a second series at the same center had better numbers: 60% at 6 months and about 43% at 1 year. The authors attributed the improvement to having less severe disease.⁷

The pattern across studies is consistent on one point: whatever relief hydrodistention provides tends to fade over time. This is not a cure. Most people who benefit will eventually see symptoms return, and some will undergo repeat procedures.

Who Is Most Likely to Benefit

Not everyone with IC/BPS responds the same way to hydrodistention, and researchers have been working to identify what predicts a good outcome. One of the strongest and most consistent predictors is the anesthetic bladder capacity measured during the procedure itself. Patients whose bladders held a larger volume under anesthesia tended to get more pain relief afterward.⁸ One study identified a specific cutoff: patients whose maximum bladder capacity reached at least 760 milliliters had a satisfactory outcome about 64% of the time, compared with lower response rates in those with smaller capacities.⁹

Interestingly, the severity of glomerulations did not cleanly predict who would respond. Patients with low-grade or no glomerulations and a large bladder capacity had the best outcomes, while those with Hunner’s lesions had the worst response rate, with only about 37% reporting satisfactory improvement. Between those extremes, the other subgroups responded at rates of roughly 40 to 44%, without clear separation from one another.

A separate analysis looked at patient characteristics beyond what the cystoscope shows. Several factors were linked to a weaker response: having Hunner’s lesions, a diagnosis of fibromyalgia, pain spread across many body sites, and a higher burden of overlapping chronic pain conditions. After statistical adjustment, the overall burden of complex medical symptoms was the factor that held up most robustly as a predictor of poor response.¹⁰ In practical terms, this suggests that patients whose pain is more localized to the bladder tend to get more from the procedure than those whose pain is part of a broader, body-wide sensitivity pattern.

Risks and What Recovery Looks Like

Hydrodistention is generally considered a low-risk procedure, but it is not risk-free. The most common issue afterward is a temporary worsening of bladder symptoms. Many patients experience more pain, urgency, and frequency in the first few days to weeks before things start to improve, which can be alarming if you are not expecting it. Blood in the urine is also common and usually resolves on its own. Urinary retention, where the bladder has difficulty emptying after the procedure, can occur but is uncommon.

A specific concern applies to patients who take blood-thinning medications. A study examining perioperative safety found that patients on antithrombotic therapy had meaningfully higher rates of complications: about 10% experienced blood transfusion or urinary retention at 3 months, compared with under 2% for patients not on blood thinners.¹¹ If you take anticoagulants or antiplatelet drugs, this is a conversation worth having with your urologist before scheduling the procedure.

The most serious but rare risk is bladder rupture, which can happen if the bladder is overdistended or if the wall is severely compromised by disease. This is one reason why the procedure is performed under carefully controlled pressure rather than simply filling the bladder until it stops. Recovery from an uncomplicated hydrodistention is typically quick in terms of getting home; most patients leave the same day or the following morning. The symptom flare that follows is the harder part of recovery for many people, and it can take several weeks to know whether the procedure has provided benefit.

Combining Hydrodistention with Other Treatments

Because the relief from hydrodistention tends to be temporary, researchers have looked into ways to extend its benefit. One approach that has shown promise is instilling a solution directly into the bladder immediately after the distention, taking advantage of the fact that the bladder is already accessed and the lining may be more receptive to treatment.

A study comparing hyaluronic acid instillation after hydrodistention to heparin instillation found that the hyaluronic acid group maintained improvement for significantly longer. At 6 months, about 78% of the hyaluronic acid group was still improved compared to 33% in the heparin group. By 9 months, the gap persisted: 50% versus 20%. The hyaluronic acid group also showed meaningful improvements in daily void counts, pain scores, and bladder capacity that were still present at 9 months, while the heparin group had lost its gains entirely.¹²

This kind of combination strategy reflects the broader clinical reality: hydrodistention is rarely a standalone treatment anymore. It is more often one component in a multimodal plan that might also include oral medications, dietary changes, pelvic floor physical therapy, or other bladder instillations over time.

Why the Procedure Has Become Less Common

If you have been reading about IC/BPS management from sources written more than a decade ago, you may have the impression that hydrodistention with cystoscopy is a standard, near-universal step in diagnosis and treatment. That has shifted. In 2011, the American Urological Association published guidelines for IC/BPS that repositioned cystoscopy with hydrodistention: rather than a routine early step, it was placed further along the treatment algorithm, recommended mainly when simpler approaches have failed or when the diagnosis is uncertain.

The effect of that guideline change was measurable. Before the guideline, the rate at which IC/BPS patients underwent outpatient cystoscopy with hydrodistention was climbing, reaching close to 17%. After the guideline, the rate dropped by about 7 percentage points and continued to decline, falling below 10% by early 2020. The decline was especially pronounced among urologists compared to other specialties.¹³

This does not mean hydrodistention has been abandoned. It remains valuable in specific situations: when the diagnosis needs confirmation by visualizing Hunner’s lesions or glomerulations, when initial conservative treatments have not provided adequate relief, or when the doctor wants to assess anesthetic bladder capacity as part of treatment planning. The shift is away from using it as a first-line diagnostic or therapeutic step for everyone and toward using it more selectively.

The Biological Mystery of Why Stretching Helps

Despite decades of use, the mechanism by which physically stretching the bladder wall relieves pain and urgency is not well understood. One clue comes from studying urine biomarkers before and after the procedure. A study that measured several markers found that two changed significantly after distention: antiproliferative factor activity dropped toward normal levels, and heparin-binding epidermal growth factor-like growth factor levels rose dramatically, from a median of 0.34 to 4.1 nanograms per milligram of creatinine. Both shifts moved these markers in the direction seen in healthy bladders. Yet changes in these urine markers did not correlate with changes in symptom scores, meaning the biochemical improvement and the clinical improvement did not track together neatly.¹⁴

One hypothesis is that the stretching disrupts overactive sensory nerve endings in the bladder wall, temporarily resetting the pain signals being sent to the brain. Another is that the controlled injury from distention triggers a healing response in the bladder lining. Some researchers have speculated that the temporary ischemia (reduced blood flow) during the stretch, followed by reperfusion (blood rushing back in) afterward, may modulate the inflammatory environment. None of these theories has been definitively proven, and the disconnect between biomarker changes and symptom relief suggests the full picture is more complicated than any single pathway.

Hydrodistention in Veterinary Research

Interstitial cystitis is not unique to humans. Cats develop a remarkably similar condition called feline interstitial cystitis (FIC), and researchers have used these animals as a model for understanding the human disease. Studies of bladder tissue from cats with FIC have found that the urothelium (the inner lining of the bladder) shows reduced barrier function and increased permeability to water and waste products after hydrodistention.¹⁵ This suggests that distention itself can alter the bladder lining’s integrity, which may explain both the initial post-procedure symptom flare (a temporarily more permeable bladder allows irritating substances to reach nerve endings) and, paradoxically, the eventual improvement if the lining regenerates in a healthier state. The feline model has not resolved the mechanism question, but it has reinforced the idea that the bladder lining’s barrier function is central to the disease and to the body’s response to distention.

Local Anesthesia Alternatives and Newer Approaches

One practical barrier to hydrodistention is that it typically requires general or spinal anesthesia, meaning an operating room, an anesthesiologist, and the associated costs and scheduling constraints. Recent work has explored whether some patients can undergo the procedure under local anesthesia instead. A study examining hydrodistention under local anesthesia in patients without Hunner’s lesions found that the approach was feasible, though patients with the most restricted bladder capacity before the procedure had meaningfully lower preoperative measurements, suggesting their disease was more advanced.¹⁶ If local-anesthesia hydrodistention proves safe and effective in larger studies, it could make the procedure more accessible and less burdensome for patients who need it, particularly for repeat procedures when the initial benefit wears off.

The field is also increasingly interested in using the information gathered during hydrodistention, such as bladder capacity, glomerulation grade, and presence of Hunner’s lesions, not just for diagnosis but for phenotyping. The idea is that grouping patients by what the cystoscope reveals could guide treatment selection more precisely than treating everyone with IC/BPS as a single population. Some patients may be better served by directed treatment of Hunner’s lesions through fulguration or injection, while others with a large, compliant bladder and minimal visible findings may benefit most from the distention itself or from behavioral and pharmacological therapies. This movement toward subtype-specific care is arguably the most important evolution in how hydrodistention fits into IC/BPS management today.