Why Do Kidney Stones Cause Pain?

P6140312Agonizing, intolerable, miserable, excruciating, stabbed with a knife, worse than childbirth.

As a urologist specializing in the treatment of patients with kidney stones I have learned a new lexicon exclusive to stone formers describing bouts of renal colic.

Pain, the hallmark symptom of stone disease, accounts for over one million emergency room visits by such patients in the United States each year.

Over the past several decades considerable progress has been made gaining insight into the physiology of renal colic and optimizing methods to treat it. However, despite improved scientific explanations we as clinicians still lack a perfect understanding of why it occurs.


Patients have been suffering from renal colic secondary to stone disease for over two thousand years. As a matter of fact, it is remarkable how little has changed in its clinical presentation over this time period. In 400 B.C. Hippocrates referred to it as first disease of the kidneys. He was one of the initial observers to comprehend the association between urinary obstruction and pain, writing:

An acute pain is felt in the kidney, the loins, the flank and the testis of the affected side; the patient passes urine frequently; gradually the urine is suppressed. With the urine, sand is passed; as the sand passes along the urethra, it causes severe pain which is relieved when it is expelled; then the same sufferings begin again.

We have since come to appreciate the complex physiologic basis for this relationship at a much deeper level.

How Pain Begins

renal-stonesThe first step in this process is acute obstruction, most commonly from a stone. But in stone formers masses of crystals can create obstruction, as can blood clots if bleeding is particularly brisk.

Urine from the kidney can no longer pass to the bladder and as a result builds up and stretches the proximal – closest to the kidney – ureter and renal collecting system. This stretch activates nociceptive nerve fibers – fibers which sense injury – within an entire neuronal network located submucosally in the renal pelvis, calyces, capsule and ureter.

Figure 1 (left) – Example of obstructing proximal ureteral stone with dilation and stretch of the collecting system above the level of obstruction.

These fibers then transmit afferent signals to the T11 – L1 spinal cord which the body interprets as pain at the corresponding level of neuronal activation. As the stone migrates from the kidney down the ureter and towards the bladder, pain usually shifts downward as well. It is commonly sensed as high as the upper flank when the stone is lodged in the proximal ureter and as low as the labia/testicle when down near the uretero-vesical junction at the entry to the bladder.

Patients passing stones may experience other symptoms in addition to pain.  Many of the nerves involved in the process of obstruction are intimately linked to innervation of adjacent organs, for example the gastrointestinal tract. Cross activation of these associated nerve fibers has been proposed as an explanation for the nausea and vomiting which so often occurs in the setting of an acute episode of renal colic.

In rare instances patients may even have alternative symptoms without any pain at all. In some cases, particularly when the stone is at the uretero-vesical junction, urinary symptoms predominate and the only appreciable symptoms are urinary frequency, urgency and discomfort while voiding. These symptoms mimic urinary infection and often result in temporary mis-treatment with antibiotics until the correct diagnosis is made.

What Happens Later

Increasing renal pelvis pressure from persistent obstruction causes a release of prostaglandin E2. This chemical mediator of injury response produces a perfect storm.

It causes ureteral hyperperistalsis (increased intensity of the waves of coordinated ureteral contractions which normally drive urine down to the bladder) and eventually even ureteral spasm. It also leads to dilation of the afferent arterioles – those tiny resistance vessels which control the flow of blood into the capillaries of the kidneys.

The arteriolar dilation increases blood flow to the kidney and promotes a temporary diuresis just as ureteral smooth muscle hyperperistalsis and ultimately spasm tighten the ureter around the stone and worsen obstruction. Spasm leads to lactic acid build up, as occurs when any muscle is over-exercised, and sets off an inflammatory cascade that itself can worsen pain.

With time, blood flow to the affected kidney falls, even though the arterioles which let blood into the renal capillaries remain dilated. It falls because the efferent arterioles, which let blood out of the capillaries where filtration occurs, begin to constrict and raise filtration by the renal glomerulae. The increased filtration maintains and can even raise pressures.

glomerulus copy

Figure 2 – Diagram of blood flow to the nephron.  Blood enters through the afferent arteriole and is then filtered within the glomerulus, producing urine in the process. Blood exits through the efferent arteriole. Both the afferent and efferent arteriole are able to dilate and constrict in order to regulate pressure and ultimately filtration via urine production.

In many ways, this complex system is analogous to the soaker hoses many people use to water their lawns. The afferent arterioles are the faucet the hose is connected to and the efferent arterioles are the opening at the end of the hose which can be closed or left open into a sprinkler.

Filtration is the many tiny flows of water all along the hose which keep the grass growing.

When working appropriately, the faucet and the end are both open and water (urine) is produced at a slow, constant rate (Figure 4 – left). With an obstructing stone the faucet – so to speak – is opened more and the end clamped more so more fluid – water – is filtered out along the length of the hose at high pressure (Figure 4 – right). In the kidney this filtration is into the nephrons and raises pressure. When the clamp is tightened, the total amount of flow through the hose can fall just as the amount of water filtered out along the hose rises.

Figure 4 – Soaker Hose Analogy to Renal Blood Flow and Filtration. On the left, there is little pressure in the system and water (urine) seeps out slowly from along its length.  On the right, the inflow is much higher than the outflow and water (urine) shoots out from along the hose at exceedingly high pressure.

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Three Phases of Pain in more Detail

The Physiology

No discussion regarding ureteral obstruction would be complete without the work of E. Darracott Vaughan, who characterized the physiology of urinary obstruction in the 1970’s.

Assuming two functional kidneys, the physiologic effects of acute unilatScreen Shot 2015-05-21 at 11.04.09 PMeral ureteral obstruction can be marked by three distinct phases.

In phase one, the effects of the inflammatory cascade described above cause a progressive rise in renal blood flow and renal pelvis and ureteral pressure. This phase lasts for approximately one to one and a half hours. This is the portion where the afferent arteriole – the faucet – is maximally opened.

Phase two is marked by efferent arteriolar vasoconstriction which causes a decrease in overall renal blood flow but an increase in ureteral pressure for up to five hours. The faucet is opened and the end clamp is tightened.

Phase three is marked by a further decrease in renal blood flow to the affected kidney and ultimately decreased ureteral pressure. The end clamp is progressively tightened so blood flow to the kidney is reduced enough that filtration and urine production begin to fall, and pressure with it.

Measurements of ureteral pressure (red) and renal blood flow (blue) after onset of acute unilateral ureteral obstruction. (Courtesy Campbell-Walsh Urology, Tenth Edition, Elsevier Inc.)

The fall in blood flow is not injurious during an acute attack, but over time it can be. This means that relief of an obstructing stone is an important matter. Commonly stones pass of themselves. But stone attacks need medical attention because if the stone continues to obstruct it must be removed.

The Symptoms

It is easy to conjecture how these three distinct phases correlate clinically to the symptoms experienced during an acute episode of colic.

The onset of pain classically correlates to phase one and the inciting obstructive event. It is at this point that the patient commonly seeks care in the emergency room or physician’s office.

The pain classically persists at a severe level for several hours (phase two) but ultimately subsides, at least partially (phase three).

In many instances pain comes in waves, potentially a sign of intermittent obstruction activating the above pathway each time urinary flow is obstructed. This occurs through a combination of the stone moving and the tensions of the ureter with increases or decreases of muscle spasm.

THE CONUNDRUM – Pain Without Obstruction

Opinions of Urologists in General

Though the physiologic basis of pain in the setting of obstruction is clear, it does not provide an explanation for one of the most commonly encountered conundrums in stone disease – the symptomatic non-obstructing stone. These can be actual free stones that have not passed, stones attached to plaque, or actual plugs in the kidney tubules that are massed together enough to show up on a CT scan as ‘stones’ though actually tissue calcifications.

There is perhaps as much variation in clinical opinion in such instances as any other clinical scenario in the field.

If one were to ask a group of urologists whether they believed that small nonobstructing stones could cause renal colic, opinions would range from absolute certainty to complete dismissal of the concept altogether.

What Happens to Patients

As a result, there is no standard of care regarding how to optimally manage such patients. In all cases it is first imperative to rule out other potential sources of pain; however, such workups often end with the same result – a patient with bothersome flank pain and evidence of one or more nonobstructing stones on imaging.

Lacking a physiologic explanation to explain their symptoms, patients with pain and non obstructing stones are often sent for detailed workups, secondary and tertiary consultations and referral to pain specialists and even psychiatrists. However, in an age where flexible ureteroscopy can be performed quite safely and on an outpatient basis one must wonder whether such patients are being treated appropriately.

A Specific Example

As an example, I recently met a patient who had been referred from several hours away seeking a fourth opinion regarding her chronic flank pain. For months she had suffered from a severe ache in her left flank that had limited her ability to work and live her normal life.

She had attributed the pain to a 7 mm lower pole nonobstructing renal stone on that side which was discovered on a CTScreen Shot 2015-05-21 at 2.32.24 PM scan during her initial presentation to an outside emergency room (Figure 3). However, none of the physicians she had seen agreed with her self diagnosis.

Figure 3 – CT image of left lower pole nonobstructing stone (red arrow).  There is no evidence of obstruction or inflammation around the kidney.

In the ER she was given narcotic pain medication and sent home to follow-up with a urologist.

The first urologist she saw told her that while the stone was visible, its location within the kidney meant that it could not possibly be causing her pain. He refilled her prescription for pain medication and sent her to see a pain specialist.

The pain specialist tried physical therapy for what he thought may be a musculoskeletal source but ultimately this did not prove effective and she was given more pain medication.

She later sought care from a second urologist who also told her that the stone could not possibly be causing her pain in the absence of obstruction. This time however she was accused of having an agenda and seeking care specifically to get pain medication. Similar visits to a variety of emergency rooms elicited more CT scans as well as accusations of seeking pain medications. Each CT result was the same though, all demonstrating a 7 mm non obstructing left lower pole stone.

On one instance a treating practitioner even admonished her, saying that nonobstructing stones don’t cause pain and he should know since he too had been diagnosed with such stones incidentally on a CT scan.

Ultimately she made her way to the clinic for consultation at which point she was offered a ureteroscopy and stone removal. The procedure went well and she was discharged with a stent for one week. She was last seen back 5 weeks after the procedure and reported complete resolution of her pain. She was no longer taking any pain medication whatsoever and there was no evidence of any stone or hydronephrosis on follow-up imaging.

What is Known to Date

Such patients are frequently encountered. Despite a lack of physiologic explanation as to why these non-obstructing stones may cause pain, there is emerging evidence that they do and therefore that removal can cure it.

In 2006 Taub et al. described outcomes of twenty such patients who had chronic flank pain as well as radiographically evident calcifications within their papillae without obvious collecting system stones. Ureteroscopy with laser papillotomy to unroof and remove all evident stone was performed on twenty seven kidneys. Pain improvement was seen in 85% of cases with a durable improvement for greater than one year in nearly 60% of cases.

This study was then repeated on a multi-institutional level with 65 patients undergoing similar procedures over a ten year period. Overall there were 176 procedures performed in this cohort with patients reporting less pain after the procedure 85% of the time. The mean duration of response was 26 months with 60% of patients having sustainable improvements in their pain levels for over one year.

Finally, this clinical scenario is seen commonly enough that it garnered its own nickname at Massachusetts General Hospital where it has been described as “small stone syndrome”In a retrospective review of patients treated there with ureteroscopic removal of small nonobstructing stones (<4mm) for reasons related to chronic pain, 11/13 patients reported being pain free after the procedure with the other two noting a partial response.

What I think

We still do not completely understand the physiologic explanation for pain in these patients. However, much like Hippocrates over two thousand years ago, clinical observation often precedes scientific understanding. In this regard it is unfair to dismiss the notion that small non obstructing stones can elicit legitimate renal colic.

Physiologic breakthroughs in the understanding of pain signaling and inflammation are currently happening at a rapid rate and it is likely that in time we may be able to better decipher which non-obstructing stones are truly responsible for symptoms. However, until then, such scenarios will continue to be a commonly encountered clinical complexity for urologists.

For the time being I would still advocate consideration of alternative causes of pain in such situations including urinary infection, obstruction and malignancy. A careful history is critical to rule out non-urologic sources such as pathology within the musculoskeletal, pulmonary, gynecologic and gastrointestinal systems. Another important element of the history is whether the patient has previously passed a stone and if the current symptoms are similar to that experience.

Once other explanations have been ruled out, offering stone removal is entirely reasonable. This not only has the potential to improve pain but may also decrease the risk of future stone growth or spontaneous passage at a later date. In such instances, I prefer flexible ureteroscopy with stone removal to shock wave lithotripsy. First, ureteroscopy maximizes the likelihood that all stones can be identified and removed which is especially important in the event that pain persists after the procedure. Second, with ureteroscopy one can inspect the inside of the kidney in high definition which has the potential to offer information not readily available on x-rays and CT scans such as embedded stones, tissue calcifications, and other pathology (Figure 4).

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Figure 4 – High definition images obtained during renal endoscopy demonstrating tubular plugging (stones embedded in the kidney) (Courtesy: AE Evan, IMCD and BD plugs: Do they have a role in stone formation). 

Finally, it is critical to establish realistic expectations before surgery in regards to pain control. Our understanding of this concept is in evolution and the published literature suggesting a treatment response is limited to relatively few patients. However, as science and history have shown us, just because we don’t fully understand the connection doesn’t mean it doesn’t exist.

More You Might Like

What Kidney Stones Are

Types of Kidney Stones

Do We Need to Analyse All Those Stones?

How Kidney Stones Form

When Crystals Plug The Kidneys

Medullary Sponge Kidneys





917 Responses to “Why Do Kidney Stones Cause Pain?”

  1. Heather C.

    Good Morning Dr.
    I was in the ER a month ago now from severe pain in my right side that put me on the floor and nauseous. I got a CT scan w/o dye. Determined it was a stone. Gave me a referral to urologist, and antibiotics Finally got an appointment with him. He dismissed my pain symptoms, ordered a cystoscopy and gave me flomax and an antibiotic I have been in pain since the first day I went to er. I have had constant bladder infections and uti’s that Havnt gone away with the antibiotics. Any activity I do from simple things cause excruciating pain followed by nausea and vomiting. I haven’t been able to work either because of this.
    At cysto appointment I was treated very bad. He came into room very dismissive and argumentative. The cystoscopy went bad. I told him it hurt and to stop which he didn’t. The camera was covered in iodine so you couldn’t see anything. From there he left without any comment or explanation. I asked and asked what to do next and he left the room. Next I know the nurse walks me to check out.
    I was wondering if I can connect with you to get assistance with information or help.
    Thank you

    • Fredric Coe, MD

      Hi Heather, My reply is a bit late. I hope things have improved. If not, please feel free to call us at 773 702 1475 so perhaps we can help in some way. Regards, Fred Coe

  2. Laura Ries Dralle

    Are you still seeing patients with televisits?

  3. Laura Ries Dralle

    Dr. Coe, My daughter (23) has spent the last 3 years suffering with kidney pain from a series of non-obstructing stones. We have seen every specialist and have a long list of what she ‘doesn’t’ have – she is being turned away from pain specialists because “nothing is wrong”, and was turned away from our local emergency room yesterday with the pain of passing a kidney stone because CTs are clear and blood/urine tests are almost normal (even though her medical history shows three years of tests/doctors visits trying to figure out her condition). Mayo Clinic denied her application for case review, every specialist sends her along to the next, and she is literally in a pain episode as I write this. This article gave me hope that there may be help for her, do you still see patients (we are in Plainfield, IL)? Thanks for the exceptional collection of information. Laura

    • Fredric Coe, MD

      Hi Laura, I do only telehealth consultation but perhaps can try to find some help for her. I am not a pain specialize not surgeon, although I have an excellent surgical colleague. Regards, Fred Coe 773 702 1475

  4. Kumar

    I have a small stone 2 .5mm x2 5mm in the right kidney. Un obstructive. Confirmed by ultrasound and CT abdomen .Urine and blood reports are normal.
    I am having pain at times and discomfort under the ribs.
    Have met 5 urologist as per them stone is not the cause of it…I am taking citrate and flomax as prescribed.

    • Fredric Coe, MD

      Hi Kumar, I suspect the character of your pain is not like that of kidney stones and your surgeons disdain to operate. I would follow their advice. Regards, Fred Coe

  5. Brian Odette

    Dr. Borofsky, thanks so much for this article. I obviously don’t know for certain if this is the case, I’m a 45 y/o male with a history of IBS, psoriasis/psoriatic arthritis, and I’ve passed 2 kidney stones previously I have recently had recurring lower abdomen that radiates to my flanks and lower outer back and ended up in the ER recently. For days it won’t hurt at all, but then it comes in waves and it makes me nauseous and feel terrible all over. Best description I could give my wife was, “I would imagine this is what it feels like if a Dementor from Harry Potter touched you.” I didn’t make any connection to potential kidney issues until I read this article…my CT showed “multiple bilateral nonobstructive renal stones measuring up to 4 mm in the inferior pole of the right kidney and 4 mm in the superior pole of the left kidney.” I also showed mild ascites (recovering alcoholic, sober since 2009 but very heavy drinker for years before that) and enteritis, but I’m not sure if that adds any context. At times I feel like the pain radiates TO my kidneys. but then at others I think it’s radiating FROM my kidneys. It is very hard to pinpoint the pain sometimes because of the radiating nature of it. .Either way. my PCP told me that I should follow up with mental to “manage my stress” about this when I talked to her yesterday. Like others have said, this gives me hope that 1) something can help I think I’ll bring this up when I follow up. I’m tired of feeling crazy and looking like a huge hypochondriac. Thank you again!

    • Fredric Coe, MD

      Hi Brian, Kidney stones can cause pain even when not passing, so the ER physicians can look for blood or crystals. Given your past history there is the possibility of pancreatic pain – pancreatitis from cysts as a possibility. Regards, Fred Coe

  6. Warwick

    Have a 19×7 non obstructing stone in left lower pole collecting system. Uro is suggesting litho is this best option? Have had aching left flank for over 12 months and the occasional bout of pain that last a few hours .

  7. Richard

    This article described exactly what i am starting to go through. My ultrasound showed I have a 1.7 cm kidney stone at the UP Junction and also a 0.6 cm in my right kidney. Instead of removing these stones which already caused my first excruciating wave of pain, my urologist wants to do a cystoscopy to check my bladder. Well, I also had an ultrasound of my bladder and they didnt find anything wrong. So I feel its a waist of time and would prefer my stones be removed immediately.

  8. Mon

    Thank you so much for writing about your own experience with this. I feel like I’ve finally looked through a window into something that can actually help me, if I can find a doctor near me that will do this for me! I was told my nonobstructing stone on the right (6mm) was too small to have them break apart because, while it was clear as day on the CT scan it was not visible on the X-ray they did at that appointment. They never mentioned a ureteroscopy was even an option. This gives me hope and tells me I should definitely get a second opinion as I constantly experience pain on my right side between my hip and my ribs, and nothing else has been diagnosed or identified and little helps.

  9. Eric Menesses

    Thank you for your article. It was very informative. I’m a 40 year old male looking for answers. I have been dealing with burning only after urination for months and some pains in the testicles, pelvic area and back. CT Scan shows a 4x6mm stone in one kidney and two smaller stones in the other. Urine culture is clean. I’ve been on two antibiotics with no help. My urologist doesn’t feel the stones could be causing this issue. Have you experienced any patients that have had urethra burning symptoms with non obstructing stones? I’m wondering if I should have the stones removed or have a cystoscopy first to look at a possible bladder issue. If you are available for a telehealth appointment that would be wonderful.

    • Fredric Coe, MD

      Hi Eric, Pain in the testicle famously arises from radiation from stones passing in the kidneys. Crystal formation and passage can cause burning and perhaps is causing it for you. Your physicians may find crystals in the urine. Of great import is the cause of all this. I do telehealth as part of my work as a university physician. My secretary is at 773 702 1475. Regards, Fred Coe

  10. Linda McClellan

    I am so glad I found this article. It gives me hope that there are doctors out there starting to realize it is not in our head, but we actually are experiencing pain from non obstructing kidney stones! I am considering going to U of Chicago to be seen. I live in southwest Michigan and having an extremely difficult time getting in to be seen by my Urologist in Kalamazoo. I was diagnosed 3 weeks ago with a 6mm stone in my right kidney and 2mm stone in my left. Last night I made a second trip to the ER for the pain, with reduced urine output. I was concerned it was obstructing. My kidney function came back good. Trace of bacteria and some WBC in my urine, as well as oxilates present. I was sent home with some pain medication, flomax, and torridol. I have been trying unsuccessfully to get an appointment with my Uro. They are not returning my phone calls or MyChart messages. I am an EMT that can’t be out of work for too long. I need to be out taking care of other patients, not being one myself. Is it possible for me to travel to Chicago to be seen? Would I need a referral from my PCP or is the CT confirmation done at the ER enough? I am really struggling with the pain.

    • Fredric Coe, MD

      Hi Linda, Given your work the ideal is probably that I see you via telehealth concerning the medical issues related to your stones, and you then come into Chicago to see my partner Dr Luke Reynolds who is a brilliant stone surgeon. That way, Luke can have whatever I can add at the beginning, and he can consider what might be worthwhile from a surgical standpoint. If that works, Banita Williams can arrange the former – 773 702 1475. Regards, Fred Coe

      • Linda McClellan

        Thank you Dr Coe, I wish I had come back and checked the page sooner. I am having lithotripsy for the 6mm x 4mm x 3mm stone on Tuesday (Jan 10th). They are doing nothing for the 2mm in the left kidney. So I would love to see you concerning the 2mm and work on a plan of action. My husband and I both feel it is worth the out of network costs to be treated by you and your colleagues. My in network provider doesn’t believe at all that stones in the kidneys cause pain. I will definitely be in touch to schedule a video consult and possible arrangement to come to Chicago.

        • Fredric Coe, MD

          Hi Linda, My secretary is at 773 702 1475. It might be most practical to do a telehealth visit first to get things in order and then plan a personal visit if it appears that surgery is really your best approach. Regards, Fred Coe


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