If, for some strange reason, you set out to design a kidney that could form stones as quickly as possible, you might end up with something like a medullary sponge kidney.
Medullary sponge kidney (MSK) is a condition in which a portion of the kidney known as the medullary pyramid is found to have dilated tubules (tubules are small tubes through which urine drains) and numerous small cysts (cysts are fluid filled hollow spaces). The cysts are small, measuring from 1 to 8mm, but are numerous. The cysts give the kidney, when cut, the appearance of a sponge – from which the name of “medullary sponge kidney” was coined. These cysts and dilated ducts lead to poor drainage, making it easier for stones to form. These abnormalities can be seen throughout both kidneys or may be localized in only one part of a kidney. The stones formed in MSK tend to be numerous and scattered throughout the kidney.
How do I know if I have medullary sponge kidney?
Medullary sponge kidney is felt to be non-hereditary (you don’t pass it on to your children). Many patients with MSK never develop problems and don’t know they have the condition. One study estimated that MSK may occur as commonly as 1 in 200 persons while other more conservative estimates report an occurrence rate of 1 in 5,000 to 20,000 persons.
Because many patients with MSK develop no symptoms and remain undiagnosed, reliable data on how many will form stones is not available. In one study of 56 patients from one hospital, the authors reported that 30% of the MSK patients that they studied never developed stones. Among the stone formers, MSK appears to be more common in females and usually first presents in the 30s.
The diagnosis of medullary sponge kidney is made with imaging studies, either with an intravenous pyelogram (an older type of x-ray) or with a contrast CT scan. These imaging studies will show a characteristic distribution of stones or calcifications in the location of the medullary pyramids and contrast pooling in dilated tubules. In order to confirm the diagnosis, the imaging study should include intravenous contrast in order to demonstrate the dilated tubules that are the hallmark of MSK. However, most CT scans for kidney stones are performed without contrast and in this case the diagnosis, while likely, is not considered definitive because other stone related conditions can also lead to an appearance similar to MSK on a non-contrast CT scan.
Non-contrast CT scan of a patient with medullary sponge kidney. Multiple stones and calcifications can be seen in both kidneys. To see examples of contrast accumulating in the medullary pyramids of MSK patients on a contrast CT scan or intravenous pyelogram, visit these sites: CT scan or intravenous pyelogram.
What are the symptoms of medullary sponge kidney?
McPhail and colleagues reported that among 56 patients with MSK, the most common presenting symptoms included:
- Flank pain in 52%
- Microscopic blood in the urine in 36%
- Visible blood in the urine in 16%
- Urinary tract infection in 7%
- Abdominal pain in 7%
- Testicular pain in 4%
- Imaging for other causes in 4%
What type of problems can medullary sponge kidney cause?
Individuals with MSK most commonly present with kidney stones, urinary tract infections, or blood in the urine. In individuals with MSK who form stones, other metabolic abnormalities that predispose someone to form stones are also commonly found, including hypercalciuria (high calcium levels in the urine) and renal tubular acidosis (a disorder with the kidney’s handling of acids).
It therefore appears that just having MSK by itself is not enough to form stones (30% of MSK patients don’t form stones). However, combine the abnormalities found in MSK with someone who has a metabolic tendency to form stones and you will often see an astounding number of stones developing throughout the kidneys.
X-rays for patients with MSK are often impressive for the sheer numbers of stones seen. Not all those stones will necessarily be in a position to drop into the ureter and cause traditional stone symptoms. In order to do so, the stones need to have access to the hollow collecting system portion of the kidney. Instead, many are often embedded in the solid tissue of the kidney (the parenchyma) where they are unlikely to result in a stone passage.
In some patients however, the non-obstructing stones seen in MSK can be associated with significant and chronic pain, even if they are not passing. The pain in this situation can be constant in nature, unlike the episodic pain traditionally seen with kidney stones. It is not certain what causes this pain but authors have proposed that the small numerous stones seen in MSK may cause obstruction of the small tubules and collecting ducts in the kidney, leading to the pain. This pain can be debilitating and treatment is challenging. Narcotic medication, even with large quantities, is often not adequate. Some success with pain control for MSK patients with this type of pain has been reported using laser lithotripsy (see below).
The most common stone types in MSK are calcium oxalate and calcium phosphate.
Thankfully, MSK does not commonly lead to kidney failure.
What can be done about medullary sponge kidney?
Treatment for MSK focuses on prevention and treatment of stones, management of pain, and prevention of infections. There is no treatment available to fix or remove the small cysts and dilated tubules associated with the condition.
In stone formers, maintaining a high fluid intake and treatment with hydrochlorothiazide (to lower urinary calcium) and/or potassium citrate (to raise urinary citrate) are used. Metabolic evaluation with urinary and blood testing can be used to identify specific metabolic abnormalities that increase a person’s risk for stones. In addition, some authors advocate the use of hydrochlorothiazide in all patients with MSK, even when urinary calcium levels are normal.
Treatment for stones that have already formed include the same approaches used for other stone patients, including ureteroscopy, shockwave lithotripsy, or less frequently, percutaneous nephrolithotripsy. Due to the large number of stones formed in MSK and the fact that many of those stones may not be within the collecting system, it is not usually necessary or possible to completely eradicate stones in a patient with MSK.
In patients who have chronic pain associated with MSK, ureteroscopy with laser lithotripsy (called “ureteroscopic laser papillotomy”) may be an option to relieve discomfort. The procedure involves fragmenting and extracting all visible stones in the kidney with the intent to “unplug” and clear obstructed ducts that may have stones trapped in them. In a paper from three institutions, Gdor and colleagues reported on their experience with a total of 65 patients who collectively underwent 176 procedures. All patients in the study had chronic flank pain and multiple non-obstructing kidney stones. 50 patients had followup information available. The majority of patients who underwent this procedure experienced a reduction in their pain (83%). On average, the duration of pain relief from surgery was 26 months. Of note, 17 of the patients in the study had a diagnosis of MSK and their pain relief was similar to that seen in non-MSK patients.
If you have been diagnosed with medullary sponge kidney, share your experience or ask a question below.
Campbell-Walsh Urology 10th Edition, 2011.
McPhail and co-authors, “Nephrolithiasis in Medullary Sponge Kidney: Evaluation of Clinical and Metabolic Features”, Urology 2012.
“Medullary sponge kidney” National Kidney and Urologic Diseases Information Clearinghouse, 2008.
Gdor and co-authors, “Multi-Institutional Assessment of Ureteroscopic Laser Papillotomy for Chronic Flank Pain Associated with Papillary Calcifications”, Journal Of Urology 2011.
Editor’s note: This post was updated on 5/15/12 to include more information on diagnosis, pain related to medullary sponge kidney, and treatment options.