Medullary Sponge Kidney (MSK) is a congenital disorder characterized by a structural abnormality in the tiny tubes within the kidney. This malformation disrupts the normal flow of urine. Although often considered benign, MSK frequently leads to complications and noticeable symptoms, often remaining undiagnosed until complications arise later in life.
Defining the Condition and Its Origin
Medullary Sponge Kidney is an anatomical defect of the kidney’s inner portion, the medulla. This region contains collecting ducts, which are small tubes that gather urine before it exits the kidney. In MSK, these collecting ducts become abnormally dilated, forming small, fluid-filled sacs called cysts.
This cystic dilatation gives the kidney tissue a “spongy” appearance, which is how the condition received its name. The condition frequently affects both kidneys, occurring bilaterally in about 70% of cases, but it can also be confined to just one kidney. This structural change is a result of a developmental error occurring during fetal life, although the exact mechanism causing this disruption remains largely unknown.
Most cases of MSK occur sporadically, meaning they happen randomly without a clear genetic link. Research suggests that a malfunction in the developing kidney’s growth factors may contribute to the collecting duct abnormalities.
Common Signs and Clinical Presentation
While many people with MSK remain asymptomatic throughout their lives, the condition often presents clinically with complications in young adulthood, typically between the ages of 20 and 30. The most common clinical manifestation is the formation of recurrent kidney stones (nephrolithiasis), affecting up to 70% of patients. The dilated collecting ducts cause urinary stagnation, which encourages calcium deposits within the kidney tissue, a process called nephrocalcinosis.
These calcium deposits can eventually break off, forming kidney stones that travel through the urinary tract, causing sudden, intense flank or abdominal pain known as renal colic. Patients are also prone to recurrent urinary tract infections (UTIs) because the abnormal collecting ducts and the presence of stones impede the normal flow of urine.
Another common sign is hematuria, or blood in the urine, which can be either microscopic or visible. This occurs due to irritation caused by the calcium deposits or the passage of kidney stones. Some individuals also exhibit a defect in the kidney’s ability to properly regulate acid, which further contributes to the stone-forming environment.
Identifying Medullary Sponge Kidney
Diagnosis of MSK is suspected when a person experiences recurrent kidney stones or frequent UTIs, prompting a medical evaluation. The characteristic structural changes are confirmed through medical imaging.
High-resolution computed tomography (CT) scans, particularly CT urography with contrast, are the preferred modern diagnostic tool. This technique reveals the cystic dilatation of the collecting tubules and the presence of calcifications in the medullary pyramids, a hallmark finding of MSK. Ultrasound may also be used, often showing characteristic bright, reflective areas in the inner kidney region.
Supporting laboratory tests include a 24-hour urine collection to analyze the chemical composition of the urine. Results frequently show elevated calcium levels and low levels of citrate, both of which promote stone formation. Blood tests assess overall kidney function and rule out other causes of kidney calcification.
Treatment Strategies and Long-Term Care
Treatment for Medullary Sponge Kidney focuses primarily on managing complications, especially preventing new kidney stones and UTIs. Stone prevention relies on aggressive fluid intake, aiming to produce at least two liters of urine daily to dilute stone-forming substances.
Dietary modifications are also important, including a reduction in sodium and animal protein intake. Medications are used to correct underlying metabolic abnormalities contributing to stone formation. For patients with high urinary calcium, thiazide diuretics can be prescribed to reduce calcium excretion.
If the urine is too acidic, potassium citrate supplements may be administered to raise the urinary pH and inhibit stone growth. Recurrent UTIs are managed with appropriate antibiotics. The overall outlook for people with MSK is positive, as the condition rarely progresses to chronic kidney failure unless severe infections or obstructions are left untreated.