AUTHOR AND EDITOR INFORMATION

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INTRODUCTION

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Background

Medullary sponge kidney (MSK) is a benign congenital disorder characterized by dilatation of collecting tubules in one or more renal papillae, affecting one or both kidneys. MSK is usually a benign condition, and patients can remain asymptomatic. Despite being a congenital disorder, MSK usually is not diagnosed until the second or third decade of life or later.

Among the most frequent complications are renal stone disease and urinary tract infection (UTI), but progression to renal failure is very rare. The diagnosis is usually made using excretory urography, which demonstrates the presence of radial striations in the renal papillae due to collection of contrast in dilated and cystic collecting tubules.

The name MSK is misleading because the affected kidney does not resemble a sponge. The names tubular ectasia and cystic dilatation of the collecting ducts have been suggested as alternatives; however, MSK is the most commonly used name for this disorder.

Pathophysiology

The most important abnormality in MSK is the spherical, oval, or irregular dilatation of the medullary and papillary portions of the collective ducts. The underlying abnormality responsible for this developmental anomaly is unknown. Despite a few cases where an autosomal dominant pattern of inheritance might be suggested, in most cases no family history of MSK is available.

The disease is bilateral in 70% of cases, and unilateral involvement of only one pyramid is uncommon. The dilated duct often communicates proximally with the collecting duct of normal size and shows a constriction of normal diameter at the point of communication with the calyx.

These cysts usually measure 1-7 mm and contain clear, jellylike material and, frequently, small calculi. The kidney may appear to be slightly enlarged when several papillae are involved.

Microscopically, communicating cysts are lined by columnar or cuboidal epithelium and rarely by transitional epithelium, which is caused by the effects of calculi. Closed cysts are lined by atrophic epithelium. The rest of the kidney usually is normal, unless pyelonephritis or renal obstruction complicates the course of the disease.

Frequency

United States

The exact prevalence of MSK is unknown. The frequency of MSK in the general population has been estimated to be 1 case per 5000 population, and the prevalence may be as much as 1 case per 1000 population in urology clinics. In patients who form calcium stones, MSK has been identified in 12-20% of them.

Approximately 0.5% of patients undergoing intravenous urography are estimated to have MSK, while another 1% have papillary blush. No autopsy series have examined the prevalence of this disease specifically.

In patients with nephrolithiasis, up to 20% may have mild degrees of MSK.

A familial form of MSK has also been reported, which is consistent with an autosomal dominant pattern of inheritance.

Mortality/Morbidity

The clinical course of MSK is usually benign. Very rarely, patients may develop renal failure as a result of repeated pyelonephritis or urinary tract obstruction.

• Major morbidity observed in approximately 10% of patients with MSK is due to repeatedly passing renal stones and to recurrent UTI. Complete obstruction of the kidney by renal stones is rare.
• Surgery is rarely required to remove the stones because they are usually very small and pass spontaneously.
• A patient with MSK is estimated to pass 1.23 stones per year compared to 0.66 stones per year in other people who form calcium stones.

Sex

• Women are affected more frequently than men are. The incidence of calcium stones is 15-20% in MSK. In women, the incidence is even higher, at 20-30%.
• A higher relative prevalence of MSK occurs in female patients compared to male patients with nephrolithiasis.

Age

• This condition is commonly diagnosed during the second or third decade of life.
• The mean age of patients diagnosed is approximately 27 years.

CLINICAL

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History

• Patients with MSK often are asymptomatic. Not infrequently, the diagnosis is made during radiological investigations, including abdominal radiograph and excretory pyelography, performed for other clinical situations. Table 1 depicts the common clinical symptoms of MSK.



• Hematuria is frequent, and gross hematuria may be present in 10-20% of cases. Gross hematuria usually results from pelvic obstruction due to stones; however, microscopic hematuria may be present with or without UTI.



• UTI is common in MSK, both with and without nephrolithiasis. Sterile pyuria also is common. Patients with MSK have more UTIs than other patients with nephrolithiasis, and the incidence of urinary infection is higher in women than in men.



• Recurrent nephrolithiasis is a major complication of MSK. The most common presenting symptom of this complication is renal colic, often accompanied by hematuria. Renal stones also result in UTI, urinary obstruction, and nephrocalcinosis. The stones in MSK are usually composed of calcium phosphate (apatite) and calcium oxalate.
• • MSK can occur in conjunction with other congenital abnormalities (see Congenital conditions associated with MSK).
  
  
  
  • As many as 10% of patients with hemihypertrophy can have MSK, and as many as 25% of patients with MSK have hemihypertrophy.
  
  
  
  • When associated with MSK, Beckwith-Wiedemann syndrome (high birth weight, macroglossia, omphalocele, visceromegaly, mental retardation, cysts in adrenal cortex, enlarged kidneys, MSK, and hemihypertrophy) has a high tumor rate, especially Wilms tumor, adrenal gland cancer, and hepatoblastoma.

   

  Table 1. Clinical Features of Medullary Sponge Kidney and Pathophysiological Correlation

  Frequency	Clinical Findings	Pathophysiology
  Common*	Nephrolithiasis (calcium oxalate, calcium apatite)	Hypercalciuria Increased oxalate concentration Tubular acidification defects Hypocitraturia
  	Hematuria (gross 10-20%, microscopic)	Acute pelvic obstruction UTI, renal stones, or absence of both
  	UTI	Sterile pyuria common even in absence of stones Presence of renal stones
  Rare	Chronic renal failure	Repeated urinary obstruction Repeated pyelonephritis due to urease-producing organisms (Proteus)

  *Asymptomatic

• Congenital conditions associated with MSK
  
  
  • Anodontia
  
  
  
  • Autosomal dominant polycystic kidney
  
  
  
  • Beckwith-Wiedemann syndrome
  
  
  
  • Caroli syndrome
  
  
  
  • Congenital hemihypertrophy
  
  
  
  • Congenital pyloric stenosis
  
  
  
  • Distal renal tubular acidosis
  
  
  
  • Ehlers-Danlos syndrome
  
  
  
  • Horseshoe kidney
  
  
  
  • Marfan syndrome
  
  
  
  • Parathyroid adenomas
  
  
  
  • Renal artery stenosis
  
  
  
  • Ureteral duplication

Physical

• Usually no physical findings are present except for hematuria.
  
  
  • Renal colic may occur.
  
  
  
  • Costovertebral angle tenderness occurs in cases of pyelonephritis or ureteral obstruction by a calculus.
  
  
  
  • Hemihypertrophy is present in 25% of cases.
  
  
  
  • Other signs of associated congenital disorders may be present (see Congenital conditions associated with MSK).

Causes

• Most cases of MSK are sporadic.
• Theories suggest that dilatation of a collecting duct may occur, caused by occlusion by uric acid during fetal life or caused by tubular obstruction due to calcium oxalate calculi secondary to infantile hypercalciuria.
• A rare autosomal dominant (AD) form is inherited in familial cases of MSK.
• A rare autosomal recessive (AR) form is associated with Caroli disease.

DIFFERENTIALS

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Other Problems to be Considered

Autosomal recessive polycystic kidney disease
Caliceal diverticula
Pyelovenous backflow in acute ureteral obstruction
Renal tuberculosis

WORKUP

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Lab Studies

• The diagnosis of MSK is usually suspected in patients presenting with renal calculi, hematuria, or multiple UTIs. Prior clinical suspicion of MSK is important because it helps in ordering the most relevant radiological tests.
• Metabolic acidosis may occur secondary to renal tubular acidosis ([RTA] type 1 or distal) and is usually diagnosed during acidification test as an inability to reduce the pH of urine to less than 5.3. Incomplete distal RTA is more common than frank type 1 RTA and so might be missed on usual electrolyte testing because incomplete RTA does not show resting metabolic acidosis. However, incomplete distal RTA has been known to contribute to stone formation.
• Defective urinary concentrating ability is the inability to achieve maximal urine osmolality (ie, 900 mOsm/kg or greater) with water restriction. However, the defect in urinary concentrating ability usually is mild and patients are asymptomatic.
• Hypercalciuria may occur in 30-50% of cases.
• A higher incidence of hypocitraturia occurs in MSK.
• Patients with MSK nephrolithiasis who are hypercalciuric have a higher incidence of renal leak–type hypercalciuria than do patients with hypercalciuric calcium stones without MSK.

Imaging Studies

• Diagnosis is usually confirmed by findings on excretory urography (see Table 2).
• • Excretory urography reveals radial linear striations in the papillae. These are often referred to as "brushlike" patterns of the affected papillae. Cystic collections of contrast media in the ectatic collecting duct are referred to as "bunches of grapes" or "bouquets of flowers."
  
  
  
  • High-quality excretory urography with renal tomograms obtained before and after injection of contrast medium and then every 4 minutes during the next 20 minutes has been described as the most accurate method of identifying MSK. The diagnosis of MSK could be missed if the preparation is suboptimal.
• Abdominal plain film may reveal nephrocalcinosis.



• CT scan can reveal papillary calcification or hyperdense papillae but usually is not as sensitive as excretory urography (see Images 1-2). CT scan can also be used to help identify other renal abnormalities, such as associated cysts, horseshoe kidney, renal abscess, and papillary necrosis. Helical CT scan has recently been demonstrated to improve the definition of the abnormalities in MSK.



• Ultrasound of the kidney in MSK may reveal calcification in the medullary region. In earlier cases of MSK without calcification, the papillae may appear bright on ultrasound.

  Table 2. Radiological Appearance in Medullary Sponge Kidney

  Radiologic Test	Appearance
  Plain radiograph	Normal or enlarged kidney Medullary nephrocalcinosis indicated by isolated, single or multiple precaliceal concretions or clusters of grapelike calcifications
  Excretory urogram*	Papillary blush Faint pyramidal striation Papillary streaking or brushlike appearance Precaliceal tubular dilatation filled with contrast Papillary blush and multiple precaliceal dilatation Bouquet of flowers
  CT scan	Papillary calcification Hyperdense papilla Ectasia of precaliceal tubules

  *Findings limited to medullary pyramids

TREATMENT

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Medical Care

• Asymptomatic adults with MSK
• • Advise patients about the benign nature of MSK, and inform them about the possibility of renal calculi and UTIs due to MSK.

  • Obtaining periodic urinalysis and abdominal radiographs is recommended, although guidelines for the frequency of radiological surveillance in asymptomatic adults are unclear.

• Patients with MSK and recurrent nephrolithiasis: Patients are advised to drink plenty of fluids to have a urine output in excess of 2 liters per day. A 24-hour urine collection for potential kidney stone risk factors (eg, calcium, citrate, uric acid, magnesium, sodium, oxalate, phosphate) can be very helpful in treating the metabolic factors contributing to nephrolithiasis.

• Asymptomatic children with MSK: Conduct regular surveillance for Wilms tumor and other abdominal tumors.

• Patients with MSK and distal RTA: Adjust the dosage and timing of potassium citrate supplementation to increase the urinary pH to a maximum of 7.0-7.2. Overalkalinization can lead to calcium phosphate precipitation and stone formation.

• Patients with MSK and microscopic hematuria: In rare instances, this condition may be associated with nephrocalcinosis. However, other causes of microhematuria, such as bladder cancer, renal tumors, and benign prostatic hypertrophy, must be excluded and often require a urology referral.

• Patients with MSK and gross hematuria
• • Bladder tumors and pelvic obstruction must be ruled out aggressively.

  • Children with MSK and gross hematuria must be evaluated for Wilms tumor.

• Patients with MSK and UTI
• • MSK in these patients must be treated aggressively until the urine is clear.

  • Proteus infection can lead to formation of struvite stones and requires aggressive antibacterial therapy.

Surgical Care

• Patients with MSK and symptomatic nephrolithiasis
• • These patients can be treated with extracorporeal shock wave lithotripsy (ESWL), percutaneous surgery, or ureteroscopy.
  • Partial nephrectomy must be performed in severe cases with segmental renal involvement.

• Patients with MSK and urosepsis: Rarely, unilateral nephrectomy is performed if a severe case of urosepsis is present.

Consultations

• A consultation with a urologist may be essential in patients with MSK presenting with recurrent nephrolithiasis or acute urinary tract obstruction.



• Patients with associated congenital abnormalities (see Congenital conditions associated with MSK) may also need urological surveillance.

Diet

• Patients with MSK and hypercalciuria should avoid a high-protein diet.
• Patients are advised to drink plenty of fluids to generate a urine output in excess of 2 liters per day.

Activity

No restriction on activity is necessary.

MEDICATION

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Thiazide therapy, in addition to restriction of animal protein intake, aggressive diuresis may be helpful for patients with MSK and hypercalciuria.

Drug Category: Diuretics

The primary role of thiazide diuretics is to decrease hypercalciuria.

FOLLOW-UP

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Further Outpatient Care

• Asymptomatic adults with MSK
• • Advise patients about the benign nature of MSK, and inform them about the possibility of renal calculi and UTIs due to MSK.
  • Obtaining periodic urinalysis and abdominal radiographs is recommended, although guidelines for the frequency of radiological surveillance in asymptomatic adults are unclear.

• Asymptomatic children with MSK: Conduct regular surveillance for Wilms tumor and other abdominal tumors.
• Symptomatic patients with MSK
• • These patients must be evaluated routinely using a renal function test, radiological surveillance, and ultrasound.
  • Urinary pH of more than 5.3 in adults and 5.6 in children in the setting of non–anion gap metabolic acidosis can indicate the presence of distal RTA (type 1). However, urinary pH can also be alkaline in the presence of UTI because of urea splitting organisms. The diagnosis of this disorder can be established simply by raising the plasma bicarbonate concentration toward the reference range (ie, 18-20 mEq/L) with an intravenous infusion of sodium bicarbonate at a rate of 0.5-1.0 mEq/kg/h. The fractional excretion of bicarbonate is less than 3%, and the urine pH remains relatively stable in type 1 disease. Raising the plasma bicarbonate concentration to 18-20 mEq/L has little effect on bicarbonate excretion in type 1 RTA because no defect in proximal reabsorptive capacity exists.
  • The presence of urinary infection with urea splitting organisms can lead to struvite stones and subsequent renal insufficiency. This must be identified and promptly treated.

• Patients with MSK and other renal or congenital abnormalities must be evaluated for oncological tumors.

Complications

• Renal stones
• Hematuria
• Distal RTA (type 1 RTA)
• Rarely, renal insufficiency

Prognosis

• Usually MSK is a benign disorder without any serious morbidity or mortality. However, renal insufficiency may occur in as many as 10% of patients with MSK.
• Occasionally, patients can have recurrent nephrolithiasis, which can lead to significant morbidity.
• If any suggestion of history of MSK in other family members exists, further investigations may be indicated to unravel the genetic pattern of transmission.
• Some physicians may encounter patients with MSK who claim severe, chronic renal pain without any manifestation of infection, stones, or obstruction. The source of this pain is unclear. These patients may be treated best by physicians comfortable with chronic pain management.

Patient Education

• Patients should receive educational materials, including handouts, informing them about the importance of maintaining volume expansion to maintain a urine output in excess of 2 liters per day. Handouts should indicate that MSK is a benign disorder and requires no specific therapy.
• Patients with MSK can have recurrent stone disease and UTI that occasionally result in gross hematuria.
• Patients with MSK should be informed of the possibility of a genetic role in their condition if other members of their families have a history of renal stones.
• Young children with MSK may need regular follow-up and evaluation because incidence of Wilms tumor and other abdominal tumors is increased in this group.
• For excellent patient education resources, visit eMedicine's Kidneys and Urinary System Center. Also, see eMedicine's patient education article Blood in the Urine.

MISCELLANEOUS

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Medical/Legal Pitfalls

• Confusing MSK for other diagnoses mentioned under Differentials leads to needless investigation.
• Failure to properly treat calculi may lead to renal impairment.
• Failure to clear urinary infection may lead to renal impairment. Hypercalciuria in patients with MSK could occur due to impaired calcium reabsorption in the damaged collecting tubules.
• Adults with MSK presenting with gross hematuria should be investigated properly for additional causes of hematuria such as bladder tumors.

Special Concerns

• Children with MSK identified in childhood must be evaluated for other urological abnormalities and must undergo surveillance for future urological and abdominal tumors.

MULTIMEDIA

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Media file 1:  Unenhanced coronal volume-rendered (VR) CT image of the kidneys demonstrates 2 small calculi in the mid portion of the right kidney and 2 small calculi in the lower pole of the left kidney (arrowheads). A large low-density lesion in the lower pole of the right kidney and a small low-density lesion in the upper pole of the left kidney (short arrows) were shown to represent benign simple renal cysts on the contrast enhanced CT images.Image courtesy of Dr. Terri J. Vrtiska, Consultant, Department of Radiology, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
	View Full Size Image
Media type:  CT

Media file 2:  IVU-like VR CT image of both kidneys demonstrates brushlike densities throughout multiple papillae of both kidneys consistent with renal tubular ectasia. Correlation of the stone disease (Image 1) with the ectatic tubules is diagnostic of medullary sponge kidney.Image courtesy of Dr. Terri J. Vrtiska, Consultant, Department of Radiology, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
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Media type:  CT

REFERENCES

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• Authors and Editors
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• Fick GM, Gabow PA. Hereditary and acquired cystic disease of the kidney. Kidney Int. Oct 1994;46(4):951-64. [Medline].
• Gambaro G, Feltrin GP, Lupo A, et al. Medullary sponge kidney (Lenarduzzi-Cacchi-Ricci disease): a Padua Medical School discovery in the 1930s. Kidney Int. 2006;69(4):663-70.
• Higashihara E, Nutahara K, Tago K, et al. Medullary sponge kidney and renal acidification defect. Kidney Int. Feb 1984;25(2):453-9. [Medline].
• Lang EK, Macchia RJ, Thomas R, et al. Improved detection of renal pathologic features on multiphasic helical CT compared with IVU in patients presenting with microscopic hematuria. Urology. 2003;61(3):528-32.
• Levine E, Hartman DS, Meilstrup JW, et al. Current concepts and controversies in imaging of renal cystic diseases. Urol Clin North Am. Aug 1997;24(3):523-43. [Medline].
• Palubinskas AJ. Renal pyramid structure opacification in excretory urography and its relation to medullary sponge kidney. Radiology. Dec 1963;81:963-70. [Medline].

Article Last Updated: Oct 6, 2006