AUTHOR INFORMATION

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Authored by Howard Trachtman, MD, Program Director, Pediatrics Research, Schneider Children's Hospital, Professor, Department of Pediatrics, Division of Nephrology, Albert Einstein College of Medicine

Howard Trachtman, MD, is a member of the following medical societies: American Society of Hypertension, American Society of Nephrology, American Society of Pediatric Nephrology, and Society for Pediatric Research

Edited by Uri S Alon, MD, Director of Research and Education, Children's Mercy Hospital of Kansas City; Professor, Department of Pediatrics, Division of Pediatric Nephrology, University of Missouri at Kansas City; Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine.com, Inc; Frederick J Kaskel, MD, PhD, Director of the Division and Training Program in Pediatric Nephrology, Vice Chair, Department of Pediatrics, Montefiore Medical Center and Albert Einstein School of Medicine; Daniel Rauch, MD, FAAP, Director, Pediatric Hospitalist Program, Associate Professor, Department of Pediatrics, New York University School of Medicine; and Craig B Langman, MD, Professor, Department of Pediatrics, Northwestern University School of Medicine; Head, Division of Kidney Diseases, Children's Memorial Hospital of Chicago

Author's Email:	Howard Trachtman, MD
Editor's Email:	Uri S Alon, MD

eMedicine Journal, December 8 2005, VOLUME 6, Number 12

INTRODUCTION

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Background: Medullary sponge kidney (MSK) is likely the result of an abnormality in renal development as evidenced by the occasional presence of embryonal tissue in the affected papillae. Medullary sponge kidney is characterized by ectasia and cystic formation in the medullary collecting duct. This characterization contrasts with autosomal recessive polycystic kidney disease and with autosomal dominant polycystic kidney disease, in which cysts predominantly develop along the cortical collecting tubule or the entire nephron, respectively. Medullary cysts give the kidney the gross anatomic appearance of a sponge. In the absence of hematuria, renal calculi, or infection, the disease is an asymptomatic nonprogressive condition.

Pathophysiology: The kidney is the primary organ affected. Ectasia and cystic malformation are present along the intrapyramidal or intrapapillary portion of the medullary collecting duct. Cysts may be heterogeneous in size within one kidney and between the 2 kidneys, ranging in size from 1-3 mm. Cysts may communicate and often contain spherical concretions composed of apatite.

Although the cause of medullary sponge kidney is unknown, family occurrence suggests a genetic component. Pathological studies suggest that medullary sponge kidney is due to an obstruction of the fetal-collecting duct or to a structural defect caused by hypercalciuria. The presence of embryonal remnant tissue in some cases links the condition to a congenital developmental defect in this nephron segment.

Medullary sponge kidney may be part of other syndromes and conditions such as Beckwith-Wiedemann syndrome (BWS), hemihypertrophy, Caroli disease, Ehlers-Danlos syndrome, Marfan syndrome, and pyloric stenosis. Medullary sponge kidney may occur in up to 12.5% of cases of BWS, if congenital hemihypertrophy is part of the clinical picture.

Frequency:

• In the US: Prevalence is 1 case per 5,000-20,000 population. Medullary sponge kidney may be detected in 0.5-1% of asymptomatic individuals who undergo renal imaging studies for assorted clinical indications.

• Internationally: Evidence indicates that worldwide incidence of medullary sponge kidney is similar to that in the United States.

Mortality/Morbidity: Morbidity or mortality is not directly related to medullary sponge kidney. In the absence of hematuria, urinary tract infection, or renal calculi, medullary sponge kidney is usually a nonprogressive asymptomatic condition.

• Under normal conditions, patients may have a mild urinary-concentrating defect or low-grade proteinuria.

• Patients are at higher risk of developing calcium oxalate/apatite or struvite renal calculi. Factors that may contribute to the susceptibility to recurrent calcium urolithiasis include: (1) urine stasis; (2) incomplete renal tubular acidosis (RTA) with a mild defect in urinary acidification and increased urine pH levels; (3) hypocitric aciduria; and (4) hypercalciuria. Patients are usually aged 20-50 years at presentation, although the condition may occur in children younger than 5 years. Up to 20% of adults with kidney stones may have medullary sponge kidney; the corresponding figure in children is unknown. Among patients with kidney stones, hypercalciuria may occur in 40-50%, and recurrent gross hematuria may occur in 10-20%.

• Although no evidence indicates that risk of urinary tract infections (UTIs) is higher in patients with medullary sponge kidney, up to 5% of males and 35% of females have a UTI. These patients do not have an increased frequency of concomitant structural anomalies (eg, vesicoureteral reflux) to account for the occurrence of UTI.

Race: No epidemiologic data indicate that incidence varies among racial or ethnic subgroups.

Sex: No evidence indicates that the frequency differs between the sexes. Fewer than 5% of cases are familial, and a clear genetic basis for medullary sponge kidney has not been established. The only genetic pattern observed in select pedigrees is an autosomal dominant type of transmission. Medullary sponge kidney appears to be somewhat more severe in women; the incidence of renal calculi and UTIs in women is higher than in men.

Age: Symptoms occur primarily in adults aged 20-50 years; however, infants as young as 2 years and adolescents have shown clinical symptoms.

CLINICAL

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History:

• Patients are usually asymptomatic.



• Patients may develop microhematuria or signs and symptoms of gross hematuria, renal stone development, or UTI.

Physical:

• Although physical examination findings are usually normal, as many as 25% of patients have hemihypertrophy, and 10% of patients with hemihypertrophy may have medullary sponge kidney, although no explanation for this association exists. Children with medullary sponge kidney and hemihypertrophy may have an incomplete form of Beckwith-Wiedemann syndrome (BWS). Moreover, because of the high risk of malignancies in patients with BWS, these patients should be screened periodically for malignancies, including abdominal tumors.



• Urinalysis findings may show hematuria, low-grade proteinuria, and mild acidification and concentrating defects.

Causes: The cause of medullary sponge kidney is unknown.

• No cases link medullary sponge kidney to a drug or environmental exposure.



• Cases occasionally occur in a familial pattern consistent with autosomal dominant transmission.

DIFFERENTIALS

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Polycystic Kidney Disease

Other Problems to be Considered:

Calyceal diverticulum
Papillary necrosis
Other causes of nephrocalcinosis

WORKUP

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Lab Studies:

• Urinalysis


• • Assessment of urinary calcium excretion
  
  
  
  • Urine culture
  
  
  
• In patients with medullary sponge kidney and hemihypertrophy, serial screening should be performed to exclude malignancies, including abdominal tumors.

Imaging Studies:

• Intravenous pyelography demonstrates radial, linear striations in the papillae or cystic collections of contrast material in ectatic collecting ducts. The result is a characteristic blushlike pattern to the papillae, the so-called "bouquet of flowers" or "paintbrush" appearance.



• Renal ultrasonography and CT scans are unnecessary except to distinguish medullary sponge kidney from papillary necrosis or autosomal dominant polycystic kidney disease.



• The role of MRI is unknown.

Other Tests:

• Appropriate workup is needed if medullary sponge kidney appears to be associated with another condition, such as hemihypertrophy or pyloric stenosis, or is part of a syndrome, such as Marfan or Ehlers-Danlos. This testing should be performed to exclude the presence of a malignancy.

Procedures:

• No additional, specific, diagnostic procedures are warranted for diagnostic evaluation.

TREATMENT

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Medical Care: No specific treatment is warranted.

• If hypercalciuria-associated kidney stone disease is present, use of thiazide diuretics or other measures to reduce the hypercalciuria may be justified.



• Renal stones are managed in the same way as in individuals without medullary sponge kidney.



• Treat UTIs with standard courses of antibiotics. Prophylactic antibiotics may help patients with medullary sponge kidney and recurrent UTIs.



• In patients with hemihypertrophy, serial screening should be performed to exclude a malignancy.

Surgical Care: Surgery is not needed for most patients with medullary sponge kidney.

Diet: Although decreased dietary calcium intake may decrease urinary calcium excretion, concern has been expressed that it might also result in skeletal undermineralization. Decreased sodium intake and increased potassium intake may improve urinary calcium excretion by themselves and are recommended in patients taking thiazide diuretics.

Activity: Because medullary sponge kidney is a nonprogressive condition with small medullary cysts, restriction of physical activity is unnecessary.

MEDICATION

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No medications are warranted for routine care. Use antibiotics in accordance with standard prescription practices to treat UTIs (see Urinary Tract Infection). Consider thiazide diuretics in patients with hypercalciuric urolithiasis.

Drug Category: Diuretics -- Thiazide diuretics may be prescribed to patients who have medullary sponge kidney and hypercalciuria, with or without urolithiasis.

Drug Name	Hydrochlorothiazide (Esidrix, HydroDIURIL, Microzide) -- Decreases hypercalciuria and reduces risk of urolithiasis by promoting calcium reabsorption in distal convoluted tubule.
Adult Dose	50-100 mg/d PO
Pediatric Dose	1-2 mg/kg/d PO
Contraindications	Documented hypersensitivity; anuria or renal decompensation
Interactions	Thiazides may decrease effects of anticoagulants, antigout agents, and sulfonylureas; thiazides may increase toxicity of allopurinol, anesthetics, antineoplastics, calcium salts, loop diuretics, lithium, diazoxide, digitalis, amphotericin B, and nondepolarizing muscle relaxants
Pregnancy	C - Safety for use during pregnancy has not been established.
Precautions	Caution in patients with renal disease, hepatic disease, gout, diabetes mellitus, or erythematosus

FOLLOW-UP

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Further Inpatient Care:

• Further inpatient care is needed only for patients with renal stones or severe UTI.



• Serial screening for malignancies is required in patients with medullary sponge kidney and hemihypertrophy.

Further Outpatient Care:

• Periodic screening for hematuria, bacteriuria, and kidney stones

In/Out Patient Meds:

• Medications are needed only for patients with UTIs or kidney stones.

Complications:

• Gross hematuria



• Renal stones



• UTIs

Prognosis:

• Medullary sponge kidney is a nonprogressive disease and has no adverse impact on renal or patient survival.

Patient Education:

• Inform the patient of possible complications.



• 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:

• Overtreatment of patients with medullary sponge kidney is a pitfall.



• Failure to discriminate medullary sponge kidney, a nonprogressive disease, from forms of cystic kidney disease that have a worse prognosis is a pitfall. Autosomal recessive polycystic kidney disease is the disease most commonly mistaken for medullary sponge kidney.

TEST QUESTIONS

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CME Question 1: An 18-year-old woman presents after an episode of gross hematuria. An intravenous pyelogram reveals characteristic findings of medullary sponge kidney. Which of the following is not a risk for this patient?

A: Urinary tract infection
B: Recurrent gross hematuria
C: Kidney stones
D: Chronic renal failure
E: Hypercalciuria

The correct answer is D: Medullary sponge kidney is a nonprogressive disease. It is an abnormality in renal development with ectasia and cystic formation in the medullary collecting duct. Medullary cysts give the kidney the gross anatomic appearance of a sponge.

CME Question 2: A 19-year-old woman with medullary sponge kidney presents with a fever, chills, urgency, and back pain. Which of the following is the most likely explanation?

A: Bladder outlet obstruction
B: Urinary tract infection
C: Kidney stone
D: Renal tumor
E: Ureteral pelvic junction obstruction

The correct answer is B: Urinary tract infections are a known complication of medullary sponge kidney. The clinical presentation of the infection in patients with medullary sponge kidney is the same as that in patients without medullary sponge kidney.

Pearl Question 1 (T/F): Autosomal recessive polycystic kidney disease (ARPKD) is the disease most commonly mistaken for medullary sponge kidney.

The correct answer is True: ARPKD is the clinical entity most often mistaken for medullary sponge kidney. In medullary sponge kidney, cysts appear in the medullary collecting duct, giving the kidney the gross anatomic appearance of a sponge. In ARPKD, cysts predominantly arise along the cortical collecting tubule.

Pearl Question 2 (T/F): Chronic kidney failure and hypertension are the 2 most common complications of medullary sponge kidney.

The correct answer is False: Urinary tract infections and renal stones are the 2 most common complications of medullary sponge kidney. Up to 5% of males and 35% of females have a urinary tract infection. Up to 20% of adults with kidney stones may have medullary sponge kidney; the corresponding figure in children is unknown.

Pearl Question 3 (T/F): Medullary sponge kidney has a worse prognosis than medullary cystic disease.

The correct answer is False: Medullary sponge kidney is a nonprogressive disorder, unlike medullary cystic disease, which is associated with a steady decline in kidney function and the need for dialysis or transplantation.

Pearl Question 4 (T/F): No treatment is usually needed for patients with medullary sponge kidney.

The correct answer is True: Patients with medullary sponge kidney are generally asymptomatic and require no specific treatment.

BIBLIOGRAPHY

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• Abeshouse BS, Abeshouse GA: Sponge kidney: a review of the litrature and a report of five cases. J Urol 1960 Aug; 84: 252-67[Medline].
• Avner ED: Medullary Sponge Kidney. In: Greenber A, Cheung AK, Coffman TM, et al, eds. NKF Primer on Kidney Disease. 1997.
• Osther PJ, Mathiasen H, Hansen AB, et al: Urinary acidification and urinary excretion of calcium and citrate in women with bilateral medullary sponge kidney. Urol Int 1994; 52(3): 126-30[Medline].
• Patriquin HB, O'Regan S: Medullary sponge kidney in childhood. AJR Am J Roentgenol 1985 Aug; 145(2): 315-9[Medline].

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