Demetrius H. Bagley, MD, FACS
Kelly A. Healy, MD
BASICS
DESCRIPTION
Medullary sponge kidney (MSK) consists of developmental abnormalities of the kidneys with ectatic or dilated terminal collecting ducts and associated medullary cysts
EPIDEMIOLOGY
Incidence
N/A
Prevalence
• Estimated at 1 in 5,000–20,000 in the general population
• Occurs more frequently in stone formers ranging from 5 to 20%
• Identification and therefore recognized incidence of MSK may be decreasing since it depends on radiographic contrast studies to detect the dilated collecting ducts
RISK FACTORS
N/A
Genetics
Many cases may be sporadic:
• Increasing evidence suggests inheritability of the disorder, possibly of an autosomal dominance based on familial studies
• Mutations in glial cell–derived neurotropic factor (GDNF) account for roughly 12% of MSK cases (1)[B]
PATHOPHYSIOLOGY
• Dilated collecting ducts and medullary pyramidal cysts which may actually represent ectatic ducts
• Dilated ducts may be filled with calcium apatite crystal
• Distal renal tubular acidosis (DRTA) (33–40%)
• Hypercalciuria (9–100%)
• Hypocitraturia (19–83%)
ASSOCIATED CONDITIONS
• Renal calculi
• Urinary tract infections (UTIs)
• Hypocitraturia and hypercalciuria (as noted above)
• Reduced bone density (2)[B]
GENERAL PREVENTION
• This developmental condition cannot be prevented
• Secondary complications (infections, urolithiasis) can be prevented by appropriate measures
DIAGNOSIS
HISTORY
• Many patients are asymptomatic and are diagnosed incidentally on contrast studies
• Pain associated with renal/ureteral calculi
• Pain without associated obstructing calculi
• Hematuria, microscopic or gross
PHYSICAL EXAM
• May be normal without associated findings
• May have flank tenderness, especially among those with episodes of pain
DIAGNOSTIC TESTS & INTERPRETATION
Lab
• Serum electrolytes usually are normal except with significant distal renal tubular acidosis (DRTA) in which serum bicarbonate and potassium may be low
• Urinary study
– Urinalysis
Microhematuria or pyuria
– 24-hr urine collections
– May show hypercalciuria (9–100%)
– Hypocitraturia in 19–83%
• Stone composition commonly calcium oxalate in 33% (pure) to 63% (mixed)
• Most common mineral
– Calcium oxalate monohydrate
• Calcium phosphate predominate in 63–67%
Imaging
• Diagnosis based on blush or “paint brush” appearance of dilated collecting ducts after contrast administration
• Intravenous urogram (IVU) or excretory urogram (EXU)
– Multiple calcifications may appear in dilated ducts as nephrocalcinosis. Often seen on scout film and appear to reside within renal parenchyma
– Plain film may be useful to detect the appearance of new calcifications
– Typically bilateral but can occur on one side or in a single renal pyramid
• CT
• Noncontrast CT (NCCT) has largely replaced contrast studies (IVU, EXU) in the diagnosis urinary calculus disease
– May demonstrate multiple calcifications and possibly localize them to the renal pyramids (3)[B]
– CT urogram (CTU) may be most useful imaging study
– After the injection of contrast for CTU, a blush of the involved papillae may be seen
• Renal ultrasonography (RUS)
– Nondiagnostic for MSK in adults
– Does not accurately distinguish intraparenchymal from intraluminal calcifications
– May be used to detect obstruction in the symptomatic patient
Diagnostic Procedures/Surgery
• Endoscopy, specifically ureteroscopy differentiates intraluminal from intraparenchymal calcifications (4)[B]
• 24-hr urine studies to identify metabolic abnormalities
Pathologic Findings
• Typical sponge appearance of the medulla results from the dilated intrapapillary collecting ducts and small medullary cysts
– Calcifications may be found in the dilated collecting ducts
DIFFERENTIAL DIAGNOSIS
• Dent disease
• Other rare abnormalities of calcium phosphate metabolism
• Primary hyperparathyroidism
• RTA
TREATMENT
GENERAL MEASURES
• Majority of asymptomatic patients can be observed
• General stone clinic measures including high fluid intake should be maintained
• Alkalinization with potassium citrate appears to be of value
• Other abnormalities such as hypercalciuria which do not resolve should be treated specifically
• Treat UTIs as necessary
MEDICATION
• Potassium citrate is employed in patients with hypocitraturia (5)
• Thiazide diuretics are used in patients with stones and nonresponsive hypercalciuria
• Specific antibiotics are indicated for the treatment of UTIs
– Suppressive antibiotics may be necessary in patients with persistent or multiply recurrent UTIs
Second Line
N/A
SURGERY/OTHER PROCEDURES
• Shock wave lithotripsy has been utilized for treatment of collecting duct stones that can be distinguished from nephrocalcinosis as well as symptomatic intraluminal calculi
• Endoscopy with ureteroscopy or occasionally percutaneous nephrostolithotomy can treat collecting system stones and unroof mucosa to remove obvious and accessible collecting duct stones
• SWL and endoscopy have been advocated to reduce the frequency of symptomatic episodes but is unproven
ADDITIONAL TREATMENT
Radiation Therapy
N/A
Additional Therapies
N/A
Complementary & Alternative Therapies
N/A
ONGOING CARE
PROGNOSIS
• Urinary calculi are the most common risk but can be followed and also may be controlled with medical treatment
• Recurrent UTIs can usually be treated
• Development of renal failure is very uncommon
COMPLICATIONS
• Stone formation and subsequent obstruction
• Recurrent/chronic flank pain
• UTI
FOLLOW-UP
Patient Monitoring
• Imaging at every 6–12 mo in stone formers to evaluate for change in existing stones or appearance of new ones
• In some patients, renal ultrasound (RUS) can be used to monitor stones and avoid radiation
• 24-hr urine collections are used to monitor stone risk factors during treatment for urinary abnormalities
• Serum studies are used to monitor changes related to medication
Patient Resources
National Kidney and Urologic Diseases
Information Clearinghouse (NKUDIC) http://kidney.niddk.nih.gov/kudiseases/pubs/medullaryspongekidney/
REFERENCES
1. Torregrossa R, Anglani F, Fabris A, et al. Identification of GDNF gene sequence variations in patients with medullary sponge kidney disease. Clin J Am Soc Nephrol. 2010;5:1205–1210.
2. Fabris A, Bernich P, Abaterusso C, et al. Bone disease in medullary sponge kidney and effect of potassium citrate treatment. Clin J Am Soc Nephrol. 2009;4:1974–1979.
3. Maw AM, Megibow AJ, Grasso M, et al. Diagnosis of medullary sponge kidney by computed tomographic urography. Am J Kidney Dis. 2007;50:146–150.
4. Miller NL, Humphreys MR, Coe FL, et al. Nephrocalcinosis: Re-defined in the era of endourology. Urol Res. 2010;38:421–427.
5. Fabris A, Lupo A, Bernich P, et al. Long term treatment with potassium citrate and renal stones in medullary sponge kidney. Clin J Am Soc Nephrol. 2010;5:1663–1668.
ADDITIONAL READING
• Fabris A, Anglani F, Lupo A, et al. Medullary sponge kidney: state of the art. Nephrol Dial Transplant. 2013;28:1111–1119.
• McPhail EF, Gettman MT, Patterson DE, et al. Nephrolithiasis in medullary sponge kidney: Evaluation of clinical and metabolic features. Urology. 2012;79:277–281.
See Also (Topic, Algorithm, Media)
• Dent Disease
• Distal Renal Tubular Acidosis
• Hypercalciuria
• Medullary Cystic Kidney Disease (MCKD)
• Medullary Sponge Kidney (MSK) Image
• Nephrocalcinosis
• Polycystic Kidney Disease
• Urolithiasis, Adult
CODES
ICD9
• 588.89 Other specified disorders resulting from impaired renal function
• 592.0 Calculus of kidney
• 753.17 Medullary sponge kidney
ICD10
• N20.0 Calculus of kidney
• N25.89 Oth disorders resulting from impaired renal tubular function
• Q61.5 Medullary cystic kidney
CLINICAL/SURGICAL PEARLS
• Be suspicious of MSK in patients with multiple papillary calculi.
• Use contrast study for diagnosis.
• Search for metabolic defects.
• Treat metabolic factors in stone formers.
• Consider treatment of renal stones in patients with recurrent symptomatic stones.
• Significant benefit in endoscopic inspection and treatment.