Medullary Sponge Kidney
Medullary sponge kidney is a benign congenital disorder characterized by dilatation of collecting tubules in one or more renal papillae, affecting one or both kidneys.  (See the image below.) The term medullary sponge kidney is misleading because the affected kidney does not resemble a sponge. Tubular ectasia and cystic dilatation of the collecting ducts have been suggested as alternative names for the disorder; however, medullary sponge kidney is the most commonly used name.
Medullary sponge kidney is usually a benign condition, and patients can remain asymptomatic. Despite being a congenital disorder, medullary sponge kidney usually is not diagnosed until the second or third decade of life or later. [2, 3] See Presentation and Epidemiology.
Urinary tract infection (UTI)
Distal renal tubular acidosis (RTA; type 1 RTA)
Renal insufficiency (rarely)
For discussion of this disorder in children, see Pediatric Medullary Sponge Kidney.
The most important abnormality in medullary sponge kidney is the spherical, oval, or irregular dilatation of the medullary and papillary portions of the collecting ducts. The underlying abnormality responsible for this developmental anomaly is unknown.
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. 
Cysts in medullary sponge kidney 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 with columnar or cuboidal epithelium and rarely by transitional epithelium, which is caused by the effects of calculi. Closed cysts are lined with atrophic epithelium. The rest of the kidney usually is normal, unless pyelonephritis or renal obstruction complicates the course of the disease.
Most cases of medullary sponge kidney are sporadic. Theories suggest that dilatation of a collecting duct may occur, caused by occlusion by uric acid during fetal life or resulting from tubular obstruction due to calcium oxalate calculi secondary to infantile hypercalciuria.
Most patients with medullary sponge kidney have no family history of the condition, although there is a rare, familial, autosomal dominant form of the disease. A rare, autosomal recessive form is associated with Caroli disease.
The exact prevalence of medullary sponge kidney is unknown. The frequency of medullary sponge kidney 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 addition, medullary sponge kidney has been identified in 12-20% of patients who form calcium stones. 
Approximately 0.5% of patients undergoing intravenous urography are estimated to have medullary sponge kidney, while another 1% have papillary blush. No autopsy series have examined the prevalence of medullary sponge kidney specifically. In patients with nephrolithiasis, up to 20% may have mild degrees of medullary sponge kidney.
Women are affected by medullary sponge kidney more frequently than are men. In addition, while the overall incidence of calcium stones is 15-20% in medullary sponge kidney, the incidence is even higher in women, reaching 20-30%. In patients with nephrolithiasis, a higher relative prevalence of medullary sponge kidney occurs in females than in males.
Medullary sponge kidney is commonly diagnosed during the second or third decade of life. The mean age at diagnosis is approximately 27 years.
Medullary sponge kidney is usually a benign disorder without any serious morbidity or mortality. However, renal insufficiency may occur in as many as 10% of patients with the disorder.
Occasionally, patients can have recurrent nephrolithiasis, which can lead to significant morbidity. Very rarely, patients may develop renal failure as a result of repeated pyelonephritis or urinary tract obstruction.
In approximately 10% of patients with medullary sponge kidney, major morbidity is caused by repeatedly passing renal stones and by 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 medullary sponge kidney is estimated to pass 1.23 stones per year, compared with 0.66 stones per year in other people who form calcium stones.
Some physicians may encounter patients with medullary sponge kidney who describe severe, chronic renal pain but have no 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.
A grading system has been devised that could identify patients with medullary sponge kidney who are at an increased risk for complications based on intravenous urographic findings.  Higher grades correlated with more frequent symptomatic stone episodes, number of hospital admissions, and number of procedures required per year. Classifications were as follows:
Patients should receive educational materials, including handouts, informing them of the importance of maintaining volume expansion in order to maintain a daily urinary output in excess of 2 L. Handouts should indicate that medullary sponge kidney is a benign disorder and requires no specific therapy. A medullary sponge kidney fact sheet is available from the National Kidney Foundation.
Patients should also be informed of the possibility of a genetic role in their condition if other members of their families have a history of renal stones. For patient education information, see Blood in the Urine and Kidney Stones.
Fick GM, Gabow PA. Hereditary and acquired cystic disease of the kidney. Kidney Int. 1994 Oct. 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 Feb. 69(4):663-70. [Medline].
Yagisawa T, Kobayashi C, Hayashi T, et al. Contributory metabolic factors in the development of nephrolithiasis in patients with medullary sponge kidney. Am J Kidney Dis. 2001 Jun. 37(6):1140-3. [Medline].
Forster JA, Taylor J, Browning AJ, et al. A review of the natural progression of medullary sponge kidney and a novel grading system based on intravenous urography findings. Urol Int. 2007. 78(3):264-9. [Medline].
Levine E, Hartman DS, Meilstrup JW, et al. Current concepts and controversies in imaging of renal cystic diseases. Urol Clin North Am. 1997 Aug. 24(3):523-43. [Medline].
Palubinskas AJ. Renal pyramid structure opacification in excretory urography and its relation to medullary sponge kidney. Radiology. 1963 Dec. 81:963-70. [Medline].
Higashihara E, Nutahara K, Tago K, et al. Medullary sponge kidney and renal acidification defect. Kidney Int. 1984 Feb. 25(2):453-9. [Medline].
Janjua MU, Long XD, Mo ZH, Dong CS, Jin P. Association of medullary sponge kidney and hyperparathyroidism with RET G691S/S904S polymorphism: a case report. J Med Case Rep. 2018 Jul 9. 12 (1):197. [Medline]. [Full Text].
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 Sep. 5(9):1663-8. [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 Mar. 61(3):528-32. [Medline].
McPhail EF, Gettman MT, Patterson DE, Rangel LJ, Krambeck AE. Nephrolithiasis in Medullary Sponge Kidney: Evaluation of Clinical and Metabolic Features. Urology. 2011 Oct 17. [Medline].
Nephrolithiasis (calcium oxalate, calcium apatite)
Increased oxalate concentration
Tubular acidification defects
Hematuria (gross 10-20%, microscopic)
Acute pelvic obstruction
UTI, renal stones, or absence of both
Sterile pyuria common even in absence of stones
Presence of renal stones
Chronic kidney disease
Repeated urinary obstruction
Repeated pyelonephritis due to urease-producing organisms (Proteus)
Normal or enlarged kidney
Medullary nephrocalcinosis indicated by isolated, single or multiple precaliceal concretions or clusters of grapelike calcifications
Faint pyramidal striation
Papillary streaking or brushlike appearance
Precaliceal tubular dilatation filled with contrast
Papillary blush and multiple precaliceal dilatation
Bouquet of flowers
Ectasia of precaliceal tubules
*Findings limited to medullary pyramids
Amit K Ghosh, MD, DM, FACP, MBA Professor of Medicine, Mayo Medical School; Consultant in General Internal Medicine, Mayo Clinic
Amit K Ghosh, MD, DM, FACP, MBA is a member of the following medical societies: American College of Physicians-American Society of Internal Medicine, American Society of Nephrology, Minnesota Medical Association, Society of General Internal Medicine
Disclosure: Nothing to disclose.
Karthik Ghosh, MD Consultant, Associate Professor of Medicine, Department of Internal Medicine, Mayo Medical School
Karthik Ghosh, MD is a member of the following medical societies: American College of Physicians-American Society of Internal Medicine
Disclosure: Nothing to disclose.
Vecihi Batuman, MD, FASN Huberwald Professor of Medicine, Section of Nephrology-Hypertension, Tulane University School of Medicine; Chief, Renal Section, Southeast Louisiana Veterans Health Care System
Vecihi Batuman, MD, FASN is a member of the following medical societies: American College of Physicians, American Society of Hypertension, American Society of Nephrology, International Society of Nephrology, Southern Society for Clinical Investigation
Disclosure: Nothing to disclose.
Eleanor Lederer, MD Professor of Medicine, Chief, Nephrology Division, Director, Nephrology Training Program, Director, Metabolic Stone Clinic, Kidney Disease Program, University of Louisville School of Medicine; Consulting Staff, Louisville Veterans Affairs Hospital
Eleanor Lederer, MD is a member of the following medical societies: American Association for the Advancement of Science, American Federation for Medical Research, American Society for Biochemistry and Molecular Biology, American Society for Bone and Mineral Research, American Society of Nephrology, American Society of Transplantation, International Society of Nephrology, Kentucky Medical Association, National Kidney Foundation, and Phi Beta Kappa
Disclosure: Dept of Veterans Affairs Grant/research funds Research
Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Medscape Salary Employment
Medullary Sponge Kidney
Research & References of Medullary Sponge Kidney|A&C Accounting And Tax Services