You are in: eMedicine Specialties > Radiology > GENITOURINARY Medullary Sponge KidneyArticle Last Updated: May 8, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 11
  Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, LRCP, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad National Guard Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia Ali Nawaz Khan is a member of the following medical societies: American Institute of Ultrasound in Medicine, Radiological Society of North America, Royal College of Physicians, Royal College of Physicians and Surgeons of the United States, Royal College of Radiologists, and Royal College of Surgeons of England Coauthor(s): Muthusamy Chandramohan, MBBS, DMRD, FRCR, Consultant Radiologist, Bradford Teaching Hospitals, UK; Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute Editors: Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Arnold C Friedman, MD, FACR, Associate Chairman, Department of Radiology, University of Florida Health Science Center; Chief, Department of Radiology, Shands-Jacksonville Hospital; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Eugene C Lin, MD, Clinical Assistant Professor of Radiology, University of Washington Medical School Author and Editor Disclosure Synonyms and related keywords: sponge kidney, MSK, cystic dilatation of renal pyramids, cystic disease of renal pyramids, cystic dilatation of renal collecting tubules, congenital cystic dilatation of renal collecting tubules, precalyceal canalicular ectasia, renal tubular ectasia, renal tubules, Cacchi-Ricci disease, Lenarduzzi-Cacchi-Ricci disease, collecting tubules, medullary pyramids, kidney disease, renal disease INTRODUCTIONSection 2 of 11
  BackgroundMedullary sponge kidney (MSK) is a developmental abnormality occurring in the medullary pyramids of the kidney. MSK is characterized by cystic dilatation of the collecting tubules in 1 or more renal pyramids in 1 or both kidneys. Although it was first recognized by G Lenarduzzi in 1939, the thorough description of this condition resulted from the multidisciplinary cooperation among Lenarduzzi, a radiologist, and 2 of his colleagues at Padua Although the pathogenesis of MSK has yet to be elucidated, its association with several developmental anomalies supports the idea that it is a developmental disorder. There are findings to suggest that MSK may be the consequence of a disruption of the ureteral-bud/metanephric-blastema interface.1 For excellent patient education resources, visit eMedicine's Kidneys and Urinary System Center. Also, see eMedicine's patient education article Blood in the Urine. Related eMedicine topics: PathophysiologyThe pathogenesis of MSK is unknown. Most authors believe that MSK is a developmental defect affecting the formation of the collecting tubules. Some authors believe that MSK is a progressive degeneration of the collecting tubules that occurs later in life. Osathanondh and Potter believed the primary abnormality is hyperplasia of part of the medullary collecting tubules.5 The size of the kidney may be normal or slightly enlarged. FrequencyInternationalThe exact prevalence of MSK is unknown. The frequency of MSK in the general population has been estimated to be 1 case per 5,000-10,000 population, and MSK is seen in approximately 0.5% of patients examined with the use of intravenous urography (IVU) for various reasons.6 Mortality/Morbidity
Related eMedicine topic: RaceNo racial preponderance is reported for MSK. SexThe sex predilection of MSK varies.
AgeMSK usually is diagnosed in persons aged 10-30 years, although MSK has been reported in children as young as 2 years. Clinical DetailsMost patients with MSK remain asymptomatic throughout life, and the condition is discovered incidentally when IVU is performed for reasons other than the assessment of MSK. Patients with MSK are usually asymptomatic, although acidification or impaired concentration of urine has been documented.7 Complications such as infection, hematuria, and stone formation may be the presenting complaint in approximately 10% of patients. The frequency of calculus disease is increased and manifested by hematuria, renal colic, flank pain, fever, and dysuria. MSK has been associated with hemihypertrophy (hemihyperplasia), Ehlers-Danlos syndrome, adult polycystic disease, congenital hypertrophic pyloric stenosis, Caroli disease, parathyroid adenoma, anodontia, Beckwith-Wiedemann syndrome, distal renal tubular acidosis, horseshoe kidney, Marfan syndrome, renal artery stenosis, pyeloureteritis cystica, and ureteral duplication. When associated with MSK, Beckwith-Wiedemann syndrome has a high rate of tumors, including Wilms tumor and hepatoblastoma. MSK has been reported to cause growth failure in children due to incomplete renal tubular acidosis type 1, and this condition accounts for hypertension in pregnancy in 1% of patients.8 Preferred ExaminationPlain radiographs may demonstrate nephrocalcinosis. Although MSK cannot be diagnosed with the use of plain radiographic findings alone, the presence of linear and rounded medullary calcifications may suggest the diagnosis. The principal method for diagnosing MSK is IVU, in which discrete linear papillary densities, characteristic of MSK, are seen.6 Ultrasonographic (US) and CT findings are more sensitive than plain radiographic findings in showing medullary calcifications, but they are less specific than IVU findings. Computed tomography (CT) scanning can be helpful in confirming the presence of nephrocalcinosis, when it is suggested on US images, and CT scans can demonstrate tubular ectasia.9, 10, 11, 12 The role of radioisotope uptake imaging is to assess renal function and to show the site of renal parenchymal scarring. Magnetic resonance imaging (MRI) has a complementary role and is a useful alternative in patients who are allergic to iodinated contrast media. Limitations of TechniquesThe specific diagnosis of MSK cannot always be made with plain radiographic findings alone because MSK is but one cause of nephrocalcinosis, which has a wide differential diagnosis (see Differentials and Other Problems to Be Considered). The CT scan appearances of MSK are nonspecific. The sonographic appearances of MSK are also nonspecific because hyperechoic medulla with or without shadowing has been documented in a large variety of conditions. DIFFERENTIALSSection 3 of 11
Hyperparathyroidism, Primary Hyperparathyroidism, Secondary Other Problems to Be ConsideredBenign tubular ectasia RADIOGRAPHSection 4 of 11
FindingsPlain radiograph findings may be normal or may demonstrate nephrocalcinosis. This finding is characteristic of MSK, with several discrete pyramidal medullary calcifications occurring in clusters. When passed into the collecting systems,6 calculi may be seen in the renal pelvis, ureter, or bladder. The renal size is usually normal, but the kidneys can be enlarged if the condition is associated with polycystic kidney disease. IVU appearances depend on the type of tubular changes present. Changes form a spectrum that ranges from mild dilatation of the renal collecting tubules (often called renal tubular ectasia), which shows discrete linear opacities in 1 or more papillae through increasing severity of tubular dilatation and cystic changes, to gross deformities with multiple cyst and cystlike cavities of various sizes with beaded or striated cavities that extend through the pyramid from tip to base. The cystic collections of ectatic collecting ducts have been likened to "bunches of grapes" or "bouquets of flowers."13 In patients with full-blown MSK, the calyces tend to be broad, shallow, distorted, and widely cupped. If calculi are present, they tend to be arranged in groups around a calyx, similar to a cluster of grapes or a bunch of flowers. Renal function decreases with subsequent poor depiction of the kidney. In view of the high incidence of nephrolithiasis in MSK, many patients have ureteral calculi. In these patients, the excretory urogram may show obstruction, calyceal distortion or destruction, and evidence of a urinary tract infection. Degree of ConfidenceAlthough a specific diagnosis of MSK cannot be made by using plain radiographic findings alone, the presence of a typical pattern of calcification suggests the diagnosis. MSK is usually bilateral; however, if MSK is unilateral or segmental with localized tubular ectasia, the adjacent calyx must be evaluated for tumor or obstructing calculi. On the other hand, segmental MSK can mimic a renal mass, which has been documented in the literature.13, 14 False Positives/NegativesPlain radiographic findings of nephrocalcinosis are nonspecific. Nephrocalcinosis can occur in a variety of conditions, such as hyperparathyroidism, renal tubular acidosis, renal papillary necrosis, primary hyperoxaluria, and in causes of hypercalcemia or hypercalciuria, such as milk-alkali syndrome, idiopathic hypercalciuria, sarcoidosis, and hypervitaminosis D. The absence of medullary nephrocalcinosis does not exclude MSK. Benign tubular ectasia is a relatively common finding that can appear similar to MSK and can produce linear paintbrush-like striations arising from the medullary pyramids. However, unlike MSK, in benign tubular ectasia, there is no evidence of cystic dilatation in the tubules or of calcification formation, and there is no evidence to suggest that benign tubular ectasia progresses to MSK. The presence of medullary nephrocalcinosis is not necessary for a diagnosis of MSK if cystic dilatation of tubules is identified with IVU. CT SCANSection 5 of 11
Findings
Degree of ConfidenceCT scan findings in patients with MSK are nonspecific. Although CT scanning has a limited role in evaluating patients with MSK, this imaging modality plays a significant role in evaluating complications such as infection or abscess formation, and CT scanning can be used to guide percutaneous drainage of these collections. False Positives/NegativesCT scanning may have some role in the evaluation of patients with MSK associated with microscopic calcification that cannot be seen on plain radiographs. However, CT scan findings can be negative despite microscopic calcification, as detected on histologic analysis. The accumulation of contrast material within the papillae can be seen in papillary blush. Segmental MSK can mimic a renal mass. Localized cystic dilatation associated with MSK can be seen in renal tuberculosis, renal papillary necrosis, and calyceal diverticula. MRISection 6 of 11
FindingsMRI is poor in depicting calcification. The role of MRI in MSK is yet to be defined, but MRI may provide an alternative to IVU in patients who are allergic to radiographic iodinated contrast media. Degree of ConfidenceSufficient experience with MRI in the diagnosis of MSK has not been gained to define the degree of confidence with this imaging modality for this condition. ULTRASOUNDSection 7 of 11
FindingsUS findings demonstrate echogenic medullary pyramids in patients with MSK, irrespective of the presence of medullary nephrocalcinosis. The echogenic medulla may cast acoustic shadowing. The increased echogenicity is seen in particular at the periphery of each pyramid between the interlobar cortices. US findings can demonstrate complications related to calculus disease. Degree of ConfidenceThe sonographic appearances of MSK are nonspecific. Hyperechoic medulla with or without shadowing has been documented in gout, Sjogren syndrome, systemic lupus erythematosus, hyperparathyroidism, glycogen storage diseases, Wilson disease, primary aldosteronism, and pseudo-Bartter syndrome. In some patients, US is more sensitive than plain radiography in detecting medullary calcification.6 False Positives/NegativesHyperechoic medulla can be seen in any condition causing medullary nephrocalcinosis, hyperuricemia, or hypokalemia. US cannot help in distinguishing MSK from other types of medullary nephrocalcinosis. In children, hyperechoic medulla can also be seen in infantile polycystic kidney disease. Other causes of hyperechoic medulla include gout, Sjogren syndrome, primary aldosteronism, Lesch-Nyhan syndrome, hyperparathyroidism, glycogen storage disease type XI, Wilson disease, and pseudo-Bartter syndrome. NUCLEAR MEDICINESection 8 of 11
FindingsThe role of radionuclide scans in MSK is limited to the assessment of renal function and to the identification of a focus of renal infection. Degree of ConfidenceIsotope renography is an excellent method for evaluating renal function, especially split or relative function, when nephron-sparing surgery is contemplated. False Positives/NegativesThe demonstration of depressed renal function is a nonspecific finding and may occur in any end-stage renal disease. INTERVENTIONSection 9 of 11
Radiologic intervention is seldom required; however, percutaneous nephrostomy may occasionally be useful in treating a ureteric obstruction due to a calculus. Although urinary tract infection occurs in approximately one third of symptomatic patients with MSK, renal abscess is a rare complication of the disorder. The diagnosis of renal abscess should be suspected in patients with MSK and acute pyelonephritis whose conditions do not respond to appropriate antibiotic therapy. CT scans may reveal large abscesses that require percutaneous or open surgical drainage or small abscesses that require prolonged high-dose antibiotic therapy. Medical/Legal Pitfalls
Related Medscape topic: Special Concerns
MULTIMEDIASection 10 of 11
REFERENCESSection 11 of 11
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