Imaging in Medullary Sponge Kidney
- Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR; Chief Editor: Eugene C Lin, MD more...
Medullary 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. (See the images below.)
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 University Hospital: Cacchi, a urologist, and Ricci, a pathologist; hence, MSK is also known as Lenarduzzi-Cacchi-Ricci disease. According to Gambaro et al, "These authors 'established' the paradigm for its diagnosis that is still used today."
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.
MSK is found in approximately 0.5% of patients examined with excretory urography. Most patients remain asymptomatic, and MSK is detected incidentally on urograms unless it is complicated by infection, stone formation, or hematuria. Most cases are sporadic, but a few hereditary cases have been reported in the literature.[2, 3] MSK has also been documented in siblings and in several generations of families. The disease occurs in persons of all ages, and the sex predilection varies according to different studies.
MSK is associated with nephrocalcinosis and recurrent calcium nephrolithiasis. Until recently, MSK was regarded as a sporadic disorder. However, since its discovery, 3 pedigrees have been described in which an apparently autosomal dominant inheritance was suggested.
A study of Fabris et al provides strong evidence that familial clustering of MSK is common and has an autosomal dominant inheritance. The authors studied family members of 50 patients with MSK systematically by means of interviews, renal imaging, and biochemical studies in an effort to establish whether MSK is an inheritable disorder. The study found that patients with MSK had first- and second-degree relatives of both sexes with MSK in all generations. There were progressively lower mean levels of serum calcium, urinary sodium, pH, and volume, combined with higher serum phosphate and potassium from patients with relatives with bilateral, to those with unilateral, and to those unaffected by MSK. The study suggests that most affected relatives have a milder form of MSK than nonaffected patients. Thus, it is important to keep the familial association in mind when investigating MSK.
Plain radiographs may demonstrate nephrocalcinosis. Although medullary sponge kidney (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 intravenous urography (IVU), in which discrete linear papillary densities, characteristic of MSK, are seen.[6, 7] Ultrasonographic (US) and computed tomography (CT) scan 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.[8, 9, 10, 11, 12, 13] 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 techniques
The specific diagnosis of medullary sponge kidney (MSK) cannot always be made with plain radiographic findings alone because MSK is but one cause of nephrocalcinosis, which has a wide differential diagnosis.
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.
MRI is insensitive in detecting calcification.
Plain radiograph findings may be normal or may demonstrate nephrocalcinosis. This finding is characteristic of medullary sponge kidney (MSK), with several discrete pyramidal medullary calcifications occurring in clusters[15, 16] . When passed into the collecting systems, 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." Radiographic characteristics of medullary sponge kidney are demonstrated below.
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 confidence
Although 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.
Plain 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.
In medullary sponge kidney (MSK), unenhanced CT scan findings may be normal or demonstrate medullary nephrocalcinosis. Enhanced scans may demonstrate contrast accumulation within the papillae.[9, 12]
CT scans readily depict obstructive changes and help to identify complications, such as interstitial infection and abscess formation.
Ill-defined areas of low attenuation that represent interstitial infection can readily be distinguished from normally enhancing renal parenchyma.
CT scans can also help in differentiating interstitial infection from abscess formation because abscesses appear as sharply defined, low-attenuation areas with thick walls. CT scans can also help in assessing the perinephric extension of abscesses, and they can guide percutaneous drainage.
CT scan characteristics of medullary sponge kidney are demonstrated below.
Degree of confidence
CT 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.
CT 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.
Magnetic Resonance Imaging
MRI is poor in depicting calcification. The role of MRI in medullary sponge kidney 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 confidence
Sufficient 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.
US findings demonstrate echogenic medullary pyramids in patients with medullary sponge kidney, irrespective of the presence of medullary nephrocalcinosis (see the image below). 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 confidence
The 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, ultrasonography is more sensitive than plain radiography in detecting medullary calcification.
Hyperechoic medulla can be seen in any condition causing medullary nephrocalcinosis, hyperuricemia, or hypokalemia. Ultrasonography 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.
The role of radionuclide scans in medullary sponge kidney is limited to the assessment of renal function and to the identification of a focus of renal infection.
Degree of confidence
Isotope renography is an excellent method for evaluating renal function, especially split or relative function, when nephron-sparing surgery is contemplated.
The demonstration of depressed renal function is a nonspecific finding and may occur in any end-stage renal disease.
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].
Thomsen HS, Levine E, Meilstrup JW, Van Slyke MA, Edgar KA, Barth JC, et al. Renal cystic diseases. Eur Radiol. 1997. 7(8):1267-75. [Medline].
Kendall AR, Pollack HM, Karafin L. Congenital cystic disease of kidney: classification and manifestations. Urology. 1974 Dec. 4(6):635-42. [Medline].
Abreo K, Steele TH. Simultaneous medullary sponge and adult polycystic kidney disease: the need for accurate diagnosis. Arch Intern Med. 1982 Jan. 142(1):163-5. [Medline].
Fabris A, Lupo A, Ferraro PM, Anglani F, Pei Y, Danza FM. Familial clustering of medullary sponge kidney is autosomal dominant with reduced penetrance and variable expressivity. Kidney Int. 2013 Feb. 83(2):272-7. [Medline].
Dahnert W. Radiology Review Manual. 6th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2007.
Di Egidio G, Masciovecchio S, Saldutto P, Paradiso Galatioto G, Vicentini C. [Imaging of medullary sponge kidney: notes for urologists]. Urologia. 2014 Oct-Dec. 81 (4):196-9. [Medline].
Maw AM, Megibow AJ, Grasso M, Goldfarb DS. Diagnosis of medullary sponge kidney by computed tomographic urography. Am J Kidney Dis. 2007 Jul. 50(1):146-50. [Medline].
Ginalski JM, Schnyder P, Portmann L, Jaeger P. Medullary sponge kidney on axial computed tomography: comparison with excretory urography. Eur J Radiol. 1991 Mar-Apr. 12(2):104-7. [Medline].
Levine E. Computed tomography of renal abscesses complicating medullary sponge kidney. J Comput Assist Tomogr. 1989 May-Jun. 13(3):440-2. [Medline].
Boag GS, Nolan R. CT visualization of medullary sponge kidney. Urol Radiol. 1988. 9(4):220-1. [Medline].
Koraishy FM, Ngo TT, Israel GM, Dahl NK. CT urography for the diagnosis of medullary sponge kidney. Am J Nephrol. 2014. 39 (2):165-70. [Medline].
Imam TH, Taur AS, Patail H. Image diagnosis: Medullary sponge kidney. Perm J. 2014 Spring. 18 (2):e130-1. [Medline].
Goldfarb DS. Evidence for inheritance of medullary sponge kidney. Kidney Int. 2013 Feb. 83 (2):193-6. [Medline].
Lalli AF. Medullary sponge kidney disease. Radiology. 1969 Jan. 92(1):92-6. [Medline].
Lang EK. Roentgenologic assessment of medullary cysts. Semin Roentgenol. 1975 Apr. 10(2):145-54. [Medline].
Kaver I, Flanders EL, Kay S, Koontz WW Jr. Segmental medullary sponge kidney mimicking a renal mass. J Urol. 1989 May. 141(5):1181-3. [Medline].