Introduction
Background
Multicystic dysplastic kidney (MCDK) is a congenital maldevelopment in which the renal cortex is replaced by numerous cysts of multiple sizes. A dysplastic parenchyma anchors the cysts, the arrangement of which resembles a bunch of grapes. The calyceal drainage system is absent. Typically, MCDK is a unilateral disorder; the bilateral condition is incompatible with life.1 Furthermore, MCDK with contralateral renal agenesis does not support life.
Several forms of MCDK have been described. Both the classic type and the less common hydronephrotic type have cysts of various sizes connected by loose, insubstantial fibrous tissue. No functional renal tissue can be identified. The classic type has a random configuration of cysts, whereas the hydronephrotic type presents with a discernible, dilated renal pelvis surrounded by cysts. Some sources identify a third type known as solid cystic dysplasia. Solid cystic dysplasia is composed of smaller cysts with a greater amount of nonfunctional parenchyma.
MCDK should not be confused with polycystic kidney disease (PCKD) or other renal cystic diseases.2 Spence recognized MCDK as a distinct entity in 1955.3 In 1986, the Urology Section of the AmericanAcademy of Pediatrics established the National Multicystic Kidney Registry, which is a large, multicenter, longitudinal database that has helped clarify the appropriate management of MCDK.
Related eMedicine topics:
Multicystic Renal Dysplasia
Cystic Diseases of the Kidney
Related Medscape topics:
Resource Center Neonatal Medicine
Resource Center Renal Cell Carcinoma
Resource Center Chronic Kidney Disease
Resource Center End-Stage Renal Disease
Pyelonephritis Complicating a Multicystic Dysplastic Kidney
Pathophysiology
Competing theories for the etiology of MCDK have been proposed. In 1971, Beck used fetal lambs to demonstrate that ureteral ligation during the first half of gestation produced uniform renal dysplasia, while ligation in the second half resulted in hydronephrosis.4 Consequently, it has been postulated that the timing of an obstruction results in the spectrum of congenital obstructive uropathy that includes classic MCDK, ureteropelvic junction obstruction (UPJO), and simple nonobstructive hydronephrosis. It should be noted that studies in humans have not shown a compelling association between the extent of obstruction and subsequent renal anomalies.
Congenital renal dysplasia may also be explained by an abnormal induction of the metanephric blastema by the migrating ureteric bud.5 In the early embryo, signaling processes induce the differentiation of mesoderm to epithelium of the nephrogenic mesenchyme. In rodent models, disruption of this molecular interaction can produce congenital anomalies similar to MCDK or other forms of renal dysplasia. Therefore, it has been suggested that displaced metanephric blastema interspersed with normal zones of nephrogenesis generates the irregular parenchyma seen in MCDK. The subsequent cystic dilatation of the dysplastic tissue is believed to compress and irreparably damage the normal renal tissue. Unlike PCKD, a single genetic defect cannot account for the spectrum of disease.
In both MCDK and UPJO, the left kidney is involved more often than the right kidney. This observation supports an anatomic factor in the etiology of these disorders.
Frequency
United States
Estimates based on routine fetal sonography in developed nations suggest that 1 in 2400 live births are affected by MCDK. MCDK is the most common type of renal cystic disease.
International
At this point, adequate data for international populations in developing nations are not available.
Mortality/Morbidity
Bilateral MCDK is incompatible with life.1 Affected children are stillborn or die in the early postnatal period. Bilateral disease has been demonstrated in as many as 25% of cases of prenatally detected MCDK.
Fortunately, most cases are unilateral and asymptomatic and are now detected by prenatal sonography.6 Provided that the contralateral kidney is normal, the life expectancy of patients with unilateral, asymptomatic MCDK is normal; however, in over 50% of cases, other urinary tract defects are also detected. UPJO and vesicoureteral reflux (VUR) are the most common defects in the contralateral kidney.7 Unidentified and untreated obstruction or reflux on the contralateral side could potentially lead to renal scarring and subsequent renal failure.
The natural history of MCDK has been characterized with sonography. The affected kidney involutes or decreases in size in 60-70% of cases. This process may occur prior to birth, or it can take up to 20 years to develop. In 50% of cases, the kidney is completely involuted by the age of 5 years. A small percentage of kidneys may actually increase in size; the rest stay the same size. This outcome is not correlated with their size at presentation.
MCDK rarely becomes symptomatic later in life.8 Evidence for an association with infection or pain is insufficient. Certainly, if the affected kidney increases in size, it could potentially compromise pulmonary or gastrointestinal (GI) function and may require intervention. In addition, an association between MCDK and hypertension has been suggested but not proven. In nearly 50% of cases, hypertension resolves after a nephrectomy.
Another controversial issue is the possibility of malignant degeneration. Twelve malignancies have been reported, but the validity of some of these cases has been questioned because of possible misdiagnoses. Six children with MCDK developed an ipsilateral Wilms tumor, and 5 of 6 adults developed ipsilateral renal cell carcinoma. Embryonic nephrogenic rests, which can be premalignant, are more prevalent in MCDK than in other conditions9 ; however, the risk of malignant degeneration is generally believed to be too low to justify a nephrectomy.
Race
No racial or ethnic prevalence has been reported.
Sex
Males have unilateral disease more often than females.
- In the US, estimates from the National Multicystic Kidney Registry report that males account for 56% of the affected population.
- Data from Great Britain suggest that 73% of children with MCDK are males.
- Bilateral disease is 2-fold more common in females than in males.
Age
- Prenatal diagnosis with routine sonography occurs at a mean gestational age of 28 weeks, depending on severity. With routine use of obstetric sonography, the number of neonates presenting with a palpable abdominal mass has significantly decreased.
- Today, the frequency of MCDK as an incidental finding in older children or adults is decreasing. Rarely, MCDK is found in older patients with an abdominal mass or pain, hematuria, urinary tract infection, or hypertension.
- Adults with solitary kidneys may have had an undiagnosed contralateral MCDK that underwent involution over time.10
Anatomy
Three forms of MCDK are recognized:
- The classic form is characterized by multiple cysts of variable sizes separated by thin, dysplastic parenchyma.
- The hydronephrotic form is characterized by a massively dilated but identifiable renal pelvis.
- The third form, solid cystic dysplasia, results in smaller cysts with predominant stroma.
In all forms of MCDK, the cysts are lined by squamous or cuboidal epithelium. The remaining dysplastic renal parenchyma is composed of immature glomeruli, primitive tubules, and metaplastic cartilage. Cartilage is the sine qua non of renal dysplasia. If there is functional renal tissue within the affected kidney, it is generally found in the medulla rather than the periphery. Connecting tubules may provide anatomic communication between the cysts on a microscopic level; however, these connections are not visualized during diagnostic sonography.
The size of the cysts and the amount of parenchyma vary in patients with MCDK. The affected kidney may also have a variable blood supply ranging from a typical renal pedicle with small vessels to no perceptible vessels at all. In the classic form of MCDK, the renal pelvis may be deformed, and the ureter can be partially or completely atretic. In the hydronephrotic form of MCDK, the pelvis is present. In rare cases, MCDK may be found only in an upper or lower pole segment of a duplicated kidney, with normal parenchyma in the unaffected segment.
Presentation
MCDK is a common cause of a palpable abdominal mass in infants (second only to hydronephrosis). Without prenatal sonography or diagnosis in infancy, children may present with anorexia or emesis due to the compressive effects of the affected kidney. More commonly, MCDK may be found incidentally on workup for other congenital anomalies. All suspected abdominal masses should be initially evaluated with sonography to rule out malignant causes and manage symptomatic compressive masses. If radiography does not help make a conclusive diagnosis, surgical exploration may be required.11
Of note, compensatory renal hypertrophy on the contralateral side may begin in utero and progress with age. With this enhanced function, total creatinine clearance and serum creatinine concentrations should reach normal levels.
Contralateral reflux is the most commonly associated abnormality, occurring in 15-20% of patients with MCDK. It is important to diagnose and treat contralateral reflux to prevent acquired renal damage in the solitary functional kidney. A minority of reflux cases occur in the ipsilateral ureter. MCDK can be found in the upper or lower pole of a duplicated kidney or on 1 side of a horseshoe kidney. Other associated findings in the contralateral kidney include UPJO and other obstructive uropathies, such as ureterovesical junction obstruction, ureteral ectopia, and ureterocele.
Infection and pain have been difficult to document in infancy. It is unclear whether MCDK can produce symptoms later in life, but thus far, no patient in the national registry has required surgery for abscess formation or urinary tract infection.
MCDK can be found in patients with other anomalies of the cardiac, respiratory, or GI systems.
Preferred Examination
Sonography is the preferred initial examination. In patients with a prenatal presentation, postnatal studies are required to differentiate MCDK from hydronephrosis. A sonogram should be obtained before a neonate is discharged from the nursery when MCDK is suspected. Reduced renal function and relative dehydration of the neonate should have no bearing on the detection of MCDK; therefore, there is no need to delay the initial sonogram.
In a patient with a symptomatic presentation, such as a palpable abdominal mass, abdominal pain, incontinence, and recurrent urinary tract infections, sonography should be the initial study. The sonographic information provides clues of other urinary tract anomalies as well as intra-abdominal or retroperitoneal malignancies.
MCDK can be detected on other forms of imaging, but sonography is fast and accurate, and it does not require sedation, radiation, or other interventions. Radionuclide imaging can be used to further differentiate the hydronephrotic form of MCDK from an obstruction in a functioning kidney. Radionuclide imaging provides information about the function of the involved renal unit and is superior to intravenous pyelography (IVP) in children. Both technetium-99m (99m Tc) mercaptoacetyltriglycine (MAG-3) and99m Tc dimercaptosuccinic acid (DMSA) studies can demonstrate lack of function in the affected kidney, but MAG-3 studies can also provide information regarding drainage in an obstructed hydronephrotic kidney.
Voiding cystourethrography (VCUG) is indicated in patients with MCDK to evaluate the urinary tract for VUR and other anomalies. Although a minority of patients will have this defect, VUR could lead to reflux nephropathy in the contralateral solitary kidney; therefore, it is important to perform a VCUG to detect a potentially damaging, but easily correctable, cause of renal damage.
Limitations of Techniques
The hydronephrotic form of MCDK can mimic UPJO, and radionuclide scanning is necessary following sonography to confirm the diagnosis. Renal function is relatively poor in the first month of life, and radionuclide imaging should be postponed until 1 month of age to avoid false-positive results.
The limitations of each technique are discussed in their respective sections below.
Differential Diagnoses
Other Problems to Be Considered
PCKD
Simple renal cysts
Multilocular cystic nephroma
Acquired cystic kidney disease
Glomerulocystic kidney disease
Cysts of the medulla
Syndromes with cystic kidneys (tuberous sclerosis, Meckel syndrome, von Hippel-Lindau disease)
Hydronephrosis
Ureteropelvic junction obstruction (UPJO)
Cystic Wilms tumor
Cystic congenital mesoblastic nephroma
Neuroblastoma
vesicoureteral reflux (VUR) (contralateral and ipsilateral kidney, potential for malignant degeneration, hypertension)
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References
Hussain S, Begum N. Multicystic dysplastic disease of kidney in fetus. J Ayub Med Coll Abbottabad. Apr-Jun 2007;19(2):68-9. [Medline].
Levine E, Hartman DS, Meilstrup JW, Van Slyke MA, Edgar KA, Barth JC. Current concepts and controversies in imaging of renal cystic diseases. Urol Clin North Am. Aug 1997;24(3):523-43. [Medline].
Spence HM. Congenital unilateral multicystic kidney: an entity to be distinguished from polycystic kidney disease and other cystic disorders. J Urol. Dec 1955;74(6):693-706. [Medline].
Beck AD. The effect of intra-uterine urinary obstruction upon the development of the fetal kidney. J Urol. Jun 1971;105(6):784-9. [Medline].
Pope JC 4th, Brock JW 3rd, Adams MC, Stephens FD, Ichikawa I. How they begin and how they end: classic and new theories for the development and deterioration of congenital anomalies of the kidney and urinary tract, CAKUT. J Am Soc Nephrol. Sep 1999;10(9):2018-28. [Medline].
Chang LW, Chang FM, Chang CH, Yu CH, Cheng YC, Chen HY. Prenatal diagnosis of fetal multicystic dysplastic kidney with 2-dimensional and 3-dimensional ultrasound. Ultrasound Med Biol. Jul 2002;28(7):853-8. [Medline].
Cambio AJ, Evans CP, Kurzrock EA. Non-surgical management of multicystic dysplastic kidney. BJU Int. Jan 8 2008;[Medline].
Weinstein A, Goodman TR, Iragorri S. Simple multicystic dysplastic kidney disease: end points for subspecialty follow-up. Pediatr Nephrol. Jan 2008;23(1):111-6. [Medline].
Blew B, Carpenter B, Leonard MP. Incidentally detected nephrogenic rests in the setting of congenital obstructive uropathy. Can J Urol. Aug 2002;9(4):1595-8. [Medline].
Belk RA, Thomas DF, Mueller RF, Godbole P, Markham AF, Weston MJ. A family study and the natural history of prenatally detected unilateral multicystic dysplastic kidney. J Urol. Feb 2002;167(2 Pt 1):666-9. [Medline].
Minevich E, Wacksman J, Phipps L, Lewis AG, Sheldon CA. The importance of accurate diagnosis and early close followup in patients with suspected multicystic dysplastic kidney. J Urol. Sep 1997;158(3 Pt 2):1301-4. [Medline].
Wiener JS. Multicystic dysplastic kidney. In: Belman AB, King LR, Kramer SA, eds. Clinical Pediatric Urology. 4th ed. London: Taylor & Francis; 2002:633-45.
Further Reading
Keywords
classic multicystic dysplastic kidney, classic MCDK, hydronephrotic multicystic dysplastic kidney, hydronephrotic MCDK, multicystic dysplasia of the kidney, MCDK, multicystic kidney, multicystic renal dysplasia, solid cystic dysplasia, renal dysplasia
