You are in: eMedicine Specialties > Radiology > PEDIATRICS Multicystic Dysplastic KidneyArticle Last Updated: Feb 19, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: John S Wiener, MD, FACS, FAAP, Chief, Division of Urology, Professor, Department of Surgery, Division of Urology, Professor, Department of Pediatrics, University of Mississippi Medical Center John S Wiener is a member of the following medical societies: American Academy of Pediatrics, American College of Surgeons, American Medical Association, American Urological Association, Society for Fetal Urology, and Society for Pediatric Urology Coauthor(s): Michaella E Maloney, BA, Urology, Duke University School of Medicine; Anamaria Gaca, MD, Fellow, Division of Pediatric Radiology, Duke University Medical Center Editors: Lori Lee Barr, MD, FACR, Clinical Associate Professor of Radiology, Department of Radiology, University of Texas Health Science Center in San Antonio; Member, Board of Directors, Austin Radiological Association; Consulting Staff, Seton Health Network, Columbia/St David's Healthcare System, Healthsouth Rehabilitation Hospital of Austin and Georgetown Hospital; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Kieran McHugh, MBBCh, Honorary Lecturer, The Institute of Child Health; Consultant Pediatric Radiologist, Department of Radiology, Great Ormond Street Hospital for Children, London, UK; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Eugene C Lin, MD, Consulting Staff, Department of Radiology, Virginia Mason Medical Center Author and Editor Disclosure Synonyms and related 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 INTRODUCTIONSection 2 of 12
  BackgroundMulticystic 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 PathophysiologyCompeting 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. FrequencyUnited StatesEstimates 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. InternationalAt this point, adequate data for international populations in developing nations are not available. Mortality/MorbidityBilateral 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. RaceNo racial or ethnic prevalence has been reported. SexMales have unilateral disease more often than females.
Age
AnatomyThree forms of MCDK are recognized:
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. Clinical DetailsMCDK 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 ExaminationSonography 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 (99mTc) mercaptoacetyltriglycine (MAG-3) and 99mTc 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 TechniquesThe 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. DIFFERENTIALSSection 3 of 12
Other Problems to Be ConsideredPCKD RADIOGRAPHSection 4 of 12
FindingsIncidental findings on kidney, ureter, and bladder (KUB) images include displacement of the bowels when the affected kidney is enlarged (see Image 1). Also, ringlike calcifications of the cyst walls may be seen on plain images. Retrograde pyelography may demonstrate an atretic or absent ureter. CT SCANSection 5 of 12
FindingsMCDK can be an incidental finding, but CT studies are not part of the diagnostic investigation. They show the typical multicystic appearance of MCDK with little or no parenchyma (see Images 8-9). Cyst wall calcification can be seen. If a contrast-enhanced CT is performed, there is no excretion seen. MRISection 6 of 12
FindingsMCDK can be an incidental finding but these MRIs are not part of the diagnostic investigation. MRIs show the typical multicystic appearance of MCDK with little or no parenchyma (see Images 8-9). ULTRASOUNDSection 7 of 12
FindingsPrenatal imaging (see Images 2-3) findings include hypoechoic cysts of variable sizes and shapes, interfaces between cysts, a nonmedial location of large cysts, the absence of an identifiable renal sinus, a lack of communication between cysts on sonograms, and minimal surrounding parenchyma. Only 20% of MCDKs have an identifiable reniform shape (compared with 90% of hydronephrotic kidneys). Bilateral MCDK may occur with oligohydramnios as a result of poor urine production. The cysts of MCDK may become enlarged, may shrink, or may involute during fetal life. Postnatal sonograms are shown in Images 4-5. The diagnostic criteria for postnatal sonography are the same as those for prenatal sonography. Degree of ConfidenceUltrasonography is an excellent diagnostic test for MCDK, with a high degree of confidence. An obstructive uropathy with little renal parenchyma can mimic MCDK, but radionuclide studies can provide confirmation of the diagnosis. Autosomal recessive PCKD is not usually mistaken for MCDK, as the cysts in PCKD are too small to be visualized on sonograms, and the parenchyma is generally homogeneously hyperechoic. Other cystic diseases typically appear with some functional parenchyma. False Positives/NegativesThe greatest source of false-positive errors occurs in the setting of hydronephrosis or UPJO. A reniform shape and/or a large cystic structure in the medial portion of the kidney are more indicative of hydronephrosis than MCDK. Unlike in hydronephrosis, where there is communication with the central renal pelvis, the cysts of the classic form of MCDK do not communicate. Regarding false-negative results, renal agenesis with non-renal cystic structures in the retroperitoneum (eg, an adrenal cystic mass) could potentially be mistaken for MCDK. NUCLEAR MEDICINESection 8 of 12
FindingsNuclear renograms are used to evaluate the perfusion, function, and drainage of the kidneys, as there is uptake of the radiotracer into a functioning kidney and excretion into the renal pelvis, ureter, and bladder. In the area of the MCDK, a photopenic region is present that represents displaced tissue with background activity only (see Image 7). Degree of ConfidenceNuclear medicine studies are the best imaging studies for differentiating between MCDK and hydronephrosis; however, severe hydronephrosis with poor renal function may still be difficult to distinguish from MCDK. The similarity may not be clinically relevant because reconstructive surgery is usually not indicated in the setting of poor (ie, <10-15%) differential function. MAG-3, diethylenetriamine-pentaacetic acid (DTPA), and dimercaptosuccinic acid (DMSA) are the preferred agents. Tests with these agents are sensitive for detecting renal function, but the anatomic resolution is relatively poor. Other forms of imaging are required to visualize the specific anatomy of the kidney. False Positives/NegativesOn a nuclear renogram, anything that impairs the renal circulation, such as a renal artery stenosis or a renal vein thrombosis, appears as a nonfunctioning kidney; nevertheless, the renal parenchyma should appear relatively normal with ultrasonography. In addition, renal agenesis may mimic the nonfunctioning kidney of MCDK, but the tissue is absent on sonograms. False-negative results may arise in the setting of severe hydronephrosis. In a poorly functioning kidney, the intervention is the same as in MCDK; therefore, discriminating between these 2 disorders may not be imperative. ANGIOGRAPHYSection 9 of 12
FindingsAngiography is not indicated for the evaluation of MCDK; however, if catheterization, CT scanning, or MRA is performed, the ipsilateral renal artery is atretic or absent. INTERVENTIONSection 10 of 12
The management of MCDK is a controversial topic. Routine nephrectomy is not indicated at this time. A few authors have recommended routine nephrectomy to prevent potential complications, but the rarity of such complications does not justify the surgical and anesthetic risks. Surgery is indicated in patients with symptomatic MCDK, suspicious enlargement, hypertension, mass effect, pain, or infection. MCDK seldom requires urgent management; therefore, the asymptomatic neonate should be given several months to adjust to postnatal life before extirpation is pursued. In fragile neonates, percutaneous cyst aspiration may be used in cases where respiratory function is compromised by the size of the affected kidney. Cases in which malignancy is suspected because of a greater solid component or growth on follow-up are the exception. In addition, nephrectomy may be undertaken in combination with ureterectomy in the setting of an ipsilateral VUR. Given the lack of definitive evidence for serious late complications, the management of asymptomatic MCDK is less straightforward. Nonoperative management requires close surveillance of the affected kidney with follow-up renal sonograms. The recommended schedule from the National Multicystic Kidney Registry calls for sonography every 3 months during the first year of life, then every 6-12 months until 5 years of age. The need for follow-up imaging after 5 years is unclear. The likelihood of malignant degeneration diminishes after the child reaches school age (>5 years). Parents can be taught to perform abdominal examinations to screen for palpable masses. Malignant growth can be rapid. Wilms tumors have been noted to develop in between screening sonograms in other high-risk groups; therefore, it is possible that a parent could detect a large, rapid-growing Wilms tumor on casual examination between the recommended 6-month sonograms. This has not been reported in MCDK, however, and there is no reason to recommend more frequent sonograms. Finally, blood pressure should be monitored for the development of hypertension. Ultimately, the patient’s parents will make the final decision regarding the management of MCDK. They should be fully informed of the risks of observation versus the risks of surgery. Some may opt for surgical management. Given the current lack of data, definitive recommendations for MCDK have not been established, and each instance should be managed on a case-by-case basis. Medical/Legal Pitfalls
Special Concerns
MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
Multicystic Dysplastic Kidney excerpt Article Last Updated: Feb 19, 2008 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
