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Renal tumors in children
R e n a l T u m o r s in C h i l d r e n By Sandra K. Fernbach and Kate A. Feinstein
L T H O U G H Wilms' tumor and neuroblastoma are the subject of numerous articles A in the pediatric, radiological and pathological literature, many other renal masses and neoplasms can occur. 1,2Each requires precise treatment, and each has a specific prognosis. The child's age (neonate, toddler, older child) and the clinical presentation are as important as the radiological findings when deciding what a renal mass is likely to be. Certain masses, such as multicystic dysplastic kidney or mesoblastic nephroma, may be diagnosed in utero by ultrasound (US) or shortly after birth by physical examination. Renal vein thrombosis, another cause of renal enlargement in the neonate, may produce hematuria. Other masses classically arise or are detected later. The most common cause of an enlarged flank in the neonate is hydronephrosis. This may be because of obstruction or reflux. Less pronounced hydronephrosis may be detected in utero or after urinary tract infection. A discussion of hydronephrosis is beyond the scope of this article, but the many appearances of hydronephrosis should be familiar to those evaluating children for potential renal masses. All imaging is directed toward answering clinical questions. Is the renal process medical or surgical? If surgical, what is the extent of local involvement, and are distant lesions also
present? Can pathology (and prognosis) be suggested? This article describes and illustrates many renal neoplasms of childhood. Leukemia and lymphoma of the kidney, usually seen in association with systemic disease, will not be presented. NEONATAL RENAL MASSES General
The techniques for evaluating renal masses have evolved from those described in valuable older references. 3,4 Excretory urography is now rarely used for this purpose. Also, the presentation of affected infants has similarly changed; renal masses are more likely to be detected on prenatal US than postnatal physical examination. Regardless of how the mass is detected, frequently the first and only imaging performed postnatally is US. Added to the usually mentioned multiple advantages of US (portability, multiplanar images, and lack of ionizing radiation and need for contrast injection) is the additional information provided by Doppler interrogation of key structures. Computed tomography (CT) and, less frequently, magnetic resonance (MR) imaging are used to evaluate those masses that are problematic after US examination° Multicystic Dysplastic Kidney
ABBREVIATIONS US, ultrasound; CT, computed tomography; MR, magnetic resonance; MCDK, multicystic dysplastic kidney; CMN, congenital mesoblastic nephroma; IVC, inferior vena eava; RVT, renal vein thrombus; ARKD, autosomal recessive polycystic kidney disease; ADKD, autosomal dominant polycystic kidney disease; CCSK, clear cell sarcoma of the kidney; RCC, renal cell carcinoma.
From the Radiology Department, Children's Memorial Hospital, Chicago, IL. Address reprint requests to Sandra K. Fernbach, MD, Radiology Dept, No. 9, Children's Memorial Hospital, Chicago, IL 60614. Copyright © 1995 by W.B. Saunders Company 0037-198X/95/3002-000855. 00/0 200
This abnormality, involving all of the kidney, is associated with atresia of the ipsilateral ureter. Bilaterality results in increased fetal loss or profound oligohydramnios with a rapid respiratory death after birth. 5 Pathological changes of multicystic dysplastic kidney (MCDK) in one renal segment have been described in kidneys drained by multiple ureters with atresia of the ureter from the abnormal segment (Fig 1). The early and complete obstruction of the kidney results in severe dysplastic changes. Nephrons diminish in number and noncommunicating cysts form. The number and size of the cysts is varied; some kidneys contain numerous small cysts and others are comprised of only one or two large cysts. Seminars in Roentgenology, Vol XXX, No 2 (April), 1995: pp 200-217
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Fig 1. Bilateralduplicated pelvocalyceal system with rightsided upper pole MCDK in an 8-day-old girl. (A} Transverse US of the right kidney with the largest cyst (arrows) located medially and deviating the lower pole segment (arrowheads) laterally, (B) VCUG showing reflux in the ipsilateral lower pole segment with displaced pelvocalyceal system (arrows) and contralateral reflux.
Contrary to earlier observations, based on operative or postmortem specimens, the MCDK is a nonstatic lesion. Sequential prenatal and postnatal US examinations have shown that cysts may enlarge, remain stable in size, or diminish.6-9 In a few children, the affected kidney may radiographically disappear and the central renal vessels may similarly undergo atrophy; in these children postnatal studies alone would suggest renal agenesis. In the infant, the typically functionless MCDK may show small amounts of renal function on
scintigraphy or CT. It is this residual function that may cause some cysts to enlarge, and it is the loss of this that may lead to eventual involution of the cysts and disappearance of the kidney. Fear that the MCDK might represent a malignant precursor and undergo malignant degeneration prompted the removal of virtually all of these until the early 1980s. Since then, several long-term studies have shown that the MCDK has no propensity toward malignant degeneration and also have documented that
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other potential complications such as infection are not likely. 1°-12Rarely, neoplasia will develop in the MCDK, as in any other tissue, but a recent report discusses the issue in actuarial terms and concludes that about 16,000 MCDK would have to be removed to prevent one Wilms' tumor-related death. ~3
Imaging There are two discrete types of MCDK, each with a specific US appearance. The classical form is comprised of multiple cysts of varying size in a random arrangement in abnormalappearing tissue (Fig 2). The hydronephrotic form, as the name suggests, simulates a dilated pelvocalyceal system; there is a large central fluid collection and the smaller cysts around it are approximately the same size and are circumferentially arrayed (Fig 3). Tests of renal function (scintigraphy), cyst puncture (or antegrade pyelogram), or retrograde ureterogram may be necessary to differentiate the hydronephrotic MCDK from the more usual causes of hydronephrosis. 14-16 The contralateral kidney must be evaluated for developmental anomalies such as ureteropel-
Fig 3. Hydronephrotic form of MCDK in 1-day-old boy, Transverse US with very large central cyst (curved arrows), multiple smaller peripheral cysts (arrowheads), and some solid tissue simulating renal parenchyma.
vic junction obstruction and vesicoureteral reflux, which occur in children with M C D K more frequently than in the general population. ~7,~8It should also be stressed that the contralateral kidney is the only functioning kidney and should be evaluated and treated as such.
Congenital Mesoblastic Nephroma
Fig 2. Classical form of MCDK in 1-week-old boy. Prone longitudinal US with larger peripheral cysts (arrows), smaller central cysts (curved arrows), and numerous other cysts (arrowheads).
This usually benign, unifocal, and unilateral renal mass comes to attention early because of intrauterine detection of the mass on US as well as recognition of the polyhydramnios that may develop when the mass impinges on and hampers emptying of the fetal stomach. 19,2° After birth, congenital mesoblastic nephroma (CMN) may be diagnosed by palpation or because of hypertension or feeding problems again attributed directly to the m a s s . 21'22 Bleeding into the mass has produced cystic change and may cause shock. 23,24 Associated hypercalcemia has been reported. 25 At least 75% of CMNs are detected by the time the child is 6 months of age. 21 Nephrectomy is generally performed rather than tumor excision; recurrence in the renal fossa or metastatic disease (to lung or brain) is rare. Pathological analysis of the tumor has been extended because microscopic review recognized it to be an entity distinct from Wilms' t u m o r . 26 On light microscopy, the tumor is
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comprised of spindle-shaped cells with few mitoses. Microscopic examination was also the first to associate some variant tumors with atypical cellularity and increased mitoses with an unusual aggressive biological behavior. 27 Cytopathological flow studies have shown that tumors with diploid cells b e h a v e i n the typical benign manner, but those with aneuploidy are more likely to recur or metastasize, as are those tumors detected in the older infant. 28 Studies of subcellular structures have also provided clues to the behavior of CMN. 29
Fig 4. CMN in a 7-week-old boy with a palpable right flank mass. (A) Abdominal radiography showing noncalcified mass displacing bowel loop from the right upper quadrant. (B) Transverse US of the solid-appearing heterogenous right upper quadrant mass (arrows) occupying the renal fossa. (C} Contrast-enhanced CT showing the nonenhancing mass with a thin rim of renal parenchyrna peripherally (arrowheads).
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Imaging Abdominal radiographs may fail to show the mass or may show displacement of adjacent bowel loops or a bulging flank (Fig 4A). Less than 5 % contain visible calcification. 21 On US, CMN is predominantly solid, but cystic or even calcified components may be identified (Fig 4B). 21 Examination of the inferior vena cava (IVC) should be performed although CMN does not extend into this; the presence of mass within the IVC suggests other
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diagnoses, such as renal vein thrombosis in the neonate or Wilms' tumor in the older infant. Computed tomography is necessary only when the diagnosis remains uncertain after US has been performed. Occasionally, renal function will be detected within the mass because of trapped but normal renal parcnchyma.3° On CT, CMN distorts the renal parenchyma, does not enhance with contrast, and may have a heterogenous appearance (Fig 4C). The intrarenal origin of the mass may be easier to appreciate with CT than US. The appearance of CMN on MR has been described but this technique is not generally needed for diagnosis.31
Renal Vein Thrombosis Most patients with renal vein thrombosis (RVT) present in the newborn period and are symptomatic. A few will be infants who had a solid renal mass or enlarged kidney detected on prenatal US. Older children with nephrotic syndrome or with a kidney transplant are also at risk for RVT. This section will be limited to RVT in the neonate. Because thrombosis begins in the interlobar and arcuate veins and progresses centrally, RVT is a misnomer. The clot may propagate to the renal vein and IVC. Depending on the extent of thrombosis and infarction, clinical signs of enlarged kidney, hematuria, and thrombocytopenia may develop. Because the normal newborn infant has a physiological oliguria associated with decreased renal blood flow, any condition that causes further reduction in renal blood flow predisposes to RVT. Dehydration or hemoconcentration may be caused by diarrhea, sepsis, maternal diabetes, or other conditions.
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Bilateral RVT may occur, or thrombosis may involve part or all of one kidney. The findings on US will be dependent on the portion(s) of the kidney(s) affected. In the acute and subacute stages, the kidney swells, corticomedullary differentiation deteriorates, and heterogenous cortical hyperechogenicity develops.3a,33 Doppler examination in the acute phase may show absent spectral or color flow in the involved segments. 34 Echogenic streaks bordering the medullary pyramids and interlobar septa representing thrombosed veins may be identified32,33 (Fig 5A). Collateral veins develop via the hilum and capsule within the first few days. In the subacute stage, flow may be present in the proper direction but lack typical pulsation from contraction of the right atrium 35 (Fig 6). Ipsilateral adrenal hemorrhage and RVT may coexist and do so more commonly on the left where the adrenal vein drains into the renal vein. The coexistence of these abnormalities may be because of (1) clot formation in one vein leading to clot in the other, or (2) overlapping risk factors such as sepsis and maternal diabetes. The appearance of the adrenal hemorrhage and the RVT will depend on age of the lesions.36.37 The US appearance at follow-up of RVT is varied. 38,39In some, kidney function and appearance return to normal. In others, the kidney retains normal function despite the finding of persistently calcified, lace-like renal veins (Fig 5B). The least favorable outcome is that of renal atrophy indistinguishable from reflux nephropathy or congenital hypoplasia. The majority, but not all, of affected children have normal renal function.g0,41
Imaging Before US was routinely available, contrast studies such as inferior vena cavography and excretory urography were the mainstays in diagnosis of RVT. Ultrasonography with highfrequency transducers and Doppler spectral and color-flow imaging is particularly well suited to evaluation of renal parenchymal and bloodflow abnormalities and is now routinely used to make the diagnosis of RVT. Both CT and MR also may be helpful if the calcification or masslike nature RVT makes it difficult to exclude CMN.
Autosomat Recessive Polycystic Kidney Disease Autosomal recessive polycystic kidney disease (ARKD), also known as infantile polycystic kidney disease, affects the kidneys and liver and has variable expression depending on whether the kidney or liver abnormalities predominate. Even siblings may have a variable presentation. 42 Pathologically, the kidney lesion is characterized by cystic dilatation of the collecting tubules with fewer-than-normal glomeruli present. The liver lesion consists of bile duct
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Fig 5. RVT in upper pole of the left kidney in a 5-week-old girl with prenatal diagnosis of kidney mass, (A) Prone transverse US of the left upper pole with echogenic interlobar veins (curved arrows) bordering the hypoechoic medullary pyramids. (B) Nonenhanced CT with calcifications in the left renal vein (arrowhead) and interlobar veins (arrows). This kidney opacified normally during contrast-enhanced CT.
hyperplasia and periportal fibrosis. Caroli disease, a nonobstructive dilatation of the biliary disease and sometimes included in the spectrum of choledochal cysts, has also been reported in infants with ARKD. 43 Normal-appearing kidneys may be present in early pregnancy, delaying diagnosis until the third trimester when enlarged echogenic kidneys are identified. Those fetuses with a small urinary bladder and oligohydramnios will have more severe renal disease. 44 In the symptomatic newborn, renal problems are dominant. The enlarged kidneys present as palpable flank masses and cause limited diaphragmatic excursion and respiratory compromise. 45,46Pulmonary hypoplasia and respiratory
distress also develop from oligohydramnios. Serum tests of renal function may be normal because in the newborn these are a reflection of maternal kidney function. However, after several days, the serum values will be representative of the degree of renal insufficiency. At times, laboratory and radiological examinations fail to differentiate ARKD from autosoreal dominant polycystic kidney disease (ADKD), especially in the older child. Clinical presentation may also overlap. Familial screening with US may fail to confirm ADKD, especially when the parents are young. In these settings, biopsy may be necessary to establish the diagnosis so that genetic counseling may be provided.
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Fig 6. RVT in 3-day-old girl with gross hematuria. Doppler spectral tracings of renal vessels show no forward flow in the artery during diastole (arrows). The venous waveform, below the baseline, lacks normal variation. The kidney itself (open arrows) is echogenic and lacks corticomedullary differentiation.
Imaging Ultrasonography is helpful in establishing the diagnosis of ARKD in the newborn period. The kidneys are enlarged, echogenic, and lack corticomedullary differentiation. A thin hypoechoic rim may be present and is thought to represent the compressed normal glomeruli or the markedly dilated tubules extending to the periphery47'48 (Fig 7A). With high frequency transducers ( > 7 MHz), some of the dilated collecting tubules may be resolved. They are then seen as tiny parallel radially oriented cysts instead of the echogenic parenchyma identified with lowerfrequency transducers (Fig 7B). Enlarged kidneys with delayed nephrograms are seen on excretory urography and contraste n h a n c e d c r . 49 On both studies contrast pooling in dilated collecting tubules produces a radially arranged striated nephrogram that may persist for many hours when the renal function is significantly decreased. The pelvocalyceal systems and ureters are not affected by ARKD. The older child with ARKD tends to have complications from portal hypertension such as gastrointestinal hemorrhage and hypersplenism. Ultrasonography findings also parallel those seen in portal hypertension from other causes:
splenic enlargement, varices, abnormal liver architecture with regions of increased echogenicity, and hepatofugal blood flow. Although the liver disease may be prominent, the kidneys are abnormal. In contrast to the disproportionate size of the kidneys in the neonatal period, the kidneys in older children may be more normal sized. Ultrasonography may detect both microcysts and macrocysts. On CT, cyst walls may contain calcifications responsible for appearance of nephrocalcinosis on US.S° THE TODDLER Wilms' Tumor
With an incidence of 7 to 8 cases per 1 million children per year, this is the most common abdominal (and renal) malignancy of childhood. There is an increased incidence of Wilms' tumor in children with sporadic aniridia, nephroblastomatosis, hemihypertrophy, horseshoe kidney, Beckwith-Wiedemann syndrome, chromosomal abnormalities, Drash syndrome, and Perlmann syndrome. 5145Renal parenchymal origin is usual, but rare extrarenal variants have been reported both within the abdomen and at distal nonabdominal sites 56 (Fig 8). The classical tumor has a triphasic (epithe-
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Fig 7. ARKD in 1-day-old boy with flank masses. (A) Coronal US of the enlarged kidney. A hypoechoic rim of parenchyma (arrowheads) encircles the echogenic medullary tissue. (B) Prone transverse US using a high-frequency transducer. Multiple small cysts (arrows) can be resolved deep to the hypoechoic rim.
lial, stromal, and blastemal) histology. Multiple derivatives of these tissues, including fat, may be identified on imaging as well as microscopic evaluation. Metastases to lung are more frequent than those to other organs; other lung complications have also been reportedS
Imaging The plain films may show mass displacing adjacent structures and filling the flank. Calcifi-
cations are rare, seen in about 5%, regardless of the imaging method used. 1,s8,59 Ultrasonography is the primary method for evaluating the site (or organ) of origin and the size, extent, and architecture of any abdominal tumor. The mass is typically quite large when detected clinically, over 10 cm in diameter. "Cysts" within contribute to the nonhomogeneous appearance; these develop because of tumor necrosis or deposits of mucin or may simply be trapped calyces.
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Fig 8. Extrarenal Wilms' tumor in a 2-year-old boy with midline abdominal mass. (A) Transverse US image through the lower abdomen shows a heterogenous mass (arrowheads) displacing bowel from this portion of the abdomen, (B) Contrastenhanced CT at a similar level, The large size of the mass (open arrows) is better appreciated on CT. The left ureter (arrow) is dilated as is the renal pelvis above (not shown) because of the mass compressing the ureter,
The IVC must be imaged to exclude tumor extension (even to the level of the right atrium), which has been identified in about 5% of children. 6° The presence of such tumor changes the staging of the tumor and the operation to be performed. 6° Intracaval extension may be shown with real-time US, and, if necessary, confirmed with Doppler. When the tumor is on the right,
compression of the IVC may narrow it and prevent its visualization. The contralatera! kidney must be examined for several reasons. Approximately 10% to 15% of tumors are bilateral at presentation, and detection of a second tumor alters the primary therapy. Anomalies that would alter surgery, such as contralateral renal agenesis or uretero-
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Fig 9. Wilms' tumor in a 6-year-old boy who complained of lump under ribs. (A} Contrastenhanced CT at the lower margin of the liver. A large low-density mass approaches the midline and displaces the left kidney inferiorly. A nodule (open arrow) of higher density tissue is continuous with the more solid-appearing mass below {Fig 9B) (B) CT scan a few centimeters below Fig 9A. The mass (open arrows) arises from the upper pole of the left kidney. The low density within the perinephric space (arrows) is caused by tumor beneath the renal capsule, Hematoma may develop because of venous obstruction and have a similar appearance.
pelvic junction obstruction, must be also be excluded. Frequently, CT is performed in the child with abdominal mass to differentiate Wilms' tumor from neuroblastoma 1,z,58,59(Fig 9). The diagnosis is likely to be Wilms' tumor if (1) the mass is intrarenal and the pelvocalyceal anatomy is distorted; or (2) vascular structures are displaced. Neuroblastoma is likely if (1) the mass has calcification (about one third do); (2) the mass is predominantly extrarenal and displaces
the kidney; (3) the mass crosses the midline; (4) vascular structures are encased; or (5) paraspinal and intraspinal extension of tumor is present. 2 Metastatic bone disease indicates that the diagnosis of neuroblastoma or renal tumor other than Wilms' is likely because this is rarely seen with the usual Wilms' tumor. 61 Magnetic resonance can show the tumor, IVC extension, and sites of metastatic disease well, but no tumor-specific signal intensity has been shown. 158,62-64However, the cost of the examina-
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tion has caused some experts to question its routine use in children with Wilms' tumor. Review of the plain films and US in children with usual-histology Wilms' tumor indicates that additional examinations rarely affect patient outcome. 65 Wilms' Tumor Variants and Other Renal Tumors
Nephroblastomatosis The persistence of primitive renal blastema beyond infancy is abnormal except in small microscopic rests. Larger amounts of primitive
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blastema, remaining in sheets in the cortex or in more discrete nodules, is termed nephroblastomatosis. 66 Recognition of nephroblastomatosis is important; it is associated with Wilms' tumor, especially bilateral Wilms' tumor. 67 It also seen in increased frequency in children with syndromes with a known association with Wilms tumor. Imaging. Nephroblastomatosis may cause multifocal distortion of the pelvocalyceal system or may be so peripheral to it that, despite extensive involvement, no changes are seen on excretory urography. 68,69Ultrasonographic detec-
Fig 10.
Nephroblastomatosis in a 3-month-old
boy with Beckwith-Wiedemann syndrome. (A) Con-
trast-enhanced CT through the upper pole of the left kidney. The recent US was normal, A single hypodense mass was present in the left upper pole. Two other cortical lesions were identified in the right kidney. (B) Coronal T2-weighted MR image through the kidneys. The left kidney {arrows) is enlarged, and there is a lesion with high signal intensity in the upper pole {arrowheads).
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tion of nephroblastomatosis is possible, but this technique lacks the sensitivity of CT and MR. 69 On US, the affected kidney may be enlarged, have an indistinct corticomedullary junction, and contain lucent nodular masses. Contrastenhanced CT superbly showS the abnormal tissue because it fails to enhance and is distinctly demarcated from adjacent normal parenchyma (Fig 10A): 69 Occasionally, regions of nephroblastomatosis are tiny and are missed with CT5 ° Because of the association of nephroblastomatosis with Wilms' tumor, there is some hesitancy to expose affected children to ionizing radiation that possibly could increase the rate of malignant transformation. For this reason, frequent detailed US examinations are performed to detect malignant change, suggested by rapid growth of any rest. However, MR can show nephroblastomatosis, and enhanced detection is possible after gadolinium injection68,71 (Fig 10B). The high cost of MR and the need for sedation seems to be limiting its use in the sequential evaluation of kidneys with nephroblastomatosis.
Clear Cell Sarcoma of the Kidney This unusual tumor (4% of renal tumors in childhood) may be difficult to differentiate from Wilms' tumor radiographically. However, clear cell sarcoma of the kidney (CCSK) is distinct histologically, with both a classical pattern containing cells with poorly staining cytoplasm and a well-described histological variant. 26,72No associated somatic abnormalities (hemihypertrophy, aniridia) have been recognized. CCSK behaves aggressively, with bony metastases (lytic more often than blastic) occurring much more frequently than in children with Wilms' tumor and the overall prognosis being much worse. 73,74
Rhabdoid Tumor of the Kidney This malignant renal tumor, accounting for about 2% of renal tumors in large series, is more frequent in infancy than any other period. 7579 AS with the other neonatal masses, it may be diagnosed in utero or because of abdominal mass, hypertension, or even hypercalcemia. Because of the age at the time of diagnosis, one may instead expect a CMN. The name, rhabdoid tumor, derives from the microscopic ap-
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pearance of tumor cells that resemble muscle cells. An association with brain tumors, especially medulloblastoma, has been recognized both in infants and in children presenting later in life. The brain tumor may precede the renal tumor or may develop several years later. Overall, the prognosis is much worse with rhabdoid tumor of the kidney than with other renal malignancies. Imaging. The preoperative radiological evaluation of the child with these two tumors does not differ from that of a child with Wilms' tumor because, in most cases, clinical presentation is similar and diagnosis is made after nephrectomy. Both CCSK and rhabdoid tumor of the kidney may have a radiological appearance indistinguishable from Wilms' tumor. 72-79 One important point is that neither of these tumors is ever bilateral. After pathological analysis indicates that CCSK or rhabdoid tumor is present, additional and specific studies should be performed. Because each of these may metastasize to bone, skeletal survey or scintigraphy is suggested. Radiological evaluation of the brain has been recommended in those with rhabdoid tumor, but because the brain tumor may not be synchronous with the kidney tumor, the need (or timing) of cranial CT or MR must be questioned.
Multilocular Cystic Nephroma An unusual tumor occurring in childhood and in adult life, the multilocular cystic nephroma derives its name from the gross appearance of the tumor. At one time, the tumor was believed to be primarily a benign lesion; previously used names for the tumor stressed this, eg, cystic adenoma, cystic lymphangioma, cystic hamartoma. 8°,81 When seen in children, the tumor affects boys more than girls; in adults, women are more frequently affected.S1,s2 An analysis of cystic tumors sent for review by the National Wilms' Tumor study group lead to a useful reclassification of these, s2 Cystic lesions with differentiated cellular elements (but no blastemal or embryonal elements) may continue to be designated cystic nephroma. This, according to the authors, is probably a neoplastic variant, although none of the five reviewed recurred or metastasized. When the septa of
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cystic renal masses contain blastemal or embryohal elements, the term cystic partially differentiated nephroblastoma is appropriate. This, too, tends to behave in a fairly benign manner, but local recurrence has been documented. The most aggressive or malignant of the cystic lesions is the solid Wilms' tumor with focal or multifocal cystic change; this, in contrast to the
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others, has distinct solid tissue within the tumor. Most of these cystic tumors are detected because of related symptoms, with renal mass being the most common clinical finding. Imaging. Older reports described the findings on excretory urography, angiography, and retrograde ureterograms. Because these tech-
Fig 11. Cystic partially differentiated nephroma in an 18month-old boy with abdominal mass, (A} Transverse US showed the multiple Iocules within the mass. The relationship to the kidney and other structures could not be shown on any one image because of the large size of the mass. (B) Contrast-enhanced CT. The affected left kidney is stretched around the septated mass, which is crossing the midline, dispacing bowel, and deforming the contour of the abdominal wall.
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niques are rarely used for evaluating masses, it is more important to be familiar with the findings on US. The cystic nature of the mass and the septations are usually easy to show (Fig 11). The solid component may be visible or may be difficult to show with US or CT. For this reason, speCific radiological diagnosis may be impossible; nephrectomy is performed and diagnosis is made after pathological analysis.
Intrarenal Neuroblastoma When arising below the diaphragm, neuroblastoma usually develops in the retroperitoneoum from the adrenal gland and displaces the kidney. However, in a few children, neuroblastoma can simulate Wilms' tumor by arising from tissue within the kidney or by invasion of the kidneybyneuroblastoma. 83,84Some neuroblastomas manifest other behaviors more typical of Wilms' tumor: pulmonary metastases, intracaval extension of tumor thrombus.85,s6,87
THE OLDER CHILD Autosomal Dominant Polycystic Kidney Disease Autosomal dominant polycystic kidney disease (ADKD) is one of the most common autosomal dominant conditions and usually presents in the third to fifth decade of life. A small subgroup with ADKD may be symptomatic in childhood, with hypertension, enlarged kidneys, proteinuria, or impaired renal function. ss,s9 Because of the prevalence of the condition, the number of children with clinically significant ADKD may be similar to that of ARKD. Another group of children are asymptomatic but have had abnormal kidneys discovered on prenatal examination or during investigation of an unrelated condition (Fig 12). Family screening of asymptomatic children is warranted because complications of ADKD such as hypertension and urinary tract infection are present in up to one third of affected postpubertal children and require treatment to delay the onset of end-stage renal disease and avert rupture of associated berry aneurysm.9° Cerebral and abdominal aortic aneurysms as well as colonic diverticular disease do not appear to be childhood problems. ADPD may be classified into two types according to the location of the abnormal gene. 91 In
Fig 12. ADKD in a 6-year-old girl with urinary tract infection. Longitudinal US of the right kidney (arrowheads) shows multiple cysts (arrows).
90%, the abnormal gene is located on the short arm of chromosome 16; the other loci have not been found.
Imaging In the past excretory urography with nephrotomography was the standard method and showed enlarged kidneys with multiple radiolucencies
Fig 13. ARKD in a 1-day-old girl with flank masses. Transverse US of the right lobe of the liver shows small cystic structures in the liver (curved arrows). Doppler showed that these were not vascular, but could not differentiate hepatic cysts from focal bUiary dilatation. The kidneys had an appearance believed to be classic for ARKD. Biopsy was performed because of the liver cysts and confirmed ARKD.
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Fig 14. ADKD in an 8-year-old boy with recent hematuria. Contrast-enhanced CT shows asymmetric involvement with many large cysts (dominant mass) in the anterior portion of the right kidney (arrowheads] and a few small cysts in the left kidney,
and distorted calyces. On US, the kidneys may contain simple or complex (hemorrhagic) cysts. The cysts arise anywhere along the nephron or collecting duct. Asymmetric involvement is not uncommon (Fig 14). Because ADPD is a progressive disease, cysts and renal enlargement become more apparent with increasing age. Ultrasonography screening of asymptomatic children in the first decade has a false-negative diagnosis rate of 36%. 9z Those with symptoms related to ADKD are more likely to have cysts that can be identified on US. Because simple cysts occur in less than 1% to 2% of children, an "at-risk" child with at least one cyst in each kidney or several cysts in one kidney should be diagnosed with ADKD. Hepatic cysts have been identified in postpubertal children (Fig 13) and may be confused with the ductal dilatation present in Caroli's disease, a known association with ARKD.93
On CT, the cysts distort the pelvocalyceal system and do not enhance with contrast on early or delayed images. Calculi and cyst calcifications are complications readily evaluated with CT. 94
Renal Cell Carcinoma
Renal cell carcinoma (RCC) comprises about 5% of all pediatric renal tumors and is more frequent in adults than children. It tends to affect older children (around 10 years of age) than does Wilms' tumor and has a much worse prognosis. 95-97 The presentation is not unlike that of all other pediatri c renal tumors. On CT, RCC is a solitary nonenhancing mass, and on US, the mass appears echogenic. %,9v Although it may calcify in as many as 75% of cases, it can be distinguished from other renal tumors by histology alone. 97
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dysplastic kidney in utero: Changing appearance on US. Radiology 159:107-109, 1986 7. Pedicelli G, Jequier S, Bowen A, et al: Multicystic dysplastic kidneys: Spontaneous regression demonstrated with US. Radiology 160:23-26, 1986 8. Avni EF, Thoua Y, Lalmand B, et al: Multicystic dysplastic kidney: Natural history from an in utero diagnosis and postnatal follow-up. J Urol 138:1420-1424, 1987 9. Mesrobian HG, Rushton HG, Bulas D: Unilateral renal agenesis may result from in utero regression of multicystic renal dysplasia. J Urol 150:793-796, 1993 10. Vinocur L, Slovis TL, Perlmutter AD, et al: Follow-up studies of multicystic dysplastic kidney. Radiology 167:311-315, 1988 11. Strife JL, Souza AS, Kirks DR, et al: Multicystic
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dysplastic kidney in children: US follow up. Radiology 186:788, 1993 12. Orejas G, Malaga S, Santos F, et al: Multicystic dysplastic kidney: Absence of complications in patients treated conservatively. Child Nephrol Urol 12:35-39, 1992 13. Beckwith JB: Ask the expert. Pediatr Nephrol 6:511, 1992 14. Kullendorff CM, Salmonson EC, Laurin S: Diagnostic cyst puncture of multicystic kidney in neonates. Acta Radiol Scand 31:287-289, 1990 15. Carey PO, Howards SS: Multicystic dysplastic kidneys and diagnostic confusion on renal scan. J Urol 139:8385, 1988 16. Greenfield SP, Samen Y, Seidel FG, et al: Diagnosis and management of the hydronephrotic type of multicystic dysplastic kidney. Child Nephrol Urol 10:44-48, 1990 17. Atiyeh B, Husmann D, Baum M: Contralateral renal abnormalities in multicystic-dysplastic kidney disease. J Pediatr 121:65-67, 1992 18. Flack CE, Bellinger MF: The multicystic dysplastic kidney and contralateral vesicoureteral reflux: Protection of the solitary kidney. J Urol 150:1873-1874, 1993 19. Bolande RP, Brough AJ, Izant RJ Jr: Congenital mesoblastic nephroma of infancy: A report of eight cases and the relationship to Wilms' tumor. Pediatrics 40:272-278, 1967 20. Matsumura M, Nishi T, Sasaki Y, et al: Prenatal diagnosis and treatment strategy for congenital mesoblastic nephroma. J Pediatr Surg 28:1607-1609, 1993 21. Hartman DS, Lesar MSL, Madewell JE, et al: Mesoblastic nephroma: Radiologic-pathologic correlation of 20 cases. AJR 136:69-74, 1981 22. Malone PS, Duffy PG, Ransley PG, et al: Congenital mesoblastic nephroma, renin production and hypertension. J Pediatr Surg 24:599-600, 1989 23. Christmann D, Becmeur F, Marcellin L, et al: Mesoblastic nephroma presenting as a haemorhragic cyst. Pediatr Radio120:553, 1990 24. Goldberg J, Liu P, Smith C: Congenital mesoblastic nephroma presenting with hemoperitoneum and shock. Pediatr Radio124:54-55, 1994 25. Ferraro EM, Klein SA, Fakhry J, et al: Hypercalcemia in association with mesoblastic nephroma: Report of a case and review of the literature. Pediatr Radiol 16:516-517, 1986 26. Beckwith JB: Wilms' tumor and other renal tumors of childhood: A selective review from the National Wilms Tumor Study Pathology Center. Hum Pathol 14:481-492, 1983 27. Joshi VV, Kasznica J, Walters T: Typical mesoblastic nephroma: Pathological characteristics of a potentially aggressive variant of congenital mesoblastic nephroma. Arch Pathol Lab Med 110:100-106, 1986 28. Barrantes JC, Toyn C, Muir KR, et al: Congenital mesoblastic nephroma: Possible prognostic and management value of assessing DNA content. J Clin Pathol 44:317-320, 1991 29. Gaillard D, Bouvier R, Sonsino E, et al: Nucleolar organizer regions in congenital mesoblastic nephroma. Pediatr Pathol 12:811-821, 1992 30. Kirks DR, Kaufman RA: Function within mesoblas-
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tic nephroma: Imaging-pathologic correlation. Pediatr Radiol 19:136-139, 1989 31. Wooten SL, Rowen SJ, Griscom NT: Pediatric case of the day. Congenital mesoblastic nephroma. RadioGraphics 11:719-721, 1991 32. Lalmand B, Avni EF, Nasr A, et al: Perinatal renal vein thrombosis. J Ultrasound Med 9:437-442, 1990 33. Cremin BJ, Davey H, Oleszczuk-Raszke K: Neonatal renal venous thrombosis: Sequential ultrasonic appearances. Clin Radiol 44:52-55, 1991 34. Alexander AA, Merton DA, Mitchell DG, et al: Rapid diagnosis of neonatal renal vein thrombosis using color Doppler imaging. J Clin Ultrasound 21:468-471, 1993 35. Laplante S, Patriquin HB, Robitaille P, et al: Renal vein thrombosis in children: Evidence of early flow recovery with Doppler US. Pediatr Radiol 189:37-42, 1993 36. Orazi C, Fariello G, Malena S, et al: Renal vein thrombosis and adrenal hemorrhage in the newborn: Ultrasound evaluation of 4 Cases. J Clin Ultrasound 21:163-169, 1993 37. Demirci A, Selcuk MB, Yazicioglu I: Bilateral adrenal hemorrhage associated with bilateral renal vein and vena cava thrombosis. Pediatr Radio121:130, 1991 38. Fishman JE, Joseph RC: Renal vein thrombosis in utero: Duplex sonography in diagnosis and follow-up. Pediatr Radiol 24:135-136, 1994 39. Jayogapal S, Cohen HL, Brill PW, et al: Calcified neonatal renal vein thrombosis demonstration by CT and US. Pediatr Radio120:160-162, 1990 40. Ricci MA, Lloyd DA: Renal venous thrombosis in infants and children. Arch Surg 125:1195-1199, 1990 41. Mocan H, Beattie TJ, Murphy AV: Renal venous thrombosis in infancy: Long-term follow-up. Pediatr Nephrol 5:45-49, 1991 42. Barth RA, Guillot AP, Capeless EL, et al: Prenatal diagnosis of autosomal recessive polycystic kidney disease: Variable outcome within one family. Am J Obstet Gynecol 166:560-561, 1992 43. Davies CH, Stringer DA, Whyte H, et al: Congenital hepatic fibrosis with saccular dilatation of intrahepatic bile ducts and infantile polycystic kidneys. Pediatr Radio116:302305, 1986 44. Estroff JA, Mandell J, Benacerraf BR: Increased renal parenchymal echogenicity in the fetus: Importance and clinical outcome. Radiology 181:135-139, 1991 45. Sumfest JM, Burns MW, Mitchell ME: Aggressive surgical and medical management of autosomal recessive polycystic kidney disease. Urology 42:309-312, 1993 46. McDonald RA, Avner ED: Inherited polycystic kidney disease in children. Semin Nephrol 11:632-642, 1991 47. Currarino G, Stannard MW, Rutledge JC: The sonolucent cortical rim in infantile polycystic correlation. J Ultrasound Med 8:571-574, 1989 48. Hayden CK, Swischuk LE, Smith TH, et al: Renal cystic disease in childhood. RadioGraphics 6:97-116, 1986 49. Kaariainen H, Jaaskelainen J, Kivisaari L, et al: Dominant and recessive polycystic kidney disease in children: Classification by intravenous pyelography, ultrasound, and computed tomography. Pediatr Radiol 18:45-50, 1988 50. Lucaya J, Enriquez G, Nieto J, et al: Renal calcifica-
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tions in patients with autosomal recessive polycystic kidney disease: Prevalence and cause. AJR 160:359-362, 1993 51. Mesrobian HGJ, Kelalis PP, Hrabovsky E, et al: Wilms tumor in horseshoe kidneys: A report from the National Wilms Tumor Study. J Urol 133:1002-1003, 1985 52. Tank ES, Melvin T: The association of Wilms' tumor with nephrologic disease. J Pediatr Surg 25:724-725, 1990 53. Knudson AG: Introduction to the genetics of primary renal tumors in children. Med Pediatr Oncol 21:193-198, 1993 54. Neri G, Martini-Neri ME, Katz BE, et al: The Perlman syndrome: Familial renal dyplasia with Wilms, fetal gigantism and multiple congenital anomalies. Am J Med Genet 19:195-207, 1984 55. Green DM, Breslow NE, Beckwith JB, et al: Screening of children with hemihypertrophy, aniridia, and Beckwith-Wiedemann syndrome in patients Wilms tumor: A report from the National Wilms Tumor Study. Med Pediatr Oncol 21:188-192, 1993 56. Andrews PE, Kelalis PP, Haase GM: Extrarenal Wilms' tumor: Results of the National Wilms Tumor Study. J Pediatr Surg 27:1181-1184, 1992 57. Bulas DI, Thompson R, Reaman G: Pulmonary emboli as primary manifestation of Wilms tumor. AJR 156:155-156, 1991 58. Cushing B, Slovis TL: Imaging of Wilms' tumor: What is important! Urol Radiol 14:241-251, 1992 59. Reiman TAH, Siegel MJ, Shackelford GD: Wilms tumor in children: Abdominal CT and US evaluation. Radiology 160:501-505, 1986 60. Thompson WR, Newman K, Seibel N, et al: A strategy for resection of Wilms' tumor with vena cava or atrial extension. J Pediatr Surg 27:912-915, 1992 61. Gururangan S, Wilimas JA, Fletcher BD: Bone metastases in Wilms' tumor--Report of three cases and review of literature. Pediatr Radiol 24:85-87, 1994 62. Belt TG, Cohen MD, Smith JA, et al: MRI of Wilms' tumor: Promise as the primary imaging method. A JR 146:955-961, 1986 63. Gylys-Morin V, Hoffer FA, Kozakewich H, et al: Wilms tumor and nephroblastomatosis: Imaging characteristics at gadolinium-enhanced MR imaging. Radiology 188: 517-521, 1993 64. Shady KL, Siegel M J, Brown J J: Preoperative evaluation of intraabdominal tumors in children: Gradientrecalled echo vs spin echo MR imaging. AJR 161:843-837, 1993 65. D'Angio GJ, Rosenberg H, Sharples K, et al: Position paper: Imaging methods for primary renal tumors of childhood: Costs versus benefits. Med Pediatr Oncol 21:205-212, 1993 66. Machin GA: Persistent renal blastema (nephroblastomatosis) as a frequent precursor of Wilms' tumor: A pathological and clinical review. Am J Pediatr Hematol Oncol 2:253-261, 1980 67. Stone MM, Beaver BL, Sun CCJ, et al: The nephroblastomatosis complex and its relationship to Wilms' tumor. J Pediatr Surg 25:933-938, 1990 68. White KS, Kirks DR, Bove KE: Imaging of nephroblastomatosis: An overview. Radiology 182:1-5, 1992 69. Fernbach SK, Feinstein KA, Donaldson JS, et al:
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Nephroblastomatosis: Comparison of CT with US and urography. Radiology 166:153-156, 1988 70. Cormier PJ, Donaldson JS, Gonzalez-Crussi F: Nephroblastomatosis: Missed diagnosis. Radiology 169:737738, 1988 71. Hausegger KA, Fotter R, Fluckiger F, et al: Can MR contribute to the diagnosis of nephroblastomatosis. A report of one case. Pediatr Radio121:533-535, 1991 72. Glass RRJ, Davidson AJ, Fernbach SK: Clear cell sarcoma of the kidney: CT, sonographic, and pathologic correlation. Radiology 180:715-717, 1991 73. Carcassonne M, Raybaud C, Lebreuil G: Clear cell sarcoma of the kidney in children: A distinct entity. J Pediatr Surg 16:645-648, 1981 74. Khali RM, Aubel S: Clear cell sarcoma of the kidney. Pediatr Radio123:407-408, 1993 75. Haas JE, Palmer NF, Weinberg AG, et al: Ultrastructure of malignant rhabdoid tumor of the kidney: A distinctive renal tumor of children. Hum Pathol 12:646-657, 1981 76. Sisler CL, Siegel MJ: Malignant rhabdoid tumor of the kidney: Radiologic features. Radiology 172:211-212, 1988 77. Eftekhari F, Erly WK, Jaffe N: Malignant rhabdoid tumor of the kidney: Imaging features in two cases. Pediatr Radio121:39-42, 1990 78. Chung CJ, Cammoun D, Munden M: Rhabdoid tumor of the kidney presenting as an abdominal mass in a newborn. Pediatr Radiol 20:562-563, 1990 79. Bonnin JM, Rubinstein LJ, Palmer NF, et al: The association of embryonal tumors originating in the kidney and in the brain: A report of seven cases. Cancer 54:21372146, 1984 80. Madewell JE, Goldman SM, Davis CJ, et al: Multilocular cystic nephroma: A radiographic-pathologic correlation of 58 patients. Radiology 146:309-321, t983 81. Banner MP, Pollack HM, Chatten J, et al: Multilocular renal cysts: Radiologic-pathologic correlation. AJR 136: 239-247, 1981 82. Josh[ VV, Beckwith JB: Multilocular cyst of the kidney (cystic nephroma) and cystic, partially differentiated nephroblastoma. Cancer 64:466-479, 1989 83. Albregts AE, Cohen MD, Galliani CA: Neuroblastoma invading the kidney. J Pediatr Surg 29:930-933, 1994 84. Rosenfeld NS, Leonidas JC, Barwick KW: Aggressive neuroblastoma simulating Wilms tumor. Radiology 166:165167, 1988 85. Panuel M, Bourliere-Najean B, Gentet JC, et al: Aggressive neuroblastoma with initial pulmonary metastases and kidney involvement simulating Wilms' tumor. Eur J Radiol 14:201-203, 1992 86. Day DL, Johnson R, Cohen MD: Abdominal neuroblastoma with inferior vena caval tumor thrombus: Report of three cases. Pediatr Radio121:205-207, 199i 87. Towbin R, Gruppo RA: Pulmonary metastases in neuroblastoma. AJR 138:75-78, 1982 88. Zerres K, Rudnik-Schoneborn S, Deget F, et al: Childhood onset autosomal dominant polycystic kidney disease in sibs: Clinical picture and recurrence risk. J Med Genet 30:583-588, 1993 89. Fick GM, Johnson AM, Strain JD, et al: Characteris-
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tics of very early onset autosomal dominant polycystic kidney disease. J Am Soc Nephrol 3:1863-1870, 1993 90. Ravine D, Walker RG, Gibson RN, et al: Treatable complications in undiagnosed cases of autosomal dominant polycystic kidney disease. Lancet 337:127-129, 1991 91. Kimberling WJ, Pieke-Dahl SA, Kumar S: The genetics of cystic diseases of the kidney. Semin Nephrol 11:596606, 1991 92. Bear JC, Parfrey PS, Morgan JM, et al: Autosomal dominant polycystic kidney disease: New information for genetic counselling. Am J Med Genet 43:548-553, 1992 93. Gabow PA, Johnson AM, Kaehny WD, et al: Risk factors for the development of hepatic cysts in autosomal
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dominant polycystic kidney disease. Hepatology 11:10331037, 1990 94. Levine E, Grantham J J: Calcified renal stones and cystic calcifications in autosomal dominant polycystic kidney disease: Clinical and CT study in 84 patients. AJR 159:7781, 1992 95. Broecker B: Renal cell carcinoma in children. Urology 38:54-56, 1991 96. Cassady JR, Filler R, Jaffe N, et al: Carcinoma of the kidney. Radiology 112:691-693, 1974 97. Kabala JE, Shield J, Duncan A: Renal cell carcinoma in childhood. Pediatr Radiol 22:209-205, 1992
L T H O U G H Wilms' tumor and neuroblastoma are the subject of numerous articles A in the pediatric, radiological and pathological literature, many other renal masses and neoplasms can occur. 1,2Each requires precise treatment, and each has a specific prognosis. The child's age (neonate, toddler, older child) and the clinical presentation are as important as the radiological findings when deciding what a renal mass is likely to be. Certain masses, such as multicystic dysplastic kidney or mesoblastic nephroma, may be diagnosed in utero by ultrasound (US) or shortly after birth by physical examination. Renal vein thrombosis, another cause of renal enlargement in the neonate, may produce hematuria. Other masses classically arise or are detected later. The most common cause of an enlarged flank in the neonate is hydronephrosis. This may be because of obstruction or reflux. Less pronounced hydronephrosis may be detected in utero or after urinary tract infection. A discussion of hydronephrosis is beyond the scope of this article, but the many appearances of hydronephrosis should be familiar to those evaluating children for potential renal masses. All imaging is directed toward answering clinical questions. Is the renal process medical or surgical? If surgical, what is the extent of local involvement, and are distant lesions also
present? Can pathology (and prognosis) be suggested? This article describes and illustrates many renal neoplasms of childhood. Leukemia and lymphoma of the kidney, usually seen in association with systemic disease, will not be presented. NEONATAL RENAL MASSES General
The techniques for evaluating renal masses have evolved from those described in valuable older references. 3,4 Excretory urography is now rarely used for this purpose. Also, the presentation of affected infants has similarly changed; renal masses are more likely to be detected on prenatal US than postnatal physical examination. Regardless of how the mass is detected, frequently the first and only imaging performed postnatally is US. Added to the usually mentioned multiple advantages of US (portability, multiplanar images, and lack of ionizing radiation and need for contrast injection) is the additional information provided by Doppler interrogation of key structures. Computed tomography (CT) and, less frequently, magnetic resonance (MR) imaging are used to evaluate those masses that are problematic after US examination° Multicystic Dysplastic Kidney
ABBREVIATIONS US, ultrasound; CT, computed tomography; MR, magnetic resonance; MCDK, multicystic dysplastic kidney; CMN, congenital mesoblastic nephroma; IVC, inferior vena eava; RVT, renal vein thrombus; ARKD, autosomal recessive polycystic kidney disease; ADKD, autosomal dominant polycystic kidney disease; CCSK, clear cell sarcoma of the kidney; RCC, renal cell carcinoma.
From the Radiology Department, Children's Memorial Hospital, Chicago, IL. Address reprint requests to Sandra K. Fernbach, MD, Radiology Dept, No. 9, Children's Memorial Hospital, Chicago, IL 60614. Copyright © 1995 by W.B. Saunders Company 0037-198X/95/3002-000855. 00/0 200
This abnormality, involving all of the kidney, is associated with atresia of the ipsilateral ureter. Bilaterality results in increased fetal loss or profound oligohydramnios with a rapid respiratory death after birth. 5 Pathological changes of multicystic dysplastic kidney (MCDK) in one renal segment have been described in kidneys drained by multiple ureters with atresia of the ureter from the abnormal segment (Fig 1). The early and complete obstruction of the kidney results in severe dysplastic changes. Nephrons diminish in number and noncommunicating cysts form. The number and size of the cysts is varied; some kidneys contain numerous small cysts and others are comprised of only one or two large cysts. Seminars in Roentgenology, Vol XXX, No 2 (April), 1995: pp 200-217
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Fig 1. Bilateralduplicated pelvocalyceal system with rightsided upper pole MCDK in an 8-day-old girl. (A} Transverse US of the right kidney with the largest cyst (arrows) located medially and deviating the lower pole segment (arrowheads) laterally, (B) VCUG showing reflux in the ipsilateral lower pole segment with displaced pelvocalyceal system (arrows) and contralateral reflux.
Contrary to earlier observations, based on operative or postmortem specimens, the MCDK is a nonstatic lesion. Sequential prenatal and postnatal US examinations have shown that cysts may enlarge, remain stable in size, or diminish.6-9 In a few children, the affected kidney may radiographically disappear and the central renal vessels may similarly undergo atrophy; in these children postnatal studies alone would suggest renal agenesis. In the infant, the typically functionless MCDK may show small amounts of renal function on
scintigraphy or CT. It is this residual function that may cause some cysts to enlarge, and it is the loss of this that may lead to eventual involution of the cysts and disappearance of the kidney. Fear that the MCDK might represent a malignant precursor and undergo malignant degeneration prompted the removal of virtually all of these until the early 1980s. Since then, several long-term studies have shown that the MCDK has no propensity toward malignant degeneration and also have documented that
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other potential complications such as infection are not likely. 1°-12Rarely, neoplasia will develop in the MCDK, as in any other tissue, but a recent report discusses the issue in actuarial terms and concludes that about 16,000 MCDK would have to be removed to prevent one Wilms' tumor-related death. ~3
Imaging There are two discrete types of MCDK, each with a specific US appearance. The classical form is comprised of multiple cysts of varying size in a random arrangement in abnormalappearing tissue (Fig 2). The hydronephrotic form, as the name suggests, simulates a dilated pelvocalyceal system; there is a large central fluid collection and the smaller cysts around it are approximately the same size and are circumferentially arrayed (Fig 3). Tests of renal function (scintigraphy), cyst puncture (or antegrade pyelogram), or retrograde ureterogram may be necessary to differentiate the hydronephrotic MCDK from the more usual causes of hydronephrosis. 14-16 The contralateral kidney must be evaluated for developmental anomalies such as ureteropel-
Fig 3. Hydronephrotic form of MCDK in 1-day-old boy, Transverse US with very large central cyst (curved arrows), multiple smaller peripheral cysts (arrowheads), and some solid tissue simulating renal parenchyma.
vic junction obstruction and vesicoureteral reflux, which occur in children with M C D K more frequently than in the general population. ~7,~8It should also be stressed that the contralateral kidney is the only functioning kidney and should be evaluated and treated as such.
Congenital Mesoblastic Nephroma
Fig 2. Classical form of MCDK in 1-week-old boy. Prone longitudinal US with larger peripheral cysts (arrows), smaller central cysts (curved arrows), and numerous other cysts (arrowheads).
This usually benign, unifocal, and unilateral renal mass comes to attention early because of intrauterine detection of the mass on US as well as recognition of the polyhydramnios that may develop when the mass impinges on and hampers emptying of the fetal stomach. 19,2° After birth, congenital mesoblastic nephroma (CMN) may be diagnosed by palpation or because of hypertension or feeding problems again attributed directly to the m a s s . 21'22 Bleeding into the mass has produced cystic change and may cause shock. 23,24 Associated hypercalcemia has been reported. 25 At least 75% of CMNs are detected by the time the child is 6 months of age. 21 Nephrectomy is generally performed rather than tumor excision; recurrence in the renal fossa or metastatic disease (to lung or brain) is rare. Pathological analysis of the tumor has been extended because microscopic review recognized it to be an entity distinct from Wilms' t u m o r . 26 On light microscopy, the tumor is
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comprised of spindle-shaped cells with few mitoses. Microscopic examination was also the first to associate some variant tumors with atypical cellularity and increased mitoses with an unusual aggressive biological behavior. 27 Cytopathological flow studies have shown that tumors with diploid cells b e h a v e i n the typical benign manner, but those with aneuploidy are more likely to recur or metastasize, as are those tumors detected in the older infant. 28 Studies of subcellular structures have also provided clues to the behavior of CMN. 29
Fig 4. CMN in a 7-week-old boy with a palpable right flank mass. (A) Abdominal radiography showing noncalcified mass displacing bowel loop from the right upper quadrant. (B) Transverse US of the solid-appearing heterogenous right upper quadrant mass (arrows) occupying the renal fossa. (C} Contrast-enhanced CT showing the nonenhancing mass with a thin rim of renal parenchyrna peripherally (arrowheads).
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Imaging Abdominal radiographs may fail to show the mass or may show displacement of adjacent bowel loops or a bulging flank (Fig 4A). Less than 5 % contain visible calcification. 21 On US, CMN is predominantly solid, but cystic or even calcified components may be identified (Fig 4B). 21 Examination of the inferior vena cava (IVC) should be performed although CMN does not extend into this; the presence of mass within the IVC suggests other
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diagnoses, such as renal vein thrombosis in the neonate or Wilms' tumor in the older infant. Computed tomography is necessary only when the diagnosis remains uncertain after US has been performed. Occasionally, renal function will be detected within the mass because of trapped but normal renal parcnchyma.3° On CT, CMN distorts the renal parenchyma, does not enhance with contrast, and may have a heterogenous appearance (Fig 4C). The intrarenal origin of the mass may be easier to appreciate with CT than US. The appearance of CMN on MR has been described but this technique is not generally needed for diagnosis.31
Renal Vein Thrombosis Most patients with renal vein thrombosis (RVT) present in the newborn period and are symptomatic. A few will be infants who had a solid renal mass or enlarged kidney detected on prenatal US. Older children with nephrotic syndrome or with a kidney transplant are also at risk for RVT. This section will be limited to RVT in the neonate. Because thrombosis begins in the interlobar and arcuate veins and progresses centrally, RVT is a misnomer. The clot may propagate to the renal vein and IVC. Depending on the extent of thrombosis and infarction, clinical signs of enlarged kidney, hematuria, and thrombocytopenia may develop. Because the normal newborn infant has a physiological oliguria associated with decreased renal blood flow, any condition that causes further reduction in renal blood flow predisposes to RVT. Dehydration or hemoconcentration may be caused by diarrhea, sepsis, maternal diabetes, or other conditions.
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Bilateral RVT may occur, or thrombosis may involve part or all of one kidney. The findings on US will be dependent on the portion(s) of the kidney(s) affected. In the acute and subacute stages, the kidney swells, corticomedullary differentiation deteriorates, and heterogenous cortical hyperechogenicity develops.3a,33 Doppler examination in the acute phase may show absent spectral or color flow in the involved segments. 34 Echogenic streaks bordering the medullary pyramids and interlobar septa representing thrombosed veins may be identified32,33 (Fig 5A). Collateral veins develop via the hilum and capsule within the first few days. In the subacute stage, flow may be present in the proper direction but lack typical pulsation from contraction of the right atrium 35 (Fig 6). Ipsilateral adrenal hemorrhage and RVT may coexist and do so more commonly on the left where the adrenal vein drains into the renal vein. The coexistence of these abnormalities may be because of (1) clot formation in one vein leading to clot in the other, or (2) overlapping risk factors such as sepsis and maternal diabetes. The appearance of the adrenal hemorrhage and the RVT will depend on age of the lesions.36.37 The US appearance at follow-up of RVT is varied. 38,39In some, kidney function and appearance return to normal. In others, the kidney retains normal function despite the finding of persistently calcified, lace-like renal veins (Fig 5B). The least favorable outcome is that of renal atrophy indistinguishable from reflux nephropathy or congenital hypoplasia. The majority, but not all, of affected children have normal renal function.g0,41
Imaging Before US was routinely available, contrast studies such as inferior vena cavography and excretory urography were the mainstays in diagnosis of RVT. Ultrasonography with highfrequency transducers and Doppler spectral and color-flow imaging is particularly well suited to evaluation of renal parenchymal and bloodflow abnormalities and is now routinely used to make the diagnosis of RVT. Both CT and MR also may be helpful if the calcification or masslike nature RVT makes it difficult to exclude CMN.
Autosomat Recessive Polycystic Kidney Disease Autosomal recessive polycystic kidney disease (ARKD), also known as infantile polycystic kidney disease, affects the kidneys and liver and has variable expression depending on whether the kidney or liver abnormalities predominate. Even siblings may have a variable presentation. 42 Pathologically, the kidney lesion is characterized by cystic dilatation of the collecting tubules with fewer-than-normal glomeruli present. The liver lesion consists of bile duct
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Fig 5. RVT in upper pole of the left kidney in a 5-week-old girl with prenatal diagnosis of kidney mass, (A) Prone transverse US of the left upper pole with echogenic interlobar veins (curved arrows) bordering the hypoechoic medullary pyramids. (B) Nonenhanced CT with calcifications in the left renal vein (arrowhead) and interlobar veins (arrows). This kidney opacified normally during contrast-enhanced CT.
hyperplasia and periportal fibrosis. Caroli disease, a nonobstructive dilatation of the biliary disease and sometimes included in the spectrum of choledochal cysts, has also been reported in infants with ARKD. 43 Normal-appearing kidneys may be present in early pregnancy, delaying diagnosis until the third trimester when enlarged echogenic kidneys are identified. Those fetuses with a small urinary bladder and oligohydramnios will have more severe renal disease. 44 In the symptomatic newborn, renal problems are dominant. The enlarged kidneys present as palpable flank masses and cause limited diaphragmatic excursion and respiratory compromise. 45,46Pulmonary hypoplasia and respiratory
distress also develop from oligohydramnios. Serum tests of renal function may be normal because in the newborn these are a reflection of maternal kidney function. However, after several days, the serum values will be representative of the degree of renal insufficiency. At times, laboratory and radiological examinations fail to differentiate ARKD from autosoreal dominant polycystic kidney disease (ADKD), especially in the older child. Clinical presentation may also overlap. Familial screening with US may fail to confirm ADKD, especially when the parents are young. In these settings, biopsy may be necessary to establish the diagnosis so that genetic counseling may be provided.
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Fig 6. RVT in 3-day-old girl with gross hematuria. Doppler spectral tracings of renal vessels show no forward flow in the artery during diastole (arrows). The venous waveform, below the baseline, lacks normal variation. The kidney itself (open arrows) is echogenic and lacks corticomedullary differentiation.
Imaging Ultrasonography is helpful in establishing the diagnosis of ARKD in the newborn period. The kidneys are enlarged, echogenic, and lack corticomedullary differentiation. A thin hypoechoic rim may be present and is thought to represent the compressed normal glomeruli or the markedly dilated tubules extending to the periphery47'48 (Fig 7A). With high frequency transducers ( > 7 MHz), some of the dilated collecting tubules may be resolved. They are then seen as tiny parallel radially oriented cysts instead of the echogenic parenchyma identified with lowerfrequency transducers (Fig 7B). Enlarged kidneys with delayed nephrograms are seen on excretory urography and contraste n h a n c e d c r . 49 On both studies contrast pooling in dilated collecting tubules produces a radially arranged striated nephrogram that may persist for many hours when the renal function is significantly decreased. The pelvocalyceal systems and ureters are not affected by ARKD. The older child with ARKD tends to have complications from portal hypertension such as gastrointestinal hemorrhage and hypersplenism. Ultrasonography findings also parallel those seen in portal hypertension from other causes:
splenic enlargement, varices, abnormal liver architecture with regions of increased echogenicity, and hepatofugal blood flow. Although the liver disease may be prominent, the kidneys are abnormal. In contrast to the disproportionate size of the kidneys in the neonatal period, the kidneys in older children may be more normal sized. Ultrasonography may detect both microcysts and macrocysts. On CT, cyst walls may contain calcifications responsible for appearance of nephrocalcinosis on US.S° THE TODDLER Wilms' Tumor
With an incidence of 7 to 8 cases per 1 million children per year, this is the most common abdominal (and renal) malignancy of childhood. There is an increased incidence of Wilms' tumor in children with sporadic aniridia, nephroblastomatosis, hemihypertrophy, horseshoe kidney, Beckwith-Wiedemann syndrome, chromosomal abnormalities, Drash syndrome, and Perlmann syndrome. 5145Renal parenchymal origin is usual, but rare extrarenal variants have been reported both within the abdomen and at distal nonabdominal sites 56 (Fig 8). The classical tumor has a triphasic (epithe-
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Fig 7. ARKD in 1-day-old boy with flank masses. (A) Coronal US of the enlarged kidney. A hypoechoic rim of parenchyma (arrowheads) encircles the echogenic medullary tissue. (B) Prone transverse US using a high-frequency transducer. Multiple small cysts (arrows) can be resolved deep to the hypoechoic rim.
lial, stromal, and blastemal) histology. Multiple derivatives of these tissues, including fat, may be identified on imaging as well as microscopic evaluation. Metastases to lung are more frequent than those to other organs; other lung complications have also been reportedS
Imaging The plain films may show mass displacing adjacent structures and filling the flank. Calcifi-
cations are rare, seen in about 5%, regardless of the imaging method used. 1,s8,59 Ultrasonography is the primary method for evaluating the site (or organ) of origin and the size, extent, and architecture of any abdominal tumor. The mass is typically quite large when detected clinically, over 10 cm in diameter. "Cysts" within contribute to the nonhomogeneous appearance; these develop because of tumor necrosis or deposits of mucin or may simply be trapped calyces.
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Fig 8. Extrarenal Wilms' tumor in a 2-year-old boy with midline abdominal mass. (A) Transverse US image through the lower abdomen shows a heterogenous mass (arrowheads) displacing bowel from this portion of the abdomen, (B) Contrastenhanced CT at a similar level, The large size of the mass (open arrows) is better appreciated on CT. The left ureter (arrow) is dilated as is the renal pelvis above (not shown) because of the mass compressing the ureter,
The IVC must be imaged to exclude tumor extension (even to the level of the right atrium), which has been identified in about 5% of children. 6° The presence of such tumor changes the staging of the tumor and the operation to be performed. 6° Intracaval extension may be shown with real-time US, and, if necessary, confirmed with Doppler. When the tumor is on the right,
compression of the IVC may narrow it and prevent its visualization. The contralatera! kidney must be examined for several reasons. Approximately 10% to 15% of tumors are bilateral at presentation, and detection of a second tumor alters the primary therapy. Anomalies that would alter surgery, such as contralateral renal agenesis or uretero-
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Fig 9. Wilms' tumor in a 6-year-old boy who complained of lump under ribs. (A} Contrastenhanced CT at the lower margin of the liver. A large low-density mass approaches the midline and displaces the left kidney inferiorly. A nodule (open arrow) of higher density tissue is continuous with the more solid-appearing mass below {Fig 9B) (B) CT scan a few centimeters below Fig 9A. The mass (open arrows) arises from the upper pole of the left kidney. The low density within the perinephric space (arrows) is caused by tumor beneath the renal capsule, Hematoma may develop because of venous obstruction and have a similar appearance.
pelvic junction obstruction, must be also be excluded. Frequently, CT is performed in the child with abdominal mass to differentiate Wilms' tumor from neuroblastoma 1,z,58,59(Fig 9). The diagnosis is likely to be Wilms' tumor if (1) the mass is intrarenal and the pelvocalyceal anatomy is distorted; or (2) vascular structures are displaced. Neuroblastoma is likely if (1) the mass has calcification (about one third do); (2) the mass is predominantly extrarenal and displaces
the kidney; (3) the mass crosses the midline; (4) vascular structures are encased; or (5) paraspinal and intraspinal extension of tumor is present. 2 Metastatic bone disease indicates that the diagnosis of neuroblastoma or renal tumor other than Wilms' is likely because this is rarely seen with the usual Wilms' tumor. 61 Magnetic resonance can show the tumor, IVC extension, and sites of metastatic disease well, but no tumor-specific signal intensity has been shown. 158,62-64However, the cost of the examina-
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tion has caused some experts to question its routine use in children with Wilms' tumor. Review of the plain films and US in children with usual-histology Wilms' tumor indicates that additional examinations rarely affect patient outcome. 65 Wilms' Tumor Variants and Other Renal Tumors
Nephroblastomatosis The persistence of primitive renal blastema beyond infancy is abnormal except in small microscopic rests. Larger amounts of primitive
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blastema, remaining in sheets in the cortex or in more discrete nodules, is termed nephroblastomatosis. 66 Recognition of nephroblastomatosis is important; it is associated with Wilms' tumor, especially bilateral Wilms' tumor. 67 It also seen in increased frequency in children with syndromes with a known association with Wilms tumor. Imaging. Nephroblastomatosis may cause multifocal distortion of the pelvocalyceal system or may be so peripheral to it that, despite extensive involvement, no changes are seen on excretory urography. 68,69Ultrasonographic detec-
Fig 10.
Nephroblastomatosis in a 3-month-old
boy with Beckwith-Wiedemann syndrome. (A) Con-
trast-enhanced CT through the upper pole of the left kidney. The recent US was normal, A single hypodense mass was present in the left upper pole. Two other cortical lesions were identified in the right kidney. (B) Coronal T2-weighted MR image through the kidneys. The left kidney {arrows) is enlarged, and there is a lesion with high signal intensity in the upper pole {arrowheads).
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tion of nephroblastomatosis is possible, but this technique lacks the sensitivity of CT and MR. 69 On US, the affected kidney may be enlarged, have an indistinct corticomedullary junction, and contain lucent nodular masses. Contrastenhanced CT superbly showS the abnormal tissue because it fails to enhance and is distinctly demarcated from adjacent normal parenchyma (Fig 10A): 69 Occasionally, regions of nephroblastomatosis are tiny and are missed with CT5 ° Because of the association of nephroblastomatosis with Wilms' tumor, there is some hesitancy to expose affected children to ionizing radiation that possibly could increase the rate of malignant transformation. For this reason, frequent detailed US examinations are performed to detect malignant change, suggested by rapid growth of any rest. However, MR can show nephroblastomatosis, and enhanced detection is possible after gadolinium injection68,71 (Fig 10B). The high cost of MR and the need for sedation seems to be limiting its use in the sequential evaluation of kidneys with nephroblastomatosis.
Clear Cell Sarcoma of the Kidney This unusual tumor (4% of renal tumors in childhood) may be difficult to differentiate from Wilms' tumor radiographically. However, clear cell sarcoma of the kidney (CCSK) is distinct histologically, with both a classical pattern containing cells with poorly staining cytoplasm and a well-described histological variant. 26,72No associated somatic abnormalities (hemihypertrophy, aniridia) have been recognized. CCSK behaves aggressively, with bony metastases (lytic more often than blastic) occurring much more frequently than in children with Wilms' tumor and the overall prognosis being much worse. 73,74
Rhabdoid Tumor of the Kidney This malignant renal tumor, accounting for about 2% of renal tumors in large series, is more frequent in infancy than any other period. 7579 AS with the other neonatal masses, it may be diagnosed in utero or because of abdominal mass, hypertension, or even hypercalcemia. Because of the age at the time of diagnosis, one may instead expect a CMN. The name, rhabdoid tumor, derives from the microscopic ap-
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pearance of tumor cells that resemble muscle cells. An association with brain tumors, especially medulloblastoma, has been recognized both in infants and in children presenting later in life. The brain tumor may precede the renal tumor or may develop several years later. Overall, the prognosis is much worse with rhabdoid tumor of the kidney than with other renal malignancies. Imaging. The preoperative radiological evaluation of the child with these two tumors does not differ from that of a child with Wilms' tumor because, in most cases, clinical presentation is similar and diagnosis is made after nephrectomy. Both CCSK and rhabdoid tumor of the kidney may have a radiological appearance indistinguishable from Wilms' tumor. 72-79 One important point is that neither of these tumors is ever bilateral. After pathological analysis indicates that CCSK or rhabdoid tumor is present, additional and specific studies should be performed. Because each of these may metastasize to bone, skeletal survey or scintigraphy is suggested. Radiological evaluation of the brain has been recommended in those with rhabdoid tumor, but because the brain tumor may not be synchronous with the kidney tumor, the need (or timing) of cranial CT or MR must be questioned.
Multilocular Cystic Nephroma An unusual tumor occurring in childhood and in adult life, the multilocular cystic nephroma derives its name from the gross appearance of the tumor. At one time, the tumor was believed to be primarily a benign lesion; previously used names for the tumor stressed this, eg, cystic adenoma, cystic lymphangioma, cystic hamartoma. 8°,81 When seen in children, the tumor affects boys more than girls; in adults, women are more frequently affected.S1,s2 An analysis of cystic tumors sent for review by the National Wilms' Tumor study group lead to a useful reclassification of these, s2 Cystic lesions with differentiated cellular elements (but no blastemal or embryonal elements) may continue to be designated cystic nephroma. This, according to the authors, is probably a neoplastic variant, although none of the five reviewed recurred or metastasized. When the septa of
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cystic renal masses contain blastemal or embryohal elements, the term cystic partially differentiated nephroblastoma is appropriate. This, too, tends to behave in a fairly benign manner, but local recurrence has been documented. The most aggressive or malignant of the cystic lesions is the solid Wilms' tumor with focal or multifocal cystic change; this, in contrast to the
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others, has distinct solid tissue within the tumor. Most of these cystic tumors are detected because of related symptoms, with renal mass being the most common clinical finding. Imaging. Older reports described the findings on excretory urography, angiography, and retrograde ureterograms. Because these tech-
Fig 11. Cystic partially differentiated nephroma in an 18month-old boy with abdominal mass, (A} Transverse US showed the multiple Iocules within the mass. The relationship to the kidney and other structures could not be shown on any one image because of the large size of the mass. (B) Contrast-enhanced CT. The affected left kidney is stretched around the septated mass, which is crossing the midline, dispacing bowel, and deforming the contour of the abdominal wall.
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niques are rarely used for evaluating masses, it is more important to be familiar with the findings on US. The cystic nature of the mass and the septations are usually easy to show (Fig 11). The solid component may be visible or may be difficult to show with US or CT. For this reason, speCific radiological diagnosis may be impossible; nephrectomy is performed and diagnosis is made after pathological analysis.
Intrarenal Neuroblastoma When arising below the diaphragm, neuroblastoma usually develops in the retroperitoneoum from the adrenal gland and displaces the kidney. However, in a few children, neuroblastoma can simulate Wilms' tumor by arising from tissue within the kidney or by invasion of the kidneybyneuroblastoma. 83,84Some neuroblastomas manifest other behaviors more typical of Wilms' tumor: pulmonary metastases, intracaval extension of tumor thrombus.85,s6,87
THE OLDER CHILD Autosomal Dominant Polycystic Kidney Disease Autosomal dominant polycystic kidney disease (ADKD) is one of the most common autosomal dominant conditions and usually presents in the third to fifth decade of life. A small subgroup with ADKD may be symptomatic in childhood, with hypertension, enlarged kidneys, proteinuria, or impaired renal function. ss,s9 Because of the prevalence of the condition, the number of children with clinically significant ADKD may be similar to that of ARKD. Another group of children are asymptomatic but have had abnormal kidneys discovered on prenatal examination or during investigation of an unrelated condition (Fig 12). Family screening of asymptomatic children is warranted because complications of ADKD such as hypertension and urinary tract infection are present in up to one third of affected postpubertal children and require treatment to delay the onset of end-stage renal disease and avert rupture of associated berry aneurysm.9° Cerebral and abdominal aortic aneurysms as well as colonic diverticular disease do not appear to be childhood problems. ADPD may be classified into two types according to the location of the abnormal gene. 91 In
Fig 12. ADKD in a 6-year-old girl with urinary tract infection. Longitudinal US of the right kidney (arrowheads) shows multiple cysts (arrows).
90%, the abnormal gene is located on the short arm of chromosome 16; the other loci have not been found.
Imaging In the past excretory urography with nephrotomography was the standard method and showed enlarged kidneys with multiple radiolucencies
Fig 13. ARKD in a 1-day-old girl with flank masses. Transverse US of the right lobe of the liver shows small cystic structures in the liver (curved arrows). Doppler showed that these were not vascular, but could not differentiate hepatic cysts from focal bUiary dilatation. The kidneys had an appearance believed to be classic for ARKD. Biopsy was performed because of the liver cysts and confirmed ARKD.
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Fig 14. ADKD in an 8-year-old boy with recent hematuria. Contrast-enhanced CT shows asymmetric involvement with many large cysts (dominant mass) in the anterior portion of the right kidney (arrowheads] and a few small cysts in the left kidney,
and distorted calyces. On US, the kidneys may contain simple or complex (hemorrhagic) cysts. The cysts arise anywhere along the nephron or collecting duct. Asymmetric involvement is not uncommon (Fig 14). Because ADPD is a progressive disease, cysts and renal enlargement become more apparent with increasing age. Ultrasonography screening of asymptomatic children in the first decade has a false-negative diagnosis rate of 36%. 9z Those with symptoms related to ADKD are more likely to have cysts that can be identified on US. Because simple cysts occur in less than 1% to 2% of children, an "at-risk" child with at least one cyst in each kidney or several cysts in one kidney should be diagnosed with ADKD. Hepatic cysts have been identified in postpubertal children (Fig 13) and may be confused with the ductal dilatation present in Caroli's disease, a known association with ARKD.93
On CT, the cysts distort the pelvocalyceal system and do not enhance with contrast on early or delayed images. Calculi and cyst calcifications are complications readily evaluated with CT. 94
Renal Cell Carcinoma
Renal cell carcinoma (RCC) comprises about 5% of all pediatric renal tumors and is more frequent in adults than children. It tends to affect older children (around 10 years of age) than does Wilms' tumor and has a much worse prognosis. 95-97 The presentation is not unlike that of all other pediatri c renal tumors. On CT, RCC is a solitary nonenhancing mass, and on US, the mass appears echogenic. %,9v Although it may calcify in as many as 75% of cases, it can be distinguished from other renal tumors by histology alone. 97
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