Radiology Quiz

Radiology quiz

Dianna M.E. Bardo, MD

aSpring 2001

A newborn boy was referred for evaluation of an abdominal mass seen on prenatal ultrasound. An abdominal ultrasound was performed.

QUESTIONS: A. What is the abnormality of the left kidney (Figure 1)?
B. What is the diagnosis?
C. What additional imaging studies should be ordered now and for long-term follow-up?
D. What other renal anomalies are commonly associated?

ANSWERS: A. Multiple anechoic, noncommunicating cysts are seen in the left renal fossa. No normal renal structures are visualized (Figure 1); a normal left kidney is not seen, and the left ureter is not seen.
B. DIAGNOSIS: Multicystic dysplastic kidney (MCDK).
C. Abdominal ultrasound is performed to determine the presence or absence of other anomalies, especially of the contralateral kidney. Renal cortical scintigraphy should be performed to confirm the lack of renal function in the suspected MCDK and the status of function in the contralateral kidney. The presence of vesicoureteral reflux is assessed using voiding cystourethrography (VCUG) or radionuclide cystography (RNC).
D. Vesicoureteral reflux (VUR) and contralateral ureteropelvic junction (UPJ) obstruction are commonly associated with MCDK.

DISCUSSION: Abnormalities of renal development range from complete renal agenesis to disturbances of normal growth and differentiation. The pathogenesis of multicystic dysplastic kidney (MCDK) is poorly understood. MCDK is believed to be secondary to abnormal branching of the ureteric bud into the metanephros, which results in an obstructing defect in the developing kidney. MCDK is therefore in the spectrum of renal pelvic or ureteropelvic junction (UPJ) obstruction. Clusters of cysts develop instead of normal renal parenchyma. The ipsilateral ureter is atretic. The timing of the insult and the site of obstruction are important factors in determining the degree of renal dysplasia. Bilateral MCDK is incompatible with postnatal life.1-3

The incidence of MCDK is 3 in 10,000 live births and is more often seen in males (2.4:1). Bilateral MCDK occurs more often in females (2:1). Many cases are diagnosed by prenatal ultrasound.1,3 When not discovered on a prenatal ultrasound exam, MCDK may be discovered in a neonate as an abdominal mass. After hydronephrosis, MCDK is the second most common abdominal mass in the neonate.4 Associated renal abnormalities include vesicoureteral reflux (VUR) and contralateral UPJ obstruction. VUR may be ipsilateral and extend into the distal segment of an atretic ureter or into the contralateral ureter and renal collecting system. Recent studies have found VUR into the contralateral ureter in 25% of cases, and into an atretic ipsilateral ureter in 16%. Contralateral UPJ obstruction is observed in 10% of cases of MCDK. MCDK occurs on the left side between 39% and 60% of the time. Nonrenal anomalies, most often cardiac, are seen in 35% of cases. Hypertension and potential for malignancy are problems that can arise with MCDK.1,3

In the newborn, renal ultrasound confirms the anatomic abnormality, the condition of the contralateral kidney, and the presence or absence of other organ system abnormalities (Figure 2). Renal cortical scintigraphy should be performed to evaluate renal function. Usually, the MCDK is not perfused, and therefore is not visualized scintigraphically (Figure 3). A voiding cystourethrogram (VCUG) or radionuclide cystogram (RNC) should be performed to demonstrate the presence of vesicoureteral reflux (Figure 4).5

In the past, the routine treatment of MCDK included resection of the dysplastic kidney. Currently, serial renal ultrasound is recommended to document stability of the size and appearance of the affected kidney and its eventual involution. Rates of complete MCDK involution are quoted as high as 73.6%.6 Current practice supports conservative treatment and serial imaging of the kidneys to monitor involution of the MCDK and development of abnormalities. Patients with documented VUR are treated with prophylactic antibiotics. Nephrectomy remains a treatment option for patients who develop hypertension, in the very rare instance of malignancy, or in whom involution is not complete.1–3

REFERENCES

1. Lazebnik N, Bellinger MF, Ferguson JE, Hogge JS, Hogge A. Insights into the pathogenesis and natural history of fetuses with multicystic dysplastic kidney disease. Prenat Diagn. 1999;19:418–423.

2. Feldenberg LR, Siegel NJ. Clinical course and outcome for children with multicystic dysplastic kidneys. Pediatr Nephrol. 2000;14:1098–1101.

3. Sukthankar S, Watson AR. Unilateral multicystic dysplastic kidney disease: defining the natural history. Acta Pediatr. 2000;89:811–813.

4. Buonomo C, Taylor GA, Share JC, Kirks DR. In: Practical Pediatric Imaging. Gastrointestinal Tract. New York, NY: Lippincott-Raven: 1998; chap 8: 836.

5. Barenewolt CE, Paltiel HJ, Lebowitz RL, Kirks DR. In: Practical Pediatric Imaging. Genitorurinary Tract. New York, NY: Lippincott-Raven: 1998; chap 9: 1049–1052.

6. Kessler OJ, Ziv N, Livne PM, Merlob P. Involution rate of multicystic renal dysplasia. Pediatrics. 1998;102(6):e73.

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