Clinical course of unilateral multicystic dysplastic kidney and contralateral kidney in Korean children: a single-center, retrospective study

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Child Kidney Dis. 2026;30(2):118-126

Publication date (electronic) : 2025 October 24

doi : https://doi.org/10.3339/ckd.25.025

Min Ji Park¹, Hee Sun Baek¹, Min Hyun Cho¹

¹Department of Pediatrics, School of Medicine, Kyungpook National University, Daegu, Republic of Korea

Correspondence to Min Hyun Cho Department of Pediatrics, Kyungpook National University Hospital, School of Medicine, Kyungpook National University, 130 Dongdeok-ro, Jung-gu, Daegu 41944, Republic of Korea E-mail: chomh@knu.ac.kr

Received 2025 August 1; Revised 2025 August 29; Accepted 2025 September 4.

Abstract

Introduction

Multicystic dysplastic kidney (MCDK) is a non-inherited cystic kidney disease resulting in a non-functioning kidney due to abnormal kidney development [1]. In 1955, MCDK was distinguished as a separate disease entity from polycystic kidney disease, a classification that remains current [2]. Although the developmental etiology of MCDK is not fully understood, two main hypotheses have been proposed. First, the obstruction theory, suggests that MCDK results from severe fetal ureteral obstruction. The second attributes MCDK to abnormal interactions between the ureteric bud and metanephric mesenchyme during kidney development [3,4]. Bilateral MCDK results in oligohydramnios and fatal pulmonary hypoplasia due to absent kidney function in the fetus and newborn, leading to nonviability in most cases. In contrast, unilateral MCDK is associated with a functioning contralateral kidney and typically presents without significant clinical issues, except for rare cases with a large abdominal mass [1].

Unilateral MCDK is among the most common kidney anomalies detected by prenatal ultrasound, with an incidence of 1 in 2,200 to 1 in 4,300 births [5]. While previous studies reported hypertension and malignancy as potential complications, recent long-term follow-up studies and systematic reviews have lessened these concerns [6-8]. However, vesicoureteral reflux (VUR) in the contralateral functioning kidney has been reported in approximately 30% of cases, and there is increasing interest in the growth and long-term function of the solitary kidney [5]. Compensatory hypertrophy of the contralateral kidney is present in about one-quarter of patients at birth and in 77% at follow-up, and is directly associated with involution of the MCDK [9,10]. In childhood and adolescence, several studies have examined the impact of compensatory hypertrophy of the contralateral kidney on residual kidney function [5,11].

Using long-term follow-up data from Korean pediatric patients with unilateral MCDK, this study analyzed the clinical course of unilateral MCDK and the contralateral kidney, including changes in kidney length and comorbid complications, and explored their associations. In particular, we evaluated the incidence and clinical significance of compensatory hypertrophy by comparing age-specific contralateral kidney length with normative data from Korean children.

Methods

Study population and data sources

This retrospective study was conducted at a tertiary referral hospital. We reviewed the medical records of 71 pediatric patients diagnosed with unilateral MCDK who were followed for more than 12 months between January 2005 and December 2024.

In our hospital, patients diagnosed with unilateral MCDK at birth underwent ultrasonography at 3, 6, 12, 18, and 24 months, and annually thereafter, with follow-up continued until the age of 10 years. All ultrasound measurements were recorded with the patient’s age at the time of imaging. Kidney length of the contralateral kidney was also monitored and compared with normative reference data from healthy Korean children. The normative data were obtained from sonographic kidney length growth charts published by Oh et al. [12], which provide mean kidney length and standard deviation (SD) values for each age group. For the analysis of serial changes in compensatory hypertrophy of the contralateral kidney by age (Figs. 1-3), five patients with moderate to severe hydronephrosis in the contralateral kidney were excluded to minimize confounding effects on kidney size. Hydronephrosis was defined as SFU grade 1 or higher according to the Society for Fetal Urology (SFU) grading system. Hydroureter was defined as ureter dilatation with diameter >4 mm in infants under 6 months, >5 mm in children 6 months to 2 years, and >7 mm in children older than 2 years, based on age-adjusted normal values. Compensatory hypertrophy was defined as a kidney length exceeding +2 SD above the age-specific mean based on normative data.

Fig. 1.

Prevalence of compensatory hypertrophy in the contralateral kidney by age: a cross-sectional analysis. Normative data were sourced from the sonographic kidney length growth charts published by Oh et al. [12], which report mean kidney length and standard deviation (SD) values for each age group. Compensatory hypertrophy was defined as a kidney length greater than +2 SD above the age-specific mean according to pediatric normative data.

Fig. 2.

Comparison of right contralateral kidney length (disease mean) in unilateral MCDK with normal right kidney length (normal mean) in healthy Korean children. Normative data were sourced from the sonographic kidney length growth charts published by Oh et al. [12], which report mean kidney length and SD values by age group. Compensatory hypertrophy was defined as a kidney length greater than +2 SD above the age-specific mean according to pediatric normative data. MCDK, multicystic dysplastic kidney; SD, standard deviation.

Fig. 3.

Comparison of left contralateral kidney length (disease mean) in unilateral MCDK with normal left kidney length (normal mean) in healthy Korean children. Normative data were sourced from the sonographic kidney length growth charts published by Oh et al. [12], which report mean kidney length and SD values by age group. Compensatory hypertrophy was defined as a kidney length greater than +2 SD above the age-specific mean according to pediatric normative data. MCDK, multicystic dysplastic kidney; SD, standard deviation.

Results

Baseline characteristics

Among the 71 patients, unilateral MCDK was located on the left side in 39 cases (54.9%). The mean age at diagnosis was 1.1 months (range, 1 day–18 months), and the male-to-female ratio was 28:43. The mean follow-up duration was 7.3 years (range, 1–17 years), and 63 patients (88.7%) were diagnosed with MCDK by prenatal ultrasonography (Table 1). In 66 of 71 patients (93.0%), MCDK was confirmed as a non-functioning kidney by DMSA scan. In 52 of 71 patients (73.2%), VCUG was performed to diagnose VUR. VUR was identified in three patients: one with ipsilateral VUR and two with contralateral VUR. Apart from VUR, other kidney and urinary tract anomalies were detected in 16 patients (22.5%): 10 involving the contralateral kidney and six involving the ipsilateral MCDK. In the contralateral kidneys, all 10 patients had hydronephrosis, and one also had hydroureter. Among the ipsilateral kidneys, three had ureterocele, two had ectopic ureter, and one had hydroureter (Table 1).

Table 1.

Baseline clinical characteristics of study patients

Clinical course of MCDK and contralateral kidney

Table 2 presents the clinical course and outcomes of the 71 patients. The mean MCDK length measured by ultrasonography in patients diagnosed within 3 months of age was 4.2±1.7 cm. Of all patients, 41 (57.7%) showed complete (n=4, 5.6%) or partial involution (n=37, 52.1%) of MCDK within 6 months of age. In total, 66 patients (93.0%) exhibited complete or partial involution of MCDK by 2 years of age, and all patients (n=5, 7.0%) who did not show regression by age 2 underwent nephrectomy due to continued increase in MCDK size. The mean length of the contralateral kidney was 5.3±0.7 cm in patients diagnosed within 3 months of age. For patients followed up to age of 10 years, the mean contralateral kidney length was 10.6±0.8 cm, and the mean estimated glomerular filtration rate (eGFR) was 102±27.2 mL/min/1.73 m². Hypertension was observed in only one patient (1.4%), and three patients (4.2%) developed low eGFR during follow-up (Table 2). The patient with hypertension had contralateral hydronephrosis and recurrent UTIs progressing to chronic kidney disease (CKD) by age 4 years and end-stage kidney disease by age 10 years, when stage 2 hypertension was documented during hospitalization and antihypertensive medication was initiated. Among the three patients with low eGFR, one presented with CKD (eGFR, 38 mL/min/1.73 m²) and severe contralateral hydronephrosis at the time of MCDK diagnosis at age 1 year. Another patient had normal kidney function until age 9 years without contralateral abnormalities, was subsequently lost to follow-up, and returned at age 17 years with decreased eGFR to 60 mL/min/1.73 m².

Table 2.

Clinical course and outcomes of patients with MCDK

Comparison according to involution status

Table 3 presents a comparison of clinical outcomes between 66 patients who experienced involution of MCDK by age 2 years and those who did not. No significant differences were observed in sex or laterality of MCDK between the groups. However, a significant difference existed in the length of the MCDK at age 2 years; this trend was also noted at birth, though it did not reach statistical significance. The presence of MCDK involution was not associated with the size of the contralateral kidney. All five patients without involution underwent nephrectomy at a mean age of 4.6 years, and all pathological findings confirmed multicystic kidney dysplasia without evidence of malignancy (Table 3). These patients had been initially diagnosed at a mean age of 7 days, with the affected kidney measuring a mean size of 5.6 cm at the time of diagnosis.

Table 3.

Clinical outcomes by MCDK involution status at 2 years

Discussion

MCDK, one of the most common congenital anomalies of the urinary tract, is characterized by multiple, non-communicating cysts of varying sizes separated by dysplastic parenchyma and absence of a normal pelvicalyceal system [3].

Unilateral MCDK has been described extensively in the literature, with clinical characteristics varying among studies and geographic regions [3,9,13-15]. Aslam and Watson [13] in the UK reported that 33% of MCDK cases had fully involuted by age 2 years in a 10-year follow-up, 47% by age 5 years, and 59% by age 10 years. VUR was observed in 19% of contralateral kidneys, with 96% of these cases being mild to moderate reflux. No patients developed hypertension, proteinuria, or malignancy during follow-up. A German study of 75 unilateral MCDK patients found total involution in 25% and size reduction in 60%. No malignancy was reported; VUR was present in only 4.5%, and compensatory hypertrophy of the contralateral kidney occurred in 43% [9]. In a U.S. study by Mansoor et al. [15], analysis of 101 children with unilateral MCDK showed VUR in 16.8%, ureteropelvic junction obstruction in 4.1%, and megaureter in 2.4% of contralateral kidneys. By age 5 years, 60% of MCDK had completely involuted, and compensatory hypertrophy was confirmed in 74.1%. Notably, the risk of CKD and hypertension was significantly increased when contralateral anomalies were present [15]. In a Japanese study of 128 children with MCDK, 50% were diagnosed antenatally, with a mean age at diagnosis of 2.8 years. VUR was found in 9.5% of contralateral kidneys, and compensatory hypertrophy was observed in 59.4% during a 1-year follow-up. One patient developed hypertension, and seven patients (5.5%) underwent nephrectomy [3]. A Korean study from 2006 reported that among 46 unilateral MCDK patients, 24% experienced complete involution and 41% partial involution over a 30-month follow-up. The average time to complete involution was 37 months. One patient developed hypertension and decreased kidney function; no cases of malignancy were observed [14]. In the present study of 71 patients, the mean age at diagnosis was 1.1 months, and 63 patients (88.7%) were diagnosed by prenatal ultrasonography. Aside from VUR diagnosed in three patients, additional kidney and urinary tract anomalies were found in 16 patients (22.5%): 10 in the contralateral kidney and six in the ipsilateral MCDK. Complete or partial involution occurred in 66 patients (93.0%) within 2 years of age. All patients (n=5, 7.0%) who did not experience regression by age 2 years underwent nephrectomy due to continued MCDK growth. Despite differences in age at diagnosis and follow-up duration among published studies, most report complete or partial involution in over 70% to 80% of cases during follow-up. Notably, this study found that 93% of patients had complete or partial involution by age 2 years. The particularly young mean age at diagnosis in this study likely reflects the high proportion of prenatal diagnoses via ultrasonography.

There is ongoing debate regarding the necessity of kidney scintigraphy and VCUG in the evaluation of unilateral MCDK [16,17]. Kidney scintigraphy demonstrates the absence of kidney function in MCDK, offering a different clinical perspective from ultrasonography. Hannallah et al. [16] retrospectively reviewed 172 unilateral MCDK cases to assess the necessity of kidney scintigraphy, comparing the prevalence of VUR, recurrent UTIs, and CKD between patients diagnosed solely by ultrasonography and those assessed with both modalities. They concluded that kidney scintigraphy is not essential for diagnosis, as no significant differences were found between groups, though it may be useful in select follow-up scenarios. In the present study, DMSA scans confirmed non-functioning kidneys in 66 of 71 patients (93.0%). VCUG is sometimes performed in all unilateral MCDK patients, depending on institutional protocols, as previous reports indicate VUR may be present in 4.5% to 47% of cases [17-19]. A recent study by Blachman-Braun et al. [17] found that the likelihood of severe VUR was low when the contralateral kidney appeared normal on ultrasound, suggesting that VCUG should be reserved for patients with suspected contralateral structural abnormalities. In this study, VCUG was performed in 73.2% of patients, specifically those with anomalies of the contralateral kidney on ultrasound or a history of UTI. Among these patients, only three cases of VUR were identified, all of which were grade 3 or lower and did not require surgical intervention. These findings suggest that the necessity of routine VCUG in MCDK patients warrants reconsideration.

Most children with a congenital solitary functioning kidney exhibit compensatory hypertrophy of the contralateral kidney [6,11]. Gaither et al. [6] reported that among patients diagnosed with unilateral MCDK before age 2 years, the mean time to involution was 5.5 years, and the mean time to contralateral hypertrophy was 2.7 years. After adjusting for MCDK side, sex, age, and cohort status, each additional year of involution after age 2 was associated with a 0.35 cm increase in contralateral kidney length compared to patients without involution. Wang et al. [11] reported that in pediatric patients with a solitary kidney, each 1 cm increase in kidney length due to contralateral hypertrophy was associated with a 7.8 mL/min/1.73 m² increase in GFR. Matsell et al. [20] noted that prognosis depends on the etiology of congenital solitary functioning kidney. Compared to unilateral MCDK, unilateral kidney agenesis is more frequently associated with genetic syndromes and genitourinary malformations, resulting in a poorer long-term prognosis due to higher rates of hypertension and proteinuria. In this study, compensatory hypertrophy was most prevalent in the first month of life, declined to its lowest at 3 to 4 years, and subsequently increased through adolescence, reaching 81.8% at 9 to 10 years. Unlike previous studies that reported a continuous increase in compensatory hypertrophy with age, our findings revealed a biphasic age-related pattern. We propose that this pattern may reflect two distinct mechanisms: an early adaptive response in neonates and progressive compensatory growth during later childhood and adolescence. Furthermore, patients with complete involution of the dysplastic kidney by 7 to 8 years showed a 2.2-fold higher likelihood of developing compensatory hypertrophy in the contralateral kidney, although this association did not reach statistical significance. Therefore, complete involution of MCDK may serve as a useful predictor of compensatory hypertrophy in the contralateral kidney. Notably, patients with left-sided MCDK had significantly higher rates of contralateral compensatory hypertrophy compared to those with right-sided MCDK, indicating more frequent compensatory hypertrophy in the right kidney. We speculate that this may be due to the typically smaller baseline size of the right kidney, allowing greater potential for compensatory growth when left-sided MCDK is present.

Conversely, according to the hyperfiltration hypothesis, sustained increases in filtration load on the contralateral kidney may result in glomerular injury, ultimately leading to glomerulosclerosis, systemic hypertension, proteinuria, and impaired kidney function [13-15,21,22]. In a systematic review by Hutchinson et al. [21], among patients with congenital solitary functioning kidney due to unilateral kidney agenesis or MCDK, the incidence rates during follow-up were 10.1% for proteinuria, 7.4% for hypertension, and 8.4% for reduced kidney function. In the present study, among patients followed up to 10 years of age, the mean contralateral kidney length was 10.6±0.8 cm, and the mean eGFR was 102±27.2 mL/min/1.73 m². Hypertension was observed in only one patient (1.41%), and three patients (4.23%) developed kidney insufficiency during follow-up. Recently, Poggiali et al. [23] proposed a clinical predictive model for kidney injury in children with congenital solitary functioning kidney, identifying serum creatinine, recurrent UTI, and contralateral kidney length as three independent predictors. In 2022, the Italian Society of Pediatric Nephrology issued consensus recommendations for the management of congenital solitary kidney, categorizing patients into three risk groups based on long-term outcomes and outlining management strategies for each group. Cases with compensatory hypertrophy were classified as low risk, those without compensatory hypertrophy or with additional genitourinary malformations as medium risk, and those with reduced kidney function, hypertension, or proteinuria as high risk. For patients in the medium- and high-risk groups, regular monitoring of kidney function was recommended [24].

This study had several limitations. First, as a retrospective single-center study, the sample size was small, and observation periods varied among patients. Consequently, it was not possible to assess the relationship between final eGFR values and compensatory hypertrophy of the contralateral kidney. Additionally, the absence of long-term follow-up data limited the evaluation of complications such as proteinuria and decreased kidney function in patients with a solitary functioning kidney. Second, potential interobserver variability in serial kidney size measurements should be considered. Despite these limitations, this study presents long-term follow-up data on unilateral MCDK in Korean children and is notable for providing the first analysis of compensatory hypertrophy of the contralateral kidney using age-specific normative data for Korean children.

In conclusion, if complete or partial involution of unilateral MCDK is confirmed by age 2 years in Korean children, spontaneous resolution is likely, and universal screening for associated VUR may not be required. Furthermore, compensatory hypertrophy of the contralateral kidney increases progressively from birth and is observed in approximately 80% of patients by age 10 years.

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