Adapting pediatric health care responses to the COVID-19 pandemic in Japan: A clinical perspective.

The COVID-19 pandemic required our pediatric health care staff to adjust to many irregularities and solve serious issues in our routine clinical practice. In outpatient clinics, many children exhibited common cold symptoms that mimic COVID-19, thus we initially screened patients via an interview form, then later via SARS-CoV-2 antigen test. Cluster infections were entirely avoided by following systematic, everyday precautions. Patientsquality of life has been difficult to maintain during the pandemic, due to social and staffing restrictions. Other unexpected repercussions - such as an unexpected lack of seasonal virus infections, then a respiratory syncytial (RS) virus outbreak - required agile management of hospital resources. While we must continue to adapt our treatment programs in response to the evolving COVID-19 crisis, it remains essential to support the well-being of children through regular health check-ups, mental health support, educational opportunities, proper socialization, and close communication with parents and families.

Detection of antiviral drug resistance in patients with congenital cytomegalovirus infection using long-read sequencing: a retrospective observational study.

BACKGROUND: Congenital human cytomegalovirus (cCMV) infection can cause sensorineural hearing loss and neurodevelopmental disabilities in children. Ganciclovir and valganciclovir (GCV/VGCV) improve long-term audiologic and neurodevelopmental outcomes for patients with cCMV infection; however, antiviral drug resistance has been documented in some cases. Long-read sequencing can be used for the detection of drug resistance mutations. The objective of this study was to develop full-length analysis of UL97 and UL54, target genes with mutations that confer GCV/VGCV resistance using long-read sequencing, and investigate drug resistance mutation in patients with cCMV infection. METHODS: Drug resistance mutation analysis was retrospectively performed in 11 patients with cCMV infection treated with GCV/VGCV. UL97 and UL54 genes were amplified using blood DNA. The amplicons were sequenced using a long-read sequencer and aligned with the reference gene. Single nucleotide variants were detected and replaced with the reference sequence. The replaced sequence was submitted to a mutation resistance analyzer, which is an open platform for drug resistance mutations. RESULTS: Two drug resistance mutations (UL54 V823A and UL97 A594V) were found in one patient. Both mutations emerged after 6 months of therapy, where viral load increased. Mutation rates subsided after cessation of GCV/VGCV treatment. CONCLUSIONS: Antiviral drug resistance can emerge in patients with cCMV receiving long-term therapy. Full-length analysis of UL97 and UL54 via long-read sequencing enabled the rapid and comprehensive detection of drug resistance mutations.

Lectin-Like Oxidized Low-Density Lipoprotein Receptor-1-Related Microglial Activation in Neonatal Hypoxic-Ischemic Encephalopathy: Morphologic Consideration.

Neonatal hypoxic-ischemic encephalopathy (nHIE) is a major neonatal brain injury. Despite therapeutic hypothermia, mortality and sequelae remain severe. The lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is associated with the pathophysiology of nHIE. In this study, morphologic change and microglial activation under the nHIE condition and LOX-1 treatment were investigated. The microglial activity and proliferation were assessed with a novel morphologic method, immunostaining, and quantitative PCR in the rat brains of both nHIE model and anti-LOX-1 treatment. Circumference ratio, the long diameter ratio, the cell area ratio, and the roundness of microglia were calculated. The correlation of the morphologic metrics and microglial activation in nHIE model and anti-LOX-1 treated brains was evaluated. LOX-1 was expressed in activated ameboid and round microglia in the nHIE model rat brain. In the evaluation of microglial activation, the novel morphologic metrics correlated with all scales of the nHIE-damaged and treated brains. While the circumference and long diameter ratios had a positive correlation, the cell area ratio and roundness had a negative correlation. Anti-LOX-1 treatment attenuated morphologic microglial activation and proliferation, and suppressed the subsequent production of inflammatory mediators by microglia. In human nHIE, round microglia and endothelial cells expressed LOX-1. The results indicate that LOX-1 regulates microglial activation in nHIE and anti-LOX-1 treatment attenuates brain injury by suppressing microglial activation.

Sulfadiazine Hypersensitivity and Desensitization in Children With Congenital Toxoplasmosis: A Report on Two Cases.

Combination therapy for toxoplasmosis consists of sulfadiazine, pyrimethamine and leucovorin. Although sulfadiazine can cause hypersensitivity reactions, such as fever, rash and liver dysfunction, there is no consensus on an effective therapy for congenital toxoplasmosis (CTox) without sulfadiazine. We attempted desensitization to sulfadiazine in 2 patients with CTox and sulfadiazine hypersensitivity. Desensitization was achieved for 1 patient.

Synergic interaction between ritodrine and magnesium sulfate on the occurrence of critical neonatal hyperkalemia: A Japanese nationwide retrospective cohort study.

Our aim was to evaluate the association between ritodrine and magnesium sulfate (MgSO4) and the occurrence of neonatal hyperkalemia or hypoglycemia among late preterm infants in a retrospective cohort study. We used a nationwide obstetrical database from 2014. A total of 4,622 live preterm infants born at 32-36 gestational weeks participated. Fourteen risk factors based on both clinical relevance and univariate analysis were adjusted in multivariable logistic regression analyses. Neonatal hyperkalemia and hypoglycemia occurred in 7.6% (284/3,732) and 32.4% (1,458/4,501), respectively. Occurrence of hyperkalemia was associated with concomitant usage of ritodrine and MgSO4 compared with no usage (adjusted odds ratio [aOR] 1.53, 95% confidence interval [CI] 1.09-2.15). Occurrence of hypoglycemia was associated with ritodrine alone (aOR 2.58 [CI 2.21-3.01]) and with concomitant usage of ritodrine and MgSO4 (aOR 2.59 [CI 2.13-3.15]), compared with no usage, and was associated with long-term usage (≥ 48 hours) of ritodrine and cessation directly before delivery. In conclusion, in late preterm infants, usage of ritodrine together with MgSO4 was associated with occurrence of critical neonatal hyperkalemia, and long-term usage of ritodrine and cessation directly before delivery were associated with neonatal hypoglycemia.

Congenital Cytomegalovirus Pneumonitis and Treatment Response Evaluation Using Viral Load during Ganciclovir Therapy: a Case Report.

Cytomegalovirus (CMV) is the most common cause of congenital infection. Pneumonitis is considered to be a rare manifestation although congenital CMV infection presents with various non-specific findings. Ganciclovir and valganciclovir are beneficial for improving neurodevelopmental sequelae and hearing outcomes of congenital CMV infection; however, treatment response evaluation is not well reported. We report a female case of congenital CMV infection presenting with pneumonitis, meningoencephalitis, and chorioretinitis. She was treated with intravenous ganciclovir for 6 weeks, and clinical features improved. Measurement of the CMV genome load by real-time polymerase chain reaction assay was performed during treatment. After the administration of ganciclovir, the CMV genome was not detected in the blood and levels decreased gradually in the urine. Physicians should consider the possibility of congenital CMV infection in neonates who present with respiratory distress. Furthermore, measurement of the CMV genome load in blood and urine may be useful for evaluating treatment response.

Respiratory Stabilization after Delivery in Term Infants after the Update of the Japan Resuscitation Council Guidelines in 2010.

BACKGROUND: The Japan Resuscitation Council (JRC) updated the guidelines for neonatal cardiopulmonary resuscitation in 2010, which recommended appropriate oxygen supplementation under the assessment of oximetry, with continuous positive airway pressure (CPAP) as a consideration in the delivery room. Whether this update has resulted in an improvement of respiratory stabilization in term neonates has not been well investigated to date. OBJECTIVES: The aim of this study is to evaluate the impact of the update of the JRC Guidelines in 2010 on the frequency of respiratory support for term neonates within 24 h of life in the nursery or neonatal intensive care unit (NICU). METHODS: We conducted a retrospective, single-center study using data of term neonates born between 2008 and 2009 (defined as 'group 1', before the update of the guidelines), and between 2011 and 2012 (defined as 'group 2', after the update of the guidelines). We compared resuscitation procedures in the delivery room and respiratory support in the nursery or NICU within 24 h of life between the two groups. Respiratory support included oxygen therapy, nasal CPAP and mechanical ventilation. RESULTS: A total of 5,036 infants were analyzed. In group 2, oxygen administration in the delivery room was significantly decreased (38.9 vs. 22.1%, p < 0.001) and face mask CPAP in the delivery room increased (1.7 vs. 11.1%, p < 0.001). The prevalence of respiratory support within 24 h of life in the nursery or NICU increased significantly in group 2 (group 1, 6.8% vs. group 2, 16.6%, p < 0.001). CONCLUSIONS: The update of the JRC Guidelines in 2010 resulted in an increase of respiratory support for term infants within 24 h of life.

Musculoskeletal abnormalities in congenital diaphragmatic hernia survivors: Patterns and risk factors: Report of a Japanese multicenter follow-up survey.

BACKGROUND: The aim of this study was to investigate the natural history and associated predictors of musculoskeletal deformities in congenital diaphragmatic hernia (CDH) survivors. METHODS: A multicenter retrospective survey was conducted among CDH patients between January 2006 and December 2010 in Japan, and a follow-up survey was performed between September 2013 and October 2013. One hundred and eighty-two (79.8%) of the 228 patients were alive. An orthopedic survey of 159 survivors without severe coexisting congenital anomalies was subsequently carried out, and the rates of pectus excavatum (PE), scoliosis and chest asymmetry were evaluated. RESULTS: Scoliosis, PE and chest asymmetry were found in 20 (12.6%), 19 (11.9%) and 12 (7.5%) patients, respectively. In total, 44 patients (27.7%) developed orthopedic abnormalities. Reduction in the oxygenation index within 24 h after birth (P = 0.044), large diaphragmatic defects (P = 0.047) and patch repair (P = 0.014) were predictive for scoliosis. In addition, Apgar score at 5 min was significantly lower in the patients who developed PE (P = 0.034); and stomach herniation (P = 0.004) and liver herniation (P = 0.013) at prenatal diagnosis and large diaphragmatic defects (P = 0.036) were predictive of chest asymmetry. CONCLUSIONS: Approximately one-quarter of the survivors developed musculoskeletal abnormalities in the present survey of CDH patients. These data suggest that each musculoskeletal abnormality has its own specific predictors.

Growth Assessment and the Risk of Growth Retardation in Congenital Diaphragmatic Hernia: A Long-Term Follow-Up Study from the Japanese Congenital Diaphragmatic Hernia Study Group.

INTRODUCTION: Little information exists about the physical growth of patients with congenital diaphragmatic hernia (CDH). This study aimed to assess the growth of patients with CDH during long follow-up periods, and to identify growth retardation (GR) risk factors. PATIENTS AND METHODS: A multicenter retrospective observational study was conducted in 2013. Of the 228 patients with CDH born between 2006 and 2010, 182 (79.8%) survived to discharge, and 174 cases were included in the study. Body weights and heights were measured at 1.5, 3, and 6 years of age. GR was defined as a Z-score relating to the weight or height of < - 2.0. Cases with GR at 1.5, 3, or 6 years of age comprised the GR group. The clinical variables of the GR and non-GR groups were compared using univariate analysis. Multiple logistic regression analyses were conducted successively on the factors that were significant at p < 0.01 in the univariate analysis and had low correlations with other factors (r < 0.7). The numerical data were divided into two groups based on a cutoff value that was calculated from a receiver operating characteristic curve. RESULTS: The GR group comprised 35 cases (22.7%). The rates of GR at 1.5, 3, and 6 years of age were 19.5 (26/133), 14.4 (16/111), and 13.5% (5/37), respectively. The body weight Z-scores improved in cases with GR between the ages of 1.5 and 3 years (p = 0.036). As the patients aged, the wasting type of GR decreased in frequency (31, 0, and 0% at 1.5, 3, and 6 years of age, respectively) and the stunting type of GR increased in frequency (27, 31, and 100% at 1.5, 3, and 6 years of age, respectively). The univariate analysis showed that birth weight and height, liver-up, large defect size of the diaphragm, use of nitric oxide, patch repair, long hospital stay, home oxygen treatment (HOT), and vasodilator administration at discharge were significant risk factors of GR. The multivariate analysis determined that a birth weight of < 2,698 g (odds ratio [OR] = 5.5, 95% confidence interval [CI] = 2.1-16.8, p < 0.001) and HOT (OR = 5.8, 95%CI = 1.6-23.8, p = 0.007) were significant risk factors for GR. CONCLUSION: GR was observed in 22.7% of the CDH survivors. Body weight improved between 1.5 and 3 years of age in the GR cases, but some patients developed chronic malnutrition via acute malnutrition. Low birth weight and the need for HOT were GR risk factors. Aggressive management of acute malnutrition may improve the growth of patients with CDH.

Surgical approaches for neonatal congenital diaphragmatic hernia: a systematic review and meta-analysis.

PURPOSE: The optimal surgical approach for neonatal congenital diaphragmatic hernia (CDH) remains unclear. We conducted a systematic review and meta-analysis of the effectiveness of endoscopic surgery (ES) for neonatal CDH. METHODS: A systematic literature search was conducted using MEDLINE and the Cochrane Library. Studies that compared surgical approaches for neonatal CDH were selected. Mortality and recurrence of herniation were analyzed as primary endpoints. Each study was evaluated following the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system. RESULTS: Eight observational studies comparing ES and open surgery (OS) met the criteria. As compared with the OS group, the ES group showed both a significantly lower mortality rate [risk ratio (RR) 0.18, 95 % confidence interval (CI) 0.09-0.38, p < 0.0001] and a significantly higher recurrence rate (RR 3.10, 95 % CI 1.95-4.88, p < 0.00001). However, serious selection bias was seen in seven of the eight studies-because the indication of ES had been determined intentionally, the ES groups may have included less severe cases. CONCLUSION: Although the evidence was insufficient, ES was clearly associated with more recurrence than was OS. Therefore, ES should not be the routine treatment for every neonate. It is crucially important to select suitable cases for ES.

Pulmonary air leak associated with CPAP at term birth resuscitation.

OBJECTIVE: The Japan Resuscitation Council (JRC) Guidelines 2010 for neonatal resuscitation introduced continuous positive airway pressure (CPAP) in delivery room. The present study evaluated the effect of CPAP for pulmonary air leak at term birth. DESIGN, SETTING AND PATIENTS: This retrospective single-centre study used the data of term neonates who were born without major congenital anomalies at our centre between 2008 and 2009, and between 2011 and 2012. INTERVENTIONS: Resuscitation according to the JRC Guidelines 2010. MAIN OUTCOME MEASURES: We examined the association between the JRC Guidelines 2010, CPAP by face mask and pulmonary air leak. RESULTS: A total of 5038 infants were analysed. The frequency of CPAP by face mask increased after the update of the JRC Guidelines in 2010 (1.7% vs 11.1%; p<0.001). Pulmonary air leak increased at early term (37 weeks: 1.0% vs 3.5%, p=0.02; 38 weeks: 0.7% vs 2.2%, p=0.02). While adjusting for confounders, the JRC Guidelines 2010 was associated with pulmonary air leak in early-term neonates (37 weeks: adjusted OR (aOR) 4.37; 95% CI 1.40 to 17.45; 38 weeks: aOR 2.80; 95% CI 1.04 to 8.91), but this association disappeared while adjusting for face mask CPAP additionally (37 weeks: aOR 1.90; 95% CI 0.47 to 8.71; 38 weeks: aOR 1.66; 95% CI 0.54 to 5.77). CONCLUSIONS: Following the update of the JRC guidelines on neonatal resuscitation, we observed an increased use of CPAP via face mask, which was associated with a higher prevalence of pulmonary air leak in early-term neonates in our centre.

Mineral status of premature infants in early life and linear growth at age 3.

BACKGROUND: Preterm infants are at significant risk of reduced bone mineral content and subsequent bone disease (metabolic bone disease of prematurity, MBDP). MBDP is frequently found in very low-birthweight (VLBW) infants, but long-term height prognosis is not well known. METHODS: VLBW infants from two major neonatal intensive care units were studied. Medical records were reviewed. A total of 143 subjects were analyzed after excluding subjects who died, or who had severe complications that could affect linear growth, Silver-Russell syndrome, severe cholestasis, and/or chromosomal abnormality. The relationship between MBDP and height at age 3 was investigated. RESULTS: Height standard deviation score (SDS) at age 3 negatively correlated with peak serum alkaline phosphatase (ALP) activity in early life (r = -0.30, P = 0.0003) and positively correlated with serum phosphorus (P) at peak ALP (r = 0.33, P = 0.0002). In addition, serum P independently affected height SDS at 3 years of age (ß = 0.19, P = 0.018), and was significantly different between infants with and without catch-up growth in height (difference: 0.23 mmol/L, 95%CI: 0.09-0.36, P = 0.0010). CONCLUSIONS: MBDP, particularly hypophosphatemia in the early period of life, is associated with linear growth until 3 years of age in VLBW infants.

A Thr72Ala polymorphism in the NKG2D gene is associated with early symptomatic congenital cytomegalovirus disease.

The potential risk factors for congenital cytomegalovirus (cCMV) infection or development of disease remain unclear. Here, we investigated the genetic polymorphisms in natural killer (NK) group 2, member D (NKG2D), an activating receptor expressed on NK cells, and in MHC class I-related chains A, the ligand of NKG2D, in 87 cCMV cases, and found that there was a significant association between cCMV disease and a single nucleotide polymorphism, Thr72Ala, in NKG2D.

Risk factors for the recurrence of the congenital diaphragmatic hernia-report from the long-term follow-up study of Japanese CDH study group.

AIM OF THE STUDY: Few follow-up studies focused on the recurrence regarding the postoperative course of congenital diaphragmatic hernia (CDH) survivors. The aim of this study was to report on risk factor for CDH patients who had the recurrence during the follow-up. MATERIALS AND METHODS: A multicenter retrospective survey was conducted on neonates diagnosed to have CDH between January 2006 and December 2010. Follow-up survey was conducted between September 2013 and October 2013 (ethical approval: No. 25-222). Nine institutions agreed to participate in this survey. Out of 228, 182 (79.8%) patients were alive and 180 patients were included in this study. Two patients were excluded because the defect had not repaired at the primary operation. The patients were divided into the recurrence group (n=21) and the nonrecurrence group (n=159). Postnatal and postoperative variables were compared between these two groups. Baseline variables which showed significance in univariate analysis were entered into multiple logistic regression analysis for analyzing the recurrence. A value of p<0.05 was considered to be statistically significant by using the JMP software program (version 9; SAS Institute, Inc, Cary, North Carolina, United States). MAIN RESULTS: Out of 180, 21 (11.7%) CDH neonates had the recurrence during the course of the follow-up. Five (2.8%) patients had the recurrence before primary discharge and 16 (8.9%) patients had the recurrence after discharge. Univariate analysis showed that liver herniation (crude odds ratio [OR], 7.4; 95% confidence interval [CI], 2.73-23.68), defect size C and D, proposed by the CDH Study Group (crude OR, 7.09; 95% CI, 2.73-19.99) and patch repair (crude OR, 5.00; 95% CI, 1.91-14.70) were risk factors. Multivariate logistic regression analysis showed liver herniation (adjusted OR, 3.96; 95% CI, 1.01-16.92) was the risk factor for the recurrence. CONCLUSION: A wide spectrum of the disease severity and the rarity of the disease mask the risk of the recurrence for CDH patients. This study showed the only factor to predict the recurrence was the liver herniation. These data will be helpful for providing information for the long-term follow-up of the CDH patients.

Prognostic factors of gastroesophageal reflux disease in congenital diaphragmatic hernia: a multicenter study.

PURPOSE: Gastroesophageal reflux disease (GERD) is one of the concomitant problems in infants with congenital diaphragmatic hernia (CDH). We assessed risk factors of GERD in CDH patients. METHODS: The retrospective observational study for CDH infants was conducted. Cases of CDH who were born between January 2006 and December 2010, were operated in the 9 participating institutions, and survived to discharge were included. Completion of medical therapy for GERD and incidence of surgery were primary outcomes. Kaplan-Meier survival analysis and Cox proportional hazards regression were used. RESULTS: In 182 cases of CDH, the medical therapies for GERD were performed in 23.8% (40/168), and were completed in 60.0% (24/40). Prenatal detection of CDH (HR 5.87, CI 1.6-18.8, p = 0.012) and tube feeding at discharge (HR 5.04, 95% CI 1.3-33.1, p = 0.016) were significantly correlated with unsuccessful weaning from medical therapy. Surgery for GERD was performed in 10.7% (18/169). Gestational age (HR 4.78, 95% CI 1.5-21.1, p = 0.006) and diaphragmatic defect of more than 75% (HR 4.3, 95% CI 1.6-12.9, p = 0.005) were significantly correlated with need for antireflux surgery. CONCLUSION: Diaphragmatic defect of more than 75% was risk factor of future need for antireflux surgery.

Polymorphisms in TLR-2 are associated with congenital cytomegalovirus (CMV) infection but not with congenital CMV disease.

BACKGROUND: Cytomegalovirus (CMV) is the most common cause of congenital virus infection. However, the risk factors for infection in utero and for progression to a severe clinical outcome remain uncertain. Recent studies have identified associations of specific single nucleotide polymorphisms (SNPs) in Toll-like receptor (TLR) genes with susceptibility to infections of some viruses and with their clinical outcome. METHODS: Genetic polymorphisms in the TLR-2, TLR-4, and TLR-9 genes were analyzed in 87 children with congenital CMV infections by the TaqMan allelic discrimination assay. The frequencies of genotypes in the general Japanese population were obtained from the National Center for Biotechnology Information (NCBI) databases. Associations between the analyzed SNPs and congenital CMV infection or disease were evaluated. RESULTS: The CC genotype at SNP rs3804100 in the TLR-2 gene was significantly associated with congenital CMV infection but not with congenital CMV disease. Furthermore, the AG genotype at SNP rs1898830 in the TLR-2 gene tended to be identified less frequently in children with congenital CMV infection. There were no statistically significant associations between SNPs in the TLR-4 and TLR-9 genes and congenital CMV infection or disease. CONCLUSION: TLR-2 polymorphisms may have some association with congenital CMV infection, although the mechanism underlying this effect remains to be clarified.

Skin and subcutaneous blood flows of very low birth weight infants during the first 3 postnatal days.

OBJECTIVE: To determine whether skin and subcutaneous blood flow measurements using a novel laser Doppler flow meter are useful for evaluating the cardiovascular status of very low birth weight (VLBW) infants during the early postnatal period. METHODS: In eight VLBW infants and eight non-VLBW infants born at Tokyo University Hospital between May 2007 and April 2008, forehead and lower limb skin blood flows were measured continuously for 72 h. Data were averaged every 8 h, and the t-test was used for analysis. RESULTS: In VLBW infants, forehead blood flow started to increase from the start of measurement to 32 h (16.6 +/- 3.9 ml/min vs. 24.1 +/- 2.1 ml/min; p = 0.002 compared with 8 h) and remained constant thereafter. Lower limb blood flow increased rapidly after 24 h (22.2 +/- 5.5 ml/min vs. 29.5 +/- 5.0 ml/min; p = 0.002 compared with 8 h) and continued increasing thereafter. In contrast, blood flows remained constant in non-VLBW infants. CONCLUSIONS: The results showed that skin and subcutaneous perfusion in VLBW infants increased spontaneously at around 24 h. Differences in blood flow changes between VLBW and non-VLBW infants demonstrate that these parameters successfully identified physiological changes in tissue perfusion in VLBW infants.

Survival in a neonate with complete urorectal septum malformation sequence after fetal vesico-amniotic shunting for a prominently dilated cloaca.

Complete urorectal septum malformation sequence (URSMS) is usually a lethal anomaly that is characterized by urethral obstruction, imperforate anus, ambiguous genitalia, renal agenesis or dysplasia, and mullerian duct maldevelopment. This anomaly is thought to be caused by the cessation of urorectal septum migration toward the caudal cloacal membrane. Teratogenic factors or a genetic abnormality is postulated as the etiology. To date, only 4 patients with URSMS have survived the neonatal period; however, 2 of these infants died before the age of 1 year. We report the survival in a case with complete URSMS who had moderate pulmonary hypoplasia and preserved left renal function. The cloacal remnant was dilated more than expected because the wall of the muscle layer was torn, perhaps in early fetal life, and timely placement of vesico-amniotic shunts prevented severe pulmonary hypoplasia caused by oligohydramnios.

Antenatally diagnosed giant multicystic dysplastic kidney resected during the neonatal period.

At 24 weeks of gestation, a fetus was suspected of having a huge intraabdominal cyst by fetal ultrasound. Multicystic dysplastic kidney (MCDK) was the most probable diagnosis; however, because a solid area was visualized in the large cystic lesion, a neoplasm of the kidney could not be ruled out. A 3529-g boy was born at 35 weeks of gestation by cesarean delivery. Eight days after birth, the tumor was resected. Histopathologic examination confirmed MCDK. The cause of MCDK in this patient was assumed to be ureteral obstruction in early fetal life. These findings suggested that the affected kidney had experienced mesenchyme-to-epithelium transition followed by interaction between the metanephric blastema and ureteral bud.