Implications of bidirectional flow in the great arteries at the 11-14-week scan.

OBJECTIVE: To determine the implications of a bidirectional Doppler flow pattern detected in one or both of the fetal great arteries in the first trimester. METHODS: Database records were reviewed for cases of bidirectional flow found on fetal echocardiography performed at less than 15 weeks of gestation between January 1999 and October 2006 inclusive. Bidirectional flow consisted of antegrade flow in systole and retrograde flow in diastole. Data including indication for fetal echocardiography, gestational age at diagnosis, the anatomical features, karyotype, nuchal translucency measurement and outcome were collected. RESULTS: From almost 2500 scans, bidirectional flow was detected in a total of 15 fetuses. The abnormal flow pattern was confined to the aorta in four, to the pulmonary artery in four, and was present in both great arteries in a further seven fetuses. Eight of the 15 fetuses had regurgitation at one or both atrioventricular valves. Additional cardiac abnormalities were detected by ultrasound in eight cases. Of the 13 cases for which the karyotype was known, 12 were abnormal and five of these had trisomy 18. None of the fetuses survived. There were two intrauterine deaths and 13 terminations of pregnancy. CONCLUSION: Bidirectional flow in one or both great arteries is an unusual finding at the first-trimester scan and must be distinguished from the retrograde flow occurring only in systole in duct-dependent heart defects. It carries a poor prognosis, which is a consequence of both the high chance of underlying chromosomal abnormality and the hemodynamic compromise associated with severe arterial valve regurgitation.

Tetralogy of Fallot in the fetus in the current era.

OBJECTIVES: To compare the spectrum of tetralogy of Fallot detected recently in fetal life with that in previous reports of prenatal and postnatal experience. METHODS: All cases of tetralogy of Fallot, including those with pulmonary atresia, diagnosed between 1998 and 2005 inclusive were identified. Additional data for the 129 cases were collected, including associated congenital heart malformations, nuchal translucency measurement, karyotype and outcome. RESULTS: The most common reason for referral was a suspicion of heart malformation at the routine obstetric ultrasonography scan and referrals increased during the study period. The mean gestational age at diagnosis was 20.6 weeks. The nuchal translucency measurement was above the 95th centile in 37 (47%) of the 78 fetuses in which it had been measured, and in 19/37 of the chromosomally normal fetuses. Of 112 fetuses with chromosomal analysis, 55 (49%) had anomalies, including 22q11 microdeletion in 15. There were additional extracardiac malformations in 65/129 cases (50%) and additional cardiac malformations in 73 (57%). In 70/129 (54%) cases, the parents chose termination of pregnancy. Overall survival to date in the continuing pregnancies is 77%. CONCLUSIONS: Tetralogy of Fallot is increasingly recognized during routine fetal obstetric scanning. However, the spectrum of disease detected in the fetus remains biased towards those cases with extracardiac malformations and those with complex disease. As a result, even in the current era, the prognosis for the whole group of fetal cases under the diagnostic heading of tetralogy of Fallot continues to be much less favorable than would be expected of a postnatal series.

Right aortic arch in the fetus.

OBJECTIVE: To examine our experience of the detection of a right aortic arch in the fetus over an 8-year period. METHODS: Between February 1998 and December 2005, all patients prospectively diagnosed with a right aortic arch at our center were identified from our database and the videotape reviewed. In addition, the videotapes of 300 normal and 110 abnormal arbitrarily selected fetal echocardiograms, as well as 123 cases of tetralogy of Fallot and nine of a common arterial trunk were reviewed. Data including indication for fetal echocardiography, gestational age at diagnosis, karyotype, nuchal translucency measurement and outcome were collected. RESULTS: A right aortic arch was diagnosed prospectively in 55 fetuses and in a further 20 on retrospective videotape review. There were 21 examples of isolated aortic arch and four thought to have a double arch. A right arch was found in association with additional intracardiac malformations in 50 cases. The detection rate of a right aortic arch increased over the study period. The majority of patients were referred for a suspicion of congenital heart disease on obstetric scanning. Mean gestational age at diagnosis was 21 weeks. The karyotype including 22q11 status was known in 45/75 cases. There were 23 confirmed karyotypic anomalies, 12 of which were 22q11 deletions, occurring in 2/25 of the isolated group and 10/48 of the complex group, with a further two complex cases that were likely to have had 22q11 microdeletions. There were 29 pregnancy interruptions, four intrauterine deaths, 31 live births, four neonatal deaths and three patients lost to follow-up. The remaining four pregnancies are continuing. Of the four with suspected double arch, three were confirmed postnatally. CONCLUSION: The diagnosis of a right-sided aortic arch can be made by fetal echocardiography, either as an isolated lesion or in association with other cardiac malformations, from as early as 12 weeks' gestation. It can be difficult to distinguish from a double arch. Its increasing incidence over time in our series probably indicates that the diagnosis was previously overlooked. Karyotyping in the absence of other abnormal findings may be unnecessary in every case, but establishment of 22q11 microdeletion status in those cases with other anomalies is important.

Relationship between nuchal translucency thickness and prevalence of major cardiac defects in fetuses with normal karyotype.

OBJECTIVE: To define the prevalence of major cardiac defects according to nuchal translucency (NT) thickness at the 11 to 13 + 6-week scan in fetuses with normal karyotype. METHODS: Specialist fetal echocardiography was carried in 6921 fetuses with normal or presumed normal karyotype at a median gestation of 20 (range 12-35) weeks. The indications for fetal echocardiography were increased NT thickness (n = 3444), detailed second-trimester scan either for assessment of risk of chromosomal abnormalities (n = 2980) or previous or family history of fetal defects (n = 497). The cardiac defects were grouped into six functional categories: septal defect, left inflow obstruction, right inflow obstruction, left outflow obstruction, right outflow obstruction and other. RESULTS: Major cardiac defects were identified in 132 (19.1 per 1000) fetuses and the prevalence increased with fetal NT thickness from 4.9 per 1000 in those with NT below the median, to 8.7 for NT between the median and less than the 95th centile, 18.2 for NT between the 95th and 99th centiles, and exponentially thereafter to 35.2, 64.4 and 126.7 for respective NTs of 3.5-4.4 mm, 4.5-5.4 mm and > or = 5.5 mm. There was no obvious difference in the distribution of NT in the different types of cardiac defects. CONCLUSIONS: The prevalence of major cardiac defects increases exponentially with fetal NT thickness and in fetuses with NT of 3.5 mm or more it is higher than in pregnancies with a family history of cardiac defects.

Likelihood ratio for trisomy 21 in fetuses with tricuspid regurgitation at the 11 to 13 + 6-week scan.

OBJECTIVE: To determine the likelihood ratio for trisomy 21 in fetuses with tricuspid regurgitation at the 11 to 13 + 6-week scan. METHODS: Fetal echocardiography was carried out by specialist pediatric cardiologists in 742 singleton pregnancies at 11 to 13 + 6 weeks' gestation and pulsed wave Doppler was used to ascertain the presence or absence of tricuspid regurgitation. To avoid confusion with other adjacent signals, a strict definition of tricuspid regurgitation was used, in that it had to occupy at least half of systole and reach a velocity of over 80 cm/s. The fetal crown-rump length (CRL) and the nuchal translucency (NT) thickness were measured and the presence of any congenital heart abnormality noted. Follow-up of the pregnancy was carried out to determine the presence of chromosomal abnormalities. The likelihood ratio for trisomy 21 in fetuses with and without tricuspid regurgitation was determined. RESULTS: The tricuspid valve was successfully examined in 718 (96.8%) cases. Tricuspid regurgitation was present in 39 (8.5%) of the 458 chromosomally normal fetuses, in 82 (65.1%) of the 126 with trisomy 21, in 44 (53.0%) of the 83 with trisomy 18 or 13, and in 11 (21.6%) of the 51 with other chromosomal defects. The prevalence of tricuspid regurgitation was also associated with fetal CRL, delta NT and the presence of cardiac defects. Logistic regression analysis, irrespective of cardiac defects, demonstrated that in the chromosomally normal fetuses significant independent prediction of the likelihood of tricuspid regurgitation was provided by fetal delta NT (odds ratio (OR), 1.26; 95% CI, 1.34-1.41; P < 0.0001), while in trisomy 21 fetuses prediction was provided by CRL (OR, 0.94; 95% CI, 0.89-0.99; P = 0.021). The likelihood ratio for trisomy 21 for tricuspid regurgitation was derived by dividing the likelihood in trisomy 21 by that in normal fetuses. In the chromosomally normal fetuses, the prevalence of tricuspid regurgitation in those with cardiac defects was 46.9% and 5.6% in those without cardiac defects, and the likelihood ratio of tricuspid regurgitation for cardiac defects was 8.4. CONCLUSION: At 11 to 13 + 6 weeks' gestation, there is a high association between tricuspid regurgitation and trisomy 21, as well as other chromosomal defects. The prevalence of tricuspid regurgitation increases with fetal NT thickness and is substantially higher in those with, than those without, a cardiac defect.

Fetal echocardiography in trisomy 18.

BACKGROUND: Previously reported pathological series suggest that cardiac malformations are universal in trisomy 18. We examined our experience of fetal echocardiography in trisomy 18 for comparison. METHODS: Of 255 fetuses with trisomy 18 detected in our centre between January 1999 and June 2004, 174 were evaluated using fetal echocardiography. Our results were compared to four previous echocardiographic and four autopsy series, comprising 89 and 110 patients, respectively. RESULTS: Of these 174 fetuses, 114 were examined between 10 and 14 weeks gestation and the remainder between 15 and 33 weeks. An increased nuchal translucency measurement was the reason for referral in most of the early cases and extracardiac anomalies in the remainder. Images were non-diagnostic in 12 cases (7%), all examined at <15 weeks gestation. Abnormal cardiac findings were detected in 118 of the remaining 162 fetuses (73%), including 15 with functional anomalies. The various heart malformations included ventricular septal defects, tetralogy of Fallot, left heart disease, and atrioventricular septal defects. In all series used for comparison, a similar diversity of disease was seen. In pathological series of trisomy 18, structural heart malformations were found in all cases, but some had lesions which would not be detectable echocardiographically in the fetus. CONCLUSION: Abnormal cardiac findings are detectable echocardiographically in the majority of cases of trisomy 18 examined during fetal life, but not in all. A wide spectrum of heart defects is seen. Diagnosis of heart malformations can be made reliably, even in the first trimester at the time of nuchal translucency measurement.

Doppler assessment of cardiac function at 11-14 weeks' gestation in fetuses with normal and increased nuchal translucency.

OBJECTIVE: To investigate cardiac dysfunction as a potential underlying mechanism for increased nuchal translucency (NT) in fetuses with chromosomal abnormality or heart defects. METHODS: Myocardial performance index (MPI) and atrioventricular valve E/A ratios for both sides of the heart were measured by Doppler echocardiography in fetuses at 11-14 weeks' gestation. The study groups consisted of 159 normal control fetuses, 199 otherwise normal fetuses but with increased NT > or = 4 mm, 142 fetuses with trisomy 21, 58 with trisomy 18, 19 with trisomy 13, 37 with Turner's syndrome and 24 with isolated heart defects. Groups were compared using Student's t-test and confidence intervals for differences between groups were calculated. RESULTS: Otherwise normal fetuses with increased NT showed no difference in any of the cardiac Doppler parameters from normal controls. Mean E/A ratio was slightly but significantly increased in trisomy 21 fetuses compared with normal controls (0.604 vs. 0.578 on the right, P = 0.011; 0.581 vs. 0.542 on the left, P = 0.0001). E/A ratio was not significantly different between any of the other groups and the normals but there was a small increase in absolute E-wave velocity in trisomy 18 fetuses. MPI was significantly decreased in trisomy 21 fetuses, (0.330 vs. 0.378, P = 0.002 on the left) and also in Turner's syndrome fetuses (0.301 vs. 0.352 on the right, P = 0.04; 0.320 vs. 0.378 on the left, P = 0.034) implying better performance, but not in the other groups. CONCLUSIONS: The magnitude and/or direction of the differences shown do not support a major role for cardiac functional abnormality in the development of NT. Important cardiac dysfunction could not be demonstrated in association with increased NT in normal or abnormal fetuses.

Tricuspid regurgitation in the diagnosis of chromosomal anomalies in the fetus at 11-14 weeks of gestation.

OBJECTIVE: To analyse patient data to elucidate the apparent association between an abnormal karyotype and tricuspid regurgitation found during fetal echocardiography at early gestations. SETTING: Tertiary referral centre for fetal medicine and cardiology. METHODS: Fetuses between 11 and 14 weeks' gestation were selected for detailed echocardiography. Referral reasons were increased nuchal translucency, a suspected cardiac or extracardiac malformation, and a family history of cardiac malformation. INTERVENTION: The fetus was imaged transabdominally. The four chamber view, outflow tracts, arterial duct, and aortic arch were assessed on cross sectional imaging and colour flow mapping. Pulsed Doppler of the atrioventricular valves was recorded if possible. Subsequently, the fetal karyotype was ascertained by chorionic villous sampling. RESULTS: Pulsed Doppler recording of the tricuspid valve was obtained for 262 fetuses. Tricuspid regurgitation was present in 70 (27%) of these, of whom 58 (83%) proved to have karyotype anomalies. In contrast, 68 (35%) of those without tricuspid regurgitation were found to have karyotype anomalies (95% confidence interval 36% to 59%, p < 0.001). Structural heart defects were detected in 34 of the 58 (59%) with tricuspid regurgitation and in 22 (32%) of those without. The chromosome defect most frequently found to be associated with tricuspid regurgitation was trisomy 21, but all types of karyotypic anomalies were seen in association. CONCLUSION: A careful search for tricuspid regurgitation is an important aspect of the evaluation of the early fetus, as this is frequently a marker for chromosomal defects even in the absence of structural heart disease.

Turner's syndrome in fetal life.

OBJECTIVE: To compare the incidence and type of heart disease found in association with 45X karyotype in fetal life with postnatal life and to examine the outcome after fetal diagnosis. METHODS: Fifty-three fetuses with a 45X karyotype were examined echocardiographically over a 4-year period between 1999 and 2002. Of these, 47 were referred because of increased nuchal translucency (NT). RESULTS: A cardiac abnormality was detected in 33/53 (62.2%) fetuses. The most common diagnosis was coarctation of the aorta in 24/53 (45.3%) fetuses, followed by the hypoplastic left heart syndrome (HLHS) in 7/53 (13.2%) fetuses. The mean NT was significantly higher in fetuses with a heart defect than in those with normal echocardiography. Termination of pregnancy was carried out in 45/53 (84.9%) fetuses and intrauterine death occurred in six cases. Two of four fetuses with a mosaic karyotype are currently alive. CONCLUSION: Turner's syndrome is associated with a higher incidence of heart defects detected prenatally when compared to postnatal reports. The commonest associated heart defects detected prenatally are HLHS and coarctation of the aorta, in contrast to postnatal life where a bicuspid aortic valve is the most common diagnosis. The typical intrauterine presentation of Turner's syndrome with a markedly increased NT or with hydrops and with a typical 45X karyotype has an extremely poor prognosis for intrauterine survival.

Fetal cardiac abnormalities identified prior to 14 weeks' gestation.

OBJECTIVE: An increasing number of patients are presenting at early gestational age as being at high risk for congenital heart disease, as a result of ultrasound screening by nuchal translucency. The feasibility and accuracy of fetal echocardiography was assessed in a series of pregnancies studied before 14 weeks' gestation. METHODS: Echocardiography was attempted in 478 fetuses of crown-rump length 40.0-85.0 mm (median, 60.3 mm) with increased nuchal translucency, suspected abnormalities on routine scan or a family history of heart defect. The findings were related to results of autopsy, karyotyping, later scans and postnatal follow-up. RESULTS: Satisfactory images were obtained transabdominally in 402/478 (84.1%) and transvaginally in a further 13 patients. Cardiac defects were confidently identified in 60 fetuses and abnormalities of uncertain significance (isolated ventricular or great artery disproportion, or tricuspid regurgitation) were observed in a further 49. Defects were suspected in an additional 20 fetuses, and 286 were passed as normal. The karyotype was subsequently demonstrated to be abnormal in 70/286 (24.5%) fetuses with normal echocardiograms, and in 94/129 (72.9%) with abnormal or suspicious cardiac findings. Validation of the scan findings was possible in 241 fetuses. Normal heart structure was confirmed in 204 fetuses, and previously unsuspected cardiac abnormalities revealed in nine. Heart defects were verified in 28 fetuses, but five of these had important additional findings. There were false positive findings in three fetuses. CONCLUSIONS: Fetal echocardiography is feasible prior to 14 weeks' gestation. Cardiac defects, when present, may be identified or suspected in the majority of cases. In the risk group studied, heart defects were frequently a manifestation of chromosomal abnormality.

Transcatheter coil occlusion of the arterial duct; results of the European Registry.

AIMS: To report on the data, collected by the Association for European Paediatric Cardiology (AEPC) Registry, on transcatheter coil occlusion of the arterial duct. METHODS AND RESULTS: A retrospective study was conducted of intention-to-treat data from 30 European and Middle Eastern tertiary referral centres which included an analysis of causes of suboptimal outcome. Since 1994, reports have been made on 1291 attempted coil occlusions of the arterial duct in 1258 patients. Median age at procedure was 4 years (range 0.1-52) and median weight was 29 kg (range 1.8-100). Following coil implantation, the immediate occlusion rate was 59%, which rose to 95% at 1 year. A suboptimal outcome occurred on 129 occasions (10% of procedures) and was defined as coil embolization, an abandoned procedure, persistent haemolysis, residual leak requiring a further procedure, flow impairment in adjacent structures and duct re-canalization. A number of clinical factors were chosen but only increasing duct size [odds ratio of 2.6:1 (CI 2-3.2)] and the presence of a tubular shaped duct [odds ratio 2.4:1 (CI 1.4-4)] were positively associated with an unfavourable outcome. CONCLUSION: The results of the European Registry support the view that transcatheter coil occlusion of the persistent arterial duct is a safe and effective procedure. Unfavourable outcomes are more likely when closing larger and/or tubular shaped ducts.

Isolated echogenic foci in the fetal heart as marker of chromosomal abnormality.

OBJECTIVE: To assess the effect of echogenic foci in the fetal heart on the risk for Down's syndrome. DESIGN: Prospective evaluation of fetal echocardiograms at a fetal cardiology referral center and systematic postnatal follow-up. A relative risk was calculated from the prevalence of echogenic foci in fetuses subsequently demonstrated to have trisomy 21 divided by that in normal fetuses. For a subgroup of 548 fetuses with echogenic foci but otherwise normal detailed anomaly scans, the expected number of trisomy 21 fetuses calculated from maternal age risks was compared with the observed number to derive a relative risk for isolated echogenic foci. RESULTS: Echogenic foci occurred in 905 of 6904 fetuses scanned, but after excluding those referred specifically because of an echogenic focus and those with heart defects, the incidence was 9.5%. Overall, echogenic foci were more frequent in fetuses with trisomy 21 than those without by a factor of 2.93. For the 548 fetuses with echogenic foci but otherwise normal detailed anomaly scans, the actual number of trisomy 21 fetuses exceeded that expected on the basis of maternal age risks by a factor of 5.54. Combination with data from several previous studies suggests a consensus relative risk of about 3.0. CONCLUSIONS: Echogenic foci are associated with increased risk of trisomy 21 even when present as an isolated finding. Their significance in an individual should be interpreted in the light of prior risk assessment based on maternal age and results of any first-trimester screening tests. We suggest that the prior risk is increased by a factor of 3.0.

Incidence of major structural cardiac defects associated with increased nuchal translucency but normal karyotype.

OBJECTIVE: To examine the association between increased nuchal translucency thickness and major cardiac defects in chromosomally normal fetuses. SETTING: Tertiary referral unit for fetal medicine and fetal cardiology. METHODS: During a 4-year period (January 1997 to January 2001), detailed echocardiography was performed in 1319 chromosomally normal fetuses with increased nuchal translucency thickness at 10-14 weeks of gestation. The incidence of major cardiac defects was examined in relation to the fetal NT at the 10-14-week scan. RESULTS: Major cardiac defects were diagnosed in 60 (4.5%) of the 1319 fetuses. In fetuses with a nuchal translucency thickness in the range of 2.5-3.4 mm, the incidence of major cardiac defects was 2.5% (18/722; 95% confidence interval, 1.5-3.9) and in those with a nuchal translucency thickness > or =3.5 mm, it was 7% (42/597; 95% confidence interval, 5.1-9.4). CONCLUSION: Specialist echocardiography is indicated in all fetuses with increased nuchal translucency thickness because, in such fetuses, the incidence of major cardiac defects is substantially higher than in pregnancies with maternal diabetes, family history and exposure to drugs, where fetal echocardiography is widely considered to be necessary.

Atrioventricular septal defects diagnosed in fetal life: associated cardiac and extra-cardiac abnormalities and outcome.

OBJECTIVES: We sought to establish the outlook for fetuses diagnosed with atrioventricular septal defect (AVSD) prenatally and its relation to additional cardiac, extracardiac and chromosomal abnormalities. BACKGROUND: Prediction of likely outcome of AVSD presenting prenatally is complicated by the wide variation in associated features. METHODS: Computerized records from 14,726 pregnancies referred to a fetal cardiology center were reviewed retrospectively. Pathological reports, postnatal records, follow-up inquiries and review of echocardiographic video recordings supplemented analysis of the records for all those with AVSD. RESULTS: Atrioventricular septal defect was confirmed in 301 fetuses. Eighty-six (39%) of the 218 with known karyotype had trisomy 21, and 21/218 (10%) had other chromosome abnormalities. Right isomerism occurred in 37/301 (12%) fetuses, left isomerism in 62 (20%), mirror image atrial arrangement in 2 (1%), and 200 (67%) had usual arrangement. Atrioventricular septal defect occurred without any other intracardiac abnormality in 155 fetuses (51%). Extracardiac abnormalities and nonkaryotypic syndromes were evident in 40 fetuses (13%, confidence interval [CI] 9.5-17.1%). Uncomplicated cardiac anatomy was significantly associated with the presence of karyotype abnormality (p < 0.0001). Parents opted for termination of pregnancy in 175/298 (58.5%). For the continuing pregnancies, Kaplan-Meier estimates for live birth, survival past the neonatal period and survival to three years were 82% (CI 75.3-88.9%), 55% (CI 46.0%-0/64.3%) and 38% (CI 27.1-48.6%), respectively. Fetal hydrops and earlier year of diagnosis were independent variables with adverse influence on survival. CONCLUSIONS: Despite some improvements in the outlook for AVSD diagnosed prenatally, the overall prognosis remains considerably poorer than that implied from surgical series. The detection of associated cardiac and extracardiac abnormalities is important in order to give the best indication of the likely outcome when counseling parents.

Early diagnosis of major cardiac defects in chromosomally normal fetuses with increased nuchal translucency.

OBJECTIVE: To determine the value of early ultrasound examination for prenatal diagnosis of cardiac defects in chromosomally normal fetuses with increased nuchal translucency thickness at 10-14 weeks of gestation. DESIGN: Prospective audit. SETTING: Fetal Medicine Centre. METHODS: Specialist fetal echocardiography was carried out in 398 chromosomally normal fetuses with a nuchal translucency measurement above the 99th centile (> or = 3.5 mm). In the first 75 pregnancies the cardiac scan was carried out at 17-22 weeks and the next 323 cases had one scan at 13-17 weeks and another at 20-22 weeks. Pregnancy outcome was obtained in all of the cases. RESULTS: Major cardiac defects were present in 29 (7.3% of 398) cases and in 28 of these the diagnosis was made by antenatal echocardiography. In 27 of the 29 fetuses with major cardiac defects echocardiography was carried out at 13-17 weeks and an abnormality was suspected in 24 of the cases (88%). CONCLUSIONS: Increased nuchal translucency in chromosomally normal fetuses is associated with an increased prevalence of major cardiac defects and, as such, is an indication for specialist fetal echocardiography. Most of the cardiac abnormalities are detectable on antenatal fetal echocardiography and many can be excluded by early scanning.

Molecular cloning of human GATA-6 DNA binding protein: high levels of expression in heart and gut.

Human GATA-6 has been cloned from foetal heart by a combination of PCR-based methods and cDNA library screening. The 3.8 kbp cDNA has a coding sequence of 1347 bp the 449 aa protein is virtually identical in the two zinc-finger binding domains to other human GATA sequences, but varies considerably in the amino and carboxy terminal regions. The sequence shows greatest similarity to GATA-6-like sequences from rat, mouse, chicken and Xenopus. Northern analysis and in situ hybridisation show that GATA-6 is expressed at high levels in human adult and foetal heart as well as in gut derivatives. It is postulated that GATA-6, in concert with GATA-4, plays a crucial role in the regulation of cardiac differentiation.

Acute pseudoaneurysm formation complicating balloon dilation of native coarctation: treatment by delayed surgical repair.

An 11-year-old boy developed an acute aortic pseudoaneurysm during balloon dilation of unoperated coarctation of the aorta. The pseudoaneurysm occurred despite the fact that the balloon catheter size did not exceed the diameter of the aorta at the diaphragm. Elective delayed surgical repair was successfully performed after 3 weeks of antihypertensive treatment when serial magnetic resonance imaging had demonstrated a reduction in the local tissue swelling.