LAUSR

Dear Editor, Aberrant right subclavian artery (ARSA) is the most common embryologic abnormality of the aortic arch. Typically, 3 large arteries arise from the aortic arch: the brachiocephalic trunk, the left common carotid artery, and the left subclavian artery. When an ARSA is present, 4 large arteries arise from the aorta: the right and left common carotid arteries, the left subclavian artery and the right subclavian artery. Several reports have demonstrated an association between non-isolated ARSA and Down syndrome. The significance of isolated ARSA, however, is less clear. Zalel et al reported that ARSA is associated with Trisomy 21 mainly when it is not an isolated finding on ultrasound (US) examination. De Le on-Luis et al reported that for isolated ARSA, the positive likelihood ratio was 0. During the last 5 years, we examined 7557 consecutive low-risk pregnant women for their prenatal anatomy survey at 14–16 weeks’ gestation using a 3–9 MHz endovaginal transducer and a 2–6 MHz abdominal transducer (Philips Healthcare, Andover, Massachusetts). Transabdominal scanning was performed when transvaginal approach was suboptimal. Heart assessment included 4-chamber view, inlet and outflow tracts, 3-vessel view, superior and inferior vena cava and pulmonary veins. For the diagnosis of ARSA, the 3 vessels and trachea view was obtained and color Doppler with a low-velocity range power Doppler imaging mode was applied, demonstrating the abnormal origin of the ARSA on the aortic arch and its retro-tracheal course toward the right shoulder (Figure 1). Pulsed-wave Doppler was used to differentiate between ARSA and the azygos vein. When an ARSA was detected, longitudinal view was obtained to confirm the diagnosis. All cases of ARSA were confirmed by second trimester fetal US examination and amniocentesis was performed for karyotype or for chromosomal microarray analysis (CMA). We identified 27 fetuses with ARSA (0.35%) that was considered to be isolated. Following delivery, in 3 cases, other associated abnormalities were diagnosed including soft cleft palate, patent foramen ovale, and abnormal CMA that showed a 54 369 KB duplication on chromosome 18 (arr 18q11.2q23(23,708,113-78,077,248)X3). No trisomy 21 cases were diagnosed in the fetuses with ARSA. Twenty-four cases of trisomy 21 were diagnosed in the study population, none of them with ARSA. Our findings show that there is no association between the presence of an isolated ARSA and trisomy 21. These results are in accordance with a recent report that showed a likelihood ratio of 1 for trisomy 21 in fetuses with isolated ARSA. In our population, the prevalence of ARSA was 0.35%, lower than the reported prevalence of 0.7% but similar to the prevalence reported in a systematic review and meta-analysis. The detection of ARSA should be followed by fetal echocardiography and comprehensive anatomy scan. Although our series is too small to establish any recommendation, we believe that CMA and karyotype should also be considered.