Discussion

Kommerell diverticulum is an uncommon congenital vascular anomaly representing a persistent remnant of the embryonic fourth aortic arch. ^{Reference Worhunsky, Levy, Stephens and Backer1} In patients with a right aortic arch and an aberrant left subclavian artery, the diverticulum arises from the descending aorta and gives rise to the left subclavian artery in a retroesophageal course. Combined with a left-sided ligamentum arteriosum, this anatomy creates a complete vascular ring that can compress the trachea and oesophagus. ^{Reference Bae, Kang and Choo2}

Early recognition of Kommerell diverticulum, particularly through prenatal diagnosis, has important clinical implications for perinatal management and postnatal surveillance. Prenatal echocardiography can identify aortic arch sidedness and raise suspicion of associated arch anomalies during routine screening. ^{Reference Suzuki, Sasaki and Kunugi3} Although the complete vascular anatomy, including the presence of a Kommerell diverticulum, is best delineated by postnatal CT or cardiac MRI, prenatal suspicion allows for planned delivery at tertiary centres with paediatric cardiac surgery expertise and enables timely evaluation and longitudinal follow-up.

This case demonstrates an exceptionally early diagnosis combined with unique morphologic features. While a right aortic arch with an aberrant left subclavian artery occurs in 0.04 to 0.4% of the population, ^{Reference Cinà, Althani, Pasenau and Abouzahr4} diagnosis on the first day of life is exceptional. Among 212 reported cases, the youngest patient was 18 days old, with mean age at diagnosis of 41.8 years. ^{Reference Tanaka, Milner and Ota5} Our day 1 diagnosis represents one of the youngest documented cases and is further distinguished by selective mid-ductal aneurysmal dilatation of the patent ductus arteriosus. Serial imaging documented ductal evolution from patency to thrombosis over four days, providing insight into the natural history of this rare variant.

The most distinctive feature was the unusual fusiform mid-ductal aneurysmal dilatation. We propose that this reflects high ductal flow volume in right aortic arch anatomy (where the left-sided ductus carries the predominant fetal blood flow) and inherent structural characteristics of the mid-ductal segment, which consists of ductal tissue without structural reinforcement from adjacent great vessel walls.

Management of asymptomatic Kommerell diverticulum in paediatric patients remains controversial. The 2022 American College of Cardiology/American Heart Association Aortic Disease Guideline suggests repair may be reasonable for diverticulum diameter ≥3 cm in adults (Class 2b recommendation), ^{Reference Isselbacher, Preventza and Hamilton Black Iii6} but no paediatric guidelines exist.

Luciano et al. advocate for prophylactic surgical resection based on cystic medial necrosis in 67% of resected diverticula, even in infants as young as 11 months. ^{Reference Luciano, Mitchell, Fraisse, Lepidi, Kreitmann and Ovaert7} Cystic medial necrosis predisposes to aneurysmal dilatation, dissection, and rupture, suggesting the diverticulum represents inherently abnormal vascular tissue supporting early intervention. ^{Reference Kim, Cambria and Isselbacher8} Conversely, Erben et al. reported very slow growth rates (mean 1.45 mm/year), with most patients remaining asymptomatic and rupture being rare, ^{Reference Erben, Brownstein and Velasquez9} supporting conservative management with surveillance.

However, vigilant long-term follow-up is essential. The persistent ligamentum arteriosum maintains the potential for vascular ring compression as the child grows, and progressive diverticulum enlargement could cause compression. Regular surveillance with serial echocardiography and cross-sectional imaging is essential. Surgical intervention should be considered if symptoms develop or significant diverticulum enlargement occurs.

In conclusion, this case provides valuable documentation of spontaneous ductal closure in neonatal Kommerell diverticulum and highlights the management dilemma in asymptomatic paediatric patients. The absence of paediatric guidelines underscores the need for long-term natural history data. Serial imaging documentation in cases like ours contributes important information to guide future recommendations.