RAA with Aberrant LSCA from Kommerell’s Diverticulum #1: Embryology and Anatomy
A right aortic arch with aberrant left subclavian artery (RAA with aberrant LSCA) is a classic aortic arch anomaly that can form a true complete vascular ring. In this configuration, the aortic arch courses to the right side of the trachea, while the left subclavian artery arises aberrantly from the posterior aspect of the descending aorta, usually from a bulbous remnant known as Kommerell’s diverticulum [1, 2].
The vascular ring becomes complete when a left-sided ductus arteriosus or postnatal ligamentum arteriosum connects the pulmonary artery to the region of the aberrant LSCA or Kommerell’s diverticulum. This creates a circumferential structure around the trachea and esophagus, producing variable degrees of airway and esophageal compression [1, 2].
1. Embryologic Concept
The embryologic basis can be simplified as a combination of right-sided persistence and left-sided regression of the paired embryonic aortic arch system.
Key embryologic events
- Persistence of the right fourth aortic arch
- Persistence of the right dorsal aorta
- Regression of the left fourth aortic arch
- Persistence of the left sixth arch / ductal structure
- Persistence of a left dorsal aortic remnant
The right fourth arch remains and becomes the dominant aortic arch segment. This produces a mature aortic arch that passes to the right of the trachea.
The right dorsal aorta remains continuous with the descending thoracic aorta, allowing the systemic arch to connect to the descending aorta through a right-sided pathway.
The normal left-sided aortic arch fails to form because the left fourth arch regresses.
The left sixth arch contributes to the ductus arteriosus. If this left-sided ductus persists in the setting of a right aortic arch and aberrant LSCA, it becomes the structure that completes the vascular ring.
The remnant at the origin of the aberrant LSCA forms Kommerell’s diverticulum, an outpouching at the base of the aberrant subclavian artery [1, 3].
Thus, the final anatomy reflects a developmental pattern in which the right arch becomes dominant, the left arch regresses, and a left-sided ductal remnant persists.
2. Final Anatomic Configuration
In RAA with aberrant LSCA, the arch vessels usually arise in the following sequence:
- Left common carotid artery
- Right common carotid artery
- Right subclavian artery
- Aberrant left subclavian artery, arising from Kommerell’s diverticulum
The aberrant LSCA typically courses posterior to the esophagus as it travels from the right-sided descending aorta toward the left upper extremity. This retroesophageal course is central to the posterior component of the vascular ring.
3. Components of the Vascular Ring
A complete vascular ring is formed by the interaction of vascular and fibrous structures surrounding the airway and esophagus.
Right-sided component
The right aortic arch forms the right lateral boundary of the ring.
Posterior component
The aberrant LSCA and Kommerell’s diverticulum course behind the esophagus and may contribute to posterior compression.
Left-sided component
The left ductus arteriosus or ligamentum arteriosum connects the left pulmonary artery to the region of the aberrant LSCA or diverticulum.
Central structures
The trachea and esophagus lie within the ring and may be compressed depending on the tightness of the ring, the size of Kommerell’s diverticulum, and the degree of associated tracheomalacia or esophageal indentation.
Therefore, RAA with aberrant LSCA is not only a branching anomaly. When combined with a left ligamentum arteriosum, it becomes a true circumferential vascular ring [2].
4. Kommerell’s Diverticulum: More Than an Anatomic Stump
Kommerell’s diverticulum is an aneurysmal or bulbous remnant at the origin of an aberrant subclavian artery. In this lesion, it represents the remnant of the left dorsal aorta and serves as the origin of the aberrant LSCA.
Its importance is threefold:
- It may act as an independent source of posterior tracheoesophageal compression.
- It may remain as a residual compressive structure after simple division of the ligamentum arteriosum.
- It may enlarge over time, particularly in adult patients, where aneurysmal degeneration, dissection, or rupture become relevant concerns [3].
For this reason, contemporary surgical strategy increasingly considers not only division of the ligamentum arteriosum, but also whether the diverticulum should be resected and whether the aberrant LSCA should be translocated or reimplanted [4, 5].
5. Clinical Presentation
Symptoms depend on the degree of tracheal and esophageal compression.
Respiratory symptoms
- Stridor
- Wheezing
- Recurrent respiratory infections
- Chronic cough
- Respiratory distress
- Persistent symptoms related to tracheomalacia
Gastrointestinal symptoms
- Dysphagia
- Feeding difficulty
- Vomiting
- Poor weight gain
- Choking or coughing during feeding
In children, respiratory symptoms are often prominent because the airway is more compliant and susceptible to extrinsic compression. Long-term outcome studies show that survival after vascular ring division is excellent, but residual respiratory symptoms can persist in some patients, often because of pre-existing or residual tracheomalacia [4].
6. Imaging and Preoperative Evaluation
The diagnosis requires accurate three-dimensional understanding of the arch, branch vessels, ductal/ligamentous anatomy, and airway relationship.
Echocardiography
Echocardiography may identify arch sidedness and associated intracardiac anomalies, but it is often insufficient for complete anatomic definition of the vascular ring.
CT angiography / MR angiography
Cross-sectional imaging is essential to define:
- Arch laterality
- Branching sequence
- Origin and course of the aberrant LSCA
- Size and morphology of Kommerell’s diverticulum
- Relationship to the trachea and esophagus
- Degree of airway compression
- Associated intracardiac or extracardiac anomalies
Bronchoscopy
Bronchoscopy may be useful when airway symptoms are prominent or when tracheomalacia is suspected. It helps distinguish fixed vascular compression from dynamic airway collapse.
7. Surgical Principles
The surgical objective is to release the ring and eliminate residual compressive structures.
Basic components of repair
- Division of the ligamentum arteriosum
- Mobilization of the esophagus and trachea from surrounding adhesions
- Assessment of Kommerell’s diverticulum
- Resection or plication of Kommerell’s diverticulum
- Translocation or reimplantation of the aberrant LSCA
This releases the fibrous left-sided component completing the ring.
This helps relieve residual compression.
If the diverticulum is large or compressive, simple ligamentum division may be insufficient.
This removes the posterior compressive component.
The aberrant LSCA may be transferred to the left carotid artery or reconstructed to preserve left arm perfusion while eliminating the retroesophageal course [5, 6].
Some authors recommend resection of Kommerell’s diverticulum when it is significantly enlarged, including when the diverticulum is more than approximately 1.5 times the diameter of the aberrant subclavian artery origin [2]. However, the precise threshold and operative approach should be individualized according to patient age, symptoms, airway compression, diverticulum morphology, and institutional surgical strategy.
8. Practical Surgical Interpretation
From a surgeon’s perspective, this anatomy should be visualized as a three-dimensional ring:
- Right aortic arch: right lateral boundary
- Aberrant LSCA: posterior retroesophageal component
- Kommerell’s diverticulum: posterior diverticular mass at the LSCA origin
- Left ligamentum arteriosum: left-sided tether completing the ring
- Trachea and esophagus: central compressed structures
The critical operative question is not simply, “Is there a ligamentum to divide?”
The more complete question is:
Is there a residual posterior compressive component, especially Kommerell’s diverticulum or a retroesophageal LSCA, that should also be addressed?
This distinction is important because simple division of the ligamentum may release the ring but may not fully eliminate posterior compression if the diverticulum is large or the aberrant LSCA remains tense behind the esophagus [5, 7].
9. Key Message
RAA with aberrant LSCA from Kommerell’s diverticulum results from persistence of the right fourth arch and right dorsal aorta, regression of the left fourth arch, and persistence of a left dorsal aortic remnant that forms Kommerell’s diverticulum. When a left ductus arteriosus or ligamentum arteriosum persists, the right arch, aberrant LSCA, Kommerell’s diverticulum, and ligamentum arteriosum form a complete vascular ring around the trachea and esophagus. Surgical management should address not only the ligamentum arteriosum, but also the potential compressive role of Kommerell’s diverticulum and the aberrant LSCA.
References
[1] Tamayo-Espinosa T, Erdmenger-Orellana J, Becerra-Becerra R, Balderrábano-Saucedo N, Segura-Standford B. Right-side aortic arch with aberrant left subclavian artery and Kommerell’s diverticulum. A cause of vascular ring. Arch Cardiol Mex. 2017;87(4):345-348.
[2] Biermann D, Holst T, Hüners I, Rickers C, Kehl T, Rüffer A, Sachweh J, Hazekamp MG. Right aortic arch forming a true vascular ring: a clinical review. Eur J Cardiothorac Surg. 2021;60(5):1014-1021.
[3] van Rosendael PJ, Stöger JL, Kiès P, Vliegen HW, Hazekamp MG, Koolbergen DR, Lamb HJ, Jongbloed MRM, Egorova AD. The Clinical Spectrum of Kommerell’s Diverticulum in Adults with a Right-Sided Aortic Arch: A Case Series and Literature Overview. J Cardiovasc Dev Dis. 2021;8(3):25.
[4] Naimo PS, Fricke TA, Donald J, Sawan E, d’Udekem Y, Brizard CP, Konstantinov IE. Long-term outcomes of complete vascular ring division in children: a 36-year experience from a single institution. Interact Cardiovasc Thorac Surg. 2017;24(2):234-239.
[5] An K, Li S, Yan J, Wang X, Hua Z. Translocation of aberrant left subclavian artery and resection of Kommerell diverticulum during the concomitant repair of intracardiac anomalies. Interact Cardiovasc Thorac Surg. 2021;32(1):118-123.
[6] Samas J, Manetta F, Meyer DB. Repair of vascular ring with resection of Kommerell diverticulum and transposition of aberrant left subclavian artery. Int J Angiol. 2013;22(4):243-244.
[7] Bidar E, Arrigoni SC, Accord RE. Resection of Kommerell Diverticulum and Reimplantation of Aberrant Left Subclavian Artery in Right Aortic Arch Vascular Ring. Semin Thorac Cardiovasc Surg. 2019;31(3):561-563.
[8] Backer CL, Bharadwaj SN, Eltayeb OM, Forbess JM, Popescu AR, Mongé MC. Double Aortic Arch With Kommerell Diverticulum. Ann Thorac Surg. 2019;108(1):161-166.