Truncus Bicaroticus With Arteria Lusoria: A Rare Combination of Aortic Root Anatomy Complicating Cardiac Catheterization

Discussion

Arteria lusoria is defined as an anomalous right subclavian artery arising distal to the origin of the left subclavian artery on the aortic arch. It has an estimated incidence of 0.5 to 2% and occurs as a consequence of abnormal embryologic involution of the right fourth aortic arch and right proximal dorsal aorta. This causes the origin of the right subclavian artery to shift onto the descending aorta and cross the mediastinum from left to right, passing behind the esophagus and the trachea.^1,3-5

ARSA is often associated with other anatomic abnormalities, including COCA, right-sided aortic arch, interrupted aortic arch, aortic coarctation, tetralogy of Fallot, truncus arteriosus, transposition of the great arteries, atrial septal defects, and ventricular septal defects.Underlying genetic disorders, such as Edwards, Down, DiGeorge syndromes, aneurysms, and arterioesophageal fistulae can accompany these vascular malformations.⁶

COCA, such as we encountered, is the presence of a single branch from the aorta giving off both right and left common carotid arteries. It has an incidence of < 0.1% in isolation and is discovered most often in cadaveric dissections or incidentally on imaging.¹ Its embryologic origin results from the third pair of cervical aortic arches persisting as a common bicarotid trunk.^1,4,5 The combination of ARSA and COCA is rare. Of the 0.5 to 2% of ARSA cases discovered, only 20% of those cases present with associated COCA for a combined prevalence estimated at < 0.05%.⁷

The majority of patients with either anatomic abnormality are asymptomatic. However, a few classic clinical manifestations have been described. ARSA can rarely present with dysphagia lusoria, a condition resulting from an incomplete vascular ring formed by the abnormal course of the right subclavian compressing the esophagus. Although not seen in our patient, it should be considered in the differential diagnosis for dysphagia.^1,2,7 Ortner syndrome can result from right laryngeal nerve compression and palsy resultant from the aberrant course of the right subclavian artery.⁸ Another clinically relevant feature of ARSA is the presence of a diverticulum of Kommerell or dilatation at the origin of the right subclavian artery. It is a type of retroesophageal diverticulum resulting from persistence of a segment of the right sixth aortic arch.⁹ Finally, the spatial arrangement of ARSA increases risk for injury during head and neck surgical procedures, such as thyroidectomy, tracheotomy, and lymph node dissection of the right paratracheal fossa.⁶ Although the incidence is not well described, COCA has been described in several case reports as causing tracheal compression with dyspnea and in some cases, ischemic stroke.^4,5,10

Diagnosis

The diagnosis of ARSA and COCA is often made incidentally on diagnostic imaging studies such as endovascular imaging, CT angiography, magnetic resonance (MR) angiography, postmortem cadaveric dissections, or, as in our case, during cardiac catheterization.^11,12 A classification system for aortic arch branching patterns exists published by Adachi and Williams.⁶ The classification includes ARSA and differentiates it into 4 subtypes (Figure 2). Our patient exhibited type H-1, indicating ARSA as the distal most branch of the aortic arch with coexistence of COCA.⁶ The primary clinical implication of ARSA and COCA in our case was increased difficulty and complexity when performing coronary angiography. Available literature has well characterized the challenges operators encounter when cannulating aberrant great vessel anatomy, often electing to perform nonselective aortography to define a patient’s anatomy.^7,9,13 A comparison of diagnostic imaging techniques for vascular rings such as ARSA have shown MR, CT, and endovascular angiography to be the most reliable modalities to delineate vascular anatomy.¹⁴