Transposition of left subclavian artery with reimplantation of isolated left vertebral artery before thoracic endovascular aneurysm repair for type B aortic dissection

Understanding and recognizing anatomic anomalies of the aortic arch is important when planning extra-anatomic debranching before thoracic endovascular aortic repair. A rare anomaly is the left vertebral artery aberrantly arising from the aortic arch; found in ∼5% of adults. When present, the artery courses through the carotid sheath at a variable length before entering the third or fourth cervical transverse foramen. In the present report, we have described the case of a 49-year-old man with a symptomatic, enlarging type B aortic dissection with an aberrant left vertebral artery and the novel methods used to surgically correct his pathology.

Acute type B aortic dissection (TBAD) is a rare, but lifethreatening, condition with an annual incidence of 3.5/100,000 persons. 1 Thoracic endovascular aortic repair (TEVAR) has become the standard of care for this complex disease process. 2,3 Although emergency repair is indicated for TBAD acutely complicated by malperfusion or rupture, the treatment of uncomplicated cases has remained primarily medical, with a focus on antiimpulse therapy with strict blood pressure and heart rate goals. For these patients, frequent repeat imaging is key to identifying disease progression, which can include distal or proximal extension and/or aneurysmal degeneration, because #45% of patients presenting with acute TBAD will develop aortic enlargement within the first year and 20% will eventually require intervention. 4,5 The treatment of choice for TBAD has become TEVAR. In the setting of aneurysmal degeneration, the primary goals include coverage of the entry tear and exclusion of the aortic aneurysm. In cases in which the intimal tear is in close proximity to the origins of the great vessels, adjunctive bypass or transposition ("debranching") could be necessary to minimize the risk of cerebral, spinal cord, and upper extremity ischemia. 6 High-quality, preprocedure imaging is essential for operative planning and to identify any aortic arch anomalies, which occur frequently in aortic dissection that includes a common origin of the innominate and left common carotid arteries (bovine arch, w30%) and an isolated left vertebral artery arising from the arch (w3%). [7][8][9] In the present report, we have described the clinical course of a patient with TBAD and the latter anomaly: an aberrant left vertebral artery originating directly from the aortic arch. He was successfully treated with staged surgical left carotidesubclavian transposition with reimplantation of the left vertebral artery into the transposed left subclavian artery, followed by TEVAR.

CASE REPORT
The patient was a 49-year-old man with hypertension, hyperlipidemia, and chronic kidney disease who had presented as the driver in a motor vehicle accident during which he had lost consciousness. On extrication, he was noted to have left hemiplegia highly suspicious for stroke. On arrival to the hospital, his blood pressure was 239/137 mm Hg. Right facial droop and left hemiplegia were present. Pulses were palpable in both wrists and feet. The patient was in respiratory distress and thus was intubated and sedated. The patient's wife, who had power of attorney for personal care, and the patient both provided verbal consent for the report of his case details and imaging studies. Repeat cross-sectional imaging was performed on hospital day 3, which revealed the absence of dissection progression or aneurysmal changes. The patient was discharged to a rehabilitation facility with a requirement for hemodialysis after a 2-month hospital stay. He underwent rehabilitation for an additional 1 month and then returned home.
The patient remained hemiplegic and required continuous hemodialysis but was awake and communicative. A follow-up CT scan at 6 months again demonstrated the TBAD. The maximal diameter of the proximal descending aorta had increased from 6.1 to 6.5 cm. However, the morphology of the TBAD was otherwise unchanged (Fig 2). It was confirmed that the left vertebral artery arose from the aortic arch and coursed posteriorly in the carotid sheath before entering the C6 transverse foramen (Fig 3). His right vertebral artery was dominant and patent.   After administration of heparin, the left subclavian artery was clamped distally, oversewn, and divided proximally. The common carotid artery (proximal to its bifurcation) was clamped proximally and distally with atraumatic vascular clamps, and a longitudinal arteriotomy was made on its anterolateral surface.
An end-to-side anastomosis of the divided left subclavian artery to the left common carotid artery was performed. After the carotidesubclavian transposition, the left vertebral artery was clamped and divided inferiorly in the wound adjacent to the proximal common carotid artery. Its proximal stump was ligated. The distal artery was transposed superficially in the wound and anastomosed to the transposed left subclavian artery. After clamp release, strong pulses were noted throughout the vascular reconstruction (Fig 4). The patient's neurologic status was unchanged postoperatively. The patient recovered uneventfully and was discharged after 2 days without ongoing antithrombotic therapy.

DISCUSSION
In the present report, we have described the rapid aneurysmal degeneration of a TBAD in a 49-year-old man with a complex presentation, including severe hypertension, trauma, intraparenchymal cerebral hemorrhage, and renal failure. The quick progression of his condition and the unusual course of the left vertebral artery arising directly from the diseased aorta prompted a staged repair, which included carotidesubclaviane vertebral transposition, followed by TEVAR. The patient recovered uneventfully, and his outcome was favorable.
In the present patient, who was already disabled by cerebral infarction from an extensive intraparenchymal hemorrhage, preservation of the systemic left vertebral and left subclavian arterial pressure and flow at TEVAR was believed to be indicated. Although somewhat controversial, the results from a recent meta-analysis  have suggested that left subclavian revascularization in adjunct to TEVAR will significantly decrease the risk of spinal cord ischemia, cerebrovascular accident, endoleak, and left upper extremity ischemia. [10][11][12] For patients with an isolated left vertebral artery, the indication is probably absolute. Autogenous subclavian artery reconstruction, in contrast to prosthetic carotidesubclavian bypass, offered several advantages for our patient, including potentially enhanced primary patency, freedom from recurrent symptoms, and a reduction of infectious complications. 5,13,14 Anomalies of the aortic arch are common, with a normal, three-vessel branching pattern only observed in w60% of adults. [15][16][17] The most common variant is the (unfortunately and incorrectly named) "bovine aortic arch," with a prevalence as high as 40%. 18 The second most common anomaly is an "isolated" left vertebral artery, taking its origin from the aortic arch, instead of the left subclavian artery. This has been shown to occur in 0.79% to 8.3% of adults, certainly common enough to be encountered by most vascular surgeons during their career. 9,[19][20][21][22][23][24] Other aberrant parent vessels of the vertebral arteries have also occasionally been described, including the external carotid artery, thyrocervical trunk, common carotid artery, internal carotid artery, carotid bulb, costocervical trunk, occipital artery, inferior thyroid artery, and ascending aorta. 9,21,22,24 Aortic arch anomalies have been frequently observed in patients with TBAD, although their prevalence has not been shown to be higher than that in the general population. 7 Although still uncertain, the results from at least one metaanalysis have positively associated the presence of arch anomalies with aortic pathologies, such as atherosclerosis and dissection. 19 A normal left vertebral artery will typically arise from the left subclavian artery, course superoposteriorly between the longus colli and anterior scalene muscles, enter the foramen transversarium of the sixth cervical vertebra, and converge in the circle of Willis to supply the spinal cord, brainstem, cerebellum, and occipital lobes. [22][23][24] However, when originating from the aortic arch, the vessel will typically remain outside the vertebral column for a longer length, coursing anterior and/or lateral to the longus colli muscle until entering the fourth or fifth transverse foramen. 16,19,20,24,25 This makes the prevertebral segment of the artery longer (w8 cm) and more surgically accessible in the neck. 24 It might even conveniently reside in the posterior aspect of the carotid sheath, such as in the present case. However, in other cases, the vertebral artery aberrancy could complicate vascular reconstruction. 9 Surgical transposition of an isolated left vertebral artery into a carotidesubclavian bypass graft has been reported in a case of TEVAR for a symptomatic aortic arch aneurysm. 26 Isolated left vertebral artery transposition to the left common carotid artery has also been performed before TEVAR for intramural hematoma. 27 The present case is rare owing to use of transposition combined with reimplantation of a vertebral anatomic variant.

CONCLUSIONS
We have reported the uncommon scenario of a patient with chronic TBAD and an aberrant left vertebral artery originating from the arch, who had undergone combined carotidesubclavianevertebral transposition before successful TEVAR. The possibility of this common aortic arch variant should be considered when planning surgical treatment for TBAD.
Anatomic variations can complicate surgical decisionmaking for patients with chronic TBAD. Careful preoperative assessment of the aortic arch anatomy, combined with operative strategies to preserve cerebrovascular and vertebral vascular blood flow, are essential to optimizing treatment outcomes.