Anatomical Variation of Left Internal Mammary Artery and Thyrocervical Trunk: A Case Report
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Abstract
We report a rare case of a left internal mammary artery (LIMA) originating from the left thyrocervical trunk (TCT), which arose directly from the aortic arch. A patient in their 70s presented with bilateral distal internal carotid artery aneurysms, diagnosed through computed tomography angiography performed for headache evaluation. Transfemoral cerebral angiography confirmed the aneurysms and incidentally revealed the anomalous origins of the TCT and LIMA, as well as a left vertebral artery directly arising from the aortic arch. This case emphasizes the importance of recognizing such rare anatomical variations prior to diagnostic or interventional procedures. Thorough preoperative evaluation is critical to avoid complications, particularly in coronary artery bypass grafting and head and neck tumor embolization.
INTRODUCTION
The anatomy of the aortic arch and its branches, including the left thyrocervical trunk (TCT) and left internal mammary artery (LIMA), has been extensively studied due to their clinical significance in vascular and cardiothoracic procedures [1-5]. The TCT is a vital vascular structure, commonly arising from the proximal third of the subclavian artery and giving rise to several branches that supply the neck and shoulder regions [4,5]. Similarly, the LIMA is widely recognized as the graft of choice in coronary artery bypass grafting (CABG) due to its superior long-term patency [6].
Anatomical variations in the origins of these vessels are well-documented; however, the simultaneous occurrence of a TCT originating directly from the aortic arch and a LIMA arising anomalously from the TCT is extraordinarily rare [7,8]. Unrecognized vascular variations may increase the risk of surgical complications and impact procedural outcomes [9].
This case report highlights a unique anatomical variation identified incidentally during the evaluation of intracranial aneurysms. The report aims to emphasize the importance of thorough preoperative vascular mapping and to contribute to the limited body of literature on such rare vascular anatomical variations. By detailing this case, we hope to enhance clinicians’ awareness and facilitate better procedural planning.
CASE REPORT
A patient in their 70s presented to another hospital with persistent headaches. Magnetic resonance angiography performed at that hospital revealed bilateral distal internal carotid artery (ICA) aneurysms. A patient was referred to our hospital for further evaluation and management.
At our institution, neck computed tomography angiography (CTA) was performed first, followed by transfemoral cerebral angiography (TFCA) to assess the aneurysms and vascular anatomy in detail. During this process, a rare and complex vascular anatomical variation was identified. A retrospective review of the initial neck CTA revealed the anomalous vascular origins, emphasizing the utility of preoperative imaging for identifying such variations. The left TCT was observed to originate directly from the aortic arch instead of the usual origin from the subclavian artery. Additionally, the LIMA arose anomalously from the TCT, and the left vertebral artery also originated directly from the aortic arch (Fig. 1A–C). The patient underwent successful endovascular coiling of the bilateral ICA aneurysms without complications.
(A) Computed tomography angiography of the neck reveals the brachiocephalic trunk, left common carotid artery, left vertebral artery (arrowhead), left thyrocervical trunk (arrow), and left subclavian artery originating directly from the aortic arch in order. (B) Left subclavian angiography reveals no left vertebral artery and thyrocervical trunk. (C) Left thyrocervical trunk angiography reveals origin of the left thyrocervical trunk directly from the aortic arch. Further, the left internal mammary artery (white arrowhead) branches along with the inferior thyroid artery (black arrowhead), transverse cervical artery (white arrow), and suprascapular artery (black arrow).
DISCUSSION
Variations in the origins of the TCT and LIMA, such as those described in this case, are exceedingly rare [7,8]. These variations complicate procedures such as CABG, tumor embolization, and other vascular interventions. The TCT, as a vital vascular structure, often supplies branches that perfuse the head and neck regions, making it particularly important in neurointerventions and tumor embolization procedures [10,11]. Anomalies in its origin or branching pattern may significantly alter the expected vascular anatomy, complicating catheter navigation and embolization planning [10]. The TCT typically arises from the subclavian artery and gives rise to several branches, including the transverse cervical, suprascapular, and inferior thyroid arteries, which supply the neck and shoulder regions [4]. In this case, the TCT anomalously originated directly from the aortic arch, a rare variation that significantly alters the vascular anatomy. Fig. 1 illustrates this anomaly and its associated branches.
For example, in tumor embolization procedures targeting head and neck malignancies, the TCT supplies branches such as the transverse cervical and suprascapular arteries, which directly perfuse the tumor [10]. Variations in its origin, such as arising directly from the aortic arch, can result in unexpected vascular pathways, potentially leading to incomplete tumor devascularization or embolization of unintended structures. Recognizing these variations through preoperative imaging, including CTA and TFCA, is critical to ensuring procedural accuracy and mitigating risks.
The LIMA, although commonly utilized as a graft in CABG due to its superior long-term patency [6], plays a relatively less significant role in neurointerventions compared to the TCT. However, anomalies in its origin, such as arising from the TCT, can complicate its use as a graft vessel. Extensive intraoperative dissection may be required to locate and harvest the vessel, potentially prolonging surgery and increasing the risk of complications. One documented case reported significant delays during CABG due to an unrecognized anomalous LIMA origin, necessitating an alternative grafting strategy [7].
Several cases in the literature illustrate the procedural challenges associated with vascular anomalies involving the TCT and LIMA. Malek et al. [8] described a patient undergoing CABG, where the LIMA originated from the TCT, and the TCT arose directly from the aortic arch. This anomaly resulted in procedural delays, but the operation was successfully completed after the anomaly was identified through coronary angiography [8]. Similarly, Nuqali et al. [7] reported dual anomalous origins of the TCT and LIMA from the subclavian artery, which were identified incidentally during coronary angiography, with no reported complications. In contrast, the current case presents a unique combination of 3 vascular anomalies: the TCT arising from the aortic arch, the LIMA branching from the TCT, and the left vertebral artery originating directly from the aortic arch. These findings, identified through CTA and TFCA, emphasize the importance of advanced imaging in detecting complex vascular variations.
Although this variation was not expected to significantly affect the treatment of intracranial aneurysms, its recognition highlights the broader implications for other interventions, such as CABG and head and neck tumor embolization, where vascular anomalies may introduce procedural challenges. For instance, in CABG, anomalous vessel origins may complicate harvesting procedures, while in head and neck tumor embolization, unexpected vascular pathways can lead to incomplete tumor devascularization or inadvertent embolization of healthy tissues.
The aortic arch and its branches undergo a complex developmental process during embryogenesis [12]. Initially, paired aortic arches form symmetrical vascular structures, which subsequently remodel into the mature arterial configuration. Disruptions in this remodeling process, whether due to genetic mutations or environmental influences, may result in unusual persistence or regression of embryonic vascular segments. For example, an anomalous TCT directly arising from the aortic arch may represent incomplete regression of embryonic vascular arcs, while a LIMA originating from the TCT may result from atypical persistence of secondary branches. Further research utilizing embryological models or high-resolution imaging is essential to elucidate these mechanisms and their clinical implications.
Preoperative imaging modalities such as CTA and TFCA are indispensable for identifying these anomalies. These tools allow for precise vascular mapping, which is essential for ensuring procedural safety, particularly in neurointerventions and tumor embolizations. The documentation of these anatomical variations provides valuable insights for future interventions, such as embolization or reconstructive surgeries, that might be affected by the altered vascular anatomy. Comprehensive vascular mapping and a multidisciplinary approach are strongly recommended to optimize patient outcomes in cases involving complex vascular anatomical variations.
Recognizing rare anatomical variations, such as the anomalous origins of the TCT and LIMA, is essential for surgical and interventional planning. Preoperative imaging evaluation is invaluable for procedural planning and mitigating surgical risks.
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Ethics Statement
The Institutional Review Board waived the requirement for informed consent (Inje University Busan Paik Hospital, approval number: 2022-10-054). We anonymized the patient information, including sex and age, which could potentially identify an individual.
Conflicts of Interest
The authors have no conflicts to disclose.
Author Contributions
Concept and design: JWB. Analysis and interpretation: JWB, JYH. Data collection: JWB. Writing the article: JYH. Critical revision of the article: JYH, JWB. Final approval of the article: JWB. Overall responsibility: JWB.