The arch of the aorta is a continuation of the ascending aorta at the level of the right second sternocostal joint, extending to the left of the trachea to continue as the descending thoracic aorta at the level of the fourth thoracic vertebra. Classically, it gives rise to three branches from right to left: the brachiocephalic trunk (BCT), left common carotid artery (LCCA), and left subclavian artery (LSA). However, numerous variations in its branching pattern have been described in anatomical, radiological, and surgical literature.

Variations of the arch of the aorta arise due to alterations in the development and regression of the pharyngeal arch arteries during embryogenesis. These variations may remain asymptomatic but can have significant clinical implications during catheterisation, angiography, aortic arch surgeries, carotid stenting, and thoracic endovascular procedures.

The increasing use of minimally invasive vascular interventions highlights the importance of precise knowledge of arch anatomy. Unexpected variations may lead to procedural difficulties, increased operative time, and risk of vascular injury.

Although many radiological studies exist, cadaveric studies provide direct visualisation and detailed anatomical insight. Therefore, the present study was undertaken to evaluate the branching pattern of the arch of the aorta in 40 cadavers and to analyse the frequency and types of variations observed.

Study Design This was a descriptive cross-sectional cadaveric study conducted in the Department of Anatomy of a tertiary care medical institution in New Delhi. Sample Size A total of 40 adult human cadaveric hearts were included in the study. Inclusion Criteria • Normal adult cadaveric hearts. Exclusion Criteria • Cadavers with gross thoracic trauma • Previous thoracic or heart surgery • Advanced decomposition affecting vascular structures Dissection Procedure During the routine dissection of the thorax for the MBBS students, the thoracic cavity was opened after removing the ribs and sternum. The pericardium was incised to expose the ascending aorta and the arch of the aorta. The arch and its branches were dissected free from surrounding connective tissue. The origin, number, and branching pattern of vessels arising from the arch were documented, and the hearts were removed from the cadavers. Already stored hearts from previous years were also studied after taking the inclusion and exclusion criteria into consideration. Data Collection The following parameters were recorded: • Number of branches arising from the arch • Order of branching • Presence of common trunks • Presence of additional branches (e.g., vertebral artery, Thyroidiea Ima artery) Photographic documentation was done for representative variations. Statistical Analysis Data were entered into Microsoft Excel and analysed using descriptive statistics. Results were expressed as frequency and percentage. FIG. 1 Dissected specimen of the heart showing branches of arch of aorta BT: Brachiocephalic trunk, LCCA: Left common carotid artery, LSA: Left subclavian artery, AOA: Arch of Aorta, PT: Pulmonary Trunk FIG. 2: An additional Branch (LVA) arising from the arch of the aorta. BT: Brachiocephalic trunk, LCCA: Left common carotid artery, LSA: Left subclavian artery, LVA: Left vertebral artery FIG. 3 Distance of the additional artery from the beginning of the brachiocephalic trunk BT: Brachiocephalic trunk LCCA: Left common carotid artery LSA: Left subclavian artery LVA: Left vertebral artery AOA: Arch of Aorta FIG 3b. An additional artery (TIA) arising from the arch of the aorta BT: Brachiocephalic trunk LCCA: Left common carotid artery TIA: Thyroidea ima artery FIG 4a. Diameter of the additional artery (LVA)at its origin between the left common carotid artery and left subclavian artery. BT: Brachiocephalic trunk LCCA: Left common carotid artery LSA: Left subclavian artery LVA: Left vertebral artery FIG 4b. Diameter of the additional artery (TIA)at its origin between the brachiocephalic trunk and the left common carotid artery BT: Brachiocephalic trunk LCCA: Left common carotid artery TIA:

Out of 40 cadavers examined, variations were observed in (22.5%) cases, while (77.5%) showed the classical branching pattern.

Table 1: Distribution of Classical and Variant Branching Patterns (n = 40)

Table 2: Types of Variations Observed (n = 14)

                                  Mean distance = 27.2 mm 

Table 3: Number of Branches Arising from the Arch of the Aorta

In the present study, the classical three-branch pattern was observed in 77.5% of cases. This is comparable to previous studies reporting classical pattern prevalence between 65% and 80%.

The most common variation observed was a common trunk for the brachiocephalic trunk and the left common carotid artery. This variation is frequently referred to as the “bovine arch,” though anatomically it differs from true bovine configuration. This pattern may predispose to embolic spread between carotid arteries.

The left vertebral artery arising directly from the arch was observed in 10% of cases. This finding is clinically significant in vertebral artery catheterisation and posterior circulation interventions.

A two-branch pattern (7.5%) was observed where a common trunk gave rise to BCT and LCCA, followed by LSA. Such variations can complicate aortic arch surgeries and supra-aortic bypass procedures.

Embryologically, these variations result from persistence or regression of segments of the embryonic aortic arch system. Altered remodelling of the third and fourth pharyngeal arch arteries contributes to abnormal branching.

Cadaveric studies provide valuable morphological insights; however, limitations include unknown demographic history and relatively small sample size.

Clinical Significance

• Essential for planning carotid artery stenting
• Important in thoracic endovascular aortic repair (TEVAR)
• Helps prevent inadvertent vascular injury
• Relevant for the interpretation of angiographic imaging
• Important in mediastinal surgeries

The branching pattern of the arch of aorta shows significant variability. In the present study, 22.5 % of cadavers exhibited variations. The most common variation was a common trunk for the brachiocephalic trunk and the left common carotid artery. Awareness of these variations is crucial for surgeons and interventional radiologists to minimise complications during diagnostic and therapeutic procedures. Non-recognition of a critical aortic arch branch variation at surgery may lead to fatal consequences. Also, knowledge of the diameters of these vessels is very useful in predicting the fraction of blood flow through these vessels. Through this study, an attempt has been made to establish a mean value for reference for diameters of additional branches of the arch of the aorta (Thyroidea ima artery, left vertebral artery) and their distance from the beginning of the brachiocephalic trunk to help surgeons during cardiovascular procedures. Further large-scale anatomical and radiological studies are recommended to better understand population-specific variations.

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