The internal thoracic artery (ITA) has been used extensively in coronary artery bypass grafting (CABG) in recent years because it is more durable, has higher survival rates, and improves postoperative quality of life when compared to saphenous vein grafts. Its favorable anatomical dimensions and intrathoracic course further contribute to its efficacy. Additionally, understanding the anatomical details of the ITA is crucial for procedures such as percutaneous transthoracic interventions, including lung needle biopsies. Here, we report an intriguing cadaveric observation involving a variation in ITA termination accompanied by a sternal anomaly. These findings draw attention to the significance of recognizing anatomical variations, particularly in the context of surgical and interventional procedures, as such variations can influence clinical strategies and outcomes.

CABG, internal thoracic artery, sternal anomaly

The internal thoracic artery (ITA), frequently referred to as the internal mammary artery (IMA), emanates from the anteroinferior branch of the proximal segment of the subclavian artery. These anatomical structures are routinely employed as receiving locations in autologous breast reconstruction procedures. They are often preferred to the thoracodorsal (TD) vessels due to their favorable accessibility, ease of manipulation, and adaptability in flap placement.‌^[1] In recent years, the utilization of the internal thoracic artery in coronary artery bypass grafting (CABG) has seen a notable increase. The importance of this artery in CABG is primarily ascribed to its favorable long-term patency and survival rates, alongside improvements in postoperative quality of life relative to saphenous vein grafts.

Its appropriate anatomical dimensions and intrathoracic trajectory enhance its overall efficacy.^[2] Furthermore, the anatomical intricacies are imperative for percutaneous transthoracic interventions, such as lung needle biopsies. Although complications have been recorded, the preponderance of these procedures is performed with a high degree of safety. Another noteworthy application pertains to subclavian vein catheterizations.^[3]

Our investigation centers on the internal thoracic artery’s origin, termination, and anatomical features. A thorough understanding of these morphological aspects and their possible variations will undoubtedly support clinicians in the proper harvesting of the artery for clinical applications.

The Institute Ethical Approval has been obtained for exemption of review, stating that the cadavers donated to the department can be used for teaching and research purposes. This variation was observed during the routine dissection of MBBS teaching. An intriguing variation in the course and termination of the internal thoracic artery (ITA) was discovered during the dissection of the thorax of a 63-year-old female cadaver that had been properly embalmed and preserved, had no known history of trauma, and was used for anatomical teaching. On the right side, the ITA is bifurcated into two terminal branches, the superior epigastric artery and the musculophrenic artery, at the level of the fourth intercostal space, deviating from the typical pattern. The length of the ITA, from its origin at the subclavian artery to the bifurcation point, could not be measured, as it was observed only after the rib cage was removed. On the left side, however, the ITA followed the usual anatomical course, terminating at the sixth intercostal space, as illustrated in Fig. 1a .

Figure 1.

(a) The ITA terminating at the 4th ICS on the right side (R) and the 6th ICS on the left side (L); (b) the xiphoid process (XP) is seen bifurcated (black outline and star). S: sternum; MP: musculophrenic artery; SE: superior epigastric; ICS: intercostal space

In addition to this vascular variation, a bifid xiphoid process was noted. The xiphoid consisted of two slender bony bars, each approximately 3 cm in length, with a median ‘V’-shaped cleft separating them (Fig. 1b) . These findings highlight the importance of recognizing variations in anatomical structures, particularly in the context of surgical procedures, as such variations can impact clinical approaches and outcomes.

Classical textbooks state that the internal thoracic artery ends at the sixth rib or the sixth intercostal space, where it branches into the superior epigastric and musculophrenic arteries. This artery is crucial for supplying blood to various structures, including the intercostal muscles, diaphragm, parts of the sternum, and the skin and tissues covering the chest. The termination levels noted in this study are consistent with those described in classical literature. Salve et al. documented a case where the internal thoracic artery ended at the third intercostal space^[4], while Agnihotri G et al. reported terminations at the fourth, fifth, and seventh intercostal spaces^[5].

Several signaling molecules and pathways are involved in regulating the growth and development of the ITA, including vascular endothelial growth factor (VEGF), notch signaling, and Ephrin/Eph receptors.^[6] Sonic Hedgehog (SHH), a protein secreted by the Hedgehog (HH) family, is essential for regulating endothelial cell growth, promoting the migration of cells, and initiating the formation of new blood vessels.^[7] Additionally, homeobox genes and other transcription factors, such as Nkx2.5, contribute to the patterning of the cardiovascular system, including the ITA.^[8] The ITA branches into several significant areas, including the mediastinal, pericardial, sternal, anterior intercostal, pericardiophrenic, terminal, and perforating branches. Paliouras et al.^[9] have found four distinct types of branching patterns. The internal thoracic arteries (ITAs) most commonly terminated by bifurcating into the superior epigastric and musculophrenic arteries (96% in LITAs and 90% in RITAs), while trifurcation with an additional diaphragmatic branch occurred in 4% and 10%, respectively. The most frequent termination point for both ITAs was at the 6th intercostal space, aligning with the level of the 6th rib as the second most common site.^[9,10] It is the primary blood supply to the sternum, and errors during surgical procedures in the thoracic cavity can disrupt this blood flow, potentially resulting in complications related to sternal injuries.^[11] Caution is essential during operations involving the thoracic walls, such as percutaneous subclavian vein catheterization and pacemaker placement.^[12] This region should be carefully avoided when performing intercostal paracentesis of the pericardial sac, ensuring that the needle is inserted at a safe distance from the sternal margin.^[13]

The ITA is particularly recognized for its role in coronary artery bypass grafting (CABG). In CABG, the ITA is carefully harvested from its anatomical position and then surgically connected to the coronary artery to restore blood flow to the heart muscle.^[2,14] Given the ITA’s critical importance in various essential procedures, any overlooked anatomical variations, like the one mentioned here, could lead to complications during CABG or other interventions involving the thoracic wall.

The enduring clinical advantages of the internal thoracic artery (ITA) in cardiothoracic surgery have been well-documented, with numerous studies exploring the specific histological features that contribute to these benefits. It is widely agreed that the ITA exhibits a transitional structure, characterized by an elastic composition in its upper segment (located in the second intercostal space), which then shifts to an elastic-muscular configuration, ultimately becoming a muscular-type artery in the remaining thoracic region.^[15] In recent times, the use of ITA branches for breast reconstruction following mastectomy has gained popularity. This technique employs tissue flaps in conjunction with ITA perforators to achieve optimal symmetry and address deformities. It effectively utilizes a dermoglandular perforating branch of the internal mammary artery (IMA) located in each of the 5 to 6 intercostal spaces, positioned laterodorsally to the lateral edge of the sternum.^[16] These branches extend superficially in a laterocaudally direction, providing blood supply to the skin of the medial two-thirds of the pectoral region in a sequential manner. Furthermore, perforators from the fourth and fifth intercostal spaces have been shown to play a role in supplying blood to the areola as well as the direct inframammary fold and surrounding area.^[17]

The xiphoid process is an important landmark during procedures such as cardiopulmonary resuscitation (CPR), median sternotomy for heart surgery, or abdominal surgeries. The molecular development of the xiphoid process involves complex interactions between various signaling pathways, transcription factors, and extracellular matrix components. Key molecular players such as Sox9, Ihh, Runx2, and Wnt signaling orchestrate the development of cartilage and bone in the xiphoid process.^[18] The mesenchyme that formed the sternum during embryonic development came from the mesodermal germ layer. During development, the xiphoid process experiences a number of compositional changes, including the ossification of cartilaginous components.^[19] MMPs (matrix metalloproteinase) degrade the extracellular matrix (ECM) during bone remodeling and ossification. The activity of MMPs is tightly regulated during the transition from cartilage to bone in the xiphoid process.^[20] Transforming growth factor-beta (TGF-β) signaling also plays a significant role in regulating cartilage matrix production and chondrocyte differentiation.^[18] It helps coordinate the cartilage remodeling and ossification processes. Variations in its development, such as delayed ossification or abnormal shape, can result from disruptions in these molecular pathways. Variations like a bifid xiphoid could potentially alter the approach or technique used during these procedures. In some cases, the bifid nature of the xiphoid may make the process more vulnerable to injury or fracture, particularly during blunt trauma or chest compressions.

Theinternal thoracic artery is a common choice for coronary artery bypass grafting (CABG) due to its favorable long-term patency rates. Knowledge of ITA variations is essential in cardiac surgery to avoid damage to the vessel and to ensure appropriate graft placement. Similarly, mastectomy and breast reconstruction surgeries also require careful consideration of ITA variations to avoid compromising the blood supply to the breast. While a bifid xiphoid process is generally a benign anatomical variant, its recognition is important in clinical practice to avoid misinterpretation, ensure accurate diagnosis, and tailor appropriate surgical or medical management if necessary.

The Institute Ethics Committee granted this study Ethical Approval for an exemption from review, allowing them to use the cadavers donated to the department for teaching and research purposes

The authors declared that no clinical trials were used in the present study.

The author declared that no experiments on humans or human tissues were performed for the present study.

The authors declared that no informed consent was obtained from the humans, donors or donors’ representatives participating in the study.

The authors declared that no experiments on animals were performed for the present study.

The authors declared that no commercially available immortalised human and animal cell lines were used in the present study.

The authors have declared that no competing interests exist.

No funding was reported.

No use of AI was reported.

All data used are referenced or included in the article.

SR: conceptualization, supervision, data curation, review; DPS and AVP: data curation; AV: manuscript preparation and revision.

None.