Co-existence of patent ductus arteriosus and left brachiocephalic artery: a case report

In normal cardiovascular development, the sixth aortic arch gives off an important branch that grows toward the developing lung bud. On both sides, the proximal part of the sixth aortic arch becomes the proximal segment of the right and left pulmonary arteries [9]. The distal segment of this arch on the right side loses its connection with the dorsal aorta and disappears while on the left side the distal portion persists during intrauterine life as the ductus arteriousus [9]. The fetal ductus arteriosus is an important structure which is essential for normal fetal development, allowing most of the blood from the right ventricle to bypass the fetus’s fluid-filled non-functioning lungs. Premature constriction or closure may lead to right heart failure, resulting in fetal hydrops [10]. Upon closure after birth, the ductus arteriosus becomes a fibrous band known as the ligamentum arteriosum. Failure of closure of the ductus arteriousus after birth leads to PDA.

In majority of individuals, the aortic arch gives rise to three classical branches, namely the brachiocephalic trunk, the left common carotid artery and the left subclavian artery. However, various branching pattern of the aortic arch have been described [3,4]. In some cases, the left common carotid artery have been shown to originate from the brachiocephalic trunk [3,4]. Rarely the left common carotid and the left subclavian arteries have been shown to have a common origin in the form of the left brachiocephalic trunk from the aortic arch [3]. Most irregularities of aortic arch branching pattern result from persistence of parts of aortic arches that usually disappear, or from disappearance of parts that normally persists.

The left common carotid artery is formed from the proximal part of the left third aortic arch while the left subclavian artery is derived from the left seventh intersegmental artery [11]. During the fourth week of development, the initial location of the left subclavian artery is shifted as a result of embryo’s cephalic folding, growth of the forebrain and elongation of the neck. The left subclavian artery which is initially fixed in the distal arm bud shifts its point of origin from the aorta at the level on seventh intersegmental artery to an increasingly higher point until it comes close to the origin of the left common carotid artery [9]. The existence of left brachiocephalic artery in this case could not be explained by the existing literature. However, we postulate two scenarios that can explain this finding. Common origin of the left common carotid and left subclavian arteries (through the left brachiocephalic trunk) could suggest that the left subclavian artery is also derived from the proximal part of the left third aortic arch. Alternatively, it could be a result of fusion of the proximal parts of the left common carotid and left subclavian arteries as a result of cranial shift of the left subclavian artery too close to the origin of the left common carotid artery.

In the present case, the clinical presentations were all consistent with the PDA. However, PDA may also exist with other cardiac anomalies, which must be considered at the time of diagnosis. PDA has been found in individuals with congenital aortic valvular diseases, as well as Coronary artery fistulas [4]. It has been reported that in the presence of complex congenital heart defects, the usual anatomy of the ductus may not be present due to the fact that anatomic abnormalities can vary widely but most are common with complex aortic arch anomalies [12]. Structures that have been mistaken for the patent ductus arteriosus (PDA) in surgical procedures include the aorta, the pulmonary artery, and the carotid artery [12]. Although the co-existence of PDA and ‘left brachiocephalic trunk’ in this case did not pose any surgical challenge, knowledge of variations in the branching pattern of the arch of the aorta is of great importance in patients who have to undergo four-vessel angiography, aortic instrumentation, or supraaortic thoracic, head and neck surgery [13]. Knowledge on variation of origin and course of a great vessel arising from the aortic arch is of great clinical value in minimizing complications that may arise especially during surgical procedures in the superior mediastinum and the root of neck. Further, while operating around the arch of aorta and the descending aorta (either for coarctation of aorta, or PDA), it is important to correctly identify the branches of the arch of aorta.

Traditional 2-dimensional imaging techniques, such as radiography, echocardiography, and angiography, have shown to be limited in the diagnosis of extracardiac intrathoracic vascular anomalies [14,15]. The use of multidetector-row computed tomography (MDCT) has been shown to be more superior over the traditional 2-dimensional techniques due to the fact the 3-dimensional MDCT are able to display the anatomy of aortic anomalies (PDA or aortic arch anomalies) and the spatial relationship of adjacent structures [14,15]. In the present case, the left brachiocephalic trunk was not picked by echocardiography. Some of the major Hospitals in Tanzania, including Bugando Medical Centre are in the process or have just established cardiothorax surgical units. Introduction of MDCT at these centres is therefore highly recommended since it will provide valuable information to surgeons prior to surgery and subsequently reduce potential risks that can result from missed diagnosis of cardiovascular anomalies.