Cervical origin of left subclavian artery: A rare anomaly.

A 22-year-old lady was referred to our institute for the management of pulmonary atresia with hypoplastic pulmonary arteries. Computed tomographic Angiography (CTA) showed right aortic arch with left brachicephalic artery as the first branch, which trifurcated into internal carotid, external carotid and subclavian artery high up in the neck at the level of third cervical vertebra. The left subclavian artery then travelled back caudally and entered into the arm after giving rise to a large collateral artery. This is the first ever-reported case of cervical origin of left subclavian artery (COLSA) in the literature. This anomaly can be explained by the absence of left fourth aortic arch with left subclavian artery arising from the left third aortic arch.

CASE REPORT

A 22-year-old lady was referred to our institute for the management of pulmonary atresia with ventricular septal defect and hypoplastic central pulmonary arteries with systemic oxygen saturation of 94%. Physical examination showed coarse facies with malar flattening, small mouth, micrognathia and a pulsatile swelling on the left side of the neck with continuous murmur over that area. Doppler ultrasonography showed a prominent anomalous arterial branch lying lateral to left common carotid artery. Echocardiography confirmed the small pulmonary arteries with multiple collaterals feeding both right and left pulmonary arteries. Confluence of the pulmonary artery could not be demonstrated. Computed tomographic Angiography (CTA) was ordered to define the pulmonary artery anatomy and aorto-pulmonary collaterals. CTA showed non-confluent pulmonary artery with multiple aorto-pulmonary collaterals feeding both the sides. Aortic arch was right sided [Figure 1b] with left brachicephalic artery as the first branch [Figure 2a]. The large left brachicephalic artery extended superiorly into the neck and trifurcated at the level of third cervical vertebra into internal carotid, external carotid and subclavian artery [Figure 3]. Left common carotid artery was absent. The left subclavian artery then travelled back caudally and entered into the arm after giving rise to a large collateral artery [Figures 1, 2b and 3]. Because of significant stealing of blood into the pulmonary circulation, the collateral artery size was larger than the subclavian artery [Figure 2b]. This abnormality can be labeled as cervical origin of left subclavian artery (COLSA) with right aortic arch. This is the left sided equivalent of cervical origin of right subclavian artery (CORSA) in patients with chromosome 22q11 deletion syndrome.

Figure 1

Computed tomography angiogram-coronal section showing the vascular anatomy. (a) showing higher up origin of left subclavian in the neck and descends down to enter the arm. (b) showing the site of origin of the large collateral artery from the subclavian artery before it enters into the arm

Figure 2

(a and c) 3D reconstructed view of vascular anatomy from anterior (a) and posterior (b) aspect. Multiple collateral arteries are seen entering into right and left pulmonary arteries

Figure 3

Computed tomography angiogram-lateral view showing the origin of left subclavian artery at the level of third cervical vertebraLt SCA: Left subclavian artery, Lt BCA: Left brachiocephalic artery, Lt ECA: Left external carotid artery, Lt ICA: Left internal carotid artery, LT VERT: Left vertebral artery, Rt CCA: Right common carotid artery, Rt SCA: Right subclavian artery, Ao: Aorta, MAPCA: Major aorto-pulmonary collateral artery

This is the first ever reported case of COLSA in the literature. This developmental anomaly can be explained by the absence of left fourth aortic arch with left subclavian artery arising from the left third aortic arch. Unilateral or bilateral absence or atresia of embryonic fourth arch is considered to be diagnostic of 22q11 deletion syndrome. Since the patient refused for genetic testing, 22q11 deletion syndrome could not be tested. The patient was kept on medical follow-up in view of non-confluent small pulmonary arteries, multiple Major aortopulmonary collateral arteries (MAPCAs) and systemic saturation of 94%.

DISCUSSION

Chromosome 22q11 deletion syndrome is associated with DiGeorge syndrome, conotruncal anomaly face syndrome, and velocardiofacial syndrome.[1] The major features of these syndromes include congenital heart disease, aplasia or hypoplasia of the thymus and/or parathyroid glands, palatal abnormalities, speech and learning disabilities and facial dysmorphism.[2] The cardiac defects commonly seen in these disorders derive from the conotruncus, the embryonic aortic arches and the ventricular septum. Deletion frequency is higher in patients with the secondary diagnosis of any arch or vessel anomaly as compared to those with a normal left aortic arch. Reported vascular anomalies include right aortic arch, cervical aorta, aberrant origin or isolation of the subclavian artery, the absence of the ductus arteriosus, major aortopulmonary collateral arteries[3] , isolation of the left pulmonary artery, vascular ring formed by the right aortic arch, retroesophageal aortic arch, and left descending aorta.[4] In patients with conotruncal malformations, anomalies of the subclavian arteries are the most important anatomical marker for the presence of monosomy 22q11, independent of the laterality of the aortic arch.[5]

Kutsche and Van Mierop[6] first described cervical origin of the right subclavian artery (CORSA) in patients with aortic arch interruption. Rauch et al.,[7] described CORSA in 11 of the 37 patients who had anomalies of origin of the subclavian arteries. The associated cardiovascular anomalies in these cases included interruption of aortic arch, pulmonary atresia with ventricular septal defect, and tetralogy of Fallot.[8] Microdeletion in the long arm of chromosome 22 in the region 22q11 was noted in all patients with CORSA. The authors concluded that detection of CORSA could represent a specific marker for monosomy 22q11. In patients with 22q11 deletion syndrome, there appears to be predilection for unilateral or bilateral absence or atresia of the embryonic fourth arch. When this occurs on the side opposite the definitive arch, the subclavian artery will arise from the third arch (which being more cephalad) in the neck rather than in the thorax.

In our patient, who was having right aortic arch, the abnormality can be explained by the agenesis of left fourth arch before the involution of left ductus caroticus (segment of dorsal aorta between the third and fourth arches). The retained left ductus caroticus bridged the connection between third arch and seventh intersegmental artery, thus completing the cervical origin of left Subclavian artery.

This is the first ever-reported case of COLSA. Knowledge of this abnormal vascular course is important before planning for complete repair or palliative procedures for complex congenital heart disease. Inadvertent vascular injury during surgical procedures, source of abnormal collateral arteries and difficulty in performing percutaneous vascular interventions are some of the problems which may be encountered in these patients. Like CORSA, COLSA may also be considered as a marker of 22q11 deletion syndrome, as our patient had typical facies with conotruncal anomaly though genetic testing could not be done.

In the current era of minimally invasive surgery and robotically assisted surgery, precise definition of aortic arch anatomy is essential for complete repair of congenital heart disease. This is especially true in patients with 22q11 deletion syndrome, in which there is a high incidence of aortic arch anomalies.