How frequent is the fifth arch artery?

Two critical events in the development of the vascular system: pruning and remodeling

The cardiovascular system is the first functional organ system to develop in the vertebrate embryo. The primitive heart and primitive vascular plexus are formed through vasculogenesis and thereafter through angiogenesis. After the establishment of new connections within the vascular network, a pruning and remodeling process occurs after which some branches are stabilized, whereas others regress. The aim of this article is to describe the most common pruning and remodeling forms, which take place during organogenesis in the experimental and human systems.

Common Arterial Trunk Coexisting With Double-Barreled Aorta

This case describes the first example of a double-barreled aorta in the setting of a common arterial trunk. Our use of annotated and segmented 3-dimensional models greatly enhanced our ability to elucidate the complex anatomy. (Level of Difficulty: Advanced.).

Morphogenesis of the Mammalian Aortic Arch Arteries

The major vessels in mammals that take blood away from the heart and deliver it to the arms and the head take their origin from the aortic arch and are derived from the arteries formed within the embryonic pharyngeal arches. These pharyngeal arch arteries, initially symmetrical, form in a cranial to caudal sequence within the pharyngeal mesenchyme. They then undergo a complex process of remodeling to produce the asymmetrical brachiocephalic arteries as seen in the adult. A complex interaction between the tissues of the pharyngeal arches and the genes they express is required to ensure that arterial formation and remodeling is able to proceed normally. If this process is disrupted, life-threatening congenital cardiovascular malformations can occur, such as interruption of the aortic arch, isolation of individual arteries, or so-called vascular rings. Here, using state-of-the-art imaging techniques, we describe the morphogenesis of the arteries in humans and mice and the cardiovascular defects in the Tbx1 mutant mouse model. We provide details of the process of remodeling, clarifying also the morphogenesis of the external carotid artery and the so-called "migration" of the left subclavian artery.

A double-barrelled aorta with high aortic Arch

A double-barrelled aorta was detected in a female newborn with 22q11.2 deletion syndrome. Double-barrelled aorta had been previously described as persistence of the fifth pharyngeal arch, but its existence continues to be debated. Recent embryologic studies suggest that double-barrelled aorta is more likely explained by other developing processes in the majority of cases. In our case, catheter angiography confirmed the presence of the high aortic arch and double-barrelled aorta. The upper lumen was located above the level of the clavicles. These findings suggested that the persistence of the segment of dorsal aorta between the third and fourth embryonic arches and the double-barrelled aorta was more likely a consequence of persistence of the third and fourth pharyngeal arches. Detailed imaging and embryologic considerations played an important role in accurate assessment of the origin of the double-barrelled aorta. <Learning objective: Double-barrelled aorta is a rare congenital anomaly. Its etiology had been previously described as persistence of the fifth pharyngeal arch, but recent embryologic studies suggest that it is more likely explained by other several developing processes. We report a case of double-barrelled aorta with high aortic arch likely arose from the third and fourth pharyngeal arches. Although the therapeutic approaches remain the same, accurate description and classification are important.>.

Maternal iron deficiency perturbs embryonic cardiovascular development in mice

Congenital heart disease (CHD) is the most common class of human birth defects, with a prevalence of 0.9% of births. However, two-thirds of cases have an unknown cause, and many of these are thought to be caused by in utero exposure to environmental teratogens. Here we identify a potential teratogen causing CHD in mice: maternal iron deficiency (ID). We show that maternal ID in mice causes severe cardiovascular defects in the offspring. These defects likely arise from increased retinoic acid signalling in ID embryos. The defects can be prevented by iron administration in early pregnancy. It has also been proposed that teratogen exposure may potentiate the effects of genetic predisposition to CHD through gene-environment interaction. Here we show that maternal ID increases the severity of heart and craniofacial defects in a mouse model of Down syndrome. It will be important to understand if the effects of maternal ID seen here in mice may have clinical implications for women.

Persistent fifth aortic arch: a single-center experience, case series

BACKGROUND

Persistent fifth aortic arch (PFAA) is an extremely rare congenital cardiovascular malformation and there is limited data in the literature. The objective of this study is to enhance our understanding and diagnosis of PFAA from echocardiography and computed tomography angiography (CTA) findings, and to evaluate the application of echocardiography in the diagnosis of PFAA.

METHODS

We retrospectively reviewed five cases of PFAA diagnosed from October 2016 to September 2019 at the Affiliated Children's Hospital of Capital Institute of Pediatrics. We described their diagnosis by echocardiography and CTA findings, and medical history.

RESULTS

Five cases of PFAA were identified in the study. Patients aged from 3 to 48 months and weighed from 4 to 12 kg presented different clinical symptoms upon clinical examination. All the patients completed a primary echocardiographic assessment; however, the first two patients were misdiagnosed by echocardiography and was confirmed by supplemental CTA while the other three patients were directly diagnosed by echocardiography. Surgery was necessary for three patients, two of whom accepted and one refused. The other two patients only needed a follow-up assessment, which showed good results.

CONCLUSIONS

The clinical manifestation of PFAA in our patient population was atypical, and their diagnosis depended on the use of echocardiography. In the case of uncertainty, the final diagnosis was confirmed by CTA. Although the nomenclature and embryonic origin of PFAA remains controversial, the accurate diagnosis of aortic arch abnormalities and associated malformations are imperative for time-sensitive treatments.

Technical considerations of coarctation stenting in double-barreled aorta - A persistent fifth arch mimic

The double-barreled aorta connecting the ascending aorta and descending aorta caudal to the normal fourth aortic arch has fascinated the interests of cardiac morphologists for over a century. This condition is commonly associated with coarctation. While the controversies surrounding the embryology of the double-barreled aorta have settled down, we present a case-based illustration of the technical aspects of coarctation stenting peculiar to this condition.

Embryological development of the human cranio-facial arterial system: a pictorial review

The embryological development of the cerebral vasculature is very complex. Historical and also more recent studies based on human embryos, comparative anatomy and cerebral angiographies allowed us to better understand this vasculature development. The knowledge and understanding of such embryological development are important for physicians interested in neurovascular pathologies. Indeed, all vascular variants and almost all vascular pathologies, such as aneurysms, dolichoectasia, atherosclerosis, and neurovascular conflicts could be explained by an alteration during the embryological life. There are also many variants of these vascular structures present in normal developed adults, which are variably associated with pathological entities. Understanding the process which leads to the development of the normal cerebral arterial system in humans is, therefore, very important to have a better knowledge of the possible clinical and surgical implications of these anomalies. In this paper, we review the embryological development of the cranio-facial arterial vasculature from its beginning at approximately days 21–50 of intrauterine life, with pictures illustrating each developmental phase.

DiGeorge syndrome and anomalous right aortic arch with arch-on-arch and figure-of-eight configurations: Aortic sac maldevelopment and left brachiocephalic artery abnormal remodeling

We report a 6-month-old female infant with deletion of chromosome 22q11.2 (DiGeorge/VFS TUPLE 1), normal atrial arrangement with concordant atrioventricular connection, pulmonary atresia, large subaortic ventricular septal defect, diminutive native pulmonary arteries, a characteristic weird-shape right aortic arch with arch-on-arch appearance and figure of 8 configuration. We presented the cardiac computed tomographic angiographic and cardiac angiographic features. Using Autodesk 3ds Max 2018 software, we explained and illustrated the speculative embryologic etiology of this bizarre aortic archanomaly with the extensive abnormal remodeling of the left brachiocephalic artery, based on a “five-embryonic aortic arches” concept. As to the best of the authors' knowledge, this is the first report of a genetically confirmed case of DiGeorge syndrome and an exceedingly rare type of right aortic arch anomaly with embryologic explanation according to the “five-embryonic-aortic-arches” concept. It seems that the constellation of pulmonary atresia, bizarreshaped right aortic arch due to abnormal development of the aortic sac, and abnormal remodeling of the left brachiocephalic artery may be strongly suggestive of DiGeorge syndrome.

How best to describe the pharyngeal arch arteries when the fifth arch does not exist?

In the accompanying article appearing in this issue of the Journal, Prabhu and his colleagues, from Bengalaru in India, describe their experience with patients having a right aortic arch. They discuss the fact that the anomalous arrangements they encountered can all be interpreted on the basis of the hypothetical double arch proposed by Edwards. They point to the fact that interpretation of the developmental changes underscoring the production of the double arch is currently confused by reference to the so-called Rathke diagram, in which six sets of arteries are shown extending through the mesenchyme of the pharyngeal arches. As the authors point out, Graham and his associates have now shown that the alleged fifth set of pharyngeal arches do not exist. Based on our own observations, we endorse this statement. It means that new explanations must now be provided for the lesions previously described on the basis of persistence of the alleged artery of the fifth pharyngeal arch. We have previously claimed to have observed such an artery in a human fetus. We now believe, on the basis of our latest findings, that our earlier observation is better explained on the basis of presence of a collateral channel. We suggest that the so-called "fifth arch arteries" are themselves then best explained either on the basis of existence of such collateral channels, or remodelling of the aortic sac, which is the manifold, during development, that gives rise to the pharyngeal arch arteries.

Isolated persistence of the fifth aortic arch in an infant presenting with congestive heart failure

The persistence of the fifth aortic arch (PFAA) in postnatal life is an extremely rare and controversial cardiovascular malformation. PFAA is defined as an extra-pericardial vessel arising from the ascending aorta proximal to the origin of the brachiocephalic arteries, terminating either in the dorsal aorta or in the pulmonary arteries through the persistently patent arterial duct. An isolated PFAA with systemic-to-pulmonary connection best fits this definition, while the vast majority of cases reported as PFAA may have alternative embryological explanations. We present a unique case of a 5-week-old patient with an isolated PFAA with systemic-to-pulmonary connection, who presented with congestive heart failure. A first differential diagnosis was made with distal aortopulmonary window and an atypical patent arterial duct. A careful analysis of the case and a systematic review of the literature made us conclude for an isolated PFAA, which is one of the only five cases ever reported.

Merged bilateral arterial duct and circumflex retroesophageal right aortic arch in a fetus with normal intracardiac anatomy

We report the case of a fetus with anamnios sequence and VACTERL syndrome, having a circumflex right aortic arch. Two arterial ducts join anteriorly to form a common vessel that connects to the pulmonary trunk with confluent pulmonary branches. Embryologically, the dorsal right 6th aortic arch did not disappear and the aortic arch development stopped in a symmetrical state with an exceptional "Y-shaped" merged bilateral arterial duct.

The ubiquitin ligase HECTD1 promotes retinoic acid signaling required for development of the aortic arch

The development of the aortic arch is a complex process that involves remodeling of the bilaterally symmetrical pharyngeal arch arteries (PAAs) into the mature asymmetric aortic arch. Retinoic acid signaling is a key regulator of this process by directing patterning of the second heart field (SHF), formation of the caudal PAAs and subsequent remodeling of the PAAs to form the aortic arch. Here, we identify the HECTD1 ubiquitin ligase as a novel modulator of retinoic acid signaling during this process. Hectd1^opm/opm homozygous mutant embryos show a spectrum of aortic arch abnormalities that occur following loss of 4th PAAs and increased SHF marker expression. This sequence of defects is similar to phenotypes observed in mutant mouse models with reduced retinoic acid signaling. Importantly, HECTD1 binds to and influences ubiquitination of the retinoic acid receptor, alpha (RARA). Furthermore, reduced activation of a retinoic acid response element (RARE) reporter is detected in Hectd1 mutant cells and embryos. Interestingly, Hectd1^opm/+ heterozygous embryos exhibit reduced retinoic acid signaling, along with intermediate increased expression of SHF markers; however, heterozygotes show normal development of the aortic arch. Decreasing retinoic acid synthesis by reducing Raldh2 (also known as Aldh1a2) gene dosage in Hectd1^opm/+ heterozygous embryos reveals a genetic interaction. Double heterozygous embryos show hypoplasia of the 4th PAA and increased incidence of a benign aortic arch variant, in which the transverse arch between the brachiocephalic and left common carotid arteries is shortened. Together, our data establish that HECTD1 is a novel regulator of retinoic acid signaling required for proper aortic arch development.

Editor's choice: The HECTD1 ubiquitin ligase is a novel modulator of retinoic acid signaling during aortic arch development and provides a model for complex interactions underlying variations in aortic arch development.

Persistent fifth aortic arch: the "great pretender" in clinical practice

Persistence of the embryonic "fifth aortic arch" in postnatal life is a rare, enigmatic - and at times controversial - condition, with variable anatomical forms and physiological consequences. First described in humans over 40 years ago by Van Praagh, the condition was labelled the "great pretender" by Gerlis 25 years later, because of its apparent propensity to mimic anatomically similar structures. Despite many subsequent case reports citing the condition, the true developmental origin of these structures remains unresolved, and has been the subject of debate among embryologists for more than a century. A persistent fifth aortic arch has been defined as an extrapericardial structure, arising from the ascending aorta opposite or proximal to the brachiocephalic artery, and terminating in the dorsal aorta or pulmonary arteries via a persistently patent arterial duct. This description may therefore encompass various anatomical forms, such as a unilateral double-lumen aortic arch, an unrestrictive aortopulmonary shunt, or a critical vascular channel for either the systemic or pulmonary circulation. The physiological properties of these vessels, such as their response to prostaglandins, may also be unpredictable. In this article, we demonstrate a number of cases that fulfil the contemporary definition of "persistent fifth aortic arch" while acknowledging the embryological controversies associated with this term. We also outline the key diagnostic features, particularly with respect to the use of new cross-sectional imaging techniques.

Development and Morphology of the Ventricular Outflow Tracts

It is customary, at the current time, to consider many, if not most, of the lesions involving the ventricular outflow tract in terms of conotruncal malformations. This reflects the introduction, in the early 1940s, of the terms conus and truncus to describe the components of the developing outflow tract. The definitive outflow tracts in the postnatal heart, however, possess three, rather than two, components. These are the intrapericardial arterial trunks, the arterial roots, and the subvalvar ventricular outflow tracts. Congenital lesions afflicting the arterial roots, however, are not currently considered to be conotruncal malformations. This suggests a lack of logic in the description of cardiac development and its use as a means of categorizing congenital malformations. It is our belief that the developing outflow tract, like the postnatal outflow tracts, can readily be described in tripartite fashion, with its distal, intermediate, and proximal components forming the primordiums of the postnatal parts. In this review, we present evidence obtained from developing mice and human hearts to substantiate this notion. We show that the outflow tract, initially with a common lumen, is divided into its aortic and pulmonary components by a combination of an aortopulmonary septum derived from the dorsal wall of the aortic sac and outflow tract cushions that spiral through its intermediate and proximal components. These embryonic septal structures, however, subsequently lose their septal functions as the outflow tracts develop their own discrete walls. We then compare the developmental findings with the anatomic arrangements seen postnatally in the normal human heart. We show how correlations with the embryologic findings permit logical analysis of the congenital lesions involving the outflow tracts.

Double-Lumen Aortic Arch: Persistence of the Fifth Aortic Arch

A persistent fifth aortic arch is exceptionally rare. We report a patient with a double-lumen aortic arch in association with a perimembranous ventricular septal defect and Cornelia de Lange syndrome. We also discuss the morphologic consequences of persistent fifth aortic, arch, which may not be limited to the double-lumen aorta but in fact may be more common.

Clarifying the anatomy of the fifth arch artery

The artery allegedly forming in the fifth pharyngeal arch has increasingly been implicated as responsible for various vascular malformations in patients with congenitally malformed hearts. Observations from studies on developing embryos, however, have failed to provide support to substantiate several of these inferences such that the very existence of the fifth arch artery remains debatable. To the best of our knowledge, in only a solitary human embryo has a vascular channel been found that truly resembled the artery of the fifth arch. Despite the meager evidence to support its existence, the fifth arch artery has been invoked to explain the morphogenesis of double-barreled aorta, some unusual forms of aortopulmonary communications, and abnormalities of the brachiocephalic arteries. In most of these instances, the interpretations have proved fallible when examined in the light of existing knowledge of cardiac development. In our opinion, there are more plausible alternative explanations for the majority of these descriptions. Double-barreled aorta is more likely to result from retention of the recently identified dorsal collateral channels while abnormalities of brachiocephalic arteries are better explained on the basis of extensive remodeling of aortic arches during fetal development. Some examples of aortopulmonary communications, nonetheless, may well represent persistence of the developing artery of the fifth pharyngeal arch. We here present one such case - a patient with tetralogy of Fallot and pulmonary atresia, in whom the fifth arch artery provided a necessary communication between the ascending aorta and the pulmonary arteries. In this light, we discuss the features we consider to be essential before attaching the tag of "fifth arch artery" to a candidate vascular channel.

Isolation of the right subclavian artery in a patient with d-transposition of the great arteries

Isolation of the right subclavian artery (RSCA) is rare, and this finding in association with d-transposition of the great arteries (d-TGA) is extremely unusual. We present a case of an isolated RSCA in a newborn with d-TGA in whom the clinical presentation was diagnostic. We discuss the imaging modalities used to confirm the diagnosis, the embryological basis of the finding, and the surgical repair.