Persistent Fifth Aortic Arch Stenosis Associated with Type A Interruption of the Aortic Arch: A Report of Six Cases
Persistent fifth aortic arch (PFAA) is a rare congenital cardiovascular malformation that occurs when the pharyngeal fifth aortic arch fails to degenerate during the embryonic period. This condition was first described in an autopsy specimen in 1969, and since then, various case reports have documented its different forms. Among these, PFAA stenosis associated with type A interruption of the aortic arch (type-A IAA) is the most common in clinical practice and typically requires surgical intervention. This report summarizes the clinical characteristics, diagnostic features, and treatment outcomes of six cases of PFAA stenosis associated with type-A IAA, diagnosed between 2013 and 2018.
Embryological Background and Pathophysiology
During embryological development, the bilateral fifth primitive aortic arches usually degenerate early after appearing or may not appear at all. However, in some cases, the fifth arch persists unilaterally or bilaterally, either completely or partially, leading to a wide variety of anatomical configurations. The persistent fifth arch is an extra-pericardial vessel that arises from the ascending aorta proximal to the origin of the brachiocephalic arteries and ends either in the dorsal aorta or in the pulmonary arteries via the sixth arch. Based on the proximal and distal connections of the vessel and the direction of blood flow, PFAA can be classified into four types: systemic-to-systemic, systemic-to-pulmonary, pulmonary-to-systemic, and bilateral. Each type has different subtypes, contributing to the diverse clinical manifestations of PFAA.
PFAA stenosis associated with type-A IAA is classified as a systemic-to-systemic connection. In this condition, the fourth aortic arch is interrupted after the left subclavian artery arises, and the fifth aortic arch originates from the ascending aorta opposite or proximal to the brachiocephalic artery, ending in the descending aorta. The distal part of the fifth arch is always narrow, and the degree of stenosis determines the severity of symptoms. This unique anatomical configuration makes the fifth aortic arch a critical channel connecting the ascending and descending aorta, essential for survival.
Clinical Presentation and Diagnosis
The clinical presentation of PFAA stenosis associated with type-A IAA varies in severity and timing. In the six cases reported, five patients exhibited symptoms within the first three months of life, while the sixth patient remained asymptomatic until the age of four. The infant patients presented with critical conditions, including pneumonia, respiratory failure, and congestive heart failure. Three neonates were admitted to the intensive care unit with additional symptoms such as jaundice, difficulty feeding, and ductal shock. Physical examination revealed hypertension, systolic murmurs, and significant differences in blood pressure between the upper and lower extremities.
Echocardiography played a crucial role in the initial diagnosis of PFAA stenosis. It provided detailed imaging of the great arteries and cardiac function, revealing the characteristic anatomical features of the condition. The diameter of the PFAA stenosis ranged from 2.0 to 3.2 mm, with pressure gradients between 64 and 73 mmHg. Intracardiac structural changes included left atrioventricular dilatation, thickened left ventricular walls, and decreased left ventricular function. In the 4-year-old patient, routine echocardiography detected PFAA stenosis with type-A IAA, showing an inner diameter of 3.6 mm and a pressure gradient of 50 mmHg.
Computed tomography angiography (CTA) further confirmed the echocardiography findings, providing detailed images of the location and connections of the PFAA. The imaging results showed interruption of the fourth aortic arch (type A), with the three brachiocephalic arteries clustered and arising from the fourth aortic arch, unconnected to the descending aorta. The fifth aortic arch originated from the ascending aorta opposite or proximal to the brachiocephalic artery and ended in the descending aorta, with varying degrees of stenosis. These imaging modalities were essential for accurate diagnosis, pre-operative planning, and determining the appropriate treatment strategy.
Surgical Treatment and Outcomes
Five of the six patients underwent surgical treatment tailored to their specific anatomical and clinical conditions. Three patients underwent resection of the fifth aortic arch with end-to-end or end-to-side anastomosis of the descending aorta. One patient required additional procedures, including resection of the fifth aortic arch, subclavian artery transplantation, and subclavian artery anastomosis of the descending aorta. The 4-year-old patient underwent a fourth artificial pipe connection while retaining the fifth aortic arch.
Before surgery, all five patients exhibited significant pressure differences between the upper and lower limbs, exceeding 40 mmHg. Post-operatively, the pressure differences were essentially normalized, indicating successful surgical correction. Follow-up evaluations revealed stable conditions in all patients, with no major complications reported.
Diagnostic Challenges and Misdiagnosis
PFAA stenosis associated with type-A IAA is often challenging to diagnose due to its rarity and the complexity of its anatomical features. The condition has been referred to as the “great pretender” because it mimics other cardiovascular malformations, particularly coarctation of the aortic arch (COA). The hemodynamic manifestations of PFAA stenosis and COA are identical, leading to potential misdiagnosis. In cases where the fourth aortic arch is interrupted, the fifth aortic arch becomes the sole aortic arch, making the diagnosis even more challenging.
The fifth aortic arch is located in an unusually inferior position, approaching the same level as the main pulmonary trunk and arterial duct. All brachiocephalic arteries appear as a cluster originating from a single connection (the fourth aortic arch) to the ascending aorta, which is unconnected to the descending aorta. These characteristic changes are crucial for correct diagnosis, emphasizing the importance of a thorough understanding of embryological aortic arch development and the diagnostic features of PFAA stenosis.
Histopathological Features
Histopathological studies have revealed that the fifth aortic arch has distinct characteristics compared to normal arterial walls. The arch is composed of narrow elastic fibers with sensitivity to prostaglandins, rather than smooth muscle fibers. These fibers can become narrower with age, contributing to the progression of stenosis. Once diagnosed, this type of PFAA requires surgical intervention to prevent further complications.
Importance of Accurate Diagnosis and Pre-operative Planning
Accurate diagnosis of PFAA stenosis associated with type-A IAA is critical for successful surgical outcomes. Misdiagnosis can lead to inappropriate surgical approaches, such as aortic arch advancement, which may be potentially unsafe. Reports have documented cases where PFAA was misdiagnosed as COA and treated with left thoracotomy, highlighting the importance of correct pre-operative diagnosis and planning.
Conclusion
PFAA stenosis associated with type-A IAA is a rare and complex congenital cardiovascular malformation that requires careful diagnostic evaluation and surgical intervention. Echocardiography and CTA are essential imaging modalities for accurate diagnosis and pre-operative planning. A complete understanding of embryological aortic arch development and the diagnostic features of PFAA stenosis is crucial for improving diagnostic accuracy and ensuring appropriate treatment. Surgical correction of the condition leads to favorable outcomes, with stable post-operative conditions observed in the reported cases. As the “great pretender,” PFAA stenosis associated with type-A IAA underscores the importance of thorough diagnostic evaluation and a multidisciplinary approach to patient care.
doi.org/10.1097/CM9.0000000000000278
Was this helpful?
0 / 0