Development of the aorta takes place during the third week of gestation. It is a complex process that can lead to a variety of congenital variants and pathological anomalies. In diagnostic and interventional radiology, knowledge of aortic abnormalities and variant branching sequence is crucially important. This article gives a systematic overview of anatomical variability of the aorta.
KEYWORDS: Thoracic aorta, embryology, anatomical variantsObjectives: Upon completion of this article, the reader should (1) understand the development of the thoracic aorta and great vessels, and (2) understand the anatomical and pathological conditions that require consideration when treating diseases of the thoracic aorta. Development of the aorta takes place during the third week of gestation.1 It is a complex process associated with the formation of the endocardial tube (day 21), which lends itself to a variety of congenital variants. Each primitive aorta consists of a ventral and a dorsal segment that are continuous through the first aortic arch. The two ventral aortae fuse to form the aortic sac. The dorsal aortae fuse to form the midline descending aorta. Six paired aortic arches, the so-called branchial arch arteries, develop between the ventral and dorsal aortae. In addition, the dorsal aorta gives off several intersegmental arteries (Fig. 1).The vessels derived from each arch are as follows: The first pair contributes to formation of the maxillary and external carotid arteries. The second pair contributes to formation of the stapedial arteries. The third aortic arch constitutes the commencement of the internal carotid artery and is therefore named the carotid arch.Proximal segments of the third pair form the common carotid arteries. Together with segments of the dorsal aortae, the distal portions contribute to formation of the internal carotid arteries. The left arch of the fourth pair forms the segment of normal left aortic arch between the left common carotid and subclavian arteries. The right fourth arch forms the proximal right subclavian artery. The distal right subclavian artery is derived from a portion of the right dorsal aorta and the right seventh intersegmental artery. Rudimentary vessels that regress early develop out of the fifth pair. The left arch of the sixth pair contributes to the formation of the main and left pulmonary arteries and ductus arteriosus; this duct obliterates a few days after birth. The right sixth arch contributes to formation of the right pulmonary artery.
2With the caudad migration of the heart in the second fetal month, the seventh intersegmental arteries enlarge and migrate cephalad to form the distal subclavian
ObjectThe purpose of this study was to assess the value of myelography using flat-panel detector–based computed tomography (fpCT) in 5 patients in whom the image quality of multislice CT (MSCT) or MR imaging was limited by metal artifacts.MethodsThe application of fpCT to myelographic imaging of the lumbar spine and cervicothoracic junction after surgery was feasible. Multiplanar, preferably sagittal, and 3D reconstructions adequately depicted disc space implants and provided high resolution images of osseous structures.ResultsThe images obtained with fpCT allowed evaluation of anatomical details such as single nerve roots and proved especially valuable in a patient with impaired MR imaging results caused by metal artifacts from an intraoperative abrasion. In a case of recurrent disc herniation, imaging results of myelographic fpCT and MSCT scanning were in good agreement.ConclusionsThe novel imaging technique the authors describe yielded adequate results in patients with a history of spinal surgery, may be superior to MSCT scanning in depicting osseous structures and metallic implants, and has the potential to provide multilevel spinal images. Myelographic fpCT scanning may be the preferred modality in patients with expected or known metal artifacts on myelographic MSCT scans and/or MR images.
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