Embryology of the Thoracic Outlet
The thoracic outlet is the area in the lower neck traversed by the brachial plexus and subclavian vessels between the thorax and axilla. This dynamic space is formed by the first thoracic vertebra, first rib, and manubrium of the sternum. The thoracic out
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Embryology of the Thoracic Outlet R. Shane Tubbs and Mohammadali M. Shoja
Abstract
The thoracic outlet is the area in the lower neck traversed by the brachial plexus and subclavian vessels between the thorax and axilla. This dynamic space is formed by the first thoracic vertebra, first rib, and manubrium of the sternum. The thoracic outlet changes in volume with the movement of the upper limbs, thorax, and neck, is occupied by scalene and prevertebral muscles and fibrous structures, and is limited by osseous structures – the clavicle, first rib, and cervical vertebrae and transverse processes. During upper limb abduction, patients with thoracic outlet syndrome (TOS) have been found to decrease the space of the outlet more compared to healthy individuals.
The thoracic outlet is the area in the lower neck traversed by the brachial plexus and subclavian vessels between the thorax and axilla. This dynamic space is formed by the first thoracic vertebra, first rib, and manubrium of the sternum (Fig. 2.1). The thoracic outlet changes in volume with the movement of the upper limbs, thorax, and neck, is occupied by scalene and prevertebral muscles and fibrous structures, and is limited by osseous structures – the clavicle, first rib, and
R.S. Tubbs, PhD (*) Section Pediatric Neurosurgery, Children’s Hospital, ACC 400 1600 7th Ave. South, Birmingham, AL, 35233, USA e-mail: [email protected] M.M. Shoja Neuroscience Research Center, Tabriz University of Medical Sciences, Tabriz, Iran
cervical vertebrae and transverse processes. During upper limb abduction, patients with thoracic outlet syndrome (TOS) have been found to decrease the space of the outlet more compared to healthy individuals [1]. The embryogenesis of the thoracic outlet is a function of harmonious and timely growth of regional osseous, fibromuscular and neurovascular elements with the emerging upper limb bud. Any disturbance in the interaction or development of these elements affects spatial features of the outlet. From a morphological point of view, the thoracic outlet is a heterogeneous region with inter-individual variability and individuals with substantially distorted outlet contours or a crowded outlet are prone to develop TOS. In this chapter, the general aspects of the development of the thoracic outlet region are described followed by an overview of the embryology of common osseous and fibromuscular anomalies associated with TOS.
K.A. Illig et al. (eds.), Thoracic Outlet Syndrome, DOI 10.1007/978-1-4471-4366-6_2, © Springer-Verlag London 2013
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R.S. Tubbs and M.M. Shoja
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Fig. 2.1 Lateral view of the thoracic outlet from the skeleton of a 30 week old fetus. Notice the more horizontal nature of the manubrium as compared to the adult and the increased concavity of the first ribs
Neurovascular Development The subclavian vessels and brachial plexus traverse the thoracic outlet. The left subclavian artery arises from the left 7th intersegmental artery and from proximal to distal, the right subclavian artery arises from the fourth aortic arch,
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