Imaging Anatomy (eBook)
598 Seiten
Georg Thieme Verlag KG
9781638536147 (ISBN)
1 Thoracic Wall
Farhood Saremi and Damián Sánchez-Quintana
Introduction
The thoracic (chest) wall is composed of the rib cage, inner and outer muscles, vessels, lymphatics, fascia, and skin. The rib cage is formed by the ribs, costal cartilages, sternum, and thoracic vertebrae. The thoracic inlet is the passage of the trachea, aortic arch arteries, major veins, and lymphatics. The outlet of the thorax is covered by the diaphragm. The thoracic wall protects the heart, major vessels, lungs, and part of the liver and spleen. It provides a flexible skeletal framework to promote respiratory movements, stabilize the actions of the diaphragm, shoulders, and arms.1 The chest also provides attachments for the proper function of the neck, chest, and upper abdomen muscles. Chest wall dysfunction is associated with significant complications and rapid life-threatening consequences. Knowledge of the anatomy and function of the thoracic wall is essential in imaging interpretation of the chest pathologies. This chapter focuses on chest anatomy and function, with emphasis on common anatomical variants and pathologies.
Embryology
The somitic mesoderm gives rise to the osseous parts of the ribs and vertebrae. The lateral plate mesoderm is where the sternum and appendicular (limb) skeleton develop whereas the cranial neural crest forms the branchial arch, craniofacial bones, and cartilage.2
Ossification of the mesoderm occurs in two forms. In the first form, ossification occurs directly within preexisting mesenchymal tissue. This type of ossification is called intramembranous which is common in flat bones (e.g., skull). In the second form, the mesenchymal progenitor cells differentiate into the chondrocytes that form hyaline cartilage and ossification occurs within hyaline cartilage. The second type is called endochondral ossification.
The rib primordium is identifiable in the fifth week of development ( ▶ Fig. 1.1). These primordial ribs are aligned ventrolaterally, next to the intervertebral disks, into the hypaxial muscle anlagen. The first seven to eight ribs increase in length, while the length of the last four ribs will be progressively shorter from cranial to caudal. By the seventh week, the first eight ribs bend toward the sternal anlagen. The primary rib ossification center is located near the angle of the ribs and mostly become cartilaginous during weeks 13 to 14 of development and later become ossified. At birth most ribs are ossified. Secondary rib ossification centers appear later at puberty. The ventral ends of the ribs remain cartilaginous, the so-called “costal cartilage.” Later in life partial calcification of the costal cartilages is a universal finding.
The sternal primordium is first identifiable at 6.5 weeks of development as three mesenchymal condensations; a single median center known as “presternal” and a pair of lateral centers known as “sternal bars.”
The presternal condensation forms the sternal manubrium in the seventh week which extends to the second rib in the eighth week. At the seventh week, the paired sternal bars move from the lateral to the inferior aspect of the manubrial primordium. By eight weeks, the sternal bars extend to the level of the seventh rib and begin to align with the manubrium and fuse with each other. The medial fusion of the sternal bars continues to the level of the fifth rib in the ninth week but remains bifid more caudally until fusion is complete in the 10th week to form the cartilaginous sternum. Sternal ossification centers appear from superior to inferior direction before birth except in the xiphoid process which appears during childhood ( ▶ Fig. 1.2). In the neonate, the manubrium contains one main ossification center. Ossification of the body of the sternum occurs shortly after birth. The number and position of ossification centers vary. By the end of the first year, most individuals have three to four center of ossifications in the sternal body separated from each other by cartilaginous bands ( ▶ Fig. 1.2). These bands are connected to the end of the costal cartilages. Union of the bands begins at about puberty and continues to the age of 25 craniocaudally ( ▶ Fig. 1.2, ▶ Fig. 1.3). The xiphoid process may remain ununited in some individuals.
All muscles develop from the somitic dermomyotomes. Muscles of the chest and abdominal wall are grouped into the hypaxial (ventral group) and epaxial (dorsal group) muscles based on their different innervations by the ventral and dorsal rami, respectively. At 5 weeks of development, separate epaxial and hypaxial myotomal compartments with separate dorsal and ventral spinal nerves will become identifiable ( ▶ Fig. 1.1).
Fig. 1.1 Bones and hypaxial muscles of the ventral body wall. Carmine-stained (41–49 days) and azan-stained (56 days) histological sections of the embryo are shown. At 41 days, the muscular mass (red arrows) and the ribs (black arrows) can be distinguished. After 44 days, the abdominal wall muscles are distinguished: green, transverse abdominal; cyan, internal oblique; red, external oblique; purple, abdominal rectus muscle. The sheath of the rectus muscle is readily visible at 56 days section (black arrow).
(Used with permission from Mekonen et al 2015.2)
Fig. 1.2 Anterior and posterior views of the chest at three ages are shown. Note that the inferior thoracic aperture is relatively wide in early life. Sternal ossification centers appear from superior to inferior direction before birth except in the xiphoid process which appears during childhood. Ossification of the body of the sternum occurs shortly after birth. The manubrium contains one main ossification center. The number and position of ossification centers of the sternal body vary. In this case, at day 5 of life, two ossification centers exist at each level. Also, note that costotransverse joints are not well developed and spinous processes are not fused in midline. By the end of the first year, most individuals have three to four centers of ossification in the sternal body separated from each other by cartilaginous bands. These bands are connected to the end of the costal cartilages. Osseous union of the band begins at about puberty. The xiphoid process may ununited in some individuals. A sternal hole is seen in the 1.5-year-old patient.
Fig. 1.3 (a) Volume-rendered computed tomography (CT) shows bony thorax in an adult. The thorax appears barrel-shaped. The costal cartilages are partially calcified. The xiphoid is ossified but remains unfused. The upper seven ribs directly articulate to the sternum by costal cartilages. The costal cartilages of the 8th, 9th, and 10th ribs connect with the 7th. The 11th and 12th ribs remain floating. (b) Superior views demonstrate the structures of the thoracic inlet. The first ribs are colored in red. IMA, internal mammary artery.
The muscle cells of the ventral body wall develop from the hypaxial half of the dermomyotome and are innervated by the ventral branch of the spinal nerves. The differentiation of the single band of hypaxial muscle into separate layers will be apparent at the end of the sixth week. At this time the external oblique, internal oblique, transverse abdominal, and rectus abdominal muscles will differentiate. The intercostal and all abdominal wall muscles become identifiable as separate entities from the common myotomal band at 6 to 6.5 weeks of development. The epaxial myotomal compartment will form the paraspinal muscles.
Bony Thorax
The thoracic skeleton is an osteocartilaginous framework that surrounds and protects the thoracic viscera and supports the mechanical function of ventilation. The bony thorax is formed by the sternum anteriorly and the thoracic vertebrae posteriorly, interconnected by the 12 paired ribs and their costal cartilages3,4,5,6 ( ▶ Fig. 1.2, ▶ Fig. 1.3, ▶ Fig. 1.4).
Fig. 1.4 Costal cartilages. (a) Noncalcified. (b) Partially calcified (tramline). The sternum consists of the manubrium, body, and xiphoid process.
Ribs
The upper seven ribs directly articulate to the sternum by costal cartilages. These first seven ribs are called true ribs. In contrast, the costal cartilages of the 8th, 9th, and 10th ribs connect to each other and with the 7th costal cartilage. These ribs are called false ribs. The 11th and 12th ribs are called floating because they have no anterior attachment. Each rib consists of a head, a neck, a shaft, and a costal cartilage ( ▶ Fig. 1.5). The head and neck are close to the spine. At costovertebral junctions, the rib’s head is articulated by two synovial demifacet joints to the posterolateral aspect of two vertebral bodies at the intervertebral disks ( ▶ Fig. 1.5). The inferior rib facet is joined with vertebral body at the same number. Exceptions are the first, 11th, and 12th ribs in which there is a single articular facet ( ▶ Fig. 1.6). The 10th rib is sometimes floating with a single costovertebral facet. The costovertebral junctions are covered with a capsule and reinforced by the radiate ligament ( ▶ Fig....
| Erscheint lt. Verlag | 5.5.2021 |
|---|---|
| Reihe/Serie | Atlas of Imaging Anatomy | Atlas of Imaging Anatomy |
| Mitarbeit |
Stellvertretende Herausgeber: Damian Sanchez-Quintana, Hiro Kiyosue, Francesco Faletra, Meng Law, Dakshesh Patel, R. Shane Tubbs |
| Verlagsort | Stuttgart |
| Sprache | englisch |
| Themenwelt | Medizin / Pharmazie ► Medizinische Fachgebiete ► Chirurgie |
| Medizinische Fachgebiete ► Innere Medizin ► Pneumologie | |
| Medizinische Fachgebiete ► Radiologie / Bildgebende Verfahren ► Radiologie | |
| Schlagworte | anatomy • cardiac anatomy • chest anatomy • heart anatomy • Imaging Anatomy • lung anatomy • mediastinum anatomy • normal radiologic anatomy • pulmonary anatomy • Surgical Anatomy • thoracic anatomy |
| ISBN-13 | 9781638536147 / 9781638536147 |
| Informationen gemäß Produktsicherheitsverordnung (GPSR) | |
| Haben Sie eine Frage zum Produkt? |
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