External Landmarks and Shape
The thorax resembles a truncated cone, flattened anteroposteriorly. In women, the shape is more conical, and in right-handed individuals, the right side is usually better developed.
Key landmarks for palpation:
- Infraclavicular fossae: depressions below the clavicles.
- Coracoid process of the scapula: palpable between the deltoid and pectoralis major muscles.
- Zigzag line: formed by the interdigitation of the serratus anterior and external oblique abdominal muscles at the level of the VII–VIII ribs.
- Rectus abdominis muscles: their origin is palpable on the sides of the sternum near the cartilages of the V–VII ribs.
Projections onto the spine:
- Jugular notch — Th2.
- Sternal angle — Th4–Th5 disc.
- Inferior border of the sternum — Th10.
- Inferior angle of the scapula — upper border of the VIII rib.
Layers of the Anterior and Lateral Walls
Skin on the anterior and lateral walls is thinner than on the back. In the region of the sternum and scapulae, sebaceous glands are numerous; their blockage can lead to atheromas. The skin has limited mobility over the sternum and is fixed in the area of the nipples.
Subcutaneous adipose tissue contains a network of superficial veins, which may undergo compensatory dilation in case of impaired outflow through the venae cavae or portal vein.
Superficial fascia is thin, forming the capsule of the mammary gland and its suspensory ligament (lig. suspensorium mammae).
The bony framework consists of the sternum and ribs. The external and internal intercostal muscles lie in the intercostal spaces. At the level of the costal cartilages, the external muscles are replaced by the external intercostal membrane (membrana intercostalis externa).
Vessels and Nerves
The main neurovascular bundle of the intercostal space runs in the costal groove (sulcus costae). The order of elements from top to bottom is strictly defined: vein, artery, nerve.
Bleeding from intercostal arteries is dangerous: the vessels form an arterial ring (anastomoses of the anterior and posterior branches), and blood flows from both ends of the damaged vessel. Furthermore, the vessel walls are fused with the periosteum and do not collapse.
Internal thoracic artery (a. thoracica interna) descends posterior to the costal cartilages. It gives off the pericardiophrenic artery (a. pericardiacophrenica). Ligation of the main trunk below this branch is used to improve myocardial blood supply.
Posterior Thoracic Wall and Fasciae
On the back, the deep fascia consists of two layers. The superficial layer covers the trapezius and latissimus dorsi muscles. The deep layer forms the fascial sheaths for the scapula and rhomboid muscles.
Thoracolumbar fascia (fascia thoracolumbaris) is the deep layer overlying the erector spinae muscle. It is thin superiorly and transitions into a dense aponeurosis inferiorly.
Feature of the posterior wall: medial to the angles of the ribs, the internal intercostal muscles are absent (replaced by the internal intercostal membrane). As a result, the intercostal vessels and nerves on the thoracic cavity side are separated only by the pleura and loose connective tissue, which facilitates the spread of inflammation from the pleura to the nerves.
Briefly: answers to topical questions
What branches does the subclavian artery give off in its first part?
In its first part, the subclavian artery gives off the transverse cervical artery and the costocervical trunk.
- Transverse cervical artery (a. transversa colli) — most commonly (50%) originates from the first part, passes between the trunks of the brachial plexus, and ramifies in the region of the trapezius muscle and scapula.
- Costocervical trunk (truncus costocervicalis) — usually (50%) branches off the first part between the vertebral artery and the thyrocervical trunk, ascends over the cupula of the pleura, and gives off the supreme intercostal and deep cervical arteries.
What are the boundaries and contents of the mediastinum?
The mediastinum is conventionally divided into 4 compartments: superior, anterior, middle, and posterior.
| Compartment | Boundaries | Contents |
|---|---|---|
| Superior | Above the imaginary plane drawn through the upper margin of the roots of the lungs | Thymus or replacement adipose tissue, brachiocephalic veins, upper part of the superior vena cava, aortic arch and its branches, trachea, esophagus, thoracic duct, sympathetic trunks, vagus and phrenic nerves, organ plexuses, fasciae, and connective tissue |
| Anterior | Below the imaginary plane, between the body of the sternum and the anterior wall of the pericardium | Connective tissue, extensions of the endothoracic fascia, internal thoracic vessels, parasternal, prepericardial, and anterior mediastinal lymph nodes |
| Middle | Occupied by the pericardium and heart | Pericardium with the heart, intrapericardial segments of great vessels, tracheal bifurcation, main bronchi, pulmonary arteries and veins, phrenic nerves with accompanying pericardiacophrenic vessels, lymph nodes, and fatty tissue |
| Posterior | Anteriorly — tracheal bifurcation and posterior wall of the pericardium; posteriorly — bodies of ThIV–ThXII | Descending aorta, azygos and hemiazygos veins, sympathetic trunks, splanchnic nerves, vagus nerves, esophagus, thoracic duct, lymph nodes, and fatty tissue |
Order of elements in the intercostal bundle from top to bottom (in sulcus costae): VAN — Vein, Artery, Nerve.
Class and exam questions
Why do the boundaries of the thoracic cage and thoracic cavity not coincide?
Inferiorly, the diaphragmatic dome protrudes into the thoracic cavity (housing the liver and spleen), while superiorly, the apex of the lungs and pleura extend beyond the thoracic cage into the neck region.
Where is the correct site to perform a pleural puncture?
Strictly along the upper edge of the underlying rib to avoid damaging the intercostal neurovascular bundle running in the costal groove along the lower edge of the rib.
What are the dangers of an intercostal artery injury?
The arteries are tightly fused with the periost and do not collapse upon trauma. They also form an anastomotic ring, resulting in bleeding from both ends of the vessel.
What else to study on this topic
- Conditional topographic lines of the chest
- Topography of the internal thoracic artery
- Layers of the intercostal space on cross-section
- Thoracic apertures (superior and inferior apertures)
- Topography of the lateral thoracic vessels and long thoracic nerve
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