6 Topographical Anatomy
6.1 Surface Anatomy, Topographical Regions, and Palpable Bony Landmarks
A Surface of the female thorax
a Anterior view; b Posterior view.
B Surface of the male thorax
a Anterior view; b Posterior view.
C Topographical anatomy of the male thorax
a Anterior view; b Posterior view.
D Surface anatomy and palpable bony landmarks in the thoracic region
a Anterior view; b Posterior view.
6.2 Anatomical Landmarks of the Thoracic Skeleton (Projection of Organs)
A Anatomical landmarks of the thoracic skeleton
The thoracic skeleton presents a number of visible and palpable landmarks that are accessible to physical and radiographic examination (see B). These landmarks can be used to define reference lines for describing and evaluating the location and extent of organs based on their relationship to the lines:
• Longitudinal reference lines (a, b) are defined by visible or palpable anterior (a) and posterior (b) bony structures and provide information on the location and extent of specific thoracic organs (e.g., the apical heartbeat is palpable in the left mid-clavicular line).
• Most horizontal reference lines (c) are defined by the position of specific thoracic vertebrae. The seventh cervical vertebra (C 7) is easily identified by palpating its very prominent spinous process. It provides a starting point from which the examiner can locate all 12 thoracic vertebrae (T 1–T 12). The levels of the T 3 and T 7 vertebrae correspond respectively to the medial end of the scapular spine and the inferior angle of the scapula.
• The ribs as anatomical landmarks (d). The levels of intrathoracic organs also correlate with specific ribs and intercostal spaces, particularly on the anterior side. The first rib is usually difficult to palpate because it is behind the clavicle. The second, however, is attached to the palpable sternal angle (where the body and manubrium of the sternum join). Past the second rib, the examiner should have no difficulty counting down the remaining ribs.
B Projection of anatomical structures onto the thoracic vertebrae
T 1 | Superior border of the scapula |
T 2/3 | Jugular notch of the sternum |
T 3 | • Medial border of the scapular spine • Posterior end of the pulmonary oblique fissure |
T 3/4 | • Tracheal bifurcation • Root of the aortic arch |
T 3–4 | Manubrium of sternum |
T 4 | End of the aortic arch |
T 4/5 | Sternal angle |
T 5 | Thoracic duct crosses the midline |
T 5–8 | Sternum |
T 7 | • Inferior scapular angle • Accessory hemiazygos vein crosses the midline to the right and opens into the azygos vein |
T 8 | • Caval opening of the diaphragm – Inferior vena cava – Right phrenic nerve • Left phrenic nerve pierces the diaphragm to the left of the central tendon • Hemiazygos vein crosses the midline to the right and opens into the azygos vein |
T 8/9 | • Xiphisternal synchondrosis • Superior epigastric vessels pass through the diaphragm • Xiphoid process |
T 8–10 | Superior border of the liver (moves with respiration) |
T 10 | • Esophageal hiatus of the diaphragm: – Esophagus – Anterior vagal trunk – Posterior vagal trunk |
T 12 | • Aortic hiatus of the diaphragm: – Aorta – Azygos and hemiazygos veins – Thoracic duct • Origin of the celiac trunk (inferior border of T 12) • Splanchnic nerves pass through the crura of the diaphragm • Sympathetic trunk passes below the medial arcuate ligament: transpyloric plane (line in abdomen, see p. 228) |
C Overview of the thorax
a Anterior view. The intercostal muscles, fasciae, and abdominal organs have been removed. b Simplified schematic view from the posterior side. The scapulae and several abdominal organs have been outlined for clarity. The thoracic cavity is one of the three main body cavities, along with the abdominal and pelvic cavities. The wall surrounding the thoracic cavity consists of
• bones: 12 thoracic vertebrae, 12 pairs of ribs, and the sternum
• connective tissue: internal fasciae of the thorax, muscle fasciae
• muscles: chiefly the intercostal muscles, internal muscles, and diaphragm
The thoracic cavity is divided into the centrally located unpaired mediastinum, which contains the mediastinal organs, and the paired pleural cavities. The mediastinum contains the central motor of the circulatory system, the heart, and the thoracic part of the digestive system, the esophagus. The pleural cavities enclose the major organs of respiration, the lungs. Also, a number of neurovascular structures pass through or terminate within the thorax.
The bony thoracic cage is open at its apex at the superior thoracic aperture (thoracic inlet), which is closely bounded and protected by muscles and connective tissue but communicates structures from the neck. The inferior aperture of the thoracic cage (thoracic outlet) is almost completely sealed from the abdominal cavity by the diaphragm and its fasciae (shown most clearly in a).
Note: The diaphragm is normally in the shape of a high dome, with a substantial superior convexity that places part of the abdominal cavity above the thoracic outlet (see the abdominal organs shadowed in b). A perforating injury perpendicular to the trunk wall, as from a gunshot or stab wound, may thus simultaneously breach both the abdominal and thoracic cavities (“multicavity injury”).
6.3 Structure of the Anterior Thoracic Wall and its Neurovascular Structures
A Neurovascular structures of the anterior trunk wall
Anterior view. On the right side of the trunk, the pectoralis major and minor have been completely removed and the external and internal abdominal obliques have been partially removed to display both epifascial (subcutaneous) and deep (subfascial) neurovascular structures. For the depiction of the superior epigastric vessels the superior part of the right rectus abdominis has been removed or rendered transparent. In order to illustrate the course of the intercostal vessels, the intercostal spaces have been exposed.
B The arterial supply of the anterior trunk wall
Anterior view. The anterior trunk wall receives its blood supply from two main sources: the internal thoracic artery, which arises from the subclavian artery, and the inferior epigastric artery, which arises from the external iliac artery. It is also supplied by smaller vessels arising from the axillary artery (superior thoracic artery, thoracodorsal artery, and lateral thoracic artery) and from the femoral artery (superficial epigastric artery and superficial circumflex iliac artery).
C Structure of the lateral thoracic wall
Coronal section through the lateral thoracic wall and costodiaphragmatic recess.
D Thorax, pleural cavities have been opened
Anterior view.
E Costomediastinal and costodiaphragmatic recesses
On the left side, the parietal pleura has been slit open parasternally and above the 9th rib so that the costomediastinal and costodiaphragmatic recesses can be located with the fingertips. On the right side, the lung together with its mediastinal pleura has been carefully loosened from the pericardium in order to display the pericardiacophrenic vessels and phrenic nerve.
6.4 Thoracic Organs in situ: Anterior, Lateral, and Inferior Views
A Mediastinum, anterior view with the anterior thoracic wall removed
Coronal section through the thorax. All connective tissue has been removed from the anterior mediastinum. This dissection displays a prominent thymus, occupying the superior mediastinum and extending inferiorly into the anterior mediastinum. Visible structures that are continued from the superior mediastinum into the neck or upper limb include branches of the aortic arch, the superior vena cava, and the trachea, although the latter is mostly obscured by the vessels surrounding the heart. The middle mediastinum, visible in this coronal section, is dominated by the heart and pericardium (fused to the diaphragm) and the associated neurovascular structures—the phrenic nerve and pericardiacophrenic vessels. These vessels descend along the pericardium toward the diaphragm while giving off pericardial branches.
