The Surface Anatomy of the Thorax
Clinical anatomy students learn to use imaginary lines and bony landmarks on the front and back of the thorax to describe locations of the anatomical structures. The lines cover the front, side, and back of the thorax. Three imaginary vertical lines on the anterior wall give you points of reference:
Midsternal (anterior median) line: Runs down the middle of the sternum
Right and left midclavicular lines: Run parallel with the midsternal line, passing through the midpoint of each clavicle
Three more vertical lines demarcate the lateral portion of the thoracic cage:
Anterior axillary line: Runs along the anterior axial fold, close to the front of the thorax
Posterior axillary line: Runs parallel with the anterior axillary line along the posterior axillary fold, close to the back
Midaxillary line: Runs midway between the anterior and posterior axillary lines, starting at the deepest part of the axilla
Finally, three lines help describe surface locations on the back:
Midvertebral (posterior median) line: Runs vertically down the midpoint of the spine
Right and left scapular lines: Run parallel with the midvertebral line but pass through the inferior angles of the scapulae
The anterior chest wall
The anterior of the chest is a main area for physical examination. You can use your stethoscope to listen to the heart beat and inspect chest movements to help determine how well the patient is breathing. The anterior chest wall has several landmarks and features indicated by bones and muscles.
Clavicles: The clavicles are visible and palpable bony structures located just below the neck. They each articulate medially with the manubrium of the sternum. You can palpate the suprasternal notch at the top of the manubrium. The superior vena cava passes behind the manubrium.
Sternal angle: The sternal angle is located at the level of the 2nd costal cartilages and corresponds to the level of the disc space between the 4th and 5th thoracic vertebrae.
Sternum: The body of the sternum is palpable in the midline of the chest between the breasts. The right border of the heart lies posterior to it. Near the sternum are four areas that are used for auscultating (listening to with a stethoscope) the heart:
Aortic area: At the 2nd intercostal space to the right of the sternum
Pulmonic area: At the 2nd intercostal space to the left of the sternum
Tricuspid area: Over the lower-left sternal border
Mitral area: At the left 5th intercostal space at the midclavicular line
Subcostal angle: The subcostal angle is at the inferior portion of the sternum, between the 7th costal cartilages. Imagine drawing lines that follow the costal margins (lower borders of the anterior rib cage) and meet at the lower part of the sternum. The angle they form is the subcostal angle.
Costal margins: The costal margins are formed by the medial portions of the 7th through 10th costal cartilages. They may be visible in a thin patient, and they’re easily palpable.
Apex beat of the heart: The apex beat of the heart is caused by the contractions of the heart as it beats. You can usually feel it at the 5th intercostal space on the left side (the mitral area), about 3.5 inches from the midline. To find the 5th intercostal space, find the 2nd rib and just slide your fingers inferiorly. Don’t forget to keep count as you go.
Axillary folds: Axillary folds frame the axillae, or armpits. The anterior axillary fold is formed by the lower border of the pectoralis major muscle, and the posterior axillary fold is formed by the latissimus dorsi and teres major muscles.
The breasts are prominently displayed on the anterior chest wall, especially in females. The intermammary cleft is formed by the cleavage between the breasts. The nipples are near the midclavicular line and are surrounded by a raised and pigmented area called the areola. In men, the nipples are at the level of the 4th intercostal space, but in women, the level varies greatly.
Each breast can be divided up into four quadrants:
The superolateral quadrant (upper outside)
The inferolateral quadrant (lower outside)
The superomedial quadrant (upper and toward the midline of the body)
The inferomedial quadrant (lower and toward the midline of the body)
The breast consists of 15 to 20 lobes of glandular tissue. Each lobe has a lactiferous duct that opens onto the surface of the nipple. Each duct has a dilated portion called the lactiferous sinus, or ampulla, located in the connective tissue deep to the areola.
The nerves of the breast come from the anterior and lateral cutaneous branches of the 4th to 6th intercostal nerves. They supply sensory fibers to the skin and sympathetic fibers to the blood vessels and smooth muscles of the nipple and skin.
The blood supply to the breasts comes from the perforating branches of the internal thoracic artery and the intercostal arteries. The lateral thoracic and thoracoacromial branches of the axillary artery may also supply blood. Venous drainage is mainly through the axillary vein, with some flow through the internal thoracic vein.
Lymph drainage of the breasts is important due to its role in the spread of cancer cells. Lymph flows from the nipple, areola, and lobes to the subareolar lymphatic plexus. From there, most lymph drains from the lateral quadrants to the axillary lymph nodes. The medial quadrants drain to the parasternal lymph nodes, whereas lymph from the inferior quadrants of the breasts passes into the abdominal lymph nodes.
The posterior chest wall
Imagine the midvertebral line running down the middle of the back. Some of the spinous processes of the thoracic vertebrae may be visible, or at least palpable. The spinous process for the 7th cervical vertebra is almost always palpable and serves as a good landmark for noting the location of any examination findings of the posterior chest wall.
The scapulae, or shoulder blades are flat, triangular bones located on the upper portion of the posterior chest wall. The superior angles at the top of the scapulae are at the level of the 2nd thoracic vertebrae. The spines of the scapulae are easy to palpate as they run obliquely toward the shoulders. You can follow the medial border of each scapula down to the inferior angle, which is at the level of the 7th thoracic vertebra.
The posterior part of the thoracic cage can be distorted due to scoliosis or ankylosing spondylitis.