Lab 5 Pre-Lab Exercise:
1. Surface anatomy of the thorax
The ability to visualize anatomical structures in the thorax in relation to the surface features is fundamental to a physical exam. Palpable surface landmarks can be used to visualize the normal outlines of the pleural cavities and the lungs and to determine the positions of the pulmonary lobes and fissures. With the help of your teammates and using the images below, find the following surface anatomy landmarks of the thorax to help you identify the pleural cavities, lungs, pleural recesses, and lung lobes and fissures.
2. Surface anatomy of the pleura
The parietal pleura projects superiorly above the first costal cartilage and extends into the neck. When viewed from the side it follows the line of the first rib. Anteriorly, the costal pleura approaches the midline posterior to the upper portion of the sternum. It extends from the medial 1/3 of the clavicle to the sternoclavicular joint. The apex lies about 2.5cm above the clavicle. A penetrating wound may injure the lung and the pleura here.
The pleura runs down the sternum to the level of the 4th costal cartilage. On the right side, this is continued as a straight line to the edge of the xiphisternal joint. The left parietal pleura does not come as close to the midline as it does on the right side and this is because the heart bulges onto the left side. Instead, the pleura arches to reach the lower edge of the left 6th chondro-sternal joint.
Inferiorly, the pleura reflects onto the diaphragm above the costal margin and courses around the thoracic wall following a rib VIII (midclavicular line), rib X (midaxillary line), rib XII (also posterior vertebra of T12) contour (see anterior, lateral, and posterior images).
3. Surface anatomy of the recesses
The pleura marks the limit of expansion of the lungs. This means that the lungs do not completely fill the area surrounded by the pleural cavities, particularly anteriorly and inferiorly. In quiet respiration the lower border of the lung is about 5cm above the lower border of the pleura. A small area of pleura is exposed in the costo-vertebral angle, below and medial to rib 12 (behind the upper pole of the kidney: here it lies in danger, notably from a loin incision to the exposed kidney). Costo-mediastinal recesses occur anteriorly, particularly on the left side in relationship to the heart bulge. Costo-diaphragmatic recesses occur inferiorly between the lower lung margin and the lower margin of the pleural cavity.
4. Surface anatomy of the lungs
The surface markings of the apices of both lungs correspond to those of the pleura. Similarly, the anterior border of the right lung corresponds to the pleura down to the 6th chondro-sternal joint. The anterior border of the left lung curves away laterally from the line of pleural reflection, beginning at the level of the 4th costal cartilage (then curves back down behind the sixth costal cartilage). This produces a cardiac notch. In quiet respiration, the inferior margin of the lungs travels around the thoracic wall following a rib VI (midclavicular), rib VIII (midaxillary), rib X (median plane) contour. In deep respiration, this border may move up 7.5cm. Posteriorly, a line drawn from the inferior border and laterally of C7 spine represents the borders of the lungs.
The hilums of both lungs lie at the level of the 2nd, 3rd, and 4th, costal cartilages, parallel and 2.5cm lateral to the borders of the sternum. Posteriorly they can be represented as vertical lines lying 5cm from the midline at the levels of T4-T6 spinous processes. In the posterior view, the oblique fissure on both sides is located in the midline near the spine of vertebra T4 (medial border of the scapulae when the arms are fully abducted). It moves laterally in a downward direction, crossing the 4th and 5th intercostal spaces and reaches rib 6 laterally. In the anterior view, the horizontal fissure on the right side follows the contour of rib 4 and its costal cartilage and the oblique fissures on both sides follow the contour of rib 6 and its costal cartilage.
5. Surface anatomy of the diaphragm
The right dome of the diaphragm is higher than the left because of the large liver inferior to the dome. During expiration, the right dome reaches as high as the 5th rib (up to the 4th intercostal space) and the left dome ascends into the 5th intercostal space. The xiphisternum is anterior to the central tendon of the diaphragm. The postero-inferior margin of the diaphragm is T12, while the antero-inferior margin is the costal margin. Therefore, the posterior margin is inferior to the anterior margin.