Part eight: Pleura The pleura is a thin membrane of fibrous tissue surfaced by a single layer of flat cells (mesothelium). It clothes each lung and lines the thoracic cavity. The parietal layer of the pleura lines the thoracic wall (rib cage, vertebrae and diaphragm), from which it is separated by loose areolar tissue, the endothoracic fascia. But the parietal pleura is attached to the inferior surface of the suprapleural membrane, at the thoracic inlet, and
to the mediastinal surface of the fibrous pericardium. The pleura is one continuous sheet. From its mediastinal layer a cuff of membrane is projected around the lung root and passes on to invest the surface of the lung. This is the visceral layer of the pleura; it extends into the depths of the interlobar clefts and is adherent to the lung surface. The pleural cavity is a completely closed space. The visceral pleura on the lung surface is in contact with parietal pleura, the surfaces being lubricated by a thin film of tissue fluid. The parietal pleura, however, extends further than the inferior lung edge, to allow space for lung expansion. In these situations the costal parietal pleura is against the diaphragmatic parietal pleura, separated by a narrow space, the costodiaphragmatic recess. The cuff of pleura projected around the lung root is too big for it and it hangs down below as an empty fold, the pulmonary ligament, in the manner of a coat cuff at the wrist. It provides ‘dead space’ into which the lung root descends with descent of the diaphragm, and allows for expansion of vessels in the lung root, especially the inferior pulmonary vein. Vessels and nerves The vessels and nerves of the parietal pleura are derived from somatic sources. The arterial supply is from the intercostal, internal thoracic and musculophrenic arteries. The venous drainage is to the azygos system of veins. The lymphatics pass to the intercostal, parasternal, diaphragmatic and posterior mediastinal nodes. Intercostal nerves supply the costovertebral pleura. The diaphragmatic pleura is supplied by the phrenic nerve over the domes, and by intercostal nerves around its periphery. The mediastinal pleura is supplied by the phrenic nerve. The arterial supply and venous drainage of the visceral pleura are provided by the bronchial vessels. The lymphatics join those of the lung (see p. 216). The visceral pleura has an autonomic nerve supply and is insensitive to ordinary stimuli. Surface markings The parietal pleura lines the costal walls of the thorax; seen from in front its lateral surface marking is the horizon of the thoracic cage (Fig. 4.28). It projects up to 2.5 cm above the junction of the middle and medial thirds of the clavicle. Due to the obliquity of the thoracic inlet, the pleura does not extend above the neck of the first rib, which lies well above the clavicle. Tracing the pleura now (Fig. 4.28) from behind the sternoclavicular joint, downwards behind the sternum and around the costodiaphragmatic gutter, there is a point to be noted at the level of each of the even-numbered ribs (2, 4, 6, 8, 10, 12). The line of pleural reflexion slopes
downwards from the sternoclavicular joint to meet its fellow at the second rib level, that is, at the sternal angle. Lying together, or even overlapping, they pass vertically behind the sternum down to the fourth costal cartilage. Here the right pleura continues vertically, but the left arches out and descends lateral to the border of the sternum, half-way to the apex of the heart. Each turns laterally at the sixth costal cartilage, and passing around the chest wall crosses the midclavicular line at the eighth rib, and the midaxillary at the tenth rib. This lower border crosses the twelfth rib at the lateral border of erector spinae and passes in horizontally to the lower border of the twelfth thoracic vertebra. There is thus a triangle of pleura in the costovertebral angle below the medial part of the twelfth rib, behind the upper pole of the kidney, a fact to be noted in incisions and wounds in this region (see Fig. 5.48, p. 283). Pleural aspiration and drainage The anatomy of an intercostal space determines the route for removing fluid (or air) from the pleural cavity. Aspiration needles or drainage tubes are passed through the chest wall close to the upper border of a rib (lower part of an intercostal space) to avoid the vessels and nerve which course along the lower border of a rib (upper part of a space) (Fig. 4.4). The choice of space may be determined by the localization of fluid, e.g. a walled-off abscess, but for general purposes the fourth space in or just in front of the midaxillary line is often chosen. A needle, trocar and cannula or drainage tube inserted here is not near any major structure and is high enough to avoid the dome of the diaphragm.
to the mediastinal surface of the fibrous pericardium. The pleura is one continuous sheet. From its mediastinal layer a cuff of membrane is projected around the lung root and passes on to invest the surface of the lung. This is the visceral layer of the pleura; it extends into the depths of the interlobar clefts and is adherent to the lung surface. The pleural cavity is a completely closed space. The visceral pleura on the lung surface is in contact with parietal pleura, the surfaces being lubricated by a thin film of tissue fluid. The parietal pleura, however, extends further than the inferior lung edge, to allow space for lung expansion. In these situations the costal parietal pleura is against the diaphragmatic parietal pleura, separated by a narrow space, the costodiaphragmatic recess. The cuff of pleura projected around the lung root is too big for it and it hangs down below as an empty fold, the pulmonary ligament, in the manner of a coat cuff at the wrist. It provides ‘dead space’ into which the lung root descends with descent of the diaphragm, and allows for expansion of vessels in the lung root, especially the inferior pulmonary vein. Vessels and nerves The vessels and nerves of the parietal pleura are derived from somatic sources. The arterial supply is from the intercostal, internal thoracic and musculophrenic arteries. The venous drainage is to the azygos system of veins. The lymphatics pass to the intercostal, parasternal, diaphragmatic and posterior mediastinal nodes. Intercostal nerves supply the costovertebral pleura. The diaphragmatic pleura is supplied by the phrenic nerve over the domes, and by intercostal nerves around its periphery. The mediastinal pleura is supplied by the phrenic nerve. The arterial supply and venous drainage of the visceral pleura are provided by the bronchial vessels. The lymphatics join those of the lung (see p. 216). The visceral pleura has an autonomic nerve supply and is insensitive to ordinary stimuli. Surface markings The parietal pleura lines the costal walls of the thorax; seen from in front its lateral surface marking is the horizon of the thoracic cage (Fig. 4.28). It projects up to 2.5 cm above the junction of the middle and medial thirds of the clavicle. Due to the obliquity of the thoracic inlet, the pleura does not extend above the neck of the first rib, which lies well above the clavicle. Tracing the pleura now (Fig. 4.28) from behind the sternoclavicular joint, downwards behind the sternum and around the costodiaphragmatic gutter, there is a point to be noted at the level of each of the even-numbered ribs (2, 4, 6, 8, 10, 12). The line of pleural reflexion slopes
downwards from the sternoclavicular joint to meet its fellow at the second rib level, that is, at the sternal angle. Lying together, or even overlapping, they pass vertically behind the sternum down to the fourth costal cartilage. Here the right pleura continues vertically, but the left arches out and descends lateral to the border of the sternum, half-way to the apex of the heart. Each turns laterally at the sixth costal cartilage, and passing around the chest wall crosses the midclavicular line at the eighth rib, and the midaxillary at the tenth rib. This lower border crosses the twelfth rib at the lateral border of erector spinae and passes in horizontally to the lower border of the twelfth thoracic vertebra. There is thus a triangle of pleura in the costovertebral angle below the medial part of the twelfth rib, behind the upper pole of the kidney, a fact to be noted in incisions and wounds in this region (see Fig. 5.48, p. 283). Pleural aspiration and drainage The anatomy of an intercostal space determines the route for removing fluid (or air) from the pleural cavity. Aspiration needles or drainage tubes are passed through the chest wall close to the upper border of a rib (lower part of an intercostal space) to avoid the vessels and nerve which course along the lower border of a rib (upper part of a space) (Fig. 4.4). The choice of space may be determined by the localization of fluid, e.g. a walled-off abscess, but for general purposes the fourth space in or just in front of the midaxillary line is often chosen. A needle, trocar and cannula or drainage tube inserted here is not near any major structure and is high enough to avoid the dome of the diaphragm.