Pneumothorax Case File

Pneumothorax Case File

Eugene C. Toy, MD, Lawrence M. Ross, MD, PhD, Han Zhang, MD, Cristo Papasakelariou, MD, FACOG

CASE 15

A 54-year-old man who had smoked two packs of cigarettes per day for 20 years complains of the acute onset of shortness of breath, and severe chest pain with respiratory movement. Physical examination reveals a barrel chest consistent with chronic obstructive pulmonary disease. There are decreased breath sounds on the right side. When the physician taps on the right chest (percussion), there is a hyperresonant (unusually hollow) sound.

⯈ What is the most likely diagnosis?

⯈ What is the anatomical disorder?

ANSWER TO CASE 15:

Pneumothorax

Summary: A 54-year-old smoker complains of acute-onset shortness of breath and severe chest pain with breathing. He has physical findings for chronic obstructive pulmonary disease with a barrel chest. There are decreased breath sounds and hyperresonance to percussion on the right side.

• Most likely diagnosis: Pneumothorax

• Anatomical disorder: Entry of air into the pleural space, resulting in lung collapse

CLINICAL CORRELATION

Air is drawn into the lungs through the trachea and bronchi by the increasing negative thoracic pressure produced by the downward movement of the diaphragm. If air enters the pleural space through the thoracic wall or the surface of the lung itself, the negative pressure of the pleural space equilibrates with atmospheric pressure, and air movement ceases. The defect that allowed air to enter the pleural space acts like a valve by preventing the air from exiting the space. Pressure increases above that of atmospheric pressure, and a tension pneumothorax results, which is characterized by lung collapse, with displacement toward the mediastinum. A severe pneumothorax may cause displacement of the mediastinum and its contents toward the intact lung and partial compression of this lung. The most serious consequence of these anatomical shifts is decreased venous return to the heart. A patient who has chronic obstructive pulmonary disease is at risk for spontaneous pneumothorax by the rupture of an emphysematous bleb on the surface of the lung. Spontaneous pneumothorax may also occur from lung surface blebs in young men. The typical clinical presentation of pneumothorax is chest pain with dyspnea, decreased breath sounds, and hyperresonance on the affected side. The diagnosis is confirmed by chest radiograph. Treatment is directed toward removal of the air from the pleural space with a needle in emergent situations or by a chest tube placed in the pleural space and directed to an underwater seal.

APPROACH TO:

The Pleural Cavities

OBJECTIVES

1. Be able to describe the contents of the pulmonary cavities: lungs and the pleural divisions

2. Be able to describe the superior and inferior limits of the pleural cavity and the lower limits of each lung

3. Be able to describe the functional importance of the pleural cavity and fluid and the pressure within the cavity

DEFINITIONS

CHRONIC OBSTRUCTIVE PULMONARY DISEASE: General term applied to permanent or temporary diseases that cause narrowing of the bronchi so as to obstruct forced expiratory flow; includes bronchitis, emphysema, and asthma

EMPHYSEMA: A lung condition in which the air spaces distal to the terminal bronchioles are larger than normal

PNEUMOTHORAX: Air or gas within the pleural cavity

CHEST TUBE: Tube inserted through the thoracic wall into the pleural cavity for the purpose of draining air or fluid from that cavity

DISCUSSION

The skeletal components of the thoracic wall are the thoracic vertebra, the attached 12 pairs of ribs, and the sternum. The interval between the ribs is closed by three layers of muscles: the external, internal, and innermost intercostal muscles. The innermost intercostal is largely laterally located, internal to the internal intercostal. The transverse thoracic and subcostal muscles are discontinuous thoracic wall muscles found anteriorly and laterally, respectively. Externally, several muscles associated with the upper limb or accessory respiratory muscles attach to the thoracic wall. These include the pectoralis major and minor, serratus anterior and posterior, scalene, and levator costarum muscles. Internally, the thoracic cavity is divided into two pulmonary cavities separated by the central mediastinum. The thoracic cavity is closed inferiorly by the diaphragm.

Each of the two laterally placed pulmonary cavities contains a lung covered with visceral pleura, and each is lined with parietal pleura. The two pleura are continuous with each other at the root of the lung, where neurovascular and airway structures enter and exit the lung. The pleura is a serous membrane composed of mesothelium and a small amount of connective tissue, and it produces the lubricating pleural fluid. The parietal pleura is divided for descriptive purposes into four parts according to the structure to which it is attached. The costal, diaphragmatic, mediastinal, and cervical portions are attached, respectively, to the inner aspect of the thoracic wall; the superior surface of the diaphragm; the lateral aspect of the mediastinum, especially the pericardial sac; and the root of the neck superior to the superior thoracic aperture.

Relative constant pleural lines of reflection are created as one portion of parietal pleura changes direction to attach to another structure (Figure 15-1). The sternal reflection line is created as the mediastinal pleura changes direction (is reflected) onto the inner thoracic wall and becomes the costal pleura. In the right pulmonary cavity, this line of reflection is close to the midline from the sternal angle to the xiphoid process. On the left side, the line of reflection courses from the sternal angle to the level of the fourth rib, and then arches to the left to the sixth rib in the midclavicular line, thus creating the cardiac notch. The curvature of the mediastinal surface in this region results in the formation of a shallow costomediastinal recess of the pleural cavity. Inferiorly, as the costal pleura are reflected onto the surface of the diaphragm, the costal reflection line is created. The surface landmarks for

Figure 15-1. The lungs (bounded by solid line) and pleura (denoted by the heavy dotted line). (Reproduced, with permission, from the University of Texas Health Science Center Houston Medical School.)

this reflection line on the right and left sides are the 8th rib at the midclavicular line (MCL), the 10th rib at the midaxillary line (MAL), and the 12th rib at the vertebral border. These landmarks also mark the inferior limits of the pleural cavity. The curved shape of the diaphragmatic pleura on the dome of the diaphragm and the vertical costal pleura form a wedge-shaped pleural cavity recess called the costodiaphragmatic recess, in which abnormal pleural cavity fluids such as blood or pus will accumulate. The lowest level of each lung at the end of expiration is the 6th rib at the MCL, the 8th rib at the MAL, and the 10th rib at the vertebral border. The cervical pleura and thus the pleural cavity extend into the root of the neck, 2 to 3 cm superior to the medial end of the clavicle.

The pleural cavity between the visceral and parietal layers of pleura is a potential space containing a small amount of lubricating pleural fluid. This fluid wets the surface of the lungs, resulting in adherence of the lung’s visceral pleura to the costal and diaphragmatic parietal pleura by surface tension forces. As the diaphragm descends and the thoracic wall expands with inspiration, the adherent lungs also expand. The pleural cavities are completely closed spaces and are at 756 mmHg of pressure, or at –4 mmHg with respect to atmospheric pressure (760 mmHg). If the visceral pleura covering the lung is ruptured or the costal parietal pleura is disrupted by trauma, air will enter the pleural cavity, causing a pneumothorax and at least equalizing pleural pressure with atmospheric pressure. This will produce at least a partial lung collapse and interfere with ventilation and gaseous exchange.

COMPREHENSION QUESTIONS

15.1 You must remove fluid from the pleural cavity of your patient (thoracentesis). You decide to insert the aspiration needle over the top of a rib, into an intercostal space inferior to the lower border of the lung in the MAL at the end of a normal expiration. Which of the following is the lowest (most caudal) level at which this procedure might safely be done without injuring the lung?

A. Fourth intercostal space

B. Fifth intercostal space

C. Sixth intercostal space

D. Seventh intercostal space

E. Eighth intercostal space

15.2 During this thoracentesis procedure, the lowest level of the pleural cavity will lie at the level of which rib at the end of expiration in the MAL?

A. Seventh

B. Eighth

C. Ninth

D. Tenth

E. Eleventh

15.3 During this procedure, the lower border of the lung will lie at the level of which rib in the MCL?

A. Fifth

B. Sixth

C. Seventh

D. Eighth

E. Ninth

ANSWERS

15.1 E. The lower border of the lung will lie at the level of the eighth rib in the MAL, enabling safe insertion of the needle into the eighth intercostal space.

15.2 D. The lowest level of the pleural cavity in the MAL lies at the level of the 10th rib.

15.3 B. The lower border of the lung at the MCL at the level of the sixth rib.

ANATOMY PEARLS

⯈ Visceral and parietal pleura are continuous with each other at the root of the lung.

⯈ The inferior extent of the pleural cavity is the 8th rib at the MCL line, the 10th rib at the MAL, and 12th rib at the vertebral border.

⯈ The inferior border of each lung at the end of expiration is the 6th rib at the midclavicular line, the 8th rib at the MAL, and the 10th rib at the vertebral border.

⯈ The pleural cavity is at −4 mmHg with respect to atmospheric pressure.

References

Gilroy AM, MacPherson BR, Ross LM. Atlas of Anatomy, 2nd ed. New York, NY: Thieme Medical Publishers; 2012:110−114. 

Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy, 7th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:106−113, 121. 

Netter FH. Atlas of Human Anatomy, 6th ed. Philadelphia, PA: Saunders; 2014: plates 193−195.

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