Radiographic aspects of pneumothorax

Radiographic aspects of pneumothorax

Robert M. Spillane

Pneumothorax refers to the abnormal presence of air in the pleural space. Pneumothorax is a common medical problem; symptoms include chest pain, dyspnea and shortness of breath. The etiology of pneumothorax may be idiopathic, traumatic, iatrogenic or a complication of systemic disease or malignancy. Pneumothorax may lead to respiratory or circulatory compromise, particularly in persons with underlying lung disease. The treatment of choice is percutaneous insertion of a chest tube.

On physical examination, findings such as hyperresonance with percussion, distant breath sounds and diminished motion of the affected hemithorax are subtle and insensitive.(1) Radiographic identification of the visceral pleural line is the mainstay for the detection of pneumothorax (Figure 1).

[ILLUSTRATION OMITTED]

It is important for all physicians to be aware of the fundamental radiographic manifestations of pneumothorax. In a study of patients in an intensive care unit (ICU), a correlation was shown between pneumothorax missed on a supine chest radiograph and a longer ICU stay and higher chance of tension pneumothorax, a life-threatening complication.(2)

Anatomy

The thorax is divided into three cavities–the right and left pleural cavities and the mediastinum. During embryogenesis, lung buds invaginate into the pleural cavities, reflecting the serosal lining into two layers, the visceral and parietal pleura. The visceral pleural layer envelops the lung and extends into the interlobar fissures. The parietal pleural layer covers the inner surface of the chest wall, the lateral aspects of the mediastinum and the superior surface of the diaphragm. The two pleural cavities do not normally communicate across the midline.

The pleural space is a potential space resulting from the apposition of the two pleural membranes. Normally only a few milliliters of fluid occupy the pleural space to lubricate the visceral and parietal pleural layers and couple their movements with respiration. The presence of air with-in the pleural space uncouples the visceral and parietal pleura and disrupts their suspensory forces on the lung. The elastic recoil of the lung then retracts it toward the hilum, and the lung “collapses.”(3)

Etiology

Air in the pleural space is the essential prerequisite of pneumothorax. Before air can enter the pleural space, the visceral or parietal pleura, or both, must be breached.

The etiology of pneumothorax is varied (Table 1). Iatrogenic pneumothorax, the result of puncture of the visceral pleura, is a relatively common complication of many diagnostic and therapeutic procedures, including thoracentesis, intercostal nerve block, endoscopic transbronchial biopsy, percutaneous biopsy or placement of central venous catheters. Iatrogenic pneumothorax is often detected on the postprocedure radiograph. Alveolar distention and rupture by positive pressure ventilation may also result in pneumothorax.(1)(3)

Pneumothorax is often caused by blunt or penetrating trauma.(4) It may also be an occult problem in persons with head trauma.(5) The pneumothorax is termed “closed” when the chest wall remains intact. Direct communication between the ambient atmosphere and the pleural space is referred to as “open” pneumothorax.(4)

TABLE 1 Selected Etiologies of Pneumothorax

Iatrogenic

Procedures such as central venous line placement

and lung biopsy

Barotrauma

Traumatic

Penetrating trauma

Blunt trauma

Spontaneous

Primary

Apical blebs

Secondary (underlying lung disease)

Interstitial diseases

Eosinophilic granuloma, sarcoid, pulmonary

fibrosis, lymphangioleiomyomatosis

Infection

Tuberculosis, fungal infections, Pneumocystis

carinii pneumonia, septic emboli

Airway diseases

Asthma, cystic fibrosis, emphysema

Malignancy

Osteosarcoma

Miscellaneous

Crack cocaine

Spontaneous pneumothorax most often occurs in tall, slender young men. It often results from the rupture of a superficial bleb near the apex of the lung (Figures 2a and 2b). Many authorities believe that blebs result from the increased traction and stresses that gravity and inspiratory forces place on the lung apex.(3) One-third to one-half of persons who experience spontaneous pneumothorax have a recurrence.(1)

[ILLUSTRATION OMITTED]

Spontaneous pneumothorax is also a common complication of many pulmonary disorders, including interstitial diseases, such as eosinophilic granuloma, sarcoidosis, pulmonary fibrosis with honeycombing, and lymphangioleiomyomatosis (a disease of abnormal pulmonary lymphatic and smooth muscle proliferation, with cyst formation and honeycombing; it affects young women); infections, including cavitary tuberculosis or fungal infections, septic emboli or Pneumocystis carinii pneumonia (PCP) with cyst formation; airway disorders such as cystic fibrosis, asthma and emphysema, and malignancy, such as osteosarcoma with pulmonary metastases, in which pneumothorax is thought to be a result of the rapid growth and necrosis of a subpleural lung metastasis or a ball-valve subpleural leak mechanism (Figures 3a and 3b). Spontaneous pneumothorax may be the presenting manifestation in many of these disorders, and careful inspection of the chest radiograph for signs of underlying pulmonary disease is essential following lung reexpansion.

[ILLUSTRATION OMITTED]

Catamenial pneumothorax is classically seen in young women during the menstrual cycle and is more common on the right side. The pathophysiology of this disorder is controversial, but one theory suggests that the pneumothorax is caused by minute implants of endometrial tissue on the visceral pleural surface.

Pneumothorax may also be the etiology of acute pulmonary complaints that follow the inhalation of crack cocaine.(6)

Radiographic Appearance

The diagnosis of pneumothorax on a chest radiograph taken with the patient in the upright position requires detection of the visceral pleural line on the film. With the patient in the erect position, air in the pleural space rises toward the apex of the lung. The visceral pleural line is seen on chest radiograph as a thin, curvilinear opacity. The pleural space is lateral to this lucency of air, and lung vessels are absent. Guidelines for labeling the size of a pneumothorax are arbitrary. With a small pneumothorax, the visceral pleural line is with-in 1 to 2 cm of the apical chest wall. Moderate and large pneumothoraxes are shown in Figures 1, 2 and 3.

Differentiating the visceral pleural line from radiographic opacities with similar appearance is often difficult. Skin folds may mimic a pleural line, falsely suggesting pneumothorax. In a classic article, Fisher(7) enumerated the key points that differentiate skin folds and pneumothorax: (1) skin folds may continue past the confines of the ribs, but pleural lines do not; (2) lung vessels are often seen peripheral to a skin fold but never peripheral to a pneumothorax, and (3) skin folds appear as broad, curvilinear opacities (Figure 4), unlike the “crisp,” thin white line of the visceral pleura in pneumothorax.(8)

[ILLUSTRATION OMITTED]

Pneumothorax is not always readily apparent on radiographs. Various maneuvers may be performed to enhance visualization of a pneumothorax. Chest radiographs are usually obtained at maximal inspiration. If pneumothorax is suspected but not initially apparent radiographically, expiratory chest radiographs may be helpful. As the lung decreases in size with expiration, the volume of air in the pleural space remains constant if pneumothorax is present (Figure 5). Thus, with expiration, the pleural line is moved further from the chest wall, facilitating its detection.(4)(9) Lateral decubitus views, taken with the affected side up, are occasionally helpful in critically ill patients who cannot sit upright.

[ILLUSTRATION OMITTED]

Radiographs are taken in the supine position in many critically ill patients, and in the supine patient, detection of the visceral pleural line may be difficult. In a recumbent patient, the highest point in the hemithorax is the anterior costophrenic recess. Unless sufficient air is present to separate the lateral visceral pleura and the parietal pleura, the pleural line may not be evident radiographically. The presence of air in the anterior costophrenic recess produces several well-known radiographic findings, which may include increased lucency over the ipsilateral upper quadrant of the abdomen, an unusually sharp definition of the anterior diaphragmatic surface (Figures 6a and 6b) or a very wide and deep costophrenic angle, the so-called deep sulcus sign.(8)(10)(11)

[ILLUSTRATION OMITTED]

Tension Pneumothorax

For the volume of air in the pleural space to increase, air must move during inspiration across the chest wall or out of the lung parenchyma through a pleural defect. If exit of air from the pleural space is prevented during expiration, the volume of air in the pleural space and the pressure it exerts on the mediastinal structures increases with each breath. This phenomenon is known as “tension” pneumothorax and represents a life-threatening medical emergency, because the increase in intrathoracic pressure rapidly compromises venous return to the heart and leads to circulatory collapse. Immediate relief of this increased pressure is required, usually through insertion of a chest tube or, in an emergency, insertion of a large-bore needle.

Radiographically, tension pneumothorax manifests as a shift of mediastinal structures away from the pneumothorax, depression of the ipsilateral hemidiaphragm and widening of the ipsilateral rib interspaces(4)(9) (Figure 3a).

REFERENCES

(1.)Wilson JD, ed. Harrison’s Principles of internal medicine. 12th ed. New York: McGraw-Hill, 1991: 1113-4.

(2.)Kollef MH. Risk factors for the misdiagnosis of pneumothorax in the intensive care unit. Crit Care Med 1991; 19:906-10.

(3.)Greene R, McLoud TC, Stark P. Pneumothorax. Semin Roentgenol 1977; 12:313-25.

(4.)Harris JH Jr, Harris WH, Novelline RA, eds. The radiology of emergency medicine. Baltimore: Williams & Wilkins, 1993:503-20.

(5.)Tocino IM, Miller MH, Frederick PR, Bahr AL, Thomas F. CT detection of occult pneumothorax in head trauma. Am J Roentgenol 1984; 143:987-90.

(6.)Eurman DW, Potash HI, Eyler WR, Paganussi PJ, Beute GH. Chest pain and dyspnea related to “crack” cocaine smoking: value of chest radiography. Radiology 1989; 172:459-62.

(7.)Fisher JK. Skin fold versus pneumothorax. Am J Roentgenol 1978; 130:791-2.

(8.)Rhea JT, vanSonnenberg E, McLoud TC. Basilar pneumothorax in the supine adult. Radiology 1979; 133(3 Pt 1):593-5.

(9.)Fraser RG, ed. Diagnosis of diseases of the chest. 3d ed. Philadelphia: Saunders, 1988:683-7.

(10.)Gordon R. The deep sulcus sign. Radiology 1980; 136:25-7.

(11.)Ziter FM Jr, Westcott JL. Supine subpulmonary pneumothorax. Am J Roentgenol 1981; 137:699-701.

COPYRIGHT 1995 American Academy of Family Physicians

COPYRIGHT 2008 Gale, Cengage Learning