Familial

More than 10% of patients with primary spontaneous pneumothorax report a family history of the disease, thought to be by autosomal-dominant inheritance. Other modes of inheritance have been suggested: more than one gene, with some cases inherited as an X-linked recessive disorder and others as an autosomal-dominant trait with incomplete penetrance. Recently, mutations in the gene encoding folliculin have been identified in individuals with familial spontaneous pneumothorax. Mutations in this gene were known previously to cause Birt-Hogg-Dubé syndrome ( Fig. 71.3 ), an autosomal-dominant inherited disease characterized by benign skin tumors, diverse types of renal cancer, pulmonary cysts, and spontaneous pneumothorax. The presence of thin-walled cysts in basilar and subpleural locations of the lung is a feature of this disease. The location of these cysts contrasts with the apical distribution of other more well-recognized causes of spontaneous pneumothorax, such as emphysematous bullae and idiopathic blebs. About 80% of patients with Birt-Hogg-Dubé syndrome manifest pulmonary cysts, and between 11% and 32% of patients develop pneumothorax. When large, the cysts may be multiseptated. A significant fraction of families with familial spontaneous pneumothorax have mutations in the folliculin gene; this should be considered a forme fruste of Birt-Hogg-Dubé syndrome.

Birt-Hogg-Dubé syndrome. (A) Facial skin photograph shows numerous facial lesions in a woman referred after skin biopsy. The patient had a history of occasional chest wall pain and shortness of breath. Skin biopsy-diagnosed fibrofolliculomas (hamartomas of the hair follicles) characteristic of Birt-Hogg-Dubé syndrome. The patient did not have any renal lesions. (B) CT image of the lower chest demonstrates numerous bilateral thin-walled cysts (arrows) ranging from 0.5 to 1.5 cm in size. Many of these are subpleural in location. (C) More basilar axial CT shows numerous thin-walled cysts bilaterally (arrows). Few cysts were located in the upper lobes (not shown).

An intrinsic abnormality of connective tissue resulting in an increased tendency to bulla or bleb formation is also important. For example, spontaneous pneumothorax is a well-known complication in patients with Marfan syndrome—an autosomal-dominant disease with a frequency of spontaneous pneumothorax of 4.4%–11%, Ehlers-Danlos syndrome, homocystinuria, mitral valve prolapse, and α1-antitrypsin deficiency.

Anatomy of the Pleura

The outer surface of the lung and the inner surface of the protective thoracic cage are covered by an elastic, serous, and lubricating membrane to form the pleural cavity. This is almost like inserting a sealed wet and stretchable plastic bag between the lung and the thoracic wall and diaphragm to decrease friction.

The anatomy of the pleura is complex. It covers the upper surface of the diaphragm and extends, in front, as low as the costal cartilage of the 7th rib; at the side of the chest, it extends to the lower border of the 10th rib on the left and to the upper border of the same rib on the right; and behind, it reaches as low as the 12th rib and sometimes even to the transverse process of the first lumbar vertebra.

The normal pleura is a thin translucent membrane and consists of five layers. These may be difficult to distinguish by light microscopy. These layers are (1) the mesothelium, flattened mesothelial cells joined primarily by tight junctions ( Fig. 71.4 ); (2) a thin layer of submesothelial connective tissue; (3) a superficial elastic tissue layer; (4) a second loose subpleural connective tissue layer rich in arteries, veins, nerves, and lymphatics; and finally, (5) a deep fibroelastic layer adherent to the underlying lung parenchyma, chest wall, diaphragm, or mediastinum.

Pathology slide: normal visceral pleura. Mesothelial cells (arrow) and vascular layer of the visceral pleura are shown on this pathology slide. Note the cuboidal shape of the mesothelial cells.

The lymphatic anatomy of the visceral and parietal pleura is important in the homeostasis of pleural fluid volume in the normal individual. The amount of fluid in the pleural cavity is regulated by the hydrostatic-osmotic pressure relationship and pleural-lymphatic drainage. Excess fluid, large particles, and cells in the pleural cavity are removed through preformed stomas assisted by respiratory movements. These naturally occurring pores exist in the caudal portions of the peripheral parietal and lower mediastinal parietal pleura. Most of the fluid that accumulates abnormally in the pleural space is derived from the lung through the visceral pleura and absorbed primarily through the parietal pleura.

The normal volume of pleural fluid in the adult is proportional to body weight (0.1–0.2 mL/kg). The normal pleural fluid has a protein concentration of approximately 1.5 g/dL. The pleural fluid has a few cells under normal conditions, including rare macrophages, mesothelial cells, and lymphocytes. The entire surface area of the pleura in an adult man is 2000 cm ² .

The parietal pleura derives its blood supply from branches of the intercostal arteries. The mediastinal pleura is supplied by the pericardiophrenic artery, whereas the diaphragmatic parietal pleura derives its blood supply from the superior phrenic and musculophrenic arteries. The visceral pleura derives most of its blood supply from the bronchial arterial system.

Radiography

Upright Chest Radiograph

The most helpful sign is a thin pleural line (<1 mm thick) parallel to the chest wall ( Fig. 71.5 ), with no lung markings projecting beyond it. Because the lung is partly collapsed by the pneumothorax, it might be anticipated that its density would be increased and that this altered density, compared with that of the normal lung, should be sufficient to suggest the diagnosis; in fact, this is often not the case. First, as the lung progressively collapses with the increasing size of the pneumothorax, blood flow through it diminishes; therefore the ratio of air to tissue and blood is not altered, and the overall density of the collapsing lung is not changed. Second, lung density is reduced in the region of pneumothorax because of the presence of air both anterior and posterior to it.

Primary spontaneous pneumothorax in a nonsmoker. (A) Posteroanterior chest radiograph in full inspiration demonstrates a thin white line of the visceral pleura (arrows) from a small right pneumothorax. (B) Chest radiograph in expiration better demonstrates the right pneumothorax. Thin-section CT (not shown) demonstrated a small apical bleb.

When pneumothorax is strongly suspected clinically but is not identified, gas in the pleural space may be detected on radiography by one of two methods: (1) chest radiograph in the erect position in full expiration, with the reason for this being that reducing the negative pleural pressure increases the relative size of the pleural space and thus allows easier detection of pneumothoraces, and (2) chest radiograph in the lateral decubitus position, with the involved side up, with the rationale being that air will be more visible over the lateral chest wall than at the apex. Compared with the erect chest radiograph, the lateral decubitus view is more sensitive. A study comparing inspiratory and expiratory upright films found that both were equally sensitive for pneumothorax detection. Given the limitations of expiratory films, inspiratory films are recommended as the initial examination of choice for pneumothorax detection.

Supine Chest Radiograph

In the supine patient, the main finding is the deep sulcus sign ( Fig. 71.6 ), a very deep radiolucent costophrenic sulcus. Note that the most nondependent portion of the pleural space in a supine patient is the inferior lateral hemithorax. It is important that the lateral costophrenic angles be included on the radiograph, as failure to diagnose pneumothorax may be life threatening because of the risk of tension. The supine view is much less sensitive for pneumothorax and grossly underestimates the true size of a pneumothorax. In one study of trauma patients, more than 50% of pneumothoraces were missed on the supine chest radiograph compared with computed tomography (CT). In a cadaver study the lateral decubitus film was most sensitive (88%), followed by the erect radiograph (59%), with the least sensitive being the supine view (37%).

Chest radiography: deep sulcus sign. Supine chest radiograph demonstrates a large, left anterior pneumothorax causing the deep sulcus sign (arrows). The left chest tube was not functioning.

Other clues to the presence of a pneumothorax on a supine view are the following: relative hypolucency in the hypochondrial region or the entire hemithorax, depression of an ipsilateral hemidiaphragm, double-diaphragm appearance, sharp delineation of the cardiomediastinal and diaphragmatic borders, increased visualization of the mediastinal fat pads (floating cardiac pad sign), lobulated appearance of mediastinal fat pad, visible inferior border of the collapsed lower lobe or the heart, band of air in the minor fissure, and visible lateral edge of the right middle lobe.

In suspected pneumothorax, if only a single chest radiograph is taken, it should be done upright, on inspiration. When a pneumothorax is suspected in a supine patient, confirmation can be readily obtained with a lateral decubitus view. CT may also be useful and has been shown to identify 50% to 64% of occult pneumothoraces in the trauma setting.

Computed Tomography

Several studies have shown that thin-section CT is a reliable method of detecting blebs and bullae in patients with spontaneous pneumothorax. The most common parenchymal abnormality associated with spontaneous pneumothorax is emphysema, which may be readily diagnosed on thin-section CT ( Fig. 71.7 ). If emphysema is not present, most patients will have an isolated bulla or bleb (see Fig. 71.2 ). In one study evidence of emphysema was seen on CT in 16 of 20 (80%) patients with spontaneous pneumothorax. In another investigation localized areas of emphysema were identified in 22 of 27 (81%) lifelong nonsmokers who had a previous spontaneous pneumothorax. The emphysema involved mainly the upper lobes and the peripheral rather than the central lung regions. The role of thin-section CT in predicting recurrence of pneumothorax is controversial. Some studies have found a significant relationship between the presence of blebs and bullae at CT after a first episode of primary spontaneous pneumothorax and the development of an ipsilateral recurrence or a contralateral episode of pneumothorax. Some researchers have questioned its role in preoperative assessment and predicting recurrence. A CT-based scoring system (dystrophic severity score) has been proposed based on size, number, and distribution of apical air-containing lesions. This score has been shown to predict ipsilateral recurrence and contralateral pneumothorax after the first episode in patients treated conservatively.

Emphysema in a patient with history of secondary spontaneous pneumothorax. Thin-section CT image demonstrates paraseptal emphysema (white arrows) adjacent to an area of localized pleural thickening (black arrow).

Ultrasonography

Ultrasonography is a sensitive and reliable method for diagnosis of a pneumothorax. Findings of pneumothorax on ultrasound have been well described, such as the absence of visceral pleural sliding movements during respiration—called disappearance of the “gliding sign,” absence of comet tail artifacts in the supine patient, absence of lung pulse—lung sliding resulting from transmitted cardiac pulsations, and identification of lung point—identification of the edge of pneumothorax by reappearance of the normal respiratory pattern (lung sliding and B lines). The presence of B lines (echogenic vertical lines moving with respiration, reaching the lower portion of field without fading), lung sliding, and lung pulse are helpful in ruling out pneumothorax. Among these factors, lung point is reported to be 100% specific when identified.

In a study of 183 patients after percutaneous needle biopsy, pneumothorax was identified in 46 patients (25%) by CT, in 44 by ultrasonography, and in 19 by chest radiography. The sensitivity of ultrasonography was 95.7%, and its specificity was 100%. Most investigations of pleural ultrasound otherwise have been limited to the trauma setting. Several meta-analyses comparing ultrasound with chest radiography, in the acute care setting, have shown the superiority of ultrasound for the diagnosis of pneumothorax. Ultrasound can also allow semiquantitative assessment of pneumothorax size by assessing the position of the lung point.

Tension Pneumothorax

Tension pneumothorax is a potentially fatal medical emergency that requires high degree of suspicion, immediate recognition, and treatment because affected patients rapidly become severely hypoxic and acidotic and often die. It is mostly seen in the setting of trauma, emergency resuscitation, or in ventilated patients. Its pathophysiology is trapping of inspired air in the pleural space, presumably on the basis of a bronchopleural ball-valve mechanism, leading to tension. Definitions for tension physiology differ in patients with a pneumothorax. Tension may be defined by mediastinal shift on the chest radiograph, by hemodynamic compromise, or by increased intrapleural pressure that remains positive throughout the respiratory cycle. The last definition is preferred as the more objective definition and clearly explains the hiss of air heard on thoracic needle decompression of tension pneumothorax. Clinical presentation depends on the ventilatory status of patients. Patients with unassisted breathing present with predominantly respiratory signs and symptoms and seldom with hemodynamic compromise. On the other hand, patients on ventilator-assisted breathing frequently present with sudden hemodynamic compromise and cardiac arrest.

Radiologic findings that may suggest tension physiology in the setting of pneumothorax include mediastinal shift, ipsilateral flattening of the heart border, hemidiaphragm depression, increased rib separation, and increased thoracic volume. Mediastinal shift is not a reliable finding because it may occur in the absence of tension physiology ( Fig. 71.13 ). Mediastinal mobility is observed more commonly in younger patients. The majority of patients with mediastinal shift do not have tension pneumothorax. In a study of 176 patients presenting to the emergency department, 30 patients had radiologic evidence of mediastinal shift, whereas only 2 had clinical signs of tension pneumothorax. Tachycardia, hypotension, and cyanosis should suggest a tension pneumothorax. The use of chest radiography for the diagnosis of tension pneumothorax can be problematic; it has been associated with a fourfold increase in mortality in two studies of ventilated patients who waited 30 minutes to 8 hours for the chest radiograph. If the patient is hemodynamically unstable (e.g., partial pressure of oxygen <92%, blood pressure <90 mm Hg, respiratory rate >10, decreased level of consciousness), immediate chest decompression must always precede a chest radiograph. However, in the awake, stable patient, a chest radiograph is the first test of choice.

Large right pneumothorax in a man with sudden onset of chest pain. Posteroanterior chest radiograph (A) demonstrates a large right pneumothorax, with mediastinal shift and collapse of the entire right lung. Note the convex margins of the pleura (white arrows) outlining the collapsed lung. A small pleural effusion (hydropneumothorax; black arrow ) is also present. Expiratory chest radiograph (B) demonstrates marked mediastinal shift, suggesting a tension pneumothorax; however, the patient was hemodynamically stable. A chest tube was placed subsequently. (C) Axial CT image obtained 48 hours after drainage of the right pneumothorax shows extensive ground-glass opacities in the right upper and lower lobes, in keeping with reexpansion pulmonary edema. The edema resolved within 24 hours.

Tension pneumothorax is treated with high-concentration oxygen and emergency needle decompression, followed by chest tube insertion. Needle decompression is typically performed in the second to third intercostal space in the midclavicular line by a large-bore (10–16 gauge) needle. A recent meta-analysis recommends a catheter of at least 6.44 cm in length to ensure that 95% of the patients would have penetration of the pleural space at the site of needle decompression and therefore a successful procedure. Diagnosis is confirmed by egress of air through the needle in most of the respiratory cycle.