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Ростовский Государственный Медицинский Университет

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Медицина общая

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5 курс / Пульмонология и фтизиатрия / Principles_of_Pulmonary_Medicine_S_E_Weinberger.pdf

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1.Percutaneous needle aspiration or biopsy

2.Endobronchial ultrasound-guided aspiration

3.Mediastinoscopy

4.Parasternal mediastinotomy

5.Video-assisted thoracic surgery

Treatment

Treatment of the various mediastinal masses depends to a large extent on the nature of the lesion. In many cases, complete removal of the mass by surgery is the preferred procedure if technically feasible. Because benign lesions may slowly enlarge and compress vital mediastinal structures, excision of even low-grade neoplasms is frequently indicated. In addition, there may be complicating hemorrhage or infection of a benign lesion and eventually even malignant transformation of an initially benign tumor; these factors also favor removal, if possible, following initial diagnosis.

Treatment of malignant tumors depends on the type of tumor and the presence or absence of invasion of other mediastinal structures. Because surgical removal of malignant lesions often is not possible, chemotherapy and radiotherapy are frequently the primary forms of treatment.

Pneumomediastinum

Normally, free air is not present within the mediastinum. When air enters the mediastinum for any number of reasons, pneumomediastinum is said to be present.

Etiology and pathogenesis

The three major sources of air entry to the mediastinum are (1) through the skin and chest wall, as occurs commonly in the setting of penetrating trauma; (2) from a tear or defect in the esophagus or the trachea, allowing air to enter the mediastinum directly; and (3) from a localized loss of integrity of the alveoli. In the last circumstance, an increase in intraalveolar pressure may induce air entry into interstitial tissues of the alveolar wall. This interstitial air may then dissect alongside the wall of blood vessels coursing through the interstitium. After air tracks back proximally, it can eventually enter the mediastinum at the site of origin of the vessels in the mediastinum. When pneumomediastinum occurs as a result of this final mechanism, it is termed the Macklin effect.

Sources of air entry in a pneumomediastinum:

1.External (penetrating trauma)

2.Tracheal or esophageal tear

3.Alveolar rupture and tracking of air proximally

Proximal dissection of extraalveolar air is probably the most common cause of a pneumomediastinum. In some cases, the reason for the increase in intraalveolar pressure is obvious—for example, severe coughing, vomiting, or straining. In patients receiving mechanical ventilation, the positive pressure produced by the ventilator may result in alveolar rupture and a pneumomediastinum, particularly if the patient’s spontaneous breathing is dyssynchronous with the ventilator. A pneumomediastinum may develop in persons with asthma, presumably because of the development of high intraalveolar pressure in a lung

unit behind a partially obstructed bronchus through which air can enter more easily than exit. In other circumstances, the immediate cause of the pneumomediastinum is not apparent, and the patient truly has a “spontaneous pneumomediastinum.”

Pathophysiology

With accumulation of air in the mediastinum, an increase in pressure might be expected to cause a decrease in venous return to the great veins, with resulting cardiovascular compromise. However, when pressure builds up within the mediastinum, air usually dissects further along fascial planes into the neck, allowing release of the pressure and preventing disastrous cardiovascular complications. In addition, an increase in mediastinal pressure sometimes results in rupture of the mediastinal pleura and escape of air into the pleural space, with consequent development of a pneumothorax (see Chapter 15).

After air has entered the soft tissues of the neck, the patient is said to have subcutaneous emphysema. With continued entry of air from the mediastinum into the neck, the air dissects further over soft tissues of the chest and abdominal walls, producing more extensive subcutaneous emphysema.

Mediastinal air often results in subcutaneous emphysema.

Because of the escape route available for mediastinal air and the opportunity for decompression, major cardiovascular complications are quite uncommon. The development of subcutaneous emphysema, although unsightly and frequently uncomfortable, usually is not associated with major clinical sequelae.

Clinical features

At the onset, patients with a pneumomediastinum often experience relatively sudden substernal chest pain. They may have dyspnea and (very rarely) cardiovascular compromise and hypotension. In some cases, the pneumomediastinum causes no symptoms, and the problem is detected on chest radiograph (e.g., on a film obtained during an acute asthma exacerbation).

Physical examination may reveal a crunching or clicking sound synchronous with the heartbeat on cardiac auscultation (Hamman sign). If the patient has subcutaneous emphysema associated with the pneumomediastinum, popping and crackling sounds (crepitations) may be heard and palpated over the affected skin and subcutaneous tissue.

Diagnostic approach

The chest radiograph and chest CT scan are the most important studies for documenting a pneumomediastinum. Gas may be seen within the mediastinal tissues and is frequently accompanied by gas within and tracking along soft tissues of the neck and/or chest wall (subcutaneous emphysema) (Fig. 16.5).

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FIGURE 16.5 Chest computed tomography scan shows air within the mediastinum

(pneumomediastinum) and air in subcutaneous tissues of the anterior chest wall

(subcutaneous emphysema).

Treatment

Generally, no treatment is necessary for a pneumomediastinum, even when accompanied by subcutaneous emphysema. The air is usually resorbed spontaneously over time. When a pneumomediastinum is a consequence of tracheobronchial or esophageal rupture, surgery may be necessary to repair the underlying tear. Esophageal rupture can result in a rapidly progressive and fatal bacterial mediastinitis, and urgent surgical intervention must be considered if esophageal perforation is suspected. In the rare circumstance when pressure builds up within the mediastinum, an incision or placement of a catheter or chest tube into the mediastinum may be necessary to allow escape of air from the mediastinum and release of positive pressure.

Pneumomediastinum

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