7. Pneumothorax and hydrothorax. Etiology, radiologic characteristics.

From greek.doctor

Pneumothorax

Pneumothorax (PTX) refers to the presence of air in the pleural space, between the lung and the chest wall. It may happen spontaneously or secondary to emphysema, lung abscess or a fractured rib.

The pressure in the pleural cavity is normally negative to allow the lungs to expand in it. When it suddenly becomes filled with air the pressure in the pleural cavity will become equal with atmospheric pressure, causing the lung to collapse.

Tension pneumothorax is a potentially life-threatening form of pneumothorax and a medical emergency. In tension PTX air enters the pleural cavity during inspiration but cannot leave during expiration, due to the formation of a one-way valve.

Secondary pneumothorax occurs when there is a rupture of the lung close to the pleural surface that allows inhaled air to enter the pleural cavity.

Etiology

Pneumothorax may be primary or secondary. In primary pneumothorax, there is no known underlying lung condition, while in secondary pneumothorax, there is. Primary pneumothorax occurs due to the rupture of air-filled so-called subpleural bullae. These bullae are asymptomatic in most cases, but because they are thin walled, they’re predisposed to rupture. Bullae form due to overload of elastic fibres, which occurs in tall and thin people, and in weed smokers.

Primary pneumothorax risk factors:

Secondary pneumothorax risk factors:

Clinical features

Patients with pneumothorax present with sudden, severe stabbing chest pain and, if the PTX is large enough, dyspnoea. Physical examination may reveal decreased breathing sounds and hyperresonant percussion on the affected side.

In tension pneumothorax, the increased intrathoracic pressure compresses thoracic structures like the contralateral lung, trachea, heart, and superior vena cava, causing severe symptoms, like haemodynamic instability, cyanosis, and frank obstructive shock.

Diagnosis and evaluation

The diagnosis of pneumothorax is based on a simple chest x-ray, which will show a thin white line (the visceral pleura) at the border of the collapsed lung, as well as absent lung markings distal to the pleural line. The length from the chest wall to the visceral pleura on the x-ray shows the "size" of the PTX. The deep sulcus sign refers to a dark and deep costophrenic angle on the affected side. X-ray and CT may also show bullae.

Suspected tension pneumothorax is a clinical diagnosis does not undergo imaging. They proceed immediately to treatment. Should a chest x-ray be made, a mediastinal shift and tracheal deviation toward the contralateral side will be present. The ipsilateral diaphragm may be flattened or inverted.


Pleural effusion

Pleural effusion, also called hydrothorax, refers to the presence of fluid in the pleural cavity. If visible on a chest radiograph, there are at least 100 mL of fluid.

If there is simultaneous pneumothorax, the condition is called hydropneumothorax.

Etiology and types

Clinical features

The pleural effusion itself may cause dyspnoea and hypoxaemia. Symptoms of the underlying cause is often present.

Decreased lung sounds and increased dullness on percussion may be felt over the affected area.

Diagnosis and evaluation

A lot can be gathered from the gross appearance of the fluid alone. Turbid fluid is suggestive of empyema or infection. Bloody fluid is suggestive of haemothorax. Milky fluid is suggestive of chylothorax.

Radiological evalation

Chest radiograph is the first choice if pleural effusion is suspected, although it can't detect effusions < 300 mL. It will show blunting of the costophrenic angle and, if large enough, opacification of parts or of the entire lung. There may be a midline shift toward the contralateral side. Pleural effusion filling the entire pleural cavity causes so-called white-out of the hemithorax, but is very rare.

If there is simultaneous pneumothorax, a horizontal fluid level called an air-fluid level (or "niveau") will be present.

A chest radiograph taken with the patient lying on their side and with the effusion-side down may allow visualisation of small amounts of subpulmonal fluid. This is sometimes called a "Frimann-Dahl image" (according to the lecture, probably a Hungarian term).

Ultrasonography and CT may also be used to visualise pleural effusion. CT is rarely necessary, unless the intention is to rule out malignancy as a cause. On ultrasound pleural fluid is seen as hypoechoic or anechoic structures in the costophrenic recess. CT can be used to measure fluid density and therefore assist in the determination of the type of fluid.

Laboratory evaluation

If the type of pleural fluid is uncertain, it should be drained with a needle for laboratory examination. If the fluid needs to be drained anyway (due to symptoms), the fluid should also be sent for laboratory examination. Only a laboratory evaluation can distinguish a transudate from an exudate.

One can analyse "regular" biochemical tests as well as microbiological tests like culture or PCR and others. Routine tests performed on pleural fluid include white blood cell count with differential, protein, LDH, and glucose. If there is an elevated WBC and it's predominantly polymorphonuclear cells, infection is most likely. If it's predominantly lymphocytes, tuberculosis and lymphoma are more likely.

If malignancy is suspected, one should send the fluid to cytology as well. If infection is suspected, Gram stain and culture should be performed.

Distinguishing between exudate and transudate

There are several approaches to distinguishing between pleural exudate and transudate. Here are two options:

UpToDate recommends using the PFO3 (pleural fluid-only three-test). This is the most simple as it does not require a concomitant blood test. According to the PFO3 criteria, the fluid is an exudate if at least one of the following is fulfilled:

  • The protein concentration of the pleural fluid is > 30 g/L
  • The cholesterol concentration of the pleural fluid is > 1.4 mmol/L
  • The LDH concentration of the pleural fluid is > 67% of the upper normal limit of serum LDH

We can also use Light's criteria to distinguish between transudates and exudates. According to the criteria, the fluid is an exudate if at least one of the following is fulfilled:

  • The protein concentration of the pleural fluid is > 50% of plasma protein concentration
  • The LDH concentration of the pleural fluid is > 60% of serum LDH concentration
  • The LDH concentration of the pleural fluid is > 67% of the upper normal limit of serum LDH

A pleural fluid pH of < 7.30 means an empyema is most likely. If the pH is 7.30 - 7.45, an exudate is more likely, and if 7.40 - 7.55, transudate is more likely. However, the pH alone is not as accurate as using any of the above criteria.