Pleural pathology, pleural effusion

Pleural pathology includes:

• chylothorax
• haemothorax
• pneumothorax
• empyema
• pleural effusion
• mesothelioma
• pleurisy

Symptoms and signs of pleural disease include:

• pleural friction rub
• pleuritic pain

A chylothorax is an uncommon phenomenon characterised by accumulation of lymph in the pleural cavity. It is the most common form of chylous effusion.

Chylothorax results from leakage from the thoracic duct or other major channel:

• most commonly due to trauma or malignancy
• sometimes, the leakage may be precipitated by penetrating or crushing wounds or may follow surgery.
• rarely, the chylothorax is due to filariasis or subclavian vein thrombosis, or occurs secondary to chylous ascites

• Chest radiology reveals an unencapsulated pleural effusion.
• Aspirates are creamy and opalescent. Once obtained, there is rapid reaccumulation of chyle. Repeated aspiration may cause protein and lymphocyte depletion.
• Microscopic examination of the aspirate shows a predominance of lymphocytes which is characteristically sterile due to the bacteriostatic nature of lymph.

Continued chyle loss is debilitating and treatment should not be delayed.

In simple trauma, the leakage may be controlled by re-expansion of the lung and restoration of normal intrathoracic pressure. If lymphatic accumulation continues, the site should be visualised, e.g. by lymphangiography, and the injured thoracic duct ligated at thoracotomy.

Chronic chyle loss results in hypoproteinaemia, malnutrition and loss of immune competence in days or weeks.

Intravenous alimentation and oral feeding with medium chain triglycerides must be given until the loss can be arrested.

The pleural cavity is a potential space which normally contains little fluid.

A pleural effusion is an accumulation of fluid within the pleural space.

The fluid may be either transudative or exudative:

• a transudate results from an alteration in the hydrostatic forces operating across the pleural membrane
• an exudate results from a change in the permeability of the membrane due to inflammation

A pleural effusion will only be detected:

• on a chest radiograph when the volume of the effusion exceeds 300 ml
• clinically when the volume exceeds 500 ml

The investigation of a pleural effusion should include the following:

• blood tests:
• ESR and CRP screen for inflammation
• serum albumin
• serum amylase
• blood culture and sensitivity including Mycobacterium tuberculosis
• thyroid function tests

• AP chest radiograph:
• water-dense shadow with a concave-upwards upper border
• a collection of fluid in the pleural space beneath the inferior surface of the lung (subpulmonic effusion) may mimic an elevated hemidiaphragm - in this case a lateral decubitus X-ray or ultrasound examination is discriminatory
• radiography may provide aetiological information:
• cardiomegaly is suggestive of congestive cardiac failure
• a bronchial neoplasm or other malignancy may be seen
• cavitating consolidation suggests tuberculosis

• diagnostic aspiration:
• a thoracocentesis is performed
• the fluid is sent for:
• protein determination
• glucose - low in effusions due to rheumatoid arthritis, tuberculosis, SLE and malignancy
• culture
• Gram and auramine (or Ziehl-Neelson) stain
• cytology:
• for diagnosis of malignant effusions
• tuberculosis and chronic effusions are lymphocyte- rich
• polyarteritis nodosa, Hodgkin's lymphoma

The effusion should be investigated by diagnostic aspiration and the fluid examined for protein content, cell type and bacteria.

If the effusion is an exudate then a pleural biopsy is useful.

If there is a large effusion then symptomatic relief can be achieved via aspiration of the effusion. Note that not more than 1000 ml of the effusion should be removed on each 'tapping'.

A chest drain is an alternative to repeated aspiration - this must be able to drain the base of pleural effusion (unlike in a pneumothorax where the doctor must ensure that the apex of the pleural space is drained).

If malignant effusions then consider chemical pleurodesis (bleomycin, tetracycline, talc).