pleural effusion

Pleural effusion :

The Normal Pleura
The lung is covered with visceral pleura
The adjacent surfaces of the mediastinum, chest wall, and diaphragm are lined by parietal pleura.
These layers are in continuity both at the hilum and below, where they form the pulmonary ligament.
The visceral and parietal pleura are separated by a potential space that normally contains only a few ml of fluid, though up to 15 ml may occasionally be present in normal individuals .
Radiologically the normal pleura is a hairline of soft tissue density which is only seen when it is parallel to the X-ray beam and flanked by air.
Normal physiology
Less than 15 ml of fluid is normally present in the pleural space.
Pleural fluid is generated as interstitial fluid in the parietal pleura, leaking through non-tight mesothelial junctions into the pleural space, whence it is removed by bulk flow through the lymphatics via parietal pleura.

Pleural pathology

Excess pleural fluid accumulates when inflow and outflow from the pleural space are mismatched.
This occurs when:
1. capillary hydrostatic pressure is increased;
2. blood oncotic pressure is low;(hypoalbunemia)
3. capillary permeability is increased;
4. lymphatic drainage is obstructed.
5.reduction of pleural space pressure.
6. trans-diaphragmatic passage of ascitic fluid.
types of fluids
Transudate
Exudate (thin or thick),
Blood and chyle.
Trasudate :
Bilateral pleural effusions tend to be transudates because they develop secondary to generalized changes that affect both pleural cavities equally — a rise in capillary pressure or a fall in oncotic pressure of the blood,(CHR , Hypoalbuminemia, Cirrhosis ,and Nephrotic syndrome..)
Exudate :
Some bilateral effusions are exudates, however, and this is seen with metastatic disease, lymphoma, or inflammatory diseases of the pleura


Hemothorax:
Fluid hematocrit > 50% blood hematocrit
Empyema , exudative fluid with pus
Chylothorax :cholestyrol and or triglyceride increment ..
Side specificity :
Right-sided effusions : are typically associated with ascites, heart failure and liver abscess& ovary.
Left effusions: with pancreatitis, pericarditis, oesophageal rupture and aortic dissection.
The radiological signs of a pleural effusion:
subpulmonic effusions.
blunted lateral costophrenic angles .
meniscus sign.
Lamellar Effusion.
Loculated (encysted ,encapsulated )..
Fissural (Interlobar) Loculation.
Air – fluid level ..
Opacified hemithorax .
subpulmonic effusions:
it is unusual for it to remain localized in this site once its volume exceeds 200–300 ml.
On a PA radiograph the signs are of a 'high hemidiaphragm'
with an unusual contour that peaks more laterally than usual, has a straight medial segment and falls away rapidly to the costophrenic angle laterally.
left-sided subpulmonary effusions, there is increased separation between the stomach gas and the apparent hemidiaphragm.
Blunting of the CP angle :
Normally there is less than 15 ml pleural fluid ..
50 – 100 ml accumulation is able to blunte the posterior costophrenic angle seen by lateral x-ray.
300-500 ml accumulation causing blunting the CP angle seen by frontal film..
Meniscus sign :
The upper margin of the opacity is concave to the lung and is higher laterally than medially.
Lamellar Effusion :
A lamellar effusion is caused by fluid between the lung and visceral pleura and it is a common finding in heart failure. It gives a vertical band shadow of soft tissue density between the lung and the chest wall above the costophrenic angle, usually occur with CHF ..


Loculated (Encysted, Encapsulated) Pleural Fluid:
Fluid can loculate between visceral pleural layers in fissures or between visceral and parietal layers.
The shape & position is unusual in thorax …
Hydropneumothorax :
air-fluid level occurrence ,when
air (pneumothorax ) present & pleural effusion..(hydropneumothorax) ..
etiology due to trauma ,surgery& bronchopleural fistula..
Hemithorax opacification :
The whole hemithorax opacity caused by pleural effusion resembling pulmonary mass lesion ..
Cardiac and tracheal displacement away from the lesional site ,against atelectasis causing pulling toward the Opacified site ..