how to differentiate pleural effusion from pleural edema?

Question

what are the characterisitics that differentiates them?

Answer 1

There's no such thing as pleural edema. I suppose you mean either pleural thickening or pulmonary edema. If you take an X ray in lateral position, the fluid of a pleural effusion will move with gravity to the most dependent area. There will be no change in pleural thickening or pulmonary edema.

Answer 2

Do you mean pleural effusion from PULMONARY edema?

The usual distinction is to clinically try and distinguish between pleural effusion and CONSOLIDATION.

Pleural edema is essentially just swelling of the pleura - probably caused by fluid from some form of inflammation. The pleura does not have much space to contain this and a pleural effusion could follow.

PLEURAL EDEMA
If there was inflammation but no pleural effusion:
(1) there might be no signs and the breath sounds would be vesicular, percussion note normally resonant
(2) there may be some signs of inflammation including an audible pleural rub
(3) there may be signs of an underlying or additional pathology: perhaps underlying consolidation - see later
There may be decreased lung excursion due to pain.

PLEURAL EFFUSION
If there was fluid in the pleural space the clinical signs are:
(1) stony dull percussion note
(2) decreased breath sounds
(3) decreased vocal resonance or vocal fremitus
OCCASIONALLY with large pleural effusions there can be tracheal deviation away from the side of the mass effect. There may be an audible pleural rub and/or decreased lung excursion.

CONSOLIDATION
If there is consolidation in the underlying lung parenchyma the clinical signs are:
(1) dull percussion note over the consolidated area - interestingly, different in quality to the stony dullness that characterizes a pleural effusion
(2) bronchial breath sounds or crackling noises with the breath sounds (rales)
(3) increased or altered vocal resonance/fremitus
In consolidation with significant lung lobe COLLAPSE there can be deviation of the trachea TOWARDS the collapsed side.

PULMONARY EDEMA is a condition where there is fluid in the interstitial spaces of the lung parenchyma. This is a characteristic of left ventricular failure. The signs are:
(1) Crackling noises with breathing (rales), predominantly in the lower (dependant) parts of the lung
(2) Decreased percussion note in the lower parts of the lung (depending on how much fluid has accumulated)
(3) Signs of Pleural effusion (see above) if sufficient fluid has accumulated

Answer 3

effusion means free fluid in the pleural cavity. I have never heard of pleural edema. The pleura is not made to hold fluid.