Pleural effusion

Objectives:

• Radiological criteria
• Differentiate complete opacification of one hemi thorax
• Different appearances
• Recognition and significance of loculation and significance of loculation
• When to order lateral decubittus
• How to differentiate etiology
• Role of ultrasound for pleural tap
• Role of CT in thoracentesis

Definition: 

• Fluid accumulates in pleural space.

You are looking at pleural effusion on left, in the Chest x-ray.

Irrespective of the nature of fluid, radiologically they will look similar. 

Q1: What are the radiological criteria for pleural effusion?

Radiological criteria are:

• Homogenous density
• Density in dependent portion
  • Upright: Costophrenic angle in PA view 
  • Lateral view: Anterior and posterior portions of gutter 
  • Lateral decubitus position: Along sides 
  • Supine position: Along posteriorly, giving diffuse haziness on the side of effusion
• Silhouette of upper limit of density
  • Upper margin high in axilla in PA view
  • Upper margin high anteriorly and posteriorly in lateral view
  • This is just an illusion
• Loss of silhouette. Note lack of identifiable left diaphragm before and visible diaphragm after clearance of fluid (Silhouette sign principle

Q2: How do you differentiate complete opacification of one hemi thorax?

Consider

• Massive pleural effusion
• Complete atelectasis or Surgical resection of lung

Mediastinum is shifted to opposite side with effusion and pulled to same side with atelectasis
Hemithorax is larger with effusion and smaller with atelectasis
There are other reasons for loss of unilatweral lung volume, but for now remembre atelectasis and resection.

Q3: What are the different appearances of pleural effusion?

• Massive
• Unilateral VS bilateral
• Sub pulmonic
• Loculated
• Supine position
• Lateral decubitus position

Q4: How do you recognize loculated effusion? What is the significance?

• Loculation should be considered when a density considered to be fluid does not correspond to anatomical location of fissures. Of course loculaton can occur within fissures. 
• You think it is fluid but in upright position it is not in gravity dependant location.

Q5: When will you order lateral decubitus film?

Lateral decubitus film is obtained

• to confirm pleural effusion as in small or sub-pulmonic effusions
• occasionally to evaluate underlying lung

Most of the time it is ordered unnecessarily with no additional benefit in large effusions.

Q6: How do you determine the etiology of effusion from chest x-ray?

Radiologically you cannot distinguish transudate, exudate, blood or pus. It mainly the associated findings suggest the etiology. Let me give few scenarios

• Bilateral effusions with cardiomegaly : Congestive heart failure
• Massive unilateral effusion: Malignancy
• Pleural effusion with apical infiltrates: Tuberculosis
• Pleural effusion with nodes or mass or lytic bone lesions: Malignancy

Q7: How does radiological procedures help in thoracentesis?

You do not need any radiological assistance to tap most of the effusions. Obtain radiological assistance to tap

• with small effusions
• loculated effusions

Ultrasound is the preferred method for localiztion of fluid and a needle can be passed through the probe. It can also be done at the bed side if necessary. CT guided tap is equally effective, except it can not be useful for bed side tap.