 Introduction/Background Under normal circumstances, approximately 0.1 to 0.2 mL/kg body weight of pleural fluid resides in the pleural space [1]. Abnormal accumulation of pleural fluid is the most common clinical manifestation of pleural disease [2], typically caused by increased pulmonary capillary pressure, increased pleural membrane permeability, decreased oncotic pressure, or lymphatic obstruction [3]. Pleural effusions are categorized as transudative or exudative [4], with transudative effusions usually reflecting the sequala of a systemic etiology and exudative effusions usually resulting from a process localized to the pleura [5]. Common causes of transudative pleural effusions include congestive heart failure, cirrhosis, and renal failure, whereas exudative effusions are typically due to infection, malignancy, or autoimmune disorders [6], emphasizing the importance of prompt diagnosis to aid in patient management [7]. In general, physical examination findings have a lower positive likelihood ratio for detection of pleural effusions [8], supporting the use of imaging to aid in identification of clinically significant pleural effusions. When imaging pleural effusions, chest radiographs can typically detect >75 mL on the lateral view and >175 mL on the frontal view [9]. Thoracic ultrasound (US) can detect >20 mL of pleural fluid [10]. Chest CT can detect >10 mL of pleural fluid, and is considered the reference standard for imaging [11]. All elements are essential: 1) timing, 2) reconstructions/reformats, and 3) 3-D renderings. Standard CTs with contrast also include timing issues and reconstructions/reformats. Only in CTA, however, is 3-D rendering a required element. This corresponds to the definitions that the CMS has applied to the Current Procedural Terminology codes.
Workup of Pleural Effusion or Pleural Disease.  Introduction/Background Under normal circumstances, approximately 0.1 to 0.2 mL/kg body weight of pleural fluid resides in the pleural space [1]. Abnormal accumulation of pleural fluid is the most common clinical manifestation of pleural disease [2], typically caused by increased pulmonary capillary pressure, increased pleural membrane permeability, decreased oncotic pressure, or lymphatic obstruction [3]. Pleural effusions are categorized as transudative or exudative [4], with transudative effusions usually reflecting the sequala of a systemic etiology and exudative effusions usually resulting from a process localized to the pleura [5]. Common causes of transudative pleural effusions include congestive heart failure, cirrhosis, and renal failure, whereas exudative effusions are typically due to infection, malignancy, or autoimmune disorders [6], emphasizing the importance of prompt diagnosis to aid in patient management [7]. In general, physical examination findings have a lower positive likelihood ratio for detection of pleural effusions [8], supporting the use of imaging to aid in identification of clinically significant pleural effusions. When imaging pleural effusions, chest radiographs can typically detect >75 mL on the lateral view and >175 mL on the frontal view [9]. Thoracic ultrasound (US) can detect >20 mL of pleural fluid [10]. Chest CT can detect >10 mL of pleural fluid, and is considered the reference standard for imaging [11]. All elements are essential: 1) timing, 2) reconstructions/reformats, and 3) 3-D renderings. Standard CTs with contrast also include timing issues and reconstructions/reformats. Only in CTA, however, is 3-D rendering a required element. This corresponds to the definitions that the CMS has applied to the Current Procedural Terminology codes.