According the diagnostic and therapeutic methods of treating

According to Merriam-Webster’s Medical Dictionary, pleural effusion occurs when “an exudation of fluid from the blood or lymph into a pleural cavity.” In other words, pleural effusion is a collection of fluid in the pleural cavity; a buildup of fluid between the tissues that line the lungs and the chest (Frank, Long, Smith, & Merrill, 2012). Pleural effusion is a disease that a respiratory specialist must evaluate frequently in order for proper treatment (Villena Garrido et al, 2014). There have been many significant changes in the diagnostic and therapeutic methods of treating pleural effusion over the last several years.
Normal Anatomy and Physiology
The pleural cavity is divided into two different parts; the visceral pleura and the parietal pleura. The visceral pleura covers the lung parenchyma including the interlobar fissures. The visceral pleura also provides lung support to the lung. This protects the lung by limiting lung expansion. The visceral pleura contributes to lung recoil and deflation, with a mean thickness of 25-83 um. The parietal pleura provides the inner lining of the thoracic cavities. It is subdivided into the costal, mediastinal and diaphragmatic pleuras. The parietal pleura is made up of a single layer of mesothelial cells with loose connective tissue. It has a mean thickness of 20-25 um (The University of Utah, 2017). Additionally, the lung is kept in an inflated state by the mechanical coupling between the chest wall and the lung. With microvilli enmesh hyaluronic acid-rich lubricants, the mesothelial cells  minimize the work of breathing. Fluid and electrolytes freely pass between these different cells. With the endothelium as the main barrier, the fluid moves in and out of the pleural cavity. Transudates in the pleural cavity are made from changes in the hydrostatic-osmotic pressure within the cavity, normally keeping the cavity dry (Wang, 1985). Negative pressure created between the two pleuras is kept by the opposite elastic forces of the chest wall and lung. This represents the balance between the thoracic cavity’s outward pull and the lung’s inward pull. Pleural pressure is not uniform, which means that their is a gradient between the lowest, most negative, superior portion of the lung and the highest, least negative, inferior portion of the lung (The University of Utah, 2017).
Modalities Used For Detecting Pleural Effusions
The most common modality used for identifying pleural effusion is a PA chest X-ray. Another easily accessible option for patients is thoracic ultrasound, which is more sensitive than conventional X-ray when identifying pleural effusion. It is also better than computed tomography for identification. Chest CT may be useful for locating usable areas for biopsy or identifying other pathological regions, when the probability of identifying malignancy in pleural effusion is modified. These regions may include the mediastinum or the lung parenchyma. A CT scan of the abdomen may be useful when ruling out pathologies causing pleural effusion. (Villena Garrido et al, 2014). Another commonly used as part of staging evaluation for malignancies is PET, or Positron Emission Tomography imaging. However due to the high false positive rate in patients, the value of PET imaging in predicting benign vs. malignant disease is limited. (Desai & Lee, 2017).
Causes of Pleural Effusion
Pleural effusion has many different causes, which can be divided into increased pleural fluid formation as well as decreased pleural fluid absorption. Causes of increased pleural fluid formation include increased interstitial fluid in the lung, which can be caused by left ventricle failure, pneumonia, or a pulmonary embolus; increased intravascular pressure in the pleura, which is caused by right or left ventricle failure, or superior vena caval syndrome; increased permeability of the capillaries in the pleura, which can be caused by inflammation or increased levels of endothelial growth; increased levels of pleural fluid protein; decreased pleural pressure, which can be caused by lung atelectasis or increased elastic recoil of the lung; increased fluid in the peritoneal cavity, caused by Ascites or peritoneal dialysis; and disruption of the thoracic duct or blood vessels in the thorax (The University of Utah, 2017). Causes of decreased pleural fluid absorption include obstruction of the lymphatics draining the parietal pleura, elevation of the systemic vascular pressures caused by superior vena caval syndrome or right ventricle failure, or disruption of the aquaporin system in the pleura (The University of Utah, 2017). 
Types of Pleural Effusion
There are two types of pleural effusion: Transudative and Exudative pleural effusion. Transudative pleural effusion is caused by fluid leaking into the pleural space. This is from a low blood protein count or increased pressure in the blood vessels; heart failure being the most common cause. Exudative effusion is caused by blocked blood vessels or lymph vessels, inflammation, lung injury, and tumors (Butland & Maskell, 2003). In order to classify an effusion as an exudate or a transudate, the total protein level in the fluid must be determined as less than or greater than 30 g/L (Barber & McGrath, 2017). In a study conducted by Barber and McGrath, a 50-year-old woman with diffuse large B-cell lymphoma showed bilateral diffusion when given a CT scan. The pleural effusions were uneven, and milky off-white or yellow fluid was aspirated. The diagnosis for this women was chylothorax, due to the distinctive appearance of the fluid. When a pleural effusion is determined as unilateral, an underlying abnormality of the pleural cavity is possible. Causes of unilateral pleural effusion include tumors, infection, chylothorax, or haemorrhage. Bilateral pleural effusion occurs when both the right and left side of the pleural cavity are effected, as opposed to unilateral pleural effusion which only effects the right or left side of the pleural cavity (Butland & Maskell, 2003). 
Different Appearances of Pleural Effusion: What the Radiographer Needs to Know 
When looking at an radiograph, pleural effusion will appear bright white, or radiopaque. The surrounding area in the pleural space will appear black, or radiolucent. A subpulmonic effusion occurs when fluid pool at the bottom of the lung, between the diaphragm and the pleura. Costophrenic angle blunting occurs when the lung’s angle increases more than 30 degrees. Loculated effusions are most commonly associated with conditions that cause intense inflammation in the pleural cavity (Villena Garrido et al, 2014). Occasionally, collection of focal intrafissural fluid may look like a lung mass. The routine chest examination consists of a PA and a left lateral chest x-ray, to demonstrate fluid in the cavity. The patient can also be examined in a lateral decubitus position, which is the most accurate position to demonstrate the volume of fluid in the cavity, as well as  determine whether a pleural effusion is mobile or loculated. When setting technical factors for the exam, the radiographer must increase routine factors, due to the displaced lung tissue as well as increased tissue density within the thoracic cavity.
Thoracentesis is often performed for diagnosis and therapeutic purposes. This is a process where the fluid is drained from the cavity using a tube that is inserted into the effusion. Thoracentesis is usually the first step of pleural effusion management, and is performed in most patients. The process allows for the assessment of improvement in patient symptoms, re-expansion of the lung, as well as recurrence rate. Thoracentesis is a safe procedure, and with the routine use of ultrasound, complication rates have significantly decreased (Desai & Lee, 2017). Some pleural effusions could possibly need surgery to break apart adhesions. Other effusions might need a procedure where different irritants are put into the pleural space to fuse the surfaces together. This procedure is called Pleurodesis. By doing this, the pleural space is sealed, and pleural effusions have difficulty reaccumulating. A rapid pleurodesis takes advantage of both management strategies and minimizes some disadvantages by using both tunneled pleural catheter insertion and thoracoscopy guided talc delivery, all in one procedure (Desai & Lee, 2017). Video-assisted thoracoscopic surgery has improved range of therapeutic solutions, by allowing direct visualization of potential pleural abnormalities, so biopsy can be preformed if needed. (Desai & Lee, 2017). The use of tunneled pleural catheters, which are silicone tubes that is placed into the pleural cavity, is increasingly common for the management of malignant pleural effusion. Tunneled pleural catheters are made with a small cuff, and the other end exits the patient with a one-way valve. This allows for easy drainage at home, a hospital, or clinic, by the patient themselves or their caregivers. There is increasing evidence that tunneled pleural catheters are safe and effective for symptom management (Desai & Lee, 2017).

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