**4. Imaging techniques**

Although standard chest radiographs can detect as little as 50 mL of PF on a lateral view,[21] it provides only suggestive findings for the diagnosis of MPE. A massive effusion increases the probability of a malignant aetiology and commonly produces a meniscus sign with fluid tracking up the lateral chest wall, a shift of the mediastinum to the contralateral side, and an inversion of the diaphragm. Radiographic signs of an MPE include circumferential lobulated pleural thickening, crowding of ribs, and elevation of the hemidiaphragm or ipsilateral mediastinal shift consistent with lung atelectasis due to airway obstruction by a tumor [22]. Due to resembling the other causes of pleural effusion other imaging studies may be necessary such as ultrasound and computed tomography (CT) scan [23].

Ultrasound is an important device during evaluating the presence of an effusion and may be used as a guide during thoracentesis. Ultrasound also may aid in distinguishing an exudates (echogenic) from a transudate (anechoic) although this finding is not definitive [24]. Ultra‐ sound is, in fact, more sensitive than radiography and can detect as little as 5 mL of pleural fluid and is superior to CT for characterization of collections for the presence of septations and loculations [25].

This defines an exudate if any one of three criteria are met. The overall accuracy of these criteria is 93% to 95% [34, 35]. Light criteria have commonly misclassify effusions when any one of three criteria has a value close to its cutoff point [36]. Although the majority of malignant pleural effusions are exudates, it is important to keep in mind that a few are transudates [37, 38]. These circumstances result from the defective implementation of diagnostic rules that classify pleural effusions or coexisting conditions with transudates, such as hypoalbuminemia, cirrhosis with ascites, or chronic heart failure [39]. This does not suggest that every individual with a transudative pleural effusion should have pleural fluid cytological examination. However, in the appropriate clinical setting and the absence of congestive heart failure or a pleural fluid LDH level close to the exudative range, determination of pleural fluid cytology

Management of Malignant Pleural Effusion http://dx.doi.org/10.5772/54441 89

The primary problem with the Light criteria is that they identify 15% to 20% of transudative effusions as exudative effusions [40]. A re-evaluation of Light's criteria demonstrates that Light's criteria have an overall sensitivity for an exudate of near 100%, but a specificity of only approximately 80% [41]. In the search for the ideal test or improvement of Light's criteria; from the first day of Light criteria that were published the most widely accepted and so far have stood the test of time. Based on a meta-analysis of study in order to find the ideal diagnostic criteria, including 1448 patients, an updated version of Light's criteria, the original light studies a slightly modified by the addition of cholesterol as a marker, recommended as the best way to determine exudate. Judged by these criteria, a patient with any of the following criteria is

The appearance of the pleural fluid obtained by thoracentesis, its consistency and color should be noted. In patients with a known underlying malignancy, it is daily practice not only to obtain the usual tests to differentiate a transudate from an exudate (total protein and lactate dehy‐ drogenase both in the fluid and in the serum) but also to obtain total and differential cell count, pH, glucose level, cholesterol and triglycerides, cytological analysis, hematocrit (if fluid is

Malignant pleural effusions may be serous, serosanguineous, or bloody, and usually are exudative in nature [21]. There are four characteristics features of pleural effusion; suggesting malignancy in patients with undiagnosed pleural effusion: that is to say, [1] a symptomatic period of more than a month, [2] absence of fever, [3] blood-tinged or bloody pleural fluid, or [4] CT findings suggestive of malignancy (pulmonary or pleural masses, pulmonary atelecta‐

Despite all the progress in the imaging of the chest, for the diagnosis of MPE cytologic or tissue biopsy is required for approval. Cytology is the simplest definitive and most accurate method to diagnose malignant pleural effusion. Recent data suggests that at least 50 mL of pleural fluid

should be studied in order to provide optimal cytological analysis [44, 45].

is suggested [17].

provided, said to be exudates [42]:

grossly bloody), and cultures. [37, 38].

sis, or lymphadenopathy) [43].

**•** Pleural fluid protein greater than 2.9 g/dL

**•** Pleural fluid cholesterol greater than 45 mg/dL

**•** Ratio of pleural fluid LDH to serum LDH greater than 0.6

Computed tomography (CT) scanning is even more accurate in detecting small effusions, including as little as 2 mL of fluid. The volume of the fluid presence can be best determined radiographically by using three-dimensional reconstruction [26]. Currently, the most useful radiographic study is a chest CT scan. CT scans help to establish the presence of a loculated pleural effusion, allow the evaluation of the pulmonary parenchyma if there is not complete lung compression, and distinguish pleural thickening from effusion. It also provides an excellent way to evaluate the mediastinum for the presence of masses or lymphadenopathy and permits detection of pleural-based nodules [27].

The role of magnetic resonance imaging (MRI) in the evaluation of pleural effusions is limited; however, it may be beneficial in better characterizing possible tumour involvement of the chest wall or diaphragm [28]. Neither MRI nor CT scan can distinguish transudates from exudates accurately although both can be helpful in evaluating the pleural contents for masses, nodules, and pleural based thickening once the fluid is removed [29].

Positron emission tomography (PET scan) with 18F-fluorodeoxyglucose provides less ana‐ tomic information but has the potential advantage of providing diagnostic information about the effusion. This information may prove useful [30]. The true value of a PET scan would be to provide additional information about disease elsewhere, not to give a diagnosis of malig‐ nancy. In addition, diagnosis or treatment of a malignant effusion will depend on the type of cancer, and this cannot be determined with a PET scan [31].
