<unk>  effusion A<unk>  effusion can form when fluid builds up in the<unk>  (labelled as<unk>  space). A pathologic collection of<unk>  fluid is called a<unk>  effusion. Mechanisms: # Lymphatic obstruction # Increased capillary permeability # Decreased plasma colloid osmotic pressure # Increased capillary venous pressure # Increased negative intrapleural pressure<unk>  effusions are classified as exudative (high protein) or transudative (low protein). Exudative<unk>  effusions are generally caused by infections such as pneumonia (parapneumonic<unk>  effusion), malignancy, granulomatous disease such as tuberculosis or coccidioidomycosis, collagen vascular diseases, and other inflammatory states. Transudative<unk>  effusions occur in congestive heart failure (CHF), cirrhosis or nephrotic syndrome. Localized<unk>  fluid effusion noted during pulmonary embolism (PE) results probably from increased capillary permeability due to cytokine or inflammatory mediator release from the platelet-rich thrombi. Transudate Exudative causes * Congestive heart failure (CHF) * Hepatic cirrhosis * Hypoproteinemia * Nephrotic syndrome * Pulmonary atelectasis * Myxedema * Peritoneal dialysis * Pulmonary embolism * Meigs' syndrome * Obstructive uropathy * Malignancy * Infection * Trauma * Pulmonary infarction * Pulmonary embolism * Autoimmune disorders * Pancreatitis * Ruptured esophagus (or Boerhaave syndrome)<unk>  fluid analysis When accumulation of<unk>  fluid is noted, cytopathologic evaluation of the fluid, as well as clinical microscopy, microbiology, chemical studies, tumor markers, pH determination and other more esoteric tests are required as diagnostic tools for determining the causes of this abnormal accumulation. Even the gross appearance, color, clarity and odor can be useful tools in diagnosis. The presence of heart failure, infection or malignancy within the<unk>  are the most common causes that can be identified using this approach. Gross appearance * Clear straw-colored: If transudative, no further analysis needed. If exudative, additional studies needed to determine cause (cytology, culture, biopsy). * Cloudy, purulent, turbid: Infection, empyema, pancreatitis, malignancy. * Pink to red/bloody: Traumatic tap, malignancy, pulmonary infarction, intestinal infarction, pancreatitis, trauma. * Green-white, turbid: Rheumatoid arthritis with<unk>  effusion. * Green-brown: Biliary disease, bowel perforation with ascites. * Milky-white or yellow and bloody: Chylous effusion. * Milky or green, metallic sheen: Pseudochylous effusion. * Viscous (hemorrhagic or clear): Mesothelioma. * Anchovy-paste (or 'chocolate sauce'): Ruptured amoebic liver abscess. Microscopic appearance Microscopy may show resident cells (mesothelial cells, inflammatory cells) of either benign or malignant etiology. Evaluation by a cytopathologist is then performed and a morphologic diagnosis can be made. Neutrophils are numerous in<unk>  empyema. If lymphocytes predominate and mesothelial cells are rare, this is suggestive of tuberculosis. Mesothelial cells may also be decreased in cases of rheumatoid pleuritis or post-pleurodesis pleuritis. Eosinophils are often seen if a patient has recently undergone prior<unk>  fluid tap. Their significance is limited. If malignant cells are present, a pathologist may perform additional studies including immunohistochemistry to determine the etiology of the malignancy. Chemical analysis Chemistry studies may be performed including pH,<unk>  fluid:serum protein ratio, LDH ratio, specific gravity, cholesterol and bilirubin levels. These studies may help clarify the etiology of a<unk>  effusion (exudative vs transudative). Amylase may be elevated in<unk>  effusions related to gastric/esophageal perforations, pancreatitis or malignancy.<unk>  effusions are classified as exudative (high protein) or transudative (low protein). In spite of all the diagnostic tests available today, many<unk>  effusions remain idiopathic in origin. If severe symptoms persist, more invasive techniques may be required. In spite of the lack of knowledge of the cause of the effusion, treatment may be required to relieve the most common symptom, dyspnea, as this can be quite disabling. Thoracoscopy has become the mainstay of invasive procedures as closed<unk>  biopsy has fallen into disuse. Disease Diseases of the<unk>  include: * Pneumothorax: a collection of air within the<unk>  *<unk>  effusion: a fluid accumulation within the<unk>  space. *<unk>  tumors: abnormal growths on the<unk> .
Pleural cavity
Lung cavity
Indium lung
Endobronchial valve
Thoracic inlet
Pulmonary bay
Thoracic diaphragm
Subclavian loop