The initial investigations for suspected<unk>  remains chest X-ray, although it cannot differentiate an<unk>  from uninfected parapneumonic effusion. Ultrasound must be used to confirm the presence of a pleural fluid collection and can be used to estimate the size of the effusion, differentiate between free and loculated pleural fluid and guide thoracocentesis if necessary. Chest CT and MRI do not provide additional information in most cases and should therefore not be performed routinely. On a CT scan,<unk>  fluid most often has a radiodensity of about 0-20 Hounsfield units (HU), but gets over 30 HU when becoming more thickened with time. The most often used "golden" criteria for<unk>  are pleural effusion with macroscopic presence of pus, a positive Gram stain or culture of pleural fluid, or a pleural fluid pH under 7.2 with normal peripheral blood pH. Clinical guidelines for adult patients therefore advocate diagnostic pleural fluid aspiration in patients with pleural effusion in association with sepsis or pneumonic illness. Because pleural effusion in the pediatric population is almost always parapneumonic and the need for chest tube drainage can be made on clinical grounds, British guidelines for the management of pleural infection in children do not recommend diagnostic pleural fluid sampling. Blood and sputum culture has often already been performed in the setting of community acquired pneumonia needing hospitalization. It should however be noted that the micro-organism responsible for development of<unk>  is not necessarily the same as the organism causing the pneumonia, especially in adults. As already mentioned before, sensitivity of pleural fluid culture is generally low, often partly due to prior administration of antibiotics. It has been shown that culture yield can be increased from 44% to 69% if pleural fluid is injected into blood culture bottles (aerobic and anaerobic) immediately after aspiration. Furthermore, diagnostic rates can be improved for specific pathogens using polymerase chain reaction or antigen detection, especially for Streptococcus pneumoniae, Streptococcus pyogenes and Staphylococcus aureus. In a study including 78 children with<unk> , the causative micro-organism could be identified using direct culture of fresh pleural fluid in 45% of patients, with an additional 28% using PCR on pleural fluid of negative cultures. Pneumococcal antigen detection in pleural fluid samples by latex agglutination can also be useful for rapid diagnosis of pneumococcal<unk> . In the previously noted study, positive and negative predictive value of pneumococcal antigen detection was 95% and 90%, respectively. File:UOTW 28 - Ultrasound of the Week 1.Pleural<unk>  as seen on ultrasound File:UOTW 28 - Ultrasound of the Week 2.Pleural<unk>  as seen on ultrasound File:UOTW 28 - Ultrasound of the Week 3.Pleural<unk>  as seen on ultrasound File:UOTW 28 - Ultrasound of the Week 4.Pleural<unk>  as seen on ultrasound
Pleural empyema
Pulmonary embolism
Pleurisy
Pleural effusion
Lung abscess
Pneumonia
Malignant pleural effusion
Lobar pneumonia