Table 2.

Differential diagnosis table for urinothorax

Differential Diagnosis	X-Ray	Ultrasound	CT	Radionuclide Study
Pleural effusion	Homogenous opacity blunting costophrenic angles, tracking up the pleural space. Curved upper border rising toward the axilla (meniscus sign) Large amounts displace the mediastinum. Outline of organs & diaphragm not visible (silhouette sign).	Anechoic or hypoechoic area bounded by thoracic structures, which moves on thoracic cycling. Echoes may be present if chronic.	A crescent-shaped attenuation in the dependent portion of the hemithorax.	Not specific. Increased activity in the hemithorax on Tc 99m methylene diphosphonate (MDP) bone scans in some malignant effusions.
Urinothorax	As above.	As above.	As above.	Tc 99m scans may demonstrate reno-pleural fistula.
Haemothorax	As above. May have evidence of trauma like broken ribs, widened mediastinum and pneumothorax.	As above. Echoes usually present. May be loculated.	As above. May show associated injuries.	Tc 99m RBC scan would demonstrate presence of blood.
Chylothorax	As above.	As above. Echoes usually present due to lymphatic fluid.	As above.	Tc 99 lymphoscintigraphy can show abnormal lymphatic drainage.
Pulmonary consolidation	Opacity confined to lobes. An air bronchogram may be present. Features vary with the causative organism. S pneumoniae-homogenous lobar opacity with air bronchograms usually right lower lobe. Aspiration pneumonia usually in the dependent portions of the right lung. K pneumoniae-fissure involvement, in upper lobes. Legionella - lower lung fields.	Hypoechoic with internal hyperechoic structures and an indistinct margin.	Displays parenchymal consolidation.	Usually hypermetabolic PET scan.