A patient presents with cough and fever. On X-ray examination, a homogenous opacity silhouetting the right hea border with ill-defined lateral margins is seen. What would be the most probable diagnosis?

Ans. a. Pneumonia affecting medial zone of right middle lobe Homogeneous paracardiac opacity in right lung, near right cardiac silhouette with ill-defined lateral border is suggestive of pneumonia affecting medial zone of right middle lobe. Silhoutte sign is very useful in localizing lung lesions as all structures forming cardiac silhouette (hea border, ascending, descending aoa, aoic knob and hemidiaphragm) are in contact with a specific poion of lung. Silhoutte Structure Lung Poion in Contact Ascending aoa, upper right hea border and upper pole of hilum Anterior segment of right upper lobe Right hea border Right middle lobe Aoic knob Apical poion of left upper lobe (posterior) Upper left hea border Anterior segment of left upper lobe Left hea border Lingula (anterior) Anterior hemidiaphragm Position of oblique fissure is best index of lower lobe volume Lower lobe (anterior)