Presence of air in the pleural cavity with signs of mediastinal shift like : Tracheal shift and Shift of Apex beat
Compared to simple pneumothorax, there will be increased percussion note, elevated jugular pressure, decreased breath sounds, weak pulse and low BP.
A tension pneumothorax impairs venous return by caval distortion from mediastinal shift and raised intrathoracic pressure with compression of the contralateral lung.
Radiological signs of tension pneumothorax :
Spreading of ribs (Space between ribs increased)
Lowering of hemidiaphragm