informal leader. An individual within an organization that is viewed as someone worth listening to due to their perceived experience and reputation among peers. The informal leader does not hold any position of formal authority or power over the peers choosing to follow their lead but can influence the decisions of others.
The mediastinum (from Medieval Latin mediastinus, midway) is the central compartment of the thoracic cavity surrounded by loose connective tissue, as an undelineated region that contains a group of structures within the thorax.he mediastinum lies within the thorax and is enclosed on the right and left by pleurae. It is surrounded by the chest wall in front, the lungs to the sides and the spine at the back. It extends from the sternum in front to the vertebral column behind, and contains all the organs of the thorax except the lungs.
Middle mediastinum. 1  Bronchogenic cyst â A benign growth with respiratory origins. 2  Lymphadenopathy mediastinal â An enlargement of the lymph nodes. 3  Pericardial cyst â A benign growth that results from an out-pouching of the pericardium (the heartâs lining).