This a specialized diagnostic procedure carried out to access the lymph glands which are lying outside the airways but inside the chest (area is called mediastinum). It is usually done for diseases like Sarcoidosis, Tuberculosis, Lymphoma, Multiple myeloma etc. A very fine needle is used to go beyond the confines of the tracheobronchial tree during the bronchoscopy. It can also be used for the diagnosis of growths or tumours present within the airways but carrying a high risk of bleeding with biopsy. It carries a diagnostic accuracy of 65 to 75% approximately.