Differential interference contrast micrograph of Charcot Leyden crystals from an endobronchial lesion. Some types of asthma are characterized by chronic inflammation of the lungs. This can lead to formation of thick, gelatinous mucus, which can obstruct the bronchi of the lungs and mimic tumors. In order to investigate such blockages, samples can be obtained using a technique called Endobronchial Ultrasound - Transbronchial Needle Aspiration (EBUS-TBNA) and analyzed using a Papanicolaou stain to detect malignant and abnormal cells. The image shows a "cotton wool" like background of fibrin (a product of tissue damage) and clumps of necrotic (dead and dying) white blood cells called eosinophils. Pointed bipyramidal Charcot Leyden crystals can be seen, which are actually hexagonal when seen in cross section. Charcot Leyden crystals are formed when numerous eosinophils release their enzymes (lysophospholipases). The specimen in this case has been examined using differential interference contrast microscopy which utilizes a combination of prisms and polarizers to refract light, and which is perceived by the eye as a three dimensional effect. Horizontal image width 215 micrometres. Supplied by William R. Geddie, courtesy of Wellcome Images.