Cyst: is defined as a pathological cavity which may or may not be lined by epithelium and is filled with solid, semi solid or gaseous material. Odontogenic cyst: a cyst in which lining of lumen is derived from epithelium produced during tooth development. Mechanism of cyst formation includes proliferation of the epithelial lining, fluid accumulation within the cyst cavity, and bone resorption. True cysts are lined by epithelium (e.g. dentigerous cyst, radicular cyst), while pseudo cysts are not lined by epithelium (e.g. solitary bone cyst, aneurysmal bone cyst). Classification of cysts of the orofacial region is based on the World Health Organization classification.