CYSTS OF THE JAWS
A cyst is an abnormal cavity filled with fluid and usually lined by epithelium. Cysts gradually enlarge replacing normal tissues. Most cysts originate from odontogenic epithelium after tooth development. Cysts can be divided into two groups: Odontogenic cysts and nonodontogenic cysts. Odontogenic cysts arise from epithelial cells associated with the development of teeth like the enamel organ, dental lamina, reduced enamel epithelium, and epithelial rests of Malassez. Nonodontogenic cysts on the other hand arise from epithelium other than that associated with tooth formation.
Clinical Features
Cysts contain fluid or semisolid material. The fluid inside a cyst exerts equal pressure in all directions which makes a cyst look spherical (balloon or hydrostatic in shape) except when it encounters unequal resistance to its growth. Cysts can cause displacement as they tend to push aside adjacent structures such as teeth. They can also cause bony expansion and usually lacking pain unless they got secondarily infected or got associated with nonvital tooth.
Radiographic Features
Cysts can be either unilocular or multilocular. Most often they are completely radiolucent. However, they can have dystrophic calcification or septa giving them multilocular appearance, overlapping of structures over cysts can cause false impression of multiloculation. Cysts can occur centrally (within the bone) or any other location in the maxilla or the mandible but rarely in the condylar head or the coronoid process. Cysts originating centrally have a well-defined border unless they got secondary infected which give them sclerotic margin. Cysts can cause displacement and resorption of adjacent teeth. Cysts may displace the mandibular canal inferiorly and cause thinning of cortical boundaries.
Former Cysts
Lately, some entities that were known to be cysts are no longer true. Primordial cysts are now known to be KCOTs, median palatal cysts are now considered to be just a variant of nasopalatine duct cyst. Median mandibular and globulomaxillary cysts do not exist anymore. Globulomaxillary cyst is now considered to be a radicular, lateral periodontal or even KCOT.
Cystic-like Lesions
Simple bone cyst (SBC) falls into this category. Because of its radiographic appearance that resembles a cyst and its historic classification, we included the SBC under the cysts category. However, it is always important to remember that SBC is not a true cyst.