Intra Oral Peri Apical Radio-graphs i.e. IOPAs are common radiographs which are used as diagnostic aid from radiological point of view.
Radiographically , Radicular Cysts are round or ovoid radiolucent areas surrounded by a narrow radio-opaque margin, which extends from Lamina Dura of involved tooth. In infected or rapidly enlarging cysts, radio-opaque margins may not be seen. Root resorption is rare but may occur.
It is often difficult to differentiate radiologically between radicular cysts & apical granulomas.
Radiologic presentation of Radicular Cyst is given in detail as follows ---
Periphery & Shape--- Periphery usually have a well defined cortical border. If Cyst is secondarily infected, the inflammatory reaction of surrounding bone may result in loss of this cortex or alteration of cortex into more sclerotic border. The outline of radicular cyst usually is curved or circular unless it is influenced by surrounding structures such as cortical boundaries.
Internal structure--- in most cases, internal structure of radicular cyst is radiolucent. Occasionally, dystrophic calcification may develop in long standing cysts appearing as sparsely distributed, small particulate radio-opacities.
Effects on surrounding structures--- If a radicular cyst is large, displacement and resorption of roots of adjacent teeth may occur. The resorption pattern may have a curved outline. In rare cases, the cyst may resorb the roots of related non-vital teeth. The cyst may invaginate the antrum, but there should be evidence of a cortical boundary between contents of cyst and internal structure of antrum. The outer cortical plates of maxilla and mandible may expand in a curved or circular shape. Cyst may displace the mandibular alveolar nerve canal in an inferior direction.