Periapical cyst (radicular cyst)

Fig a: OPG of 14 year old male with h/o caries tooth shows subtle oval lytic lesion at the apex of root of second molar tooth.

Fig b: Coronal reformatted image shows well defined cystic lesion at the apex of tooth (arrow) and is better demonstrated by the 3D volume rendering image in fig c (arrow). The features are consistant with periapical cyst.

The periapical (radicular) cyst is the most common odontogenic cyst and results from inflammation secondary to caries or other entities. The peak prevalence of this asymptomatic cyst occurs between the fourth and sixth decades of life. Typically, infection spreads to the apex (root) of the tooth, leading to secondary apical periodontitis, granuloma, or abscess and, finally, cyst formation. The cyst appears as a round or pear-shaped, well-defined radiolucent lesion with sclerotic borders. Most periapical cysts are less than 1 cm in diameter. It is important to note that radiology cannot always help distinguish a granuloma from a cyst.