OPG (Orthopantomogram) showing PERIAPICAL RADICULAR CYST at the apex of cairous left lower third molar .

An odontogenic cyst of inflammatory origin that is preceded by a chronic periapical granuloma.

It is a liquid-filled cavity lined with epithelium.

Radiologic features.

1)Rounded,well circumscribed radiolucency at the apex of a nonvital tooth.

2)Often with a distinct thin line of cortication.

Differential diagnosis.

1)Periapical granuloma.

2)Traumatic bone cyst.

3)Cementoma (Periapical cemento osseous dysplasia cyst).