Diagnosis
Radiographic appearance: well-defined, round or ovoid periapical radiolucency with a corticated (white) border — the cortical lining indicates a slow-growing, benign lesion.
Periapical radiograph shows the cyst in continuity with the apex of the non-vital tooth. The lamina dura at the apex is lost.
CBCT (Cone Beam CT) for large lesions: determines three-dimensional extent, cortical plate integrity, relationship to adjacent structures (inferior alveolar nerve, maxillary sinus).
Pulp vitality testing: the involved tooth tests non-vital; if a tooth tests vital, radicular cyst is unlikely — consider other lesions (periapical cemental dysplasia, ameloblastoma, keratocystic odontogenic tumor).
Definitive diagnosis: histopathological examination of the excised cyst lining showing non-keratinized squamous epithelium with cholesterol clefts and chronic inflammatory infiltrate.