A periradicular radiolucency of endodontic origin may correspond to any of the following histological diagnoses EXCEPT:

Correct answer: D. Dentigerous cyst

• A. A periapical abscess is a collection of pus at the apex resulting from pulp necrosis and is very much endodontic in origin.
• B. The periapical granuloma is the most frequent histological finding in an apical radiolucency of pulpal origin.
• C. A radicular (periapical) cyst is the most common odontogenic cyst and is by definition inflammatory and endodontic in origin, arising from the rests of Malassez.
• D. CORRECT — this is the exception. A DENTIGEROUS CYST is a DEVELOPMENTAL odontogenic cyst that forms around the crown of an UNERUPTED tooth, attaching at the cementoenamel junction. It has no relationship to pulp necrosis, and the associated tooth is unerupted rather than endodontically involved. It cannot be the histology behind an apical lesion of endodontic origin.

Note: Granuloma, cyst and abscess cannot be told apart radiographically — only histologically. All three respond to proper root canal treatment, which is why biopsy is not the first step.