The periapical radiograph shows a well-defined radiolucency along the LATERAL aspect of the root, coronal to the apex. The tooth responds normally to pulp testing. All of the following belong in the differential diagnosis EXCEPT:

Correct answer: B. Periapical (apical) abscess

• A. A LATERAL PERIODONTAL ABSCESS arises from the periodontium rather than the pulp, produces a lateral radiolucency, and characteristically occurs in a tooth that remains VITAL with a deep probing defect.
• B. CORRECT — this is the EXCEPTION. A PERIAPICAL abscess is by definition centred on the APEX and requires a NECROTIC pulp. The stem gives a lesion that is lateral rather than apical, in a tooth that tests VITAL — both features exclude a lesion of pulpal origin.
• C. A CENTRAL GIANT CELL GRANULOMA can present as a well-defined radiolucency anywhere in the jaws, most often anterior to the first molar in the mandible, and does not depend on pulp status.
• D. The LATERAL PERIODONTAL CYST is the archetypal lateral radiolucency: a well-defined, often teardrop-shaped developmental cyst beside the root of a VITAL tooth, with a strong predilection for the mandibular premolar–canine region. It belongs squarely in this differential.

Note: Pulp vitality is the discriminator that does most of the work here. A vital tooth immediately removes every lesion of endodontic origin — periapical granuloma, radicular cyst, apical abscess, condensing osteitis — and leaves the periodontal and developmental lesions in play.