A tooth with a periapical lesion was extracted. One year later the radiolucency in that site is larger. What is the most likely explanation?

Correct answer: C. A residual cyst left behind because the lesion was not curetted at extraction

• A. Normal socket healing is complete radiographically within 6–12 months and produces INCREASING radiopacity, not an enlarging lucency.
• B. An adjacent tooth could produce a new lesion, but that would require its own necrotic pulp and would be centred on that tooth's apex rather than enlarging in the extraction site.
• C. CORRECT. This is a RESIDUAL CYST — a radicular cyst whose epithelial lining was left in the bone when the causative tooth was removed. Deprived of the tooth it does not resolve; the lining persists, continues to proliferate and the cyst enlarges. The remedy is enucleation, and the preventive measure is thorough curettage of any apical lesion at the time of extraction.
• D. Osteosarcoma is exceedingly rare, produces a sunburst periosteal reaction and symmetrical PDL widening, and would not present simply as a slowly enlarging well-defined lucency.

Note: Always curette the socket when extracting a tooth with an apical lesion, and submit anything substantial for histopathology.