Histopathology of a periapical lesion shows a cavity lined by STRATIFIED SQUAMOUS EPITHELIUM within fibrous connective tissue. What is the diagnosis?

Correct answer: B. Periapical (radicular) cyst

• A. A periapical ABSCESS is a collection of neutrophils, necrotic debris, and pus — acute, painful, with no epithelial lining.
• B. CORRECT. The presence of an EPITHELIAL LINING is the defining histologic feature of a RADICULAR (periapical) CYST. The epithelium derives from the rests of Malassez, which proliferate in response to chronic inflammation, and the resulting cavity fills with fluid. It is the MOST COMMON cyst of the jaws. Radiographically it cannot be reliably distinguished from a granuloma — histology is the only definitive determination.
• C. A periapical GRANULOMA is chronic granulation tissue with lymphocytes, plasma cells, and macrophages, and NO epithelial-lined cavity (though epithelial rests may be present without forming a cyst).
• D. Condensing osteitis is a bone response with increased trabeculation, not a soft-tissue lesion.

Note: Radicular cyst = epithelium-lined cavity. Granuloma = granulation tissue. You cannot tell them apart on a radiograph.