Pathology · patient case question
The epithelium lining this cyst is derived from which structure?
Patient case: Facial swelling with a radiolucency at the distal root of #18
Patient: Female, 39 years old
Chief complaint: “My face is swollen.”
History: Currently taking amoxicillin prescribed by an urgent care clinic.
Findings: Distal-occlusal decay on tooth #18 with vestibular oedema and active purulent drainage. A well-circumscribed radiolucency is associated with the distal root. Tooth #18 does not respond to cold. A biopsy of the excised lesion is reported as a radicular cyst.
Show answer and explanation
Correct answer: B. Epithelial rests of Malassez
- A. Reduced enamel epithelium is the ameloblast layer remaining after enamel formation. It gives rise to the DENTIGEROUS cyst, which surrounds the crown of an UNERUPTED tooth — a different mechanism entirely.
- B. CORRECT. The EPITHELIAL RESTS OF MALASSEZ are remnants of Hertwig's epithelial root sheath that persist in the periodontal ligament. Inflammation from a necrotic pulp stimulates these dormant rests to proliferate; the expanding epithelial mass outgrows its blood supply, the centre breaks down, and a cyst cavity forms. This is the origin of every radicular cyst, and it is why radicular cysts occur only at NON-VITAL teeth.
- C. The epithelial rests of Serres are remnants of the dental lamina. They give rise to the odontogenic keratocyst, the lateral periodontal cyst and the gingival cyst.
- D. The stratum intermedium is a layer of the enamel organ that supports ameloblast function during amelogenesis. It does not persist to form cysts.
Note: The three-way map is worth memorising — rests of Malassez to radicular cyst, reduced enamel epithelium to dentigerous cyst, rests of Serres to keratocyst and lateral periodontal cyst.