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Pathology · patient case with 2 questions

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.

Question 1

The epithelium lining this cyst is derived from which structure?

  1. Reduced enamel epithelium
  2. Epithelial rests of Malassez
  3. Epithelial rests of Serres
  4. Stratum intermedium
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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.

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Question 2

A separate patient presents with a painless bump on the gingiva. Tooth #7 gives no response to cold, is not tender to percussion, and shows a well-defined periapical radiolucency. Biopsy shows chronic inflammatory infiltrate, cholesterol clefts and a lining of non-keratinised stratified squamous epithelium. What is the diagnosis?

  1. Periapical cyst
  2. Periapical granuloma
  3. Parulis
  4. Periapical scar
Show answer and explanation

Correct answer: A. Periapical cyst

  • A. CORRECT. The decisive histologic feature is the EPITHELIAL LINING. A periapical (radicular) cyst is defined by a cavity lined with non-keratinised stratified squamous epithelium, with a wall of chronically inflamed fibrous connective tissue containing cholesterol clefts and, often, Rushton bodies and haemosiderin. Cholesterol clefts come from breakdown of red cell membranes within the lesion.
  • B. A periapical granuloma is granulation tissue with chronic inflammatory cells and NO epithelial lining. That is the whole distinction, and it can only be made histologically — the two are indistinguishable radiographically.
  • C. A parulis is the soft-tissue swelling at the mouth of a sinus tract, composed of granulation tissue. It has no cystic cavity and no epithelial lining beyond the surface mucosa.
  • D. A periapical scar is dense fibrous tissue that persists after healing, with minimal inflammation, no epithelium and no cholesterol clefts. It follows treatment rather than preceding it.

Note: Both lesions require a NON-VITAL tooth. Treatment for both is root canal treatment first; surgery is reserved for lesions that fail to resolve.

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