Pathology · patient case question
What is Patient B's lesion, and why does the diagnosis matter?
Patient case: Two radiolucencies that are not what their names suggest
Patient: Two patients
Chief Complaint: A: incidental finding at a new patient examination. B: incidental finding on a panoramic taken before orthodontic assessment.
Background: A, 34-year-old male: asymptomatic, no history of trauma or caries in the region. B, 25-year-old female: healthy, no extractions ever performed.
Findings: A: an inverted pear-shaped radiolucency between the roots of the maxillary lateral incisor and canine, with the roots divergent. BOTH teeth respond normally to cold and electric pulp testing. B: a well-defined corticated radiolucency in the posterior mandible occupying the position where a third molar never developed. No tooth is present and none is visible elsewhere.
Show answer and explanation
Correct answer: B. Primordial cyst — and in current classification the great majority prove to be odontogenic keratocysts
- A. A traumatic (simple) bone cyst is an empty, unlined cavity that characteristically SCALLOPS UP between the roots of adjacent VITAL teeth. It is unrelated to a missing tooth germ, and it occurs typically in young patients in the posterior mandible.
- B. CORRECT. A PRIMORDIAL CYST develops from the enamel organ BEFORE any hard tissue forms, so it occupies the position of a tooth that NEVER DEVELOPED — most often the third molar region, exactly as here. The reason the diagnosis matters is that the great majority of lesions historically labelled primordial cysts prove on histology to be ODONTOGENIC KERATOCYSTS, and the term has largely been superseded for that reason. That changes management entirely: OKCs recur at a high rate and require thorough enucleation with adjunctive treatment such as peripheral ostectomy or Carnoy's solution, plus long-term radiographic follow-up.
- C. A dentigerous cyst forms around the CROWN of an unerupted tooth and requires a tooth to be present. There is no tooth here.
- D. A residual cyst is a radicular cyst left behind after extraction of the causative NON-VITAL tooth. This patient has never had an extraction, and a tooth must have existed for this diagnosis to apply.
Note: Multiple keratocysts, or a keratocyst in a patient under about twenty, should prompt screening for GORLIN-GOLTZ syndrome — skull film for falx calcification, chest film for bifid ribs, dermatology referral for basal cell carcinomas.