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Radiology · patient case with 3 questions

Radiographic Differential — Impacted Canine

demo: 19-year-old male

chief: Referred for evaluation of a retained primary canine.

history: Non-contributory.

meds: None

findings: Panoramic radiograph shows tooth #6 impacted high in the maxilla with an associated well-defined radiolucency surrounding the crown. Images below illustrate two of the entities under consideration.

Case image

Question 1

All of the following are reasonable radiolucent differentials associated with an impacted tooth EXCEPT:

  1. Odontogenic keratocyst
  2. Dentigerous cyst
  3. Adenomatoid odontogenic tumor
  4. Radicular cyst
Show answer and explanation

Correct answer: D. Radicular cyst

  • A. OKC frequently presents around impacted teeth and can mimic a dentigerous cyst radiographically.
  • B. A dentigerous cyst attaches at the CEJ of an unerupted crown and is the single most common cyst associated with an impaction.
  • C. AOT is classically associated with an impacted canine in a young patient, which is exactly this scenario.
  • D. Correct — this is the exception. A radicular cyst arises from the rests of Malassez following pulpal necrosis of an erupted tooth. An impacted, unerupted tooth has an intact pulp and cannot generate one.

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Question 2

The adenomatoid odontogenic tumor is characteristically associated with which structure, and from what does it originate?

  1. The follicle of an impacted tooth, arising from odontogenic epithelium — remnants of dental lamina or reduced enamel epithelium
  2. The periapex of a non-vital tooth, arising from the rests of Malassez
  3. The inferior alveolar canal, arising from neural tissue
  4. The maxillary sinus lining, arising from respiratory epithelium
Show answer and explanation

Correct answer: A. The follicle of an impacted tooth, arising from odontogenic epithelium — remnants of dental lamina or reduced enamel epithelium

  • A. Correct. AOT is a developmental benign odontogenic tumor that envelops the follicle of an impacted tooth — most often a maxillary canine in a teenage girl. Histology shows spindle-shaped epithelial cells in rosette-like structures with a fibrous capsule and scattered calcifications.
  • B. Malassez rests give rise to radicular cysts, not AOT.
  • C. Neural origin describes a schwannoma or neurofibroma.
  • D. Respiratory epithelium origin describes sinus pathology, not an odontogenic tumor.

Note: AOT is the “two-thirds tumor”: two-thirds in females, two-thirds in the maxilla, two-thirds associated with an impacted canine, two-thirds in the second decade.

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Question 3

Which feature on the radiograph would most favor odontogenic keratocyst over dentigerous cyst?

  1. Attachment strictly at the cementoenamel junction
  2. Uniform ballooning expansion of both cortices
  3. A radiopaque tooth-like mass within the lumen
  4. Growth along the length of the marrow space with minimal buccolingual expansion
Show answer and explanation

Correct answer: D. Growth along the length of the marrow space with minimal buccolingual expansion

  • A. CEJ attachment is the defining feature of a dentigerous cyst.
  • B. Marked balloon-like expansion is more typical of a dentigerous cyst or ameloblastoma.
  • C. Tooth-like radiopacities within the lumen describe an odontoma.
  • D. Correct. OKCs characteristically propagate anteroposteriorly through cancellous bone with little cortical expansion, which is why they reach a large size before detection.

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