Interpretation of Odontogenic and Non-Odontogenic Cysts and Tumors
Cysts
Classify odontogenic cysts: radicular (periapical), dentigerous, odontogenic keratocyst (OKC), lateral periodontal, and calcifying odontogenic cyst. Non-odontogenic: nasopalatine duct cyst, nasolabial cyst. Know typical location, border characteristics (well-defined, corticated), and effect on adjacent teeth (displacement vs resorption). OKC tends to grow along the bone with minimal expansion and has a high recurrence rate; dentigerous cyst surrounds the crown of an unerupted tooth.
Tumors
Odontogenic tumors: ameloblastoma (multilocular soap-bubble, mandibular angle), odontoma (compound vs complex), cementoblastoma (attached to root), and odontogenic myxoma. Non-odontogenic: ossifying fibroma, fibrous dysplasia (ground-glass), and malignancies (e.g., squamous cell carcinoma, osteosarcoma). Know benign vs malignant features: well-defined vs ill-defined borders, cortical destruction, periosteal reaction, and rapid growth.
Approach
Use a systematic method: location, size, borders, internal structure, effect on adjacent structures, and associated teeth. Correlate with clinical history and, when needed, biopsy. Recognize that imaging alone rarely gives a definitive diagnosis; the goal is a differential.
Traps
Questions test classic appearances (ameloblastoma vs OKC vs dentigerous cyst) and whether a lesion is odontogenic vs non-odontogenic. Watch for confusion between fibrous dysplasia (ground-glass, blends with bone) and ossifying fibroma (well-defined).
Rule of thumb
Well-defined + corticated + associated with a tooth = cyst or benign tumor; ill-defined + cortical destruction + periosteal reaction = malignancy.