Infrequent clinicopathologic features of keratocystic odontogenic tumour: a 29‐year multi‐institutional retrospective review

Aim:  Keratocystic odontogenic tumour (KCOT), formerly known as odontogenic keratocyst, is an interesting and challenging entity. This study addresses the spectrum of clinicopathologic features of KCOT other than those classically described. Materials and methods:  Three hundred forty-seven cases of KCOT from the records of three institutions over a period of 29 years were retrospectively reviewed to analyse their clinical presentation, radiographic features, histopathology and biological behaviour. Results:  Six cases of KCOT with infrequent findings were retrieved, none of which was associated with the nevoid basal cell carcinoma syndrome. Two lesions gave an erroneous radiographic impression of radicular cyst and nasopalatine duct cyst, respectively; the former periapical KCOT showed recurrence. An additional small KCOT adjacent to the initially presenting lesion was incidentally discovered, and both periradicular KCOT recurred twice. In interradicular KCOT, the growth rate of 2.4 mm per year was successfully estimated on radiographs. One paediatric KCOT showed a deceptive feature of eruption cyst and recurrence was not evident, despite of the fenestration. Microscopic rarities included mural cartilaginous metaplasia in a recurrent periradicular KCOT. Conclusions:  This series of cases substantiates the preceding observations that KCOT has a reputation for clinically confusing jaw lesions, often resulting in a potential endodontic or periodontal misdiagnosis. Believed to exhibit occasional recurrent behaviour, missing a diagnosis of KCOT has serious implications for the patient. Both in principle and in practice, the differential diagnosis of KCOT deserves consideration in non-healing radiolucencies associated with the roots of teeth.