The variability and complexity of ameloblastoma: Carcinoma ex ameloblastoma or primary ameloblastic carcinoma

Ameloblastoma is characterized by slow-growing, local invasiveness and high incidence of local recurrence. It usually presents with a benign histological appearance. However, ameloblastoma occasionally demonstrates a clinical course that is characteristic of malignant transformation. Here, we present a case of ameloblastoma with an aggressive clinical course, including multiple recurrences, a short disease-free interval, pulmonary metastasis and extensive skull-base infiltration. With a careful re-evaluation of the histology and cytology of the specimens of primary and recurrent ameloblastoma in 2006 and 2007, malignant transformation was observed and carcinoma ex ameloblastoma was ultimately diagnosed.