Morphological characteristics of ameloblastoma with a mixed histological structure; [混合组织学结构的成骨细胞瘤的形态学特征]; [Морфологическая характеристика амелобластомы со смешанным гистологическим строением]

Ameloblastoma is an odontogenic tumor with locally destructive growth, capable of relapsing. The relapse occurrence depends on the morphological variant of the tumor structure. Most commonly, the tumor is localized in the lower jaw. Often, the formation grows asymptomatically and is initially detected at an X-ray examination, with a “soap bubble” pattern revealed on the scan. The tumor may have a size from 1 to 16 cm and lead to facial asymmetry, bite change, and dentition displacement. There are plexiform, follicular, acantomatous, basal cell, desmoplastic, monocystic, granular cell and extraosseous variants of ameloblastoma. However, the classification lacks a mixed type of structure. According to various authors, mixed variants of the structure are found in 3.3% to 20% of cases. In our earlier studies, it was shown that the prognosis of the disease largely depends on the histological variant of ameloblastoma. Purpose of the study. To determine the histological characteristics of ameloblastoma with the identification of mixed variants of the structure and to study the relationship with an aggressive clinical course. Material and Methods. The total number of samples studied was 92, and clinical data were collected for them. The identified cases with a mixed histological structure in the amount of 32 were sent for immunohistochemical study with monoclonal rabbit antibodies to the Ki-67 protein. The statistical analysis was carried out considering the following parameters: gender, average age, tumor size and histological structure. Results. In the present study, 92 cases of ameloblastoma with bone involvement were considered, of which 32 had a mixed histological structure, which amounted to 35%. The combinations of the various structures were different. Among the combinations, there were combinations of the follicular variant with acantomatous, plexiform and granular cells. In 65.6% of cases, a mixed histological structure was found in women. The average age at diagnosis was 43.4 years, and the range was from 8 to 74 years. A higher percentage of proliferative activity for the Ki-67 protein was noted in the follicular, plexiform, and acantomatous types, and the maximum value of the marker expression was noted in the basal cell type. In the mixed variant of the structure of ameloblastoma, follicular (78.1%) and plexiform (62.5%) patterns were more common, while desmoplastic pattern was observed only in 6.2% of cases. Of 32 cases with mixed histological ameloblastoma, 28 had a relapse. The estimated risk of relapse for the follicular pattern was 86.4%. Conclusion. Thus, a mixed variant of ameloblastoma with a follicular component can be considered one of the aggressive tumor types. Some authors have recommended a wide resection of the jaw in cases of an aggressive ameloblastoma type detection, thus, a more extensive surgical intervention can be recommended if a follicular component is detected in the composition of a mixed ameloblastoma. © Team of authors, 2022