Cystic Plexiform Ameloblastoma – an important diagnostic challenge

Background Ameloblastoma is a benign, locally aggressive neoplasm of the jaws and accurate diagnosis is important to provide timely treatment and reduce the risk of recurrence and local destruction. Ameloblastoma may show various histologic patterns, including a cystic plexiform pattern that lacks the typical ameloblast-like features and causes difficulties in the interpretation of incisional biopsies. Objectives This is a retrospective study to identify and characterize cases of ameloblastoma that presented only a cystic plexiform epithelial proliferation lacking the pathognomonic features of ameloblastoma on incisional biopsy. Methods We reviewed cases of ameloblastoma in our diagnostic biopsy service from 2004 to 2023 inclusive. Cases with a microscopic description that included cystic plexiform epithelial proliferation were retrieved for review of histopathologic features and associated clinical and radiographic information. Results We identified a rare subset of ameloblastoma (3.7%, 7 of 188 ameloblastoma cases) that presented exclusively the cystic plexiform pattern, with absent or inconspicuous ameloblast-like features (CP-AM). The histologic appearance was characteristically uniform throughout the incisional biopsy and differed from the plexiform subtype of conventional ameloblastoma and plexiform unicystic ameloblastoma. Careful clinical and radiographic correlation with histologic findings was essential for a definitive diagnosis to guide treatment. Immunohistochemical staining for the BRAF p.V600E mutation was performed retrospectively and shown to be a useful adjunct for diagnosis that should be considered for future cases of CP-AM. Conclusion Our study highlighted an uncommon and challenging histologic pattern of ameloblastoma. A coordinated approach using clinical, radiographic, histologic, and molecular studies are needed for a timely and accurate diagnosis.