Ameloblastoma with adenoid features is characterized by the formation of cribriform or glandular tubular structures in addition to the conventional ameloblastoma; however, many aspects of the clinical and histologic characteristics are unclear. We report a case of ameloblastoma with adenoid features that occurred in the mandible and had multiple recurrences. The patient was a 54-year-old woman who presented with a chief complaint of painless swelling in the left mandibular molar region. On the first visit, a bone expansion was noted in the lingual alveolar region of the left mandibular molar. Panoramic radiograph and computed tomography revealed a unilocular radiolucent finding extending from the left mandibular first molar to the anterior edge of the left mandibular ramus. A biopsy was performed and the diagnosis was ameloblastoma. Therefore, we performed left mandibular tumor resection. Histopathologic findings showed that tissue corresponding to the conventional ameloblastoma had proliferated, and the tumor nests had a duct-like and cribriform structure. However, no whorl/morula-like structure or dentinoid was observed, leading to a diagnosis of ameloblastoma with adenoid features. Thereafter, the tumor recurred twice, and resection surgery was performed, but both cases showed the same histopathologic findings as the initial surgery. Morphologic features are important to distinguish between ameloblastoma with adenoid features and conventional ameloblastoma. In addition, ameloblastoma with adenoid features has a stronger tendency to recur than conventional ameloblastoma, and surgical resection with a sufficient margin of safety and strict postoperative follow-up are necessary.

高悪性度転化（high-grade transformation：HGT）は，腺様囊胞癌（adenoid cystic carcinoma：AdCC）ではまれな現象であり，HGTにより悪性度の高い状態となり，典型的なAdCCと比較して，頸部リンパ節転移や遠隔転移を生じる傾向が高い。患者は69歳女性で，口蓋正中部の腫脹の精査を主訴に受診した。初診時，口蓋正中やや左側寄りに30×15mm大の広基性腫瘤を認めた。生検の結果，口蓋腺より発生した唾液腺悪性腫瘍との診断であったが，確定診断には至らなかった。そのため，全身麻酔下に全切除術を施行した。初診から切除までの間にも腫瘍は著明な増大を示した。切除標本は，定型的なAdCCの部分と，それに接して存在するHGT部分の2つの要素で構成されており，急速に増大した部分は，病理組織学的にHGT-AdCCで占められていた。切除標本にて断端陽性の所見を認めたため，術後放射線照射を行い，局所においては占拠性病変の出現はなかったが，その後の画像評価にて転移性肺腫瘍を認め，同時化学放射線療法を施行するも，死亡の転帰をとった。

The purpose of this study was to compare the accuracy of maxillary repositioning using customized maxillary bone-dental-supported guides with that using an intermediate computer-aided design and computer-aided manufacturing (CAD/CAM) splint. This retrospective cohort study included patients with dentofacial deformities on computed tomography before and 3 months after surgery. Differences between the planned and actual postoperative positions of the maxilla were measured using simulation software for 3 landmarks. Twenty-two patients were treated using customized maxillary bone-dental-supported guides (group A) and 22 patients were treated using intermediate CAD/CAM splints (group B). For all 3 axes, discrepancies for all 3 landmarks tended to be smaller in group A than in group B. In particular, intermediate splints, calculated over the 22 cases and all 3 landmarks, showed significantly larger discrepancies on all 3 axes than the customized maxillary bone-dental-supported guides, calculated over the 22 cases and all 3 landmarks. In conclusion, customized maxillary bone-dental-supported guides appear more effective than intermediate CAD/CAM splints in achieving accurate transfer from 3D simulation to real surgery.