Introduction

Adenomatoid odontogenic tumor (AOT) is a benign slow growing epithelial odontogenic neoplasm representing 2% to 7% of all odontogenic tumors
(1, 2). Ethnic differences have been reported on the prevalence of AOT, which show the lowest percentage in Europe and the highest in Africa (1, 3). It appears that dental lamina in the gubernacular cord of the developing permanent incisor, canine or premolar is the embryonic source of the majority of AOTs (4). It shows a predilection in the anterior portions of the maxilla and patients under 30 years (1, 3). The majority of cases demonstrate a well-circumscribed, unilocular radiolucency containing the crown of an unerupted tooth (follicular type) which mimic dentigerous cysts. However, an AOT encircles the crown as well as the root while dentigerous cysts envelop only the crown and is attached to the cemento-enamel junction (3).  The extrafollicular variant is a well-delineated, unilocular radiolucency that is located between the roots of erupted teeth. The rare extraosseous type is also reported. Albeit, AOT may be entirely radiolucent or it could contain fine (snowflake) calcifications  (1, 2, 4). It appears that the cut surface of the lesion is predominantly solid or may reveal some degrees of cystic change (2). In some cases, the solid portion may be present only as masses in the wall of a cyst (5, 6). Some studies have reported cases of purely cystic AOT (3, 5, 6). The aim of this case report is to present a rare case of extrafollicular cystic AOT affecting a 28 -year-old male.

Case report

 A 28-year-old man was referred to the Department of Oral and Maxillofacial Pathology, Shahid Beheshti University of Medical Sciences, Tehran, Iran, for evaluation of the painless swelling of the right maxillary vestibule in the area of 13, 14  for eight months.  The patient had no history of previous trauma or medical problems. Intraoral examination revealed buccal cortical expansion in the area of right maxillary canine and the first premolar. Additionally, the overlying mucosa was intact and pink in color and the panoramic radiograph indicated a well-defined corticated radiolucent lesion between roots of 13 & 14, measuring 2×2 cm. Displacement of the adjacent vital teeth was also evident (Fig. 1). There was no cervical lymphadenopathy and blood investigation was within normal limits. Aspiration of the lesion showed a serous-like fluid. Due to radiographic features, fluid aspiration and vitality tests, a developmental cystic lesion such as odontogenic keratocyst (OKC) or lateral periodontal cyst (LPC) were considered in the differential diagnosis. The lesion was completely excised under local anesthesia. The gross was a cystic creamy elastic tissue and the maximum wall thickness was 2mm. The histopathologic sections demonstrated a cystic lesion lined with thin, non-keratinized flattened epithelium with clear cytoplasm (Fig. 2). Along with some area of the cystic wall, there was a proliferation of clear and spindle cells admixed with dentinoid material, cementum-like and dystrophic calcification (Fig. 3). A distinctive diagnosis based on these microscopic features and the radiographic image was impossible; thereby, the serial sections of the paraffin block were carried out. Interestingly, some epithelial islands composed of spindle cells were found that formed whorled masses of cells and duct-like structures in the fibrous wall of the cyst within deep sections. Inductive change of the connective tissue around the islands was evident (Fig. 4). According to these findings, the diagnosis of an extrafollicular cystic AOT was performed. Consequently, clinical follow-up was done after conservative surgery and the patient was free of tumor for 1 year postoperatively.

Figure1. The periapical radiograph revealed a well-defined corticated unilocular radiolucent
lesion with root divergence of 13, 14

Figure2. A) Microscopic sections show a cystic lesion lined by thin non-keratinized flattened epithelium (black arrow) (hematoxylin-eosin stain, original magnification×40). B) Thin cystic lining with clear cytoplasm (×400)

Figure3. Nests and sheets of clear cells (black arrow) admixed with large masses of
dentinoid material (red arrow) (×100).

Figure4. A) Fibrous wall of the cyst shows spindle cells that formed whorled masses of cells and duct-like structures (black arrow). Dentinoid (red arrow) and cementum-like materials are also seen (×100).
B) island of AOT, dentinoid (black arrow) and cementum-like material (red arrow) (×400).