A 78-year-old female was referred from a local clinic to Wonkwang Dental Hospital for a cystic lesion in the left mandibular posterior region. This lesion was incidentally observed on a panoramic radiograph. There were no remarkable clinical findings except tooth mobility (++) of the left mandibular second molar. The past medical history revealed that the patient had experienced some facial trauma four years ago. The facial computed tomography (CT) taken at the medical hospital showed no definite bony fracture line on the facial bone, but there was a cystic lesion on the left mandibular angle that had not been reported by the medical radiologist. This cystic lesion had a unilocular ovoid shape (11.8 mm×5.2 mm) (Fig. 1) and was incidentally, retrospectively observed at our dental hospital after four years by an oral radiologist.

A panoramic radiograph and cone-beam CT (CBCT) were taken at the dental hospital. The panoramic radiograph showed a lobulated lesion with a well-defined, scalloped margin from the left lower second molar to the left mandibular ramus, with slight involvement of the apices of the mandibular second molar. There was no tooth displacement, but the external root resorption of the second molar was remarkable (Fig. 2). The CBCT represented a lobulated margin and the thinning, erosion, and perforation of the lingual cortex. Further, a mild expansion of the lingual cortex was observed. This lesion had changed into a more expanded ovoid shape (26.0 mm×11.3 mm) (Fig. 3). The provisional diagnosis was an ameloblastoma due to the extensive root resorption. Because of the rare occurrence of GOC in the jaw, we did not consider GOC for the differential diagnosis.

The histopathological examination showed multiple cystic compartments. The cyst was lined by several surface eosinophilic cuboidal cells exhibiting apocrine snouting. Microcysts and papillary projections that had formed adjacent to "open" microcysts were also noted. Cilia were not evident (Figs. 4 and 5). The histopathological diagnosis was GOC.

The treatment was composed of the extraction of the lower second molar, cyst enucleation, and peripheral osteotomy. We carried out close follow-up for recurrence.

This report described a very rare case of GOC, which was found in the posterior mandible of an elderly female. The lesion had showed various radiographic features during the past four years. The lesion shape had changed from a small ovoid shape to that of a more expanded cyst. The small lesion had shown unilocularity and a well-defined border, whereas the expanded lesion produced cortical perforation and a lobulated margin. All GOCs larger than 6 cm in diameter showed perforated margins radiologically in a case report by Noffke and Raubenheimer.11 In this case, cortical perforation and erosion were also observed, suggesting its aggressiveness; however, the mild expansion of the lingual cortex represents the benign nature of the lesion. There was no tooth displacement, but extensive external root resorption of the second molar was seen (Fig. 2). Therefore, we suspected ameloblastoma because ameloblastoma commonly presents extensive root resorption of the adjacent tooth; however, the patient's old age (78 years) was a factor responsible for the hesitation in the radiographic diagnosis. Ameloblastoma usually presents in the second half of the fourth decade, whereas the age range of GOC was reported to be 14-85 years (mean age: 49 years) and the majority of patients were older than 40 years.11 In contrast, East Asians with GOCs were nearly a decade younger.3 Another possible lesion was keratocystic odontogenic tumor (KCOT). KCOT is commonly found in the posterior mandible, in patients between 10 and 30 years of age.12 Resorption of the adjacent root is less common. Although radiologically, the GOC lacked specific features, making the distinction from ameloblastoma and KCOT difficult, the radiographic appearance of multiple foci of the cortical perforation in this case was helpful in distinguishing the GOC from ameloblastoma and KCOT.11 Other jaw lesions necessary for a radiographic differential diagnosis with GOC include the central giant cell lesion, lateral periodontal cyst, botryoid odontogenic cyst, simple bone cyst, and central mucoepidermoid tumor depending on the multilocularity.11,13

Numerous histopathological features for the GOC have been described, but the exact microscopic criteria necessary for the diagnosis have not been universally accepted. Furthermore, some of the microscopic features of GOC might be found in dentigerous, botryoid, radicular, and surgical ciliated cysts.14 Kaplan et al2,13 added that a diagnosis of GOC had to be based on the mandatory presence of the following five major features: squamous epithelium, varying thickness, cuboidal eosinophilic (hobnail) cells, mucous (goblet) cells, and intraepithelial glandular or duct-like structures. The histopathology of this cyst consisted of cuboidal epithelial cells with papillary projections extending into the lumen. Occasional very small duct-like structures were seen to be lined by cuboid or polygonal cells. Cilia were not visible on the surface epithelium (Figs. 4 and 5). These histopathological findings were compatible with those of GOC as described by Kaplan et al. The clinical importance of GOC relates to the fact that it has a high recurrence rate2 and an aggressive growth potential15 and that it may be confused microscopically with central mucoepidermoid carcinoma.14 The lesions vary considerably in size and aggressiveness, and the treatment ranges from simple curettage to marginal resection.16 A more aggressive surgical removal rather than simple curettage was suggested, and cases should be followed up carefully.11 Cyst enucleation and peripheral osteotomy for safe removal were performed for this patient, and close follow-ups have been carried out for recurrence.

Considering our case of GOC with characteristic radiographic features, we can conclude that GOC can grow in people in their seventies, changing from a unilocular form to a lobulated lesion in a few years.