Dentigerous cyst is considered one of the representative cystic lesions, which accounts for approximately 15%-30% of the odontogenic cysts. Although its recurrence rate is low, a small proportion of dentigerous cysts converted into ameloblastomas, squamous cell carcinomas, and mucoepidermoid carcinomas. Here we present an uncommon case characterized by histopathological transformation from a dentigerous cyst to an ameloblastoma, and further investigate the factors contributing to its conversion.

Rushton bodies are known to be the aberrant keratinization and calcification in the epithelium of odontogenic cyst, which are similar to the features of calcifying odontogenic cyst and pilomatricoma. However, the pathogenetic mechanism of keratinization and calcification of Rushton bodies has not been clearly elucidated. Here, a case of Rushton bodies found in dentigerous cyst was examined by immunohistochemical method using antisera of PCNA, pAKT, HIF, PIM1, and PARP. The globular keratinization in lamellate fashion showed weak birefringency under polarizing microscope, and the Rushton bodies frequently underwent the dystrophic calcification. The polygonal keratinocytes of Rushton bodies were strongly positive for HIF and PARP, and the cyst epithelium was diffusely positive for pAKT and PIM1. Particularly, the cyst epithelium was hyperplastic and focally invaginated into cyst wall with positive reaction of PCNA. These findings may indicate the active response of odontogenic epithelium against the apoptotic stress of the cyst, producing the globular keratinization and irregular calcification in the polygonal keratinocytes. Therefore, it is presumed that the lamellate keratinization and dystrophic calcification of Rushton bodies are aberrant products of retrograding keratinocytes slowly undergoing apoptotic progresses similar to the phenomena of the ghost cells in calcifying odontogenic cyst and pilomatricoma, and also may have a potential for oncogenic proliferation.

A dentigerous cyst (DC) and an odontogenc fibroma (OF) in the jaws are well known entities, which have been reviewed extensively. However, the presence of OF components in the wall of dentigerous cyst is a very rare event. A case of DC in the left mandible displaying the foci of an OF-like lesion is described. It is unclear whether the two lesions were just coincidental or were actually related to each other. However, OF-like proliferation may be arised from secondary epithelial and mesenchymal interactions in a pre-existing DC, although the initiating stimulus could not be identified.

A rare case of primary intraosseous squamous cell carcinoma(PISCC) arising from lining epithelium of a dentigerous cyst is described. The case occurred at the left mandibular 3rd molar region in a 56-year-old Japanese woman. Clinical observation revealed cyst formation with an impacted 3rd molar, a common finding in dentigerous cyst, in the left mandible. Histopathologically, the lining epithelium of the cyst demonstrated transition from epithelial dysplasia to invasive squamous cell carcinoma(SCC). This case was diagnosed as PISCC arising from lining epithelium of a dentigerous cyst.

The dentigerous cyst(DC) and giant cell granuloma(GCG) in the jaws are well known entities that have been extensively reviewed. However, a search of the literature failed to reveal simulataneous occurrence of these two lesions. We describe a case of DC displaying foci of GCG-like lesion of a 11-year-old Korean girl. The lesion exhibited the characteristic histologic features of DC, which included a lining epithelium with underlying fibromyxoid stroma. The most intersting aspect of this lesion, however, was the presence of a prominant histologic component that resembled GCG. The most probable diagnosis was GCG-like lesion in association with a DC.