Primary Intraosseous Squamous Cell Carcinoma Arising from a Dentigerous Cyst of the Maxillary Wisdom Tooth

The World Health Organization defines primary intraosseous squamous cell carcinoma (PIOSCC) as a squamous cell carcinoma (SCC) arising primarily within the jaws and having no connection with the oral mucosa. Here, we report a case of PIOSCC in which it was difficult to differentiate the condition from pericoronitis of an impacted maxillary wisdom tooth. The patient was a 27-year-old pregnant woman with a pain in the right maxillary wisdom tooth. The pain was diagnosed as pericoronitis of the right maxillary wisdom tooth, and the tooth was extracted under local anesthesia. During extraction, soft tissue was observed in the coronal part of the tooth, and it was diagnosed as SCC arising in a dentigerous cyst. Because the tumor may still be present, surgical resection was performed under general anesthesia. There has been no recurrence or metastasis at the 1-year follow-up. This case was histopathologically considered from being a benign odontogenic tumor to a malignant tumor. However, it revealed an extensive aberrant type and invasion equivalent to SCC. Thus, the histopathological diagnosis was PIOSCC arising from a dentigerous cyst. Although advanced cases of PIOSCC have been published, diagnosis of PIOSCC in the early stages is rare. In this case, we diagnosed pericoronitis of an impacted maxillary wisdom tooth and extracted the tooth. Therefore, we discovered it accidentally. In the early stages, diagnosis can be difficult both clinically and histopathologically.