Ectopic Maxillary Third Molar with a Large Odontogenic Keratocyst in Roof of Maxillary Sinus - A Case Report.

Odontogenic keratocysts (OKCs) are aggressive odontogenic cysts with a high recurrence potential. Maxillary sinus involvement is exceedingly rare, and association with an ectopic third molar located near the sinus roof is rarer still. A 26-year-old female presented with vague midfacial fullness and an unerupted maxillary third molar. Panoramic radiography and CBCT revealed an ectopic 18 near the superior sinus wall enveloped by a well-defined radiolucent lesion of higher soft-tissue density than typical dentigerous cysts. The lesion showed scalloped borders, cortical thinning, and anteroposterior spread, suggestive of OKC. Complete enucleation with peripheral ostectomy via a Caldwell-Luc antrostomy was performed, along with removal of the ectopic molar. Healing was uneventful. Histopathology confirmed OKC. This case broadens the limited documentation of OKC in the sinus roof region and highlights the need for long-term follow-up given its recurrence profile.