A Case of Sinonasal Actinomycosis Associated With an Odontogenic Cyst of Ectopic Dental Origin.

Actinomycosis rarely occurs in the sinonasal region. Here, we report a case of sinonasal actinomycosis associated with an odontogenic cyst of ectopic dental origin. A 28-year-old female patient was referred to our department with a complaint of left buccal pain. Nasal endoscopy revealed a polypoid mass with purulent discharge in the left nasal cavity. Contrast-enhanced computed tomography revealed a mass lesion occupying the left maxillary sinus and nasal cavity, along with an ectopic tooth adjacent to the lesion. T2-weighted magnetic resonance imaging showed a mass lesion with a low-intensity signal. We performed endoscopic sinus surgery and resected the mass lesion and the ectopic tooth. Histopathological examination revealed the presence of Actinomyces species. No tissue-invasive Actinomyces were detected in the resected tissues. At the two-year follow-up, no recurrence of actinomycosis was observed despite the absence of antibiotic therapy. To our knowledge, there have been no reports of actinomycosis associated with odontogenic cysts of ectopic dental origin. Although surgery followed by antimicrobial therapy is generally recommended for actinomycosis, sinus surgery alone may have a sufficient bactericidal effect against Actinomyces by exposing the lesion to the open air. The clinical course of this case supports the notion that postoperative antibiotic therapy is not mandatory for patients with sinonasal actinomycosis.