A Rare Case of Sinonasal Actinomycosis.

Actinomycosis is an infection caused by Actinomyces species--filamentous, gram-positive, anaerobic bacteria commonly found in the oral cavity. Although cervicofacial involvement is more frequently encountered, actinomycosis may involve the sinonasal tract and present with imaging findings that resemble neoplastic lesions. We report a 79-year-old woman who presented with a six-month history of left-sided purulent nasal discharge and nasal obstruction. Computed tomography (CT) and magnetic resonance imaging (MRI) revealed an expansile soft-tissue lesion with bone destruction in the left maxillary sinus, suggestive of odontogenic sinusitis. We performed endoscopic sinus surgery (ESS) combined with endoscopic modified medial maxillectomy (EMMM), which revealed marked granulation tissue and caseous purulent material without evidence of malignancy. Histopathological examination confirmed colonies consistent with Actinomyces. The patient received cefazolin (1 g/day) for two days postoperatively as standard perioperative antibiotic prophylaxis only, resulting in complete recovery without recurrence at six months. This case highlights the importance of considering Actinomyces infection in patients with unilateral maxillary sinus disease following dental procedures. Advances in endoscopic techniques, such as EMMM, allow complete debridement with minimal invasiveness and may reduce the need for prolonged therapeutic antibiotic therapy.