A case of external dental fistula difficult to diagnose

External dental fistula is associated with the formation of a sinus tract as the route of excretion of chronic purulent inflammatory material, that pierces the jawbone and creates a fistula in the skin of the face or neck, often away from the teeth. The patient was a 68-year-old woman, who presented to our department with mass in the left lower jaw. We recognized a 30 mm mass in the left lower jaw. Based on the findings of ultrasonography and fine-needle aspiration biopsy, the mass was suspected as an inflammatory tumor, and the patient was followed up. However, the amount of granulation increased and the surrounding skin was depressed. The diagnosis of external dental fistula was suspected from the findings of pantomography and magnetic resonance imaging, and fistula extraction, tooth extraction and curettage was performed as long as 2 years and 2 months after the initial medical examination. The postoperative course was favorable and there has been no recurrence. Early diagnosis and appropriate treatment are of importance in patients with an external dental fistula.