The correct answer is cutaneous sinus tract of odontogenic origin (choice “d”).
These uncommon lesions are known by several names, including odontogenic fistula. Invariably, they are misdiagnosed as an “infection” and treated with antibiotics, which only calm these lesions until they inevitably return to their pretreatment appearance. Though bacteria (mostly Peptostreptococcus—the anaerobe predominating in the mouth) are involved, this is not an infection as it usually manifests.
The underlying process of this condition is caused by a periapical abscess: as it grows in size and pressure, it enters into the mouth or fistulizes out through the buccal tissue, continuing until it penetrates the skin and begins to release its pustular contents. Eighty percent manifest on the submental or chin area, while 20% tunnel inwards toward the oral cavity.
They initially manifest as papules with a 2-to-3-mm surface that soon drain pus from a central sinus. As this continues, the epithelium responds to the chronic inflammation by forming a mass of pseudoepitheliomatous hyperplasia. Biopsy would reveal that the mass also shows signs of chronic inflammation. Ordinary bacterial culture often shows nothing because the predominant organism is an anaerobe. At most, one might see a polymicrobial result.
For affected patients, a dentist can be considered for radiography of the area to confirm the location of the periapical abscess. Then the tooth is usually extracted, resulting in a cure. No further treatment of the sinus tract is necessary because it will essentially disappear over time. The tract does not require excision because it is lined with reactive granulation tissue and not epithelium (as is the case for many other fistular processes).
If the dental exam and radiograph fail to show the expected result, the other diagnoses—thyroglossal duct cyst, branchial cleft cyst, squamous cell carcinoma—would have to be considered.