Oral cutaneous fistulas (OCF) are infrequent conditions in which there is a pathologic communication between the oral cavity and the skin. In medical and dental literature, the terms fistulas and sinus tracts are often used to describe the same condition. Chronic dental infections, trauma, dental implant complications, salivary gland lesions, and neoplasms are the most common causes of oral cutaneous fistulas. Affected patients usually seek help from dermatologists or surgeons rather than from dentists. As the clinical cutaneous and oral manifestations are generally scarce and often nonspecific, the diagnosis of OCF requires a high degree of suspicion. Prognosis is excellent when treatment initiates promptly, particularly if there was a dental infection. Otherwise, OCF associated with malignancies can lead to complications and may be life-threatening.

Odontogenic cutaneous fistulas are responsible for most cases of oral cutaneous fistulas reported in the literature. They arise as sequelae to bacterial invasion of the dental pulp resulting in apical periodontitis caused by a carious lesion, trauma or other causes. This condition occurs when the pulp becomes necrotic, and the infection spreads into the periradicular area. Subsequently, infection leads to bone resorption and dissects along the path of least resistance from the root apex to finally erupts through the skin.[1]

Cutaneous fistulas and sinuses in the maxillofacial region secondary to osteomyelitis rarely appear in clinical practice.[2] It is more likely to develop in patients with uncontrolled diabetes, in those with osteoradionecrosis who have undergone jaw irradiation and in those with metabolic bone diseases such as osteitis deformans “Paget disease” or osteopetrosis.

An additional cause of OCF is medication-related osteonecrosis of the jaw.[3] Biphosphonates and other anti-resorptive medications, as well as IV antiangiogenic therapies, have been reported to induce osteonecrosis of the jaw.[3] These medications have roles in the treatment of diseases such as lytic bone metastases, malignant hypercalcemia, multiple myeloma, and osteoporosis.

Traumatic fistulas may be the result of injury or surgical repair. In a study by Dawson et al., which explored factors associated with the formation of orocutaneous fistula following head and neck reconstructive surgery, they found that patients who had previous chemoradiotherapy had a significantly higher probability of developing a fistula than those who had not (p = 0.008).[4]

Complications of dental implants usually result from a combination of infection and host of inflammatory responses or a lack thereof. The literature reports a case report of oral cutaneous fistula associated with an osseointegrated dentoalveolar implant which occurred after three months.[5]

There are also reports of fistulas mimicking a brachial cyst caused by an ectopic salivary gland. In one case a 24-year-old man presented with intermittent clear drainage on both sides of the middle neck. The lesion underwent surgical excision, and the pathological examination revealed heterotopic salivary gland tissue.[6]

Periapical actinomycosis is among the rarest forms of actinomycosis in the maxillofacial region. Although rare, it is one of the most common infections that result in an orocutaneous fistula.[7] More rarely OCF is secondary to a neoplasm.  Squamous cell carcinoma is the most common oral cavity neoplasm, and if the fistula occurs, it has a poor prognosis because lymphatic drainage has most likely taken place by the time of diagnosis.

In the largest study of odontogenic cutaneous fistulas reported by Guevara-Gutiérrez et al., which examined 75 cases during an eleven-year timeframe, the mean age was 45 years. The most affected age group was 51 years and over (28%). Female to male ratio was 1.14 to 1.[1] Many factors were suspected of inducing dental infections and facilitating the formation of sinus tracts such as poor oral hygiene, xerostomia, and unsatisfactory surgical procedures. In the study of Lee et al., in two out of 33 patients, fistulas were related to actinomycosis. In one patient, the fistula was presumed to have been caused by osteoradionecrosis after radiation therapy for mandible cancer.[8]

The possibility of a neoplastic cause may require a histopathological examination of oral cutaneous fistula. A biopsy is also useful for the diagnosis of actinomycosis which has characteristic pseudohyphae appearing as clublike projections that stretch out from a central basophilic staining core [7].