Post-traumatic parotid-cutaneous fistula

A 30-year-old male was referred for left parotid sialography with a complaint of watery discharge from a lacerated wound in the left zygomaticomaxillary region. The patient had a history of assault by a sharp object on the left side of the face five days ago. The patient specifically complained of exaggerated secretion of fluid after meals and citrus fruits, suggesting the secretion to be of salivary origin.

Sialography in oblique projection (Figure 1) showed an abnormal, linear contrast collection with irregular outlines in the left zygomaticomaxillary region. The collection was longitudinally oriented along the posterior wall of the maxilla. Normal parotid duct and its branches were seen, suggesting extraductal glandular injury.

Ultrasonography (Figures 2a, 2b and 2c) demonstrated a thick, linear, anechoic collection with irregular margins measuring approximately 44x7 mm traversing the left parotid gland, extending from the superficial subcutaneous plane to the deep muscular plane involving masseter muscle. The collection showed conglomerated areas of echogenic focus with dirty shadowing representing air bubbles possibly introduced during duct opacification.

Parotid gland injuries usually occur following penetrating trauma of the parotid region. They are important to evaluate as they are associated with injuries to adjacent facial structures such as the facial and auriculotemporal nerves, underlying bones, and the ipsilateral ear. Another cause of parotid gland injury is blunt trauma [1]. Often, the diagnosis of parotid gland injury can be delayed due to its low incidence, leading to complications like facial scarring, sialocele formation, sialocutaneous fistula formation, and other long-term complications such as infection and abscess formation [2].

Rarely, injury to the main parotid duct may result in the formation of a persistent subcutaneous or external salivary fistula. Other aetiologies include congenital causes, chronic inflammatory conditions of the face, iatrogenic trauma, rupture of a parotid abscess, and as a complication of superficial parotidectomy [3]. Clinical features are pain, swelling over the parotid region with an expanding mass due to salivary fluid extravasation in adjacent soft tissues, and over the parotid gland (sialocele formation). Injury to the parotid duct is difficult to diagnose, and once diagnosed, they are difficult to heal because of the continuous flow of saliva. Complete cure depends upon early diagnosis and appropriate intervention [4].

Sialography is the radiographic visualisation of the salivary glands by introducing a water-soluble contrast agent into the orifices of the salivary ducts and their radiographic visualisation. The parotid gland is the most easily evaluated gland by this means, as well as with ultrasound, since the gland is situated superficially [5].

There is no controversy that acute parotid fistulas should be repaired; however, it is not clear whether chronic fistulas should be treated conservatively or surgically [6]. Glandular fistulas tend to heal spontaneously with conservative treatment compared to ductal fistulas, which require surgical intervention [4]. Several surgical methods can be employed when indicated, including pressure draining and antisialagogues, total parotidectomy, tympanic neurectomy, transposition of the parotid duct, radiation, botulinum therapy, and the use of sclerosing agents and fibrin glue [7]. A case report described by Virendra et al. demonstrated the management of chronic parotid fistula with sodium tetradecyl sulphate in three cases [4].

Take Home Message

Parotid-cutaneous fistulas are rare. A typical history of watery discharge from a parotid wound exaggerated after meals and water should lead to strong suspicion of fistula formation and should be urgently evaluated. Sialography is the mainstay for diagnosing ductal injury, with ultrasonography as an adjunct. Radiologists must be aware of findings, as early diagnosis in acute settings is associated with a favourable outcome.