The Management of Salivary Fistulas

Abstract

Postoperative salivary fistula is an especially undesirable complication because it can be difficult to address, may delay postoperative radiation, and always delays enteral nutrition. Patients who are malnourished, have already undergone radiotherapy, or are hypothyroid are at higher risk of developing this problem. Conservative measures work in most patients, but a significant percentage of patients require intervention beyond pressure dressings and tincture of time. Medications, hyperbaric oxygen therapy, and surgical intervention may be required when fistulas do not heal in a timely manner. Decisions about the approach and timing of more aggressive interventions are part of the art of medicine since definitive scientific protocols are lacking.

A unique challenge for the head and neck surgical oncologist is the management of postoperative salivary leak. Risk of salivary leak accompanies all ablative procedures wherein the mucosal or capsular salivary barrier is breached, including total laryngectomy, resection of major oral cavity, oropharyngeal and hypopharyngeal cancers, and subtotal parotidectomy. Incidence of salivary leak has been estimated at 3% to 65% in patients undergoing major head and neck procedures, with higher risks associated with procedures involving the larynx or pharynx. ^{1 2 3} The introduction of saliva to the previously sterile soft tissues of the neck results in exposure of soft tissues not only to the microbes contained within saliva but also to its enzymes with resulting tissue inflammation, tissue necrosis, and infection. Salivary leaks have been associated with prolonged hospital stays, increased rates of postoperative infection and free flap failure, delays in adjuvant treatment and oral feeding, and increased treatment costs. ^{1 4} In rare circumstances, the leakage of salivary enzymes can result in devastating complications such as carotid blowout and mortality. As such, it is imperative there be early recognition of salivary leaks and timely initiation of treatment to reduce the risk of morbidity.

Preoperative identification of at-risk patients allows for surgical optimization, proper surgical planning, and patient counseling. Hypothyroidism, severe protein malnutrition, anemia, active tobacco use, and poorly controlled diabetes are significantly associated with poor wound healing and increased risk of salivary leak in the postoperative setting. ^{5 6} Thyroid hormone supplementation, initiation of parenteral feeding, tobacco cessation, and endocrine consultation for glycemic control prior to surgery may help minimize the risk of postoperative salivary leak and increase wound healing overall. A prior history of radiation therapy has also been linked to an increased rate of salivary leak ¹ and thus a higher index of suspicion should be maintained in the postoperative management for such patients.

Salivary leaks often clinically manifest as face/neck swelling, erythema, and increased tenderness. When drains are present, frank saliva may be observed in the drain, and salivary leak can be confirmed with testing of the fluid for amylase in cases of clinical ambiguity. The source of the leak may be identified by thorough visual inspection of the surgical wound or contrasted swallow study depending on the surgical site. Upon confirmation of salivary leak and localization, management may consist of conservative and/or surgical treatment. A review of the surgical and nonsurgical management for salivary leaks is presented in what follows.

Nonsurgical Management

Sialoceles and Salivary Fistulas

Sialoceles and salivary fistulas most commonly occur as iatrogenic complications of surgery, with the remaining occurring primarily from trauma. The presentation of a sialocele is typified by a painless, often ballotable swelling over the parotid region 7 to 14 days after surgery with an estimated incidence of 2% to 6%. ⁷ There will be clear fluid draining through a skin defect in the case of transformation to a salivary fistula. These complications can become painful if infected. The diagnosis is primarily clinical, though adjunctive diagnostic testing by assessment of amylase level may be useful. The presence of elevated salivary amylase (often over 10,000 U/L) in the collected fluid is confirmatory as is a history of increased swelling or drainage with eating. Imaging studies are typically not necessary; however, CT, ultrasound, and sialography can all be useful modalities.

In the case of a parotid sialocele, conservative management is recommended as first-line therapy. This includes the use of pressure dressings, aspiration, seroma catheters, suction drains, and anticholinergic medications. More aggressive nonsurgical management consists of injecting botulinum toxin and radiation therapy to atrophy the salivary gland in recalcitrant situations. ⁸

Aspiration of the fluid collection followed by the application of a compression dressing is easily employed and may be repeated multiple times. Most authors report re-accumulation of the sialocele following aspiration; however, interestingly, Witt found that there was no difference in the resolution rates of sialoceles treated with observation versus needle aspiration. ⁹ Furthermore, all sialoceles in their study resolved within 1 month. In cases where fluid continues to collect despite pressure wrap placement and several rounds of aspiration, he recommends consideration of indwelling seroma catheter or a larger suction drain.

Anticholinergic medications, which inhibit the parasympathetic secretomotor activity of the parotid, can be employed for their antisialagogue properties. Many different anticholinergics have been used for this purpose, including propantheline bromide, glycopyrrolate, atropine, and scopolamine. Their use is often limited by the systemic anticholinergic effects including xerostomia, constipation, urinary retention, and tachycardia. Botulinum toxin is a neurotoxin that prevents the presynaptic release of acetylcholine and thus inhibits the secretion of saliva. A recent meta-analysis of the use of botulinum toxin A for the management of sialoceles found success rates between 70% and 100%. ¹⁰ Doses ranged from 10 to 200 units, with the majority of patients requiring a single dose administered percutaneously to the residual parotid parenchyma.

Radiation remains a less utilized treatment option for salivary fistulas refractory to maximal medical therapy. ¹¹ This is a less desirable option given the sequelae of radiation. However, for refractory sialoceles or salivary fistulas in patients requiring radiation therapy for oncologic reasons, use of this modality may be very practical.

Pharyngocutaneous Fistulas

Pharyngocutaneous fistula is a problematic complication of head and neck surgery, which can be complex and potentially life threatening. Fistulas occur in up to 25% of cases involving pharyngeal and laryngeal defects, with the highest rates occurring in previously irradiated patients and those with hypothyroidism and/or malnutrition. Conservative, nonsurgical management remains a mainstay in treatment with success rates as high as 65%, though this drops to 30% to 40% in those patients who had previously undergone radiation. ^{12 13 14 15}

There is controversy regarding the role and timing of operative intervention in these instances, but many authors have found that conservative management with debridement and wound care is often successful and avoids the need for additional surgery. Hyman et al describe their approach for management of salivary fistulas in which bedside debridement, aggressive wound care, and intraoral/cervical packing are performed in addition to maintaining a nil per os status and initiation of antibiotics. In their retrospective study of 637 patients who underwent microvascular reconstruction, 81% of those with a fistula occurring within 30 days of surgery were successfully managed with conservative measures and did not need operative intervention. ¹⁶

The combination of pressure dressings and either passive (e.g., Penrose) or active (e.g., negative pressure) drains is frequently utilized as the drains evacuate and divert the saliva, while the pressure wrap helps prevent fluid extravasation from the gland. Bastian and Park have demonstrated noninferior outcomes of managing salivary fistulas with drain placement compared with surgical diversion of the fistula fluid. ¹⁷ The use of negative pressure wound therapy offers some advantages compared with more traditional dressings including the accelerated development of granulation tissue and wound closure as well as the less frequent dressing changes required. The success of these negative pressure dressings, however, relies on establishment of a hermetic seal, which may be complicated by proximity to a laryngectomy stoma and/or the presence of copious secretions or saliva. ¹⁸

Medical therapies in the management of pharyngocutaneous fistulas have more limited evidence. Some surgeons have advocated for the use of targeted botulinum toxin injections into the major salivary glands to induce a temporary chemodenervation. ¹⁹ Others have articulated in case reports the use of octreotide (a synthetic analog of somatostatin) in the setting of fistula management. ^{20 21 22} The mechanism of this has yet to be fully elucidated, though there is emerging evidence that octreotide may induce changes in the salivary proteome that may be more favorable for wound healing.

Surgical Management

There is general consensus that surgical management should be considered when conservative measures fail, the fistula is large, the fistula is in a high-risk site, when there is exposed hardware, or when local tissues have poor wound-healing potential. The nuances of these scenarios are far less clear, unfortunately.

The time point at which conservative therapy is deemed a failure is widely variable, with most authors arguing for failure after 4 to 6 weeks, ^{4 16} while others advocating for a lengthier trial of conservative therapy up to 6 months prior to consideration of surgery. ²³ Late fistulas, which develop more than 30 days after surgery, have been shown to have a lower success rate of healing via conservative measures, so most authors advocate for early surgical intervention in this context. ^{1 3} In a study by Hyman et al, 50% of late fistulas were successfully managed with conservative measures compared with 81% of early fistulas. ¹⁶ Fistula size warranting surgical correction has been rather controversial with some studies promoting consideration of surgery when fistula size exceeds 5 × 5 mm ⁴ and others recommending a minimum threshold of 2 cm in area. ²⁴ Fistula site, including proximity to the tracheal stoma and the great vessels, is another important consideration that may warrant surgical intervention sooner rather than later to minimize risk of aspiration and carotid blowout. Finally, tissue characteristics, including previously irradiated tissues and chronically infected tissues, also prompt consideration of early surgical intervention due to the low likelihood of success with conservative measures in these settings. In the absence of strict criteria for when surgical management ought to be initiated, the decision to proceed with surgery ultimately lies at the discretion of the surgeon in conjunction with patient preferences. In every case, one should optimize as many factors as possible (e.g., quitting tobacco, lowering blood sugar, achieving a euthyroid state, improving nutrition) before undertaking yet another surgical procedure.

The general principle for surgical management involves the restoration of the salivary epithelial barrier with well-vascularized tissue and a tension-free closure. Surgical intervention may range from simple debridement with local tissue arrangement and primary closure to reconstruction with local or regional flaps or free tissue transfer. Selection will depend on local tissue quality, fistula size (taking into account the extent of required local tissue debridement), extent of the prior surgical field, and the quality of vessels available for microvascular anastomosis. Options for flaps include the pectoralis major myocutaneous flap, the sternocleidomastoid flap, the supraclavicular artery island flap, the submental island flap, and the radial forearm and anterolateral thigh free flaps.

Pedicled Flaps

Of the pedicled flaps, the pectoralis major flap is often utilized in this setting. First described in 1980 by Theogaraj et al, ⁶ the strengths of this flap include ease of harvest, proximity to the neck while being far away from a salivary leak or prior radiation, reliability of the pedicle, and tissue bulk. ²⁵ It may be raised as a muscle flap to reinforce the neopharynx suture line and protect the great vessels or as a musculocutaneous flap to reconstruct a pharyngeal or cutaneous defect. Criticisms of the pectoralis flap include the excessive thickness of the flap due to variable adiposity of the subcutaneous layer, which may impact swallowing, the arc of rotation required particularly with reconstruction of cutaneous defects, and poor cosmesis of the donor site. ²⁶ Nevertheless, it remains a workhorse flap for the surgical management of salivary leaks and is an important option in resource-limited settings or patients who are not candidates for free tissue transfer.

The sternocleidomastoid flap, in contrast, is less widely utilized but represents an adjunctive technique that may be useful during either the initial surgery or in a takeback situation to protect the great vessels or reinforce a neopharynx suture line. Fleming et al describe a technique wherein the sternal heads of the sternocleidomastoid muscle may be freed from the sternum and rotated medially across the great vessels to be secured to the prevertebral fascia. ² This technique is limited in cases where the sternocleidomastoid needs to be resected oncologically in a radical neck dissection or if the patient anatomy results in excessive compression of the great vessels or a free flap pedicle. In their series, Fleming et al described a reduction in the need for pectoralis flap for coverage of the great vessels with salivary leak and no cases of actual or threatened carotid blowout.

The supraclavicular artery island flap is based on the supraclavicular artery, a branch of the transverse cervical artery. Unlike the pectoralis and sternocleidomastoid flaps, it is a fasciocutaneous flap and therefore provides a thin, pliable, and hairless flap for reconstruction of mucosal defects and may be de-epithelialized with ease for other insets. It has an arc of rotation up to 180 degrees ²⁷ and can be raised easily and quickly by the experienced surgeon. It is highly versatile and can be used to reconstruct several mucosal defects of the head and neck and provides a good color match for cutaneous defects. Its limitations include the length of the required flap, with the distal tip of longer flaps (>22 cm) being the most susceptible to devascularization, ²⁷ and in cases of previously dissected necks where the integrity of the transverse cervical artery is unknown. Magnetic resonance arteriography may be of value in this latter setting to assess the potential of using this flap.

Finally, the submental island flap was first described by Martin et al in 1993. ²⁸ It is an axial pattern flap based on the submental artery, a branch of the facial artery that runs anteromedially from the facial artery superficial to the submandibular gland and deep to the anterior belly of the digastric muscle. It provides good color match for facial and neck defects, and good reach for oral defects, and can be used to provide reconstruction where hair-bearing skin is desired in men. ²⁹ Its major criticism is its dependence on an intact facial artery system, which is often disrupted in oncologically sound bilateral level 1B neck dissections. It may, however, be a consideration in cases where unilateral neck dissection in an N0 neck is required or level 1B is spared. If this flap is planned concomitantly with a neck dissection in a node-negative neck, the flap must be elevated prior to the neck dissection with meticulous attention to level 1B to remove all lymph nodes while preserving the blood supply to the flap.

Free Flaps

Free tissue transfer for repair of salivary leak is generally reserved for cases where local or regional flaps fail or are otherwise unavailable. Free flaps confer several advantages over local and regional flaps including well-vascularized tissue, distance from previously radiated fields, and the ability to accommodate geometrically complex defects. ¹⁵ Their use is contingent upon the presence of available vessels in the neck for microvascular anastomosis, and the patient must be deemed medically cleared as able to withstand the extended surgical time. The workhorse free flaps for salivary fistula management are the radial forearm free flap and anterolateral thigh flap, with the former heralded as being faster to raise, more reliable, and more versatile, ¹⁵ and the latter boasting reduced donor-site morbidity and higher success rate with repair of salivary fistulas in some studies. ³⁰

Special Considerations

In the case of postparotidectomy sialoceles and iatrogenic or traumatic injury to Stensen's duct, surgery in the form of gland exploration, repair or ligation of the duct, or salivary diversion into the mouth may be considered in cases refractory to conservative measures. ³¹ Adjunct hyperbaric oxygen therapy in the perioperative setting is an accepted treatment for many complex wounds, but there has been limited, higher level research regarding its specific use in pharyngocutaneous fistulas. ^{32 33 34} More research is needed to assess its effectiveness and timing in the treatment of head and neck oro/pharyngocutaneous fistulas. A final consideration is that of fistulas occurring after free tissue transfer reconstruction of the primary surgical defect. The vast majority of literature focuses on the use of free tissue flaps to reconstruct orocutaneous or pharyngocutaneous fistulas, but there is limited research published on surgical intervention when a fistula occurs after free tissue transfer. Intervention to divert the fistula and wash out the neck to protect the flap pedicle is counterbalanced by the granulation tissue that obscures surgical planes, which increases the risk of pedicle disruption inherent in any neck exploration in the acute postanastomotic setting. Two older articles revealed that fistulas post free flap behave the same as other fistulas. ^{35 36 37} Given the lack of specific, higher level research, fistulas in the post free tissue transfer setting should be managed the same as other fistulas, but every patient with a fistula should be assessed on an individual basis.

Conclusion

Salivary leaks and fistulas are unfortunate complications in head and neck surgery, which can be challenging for both surgeon and patient alike. Patients with prior radiation, malnutrition, and hypothyroidism are at increased risk for developing fistulas. While many of these complications can be successfully managed with conservative measures, the prompt recognition of when and how to escalate therapy is critical to avoid potentially devastating complications. Future investigation into medical therapies (e.g., octreotide and the use of botulinum toxin A in settings other than parotid surgery ³⁸ ) may help add options to the nonsurgical armamentarium. Medical optimization of patients is paramount to increase the chances of healing, especially when a second surgical procedure is needed to achieve salivary fistula closure.