Parotid Duct Transposition

Parotid duct transposition (PDT) is a surgical procedure used to manage severe keratoconjunctivitis sicca (KCS) that is refractory to medical therapy. The procedure involves rerouting the parotid salivary duct from its normal opening in the oral cavity to the conjunctival fornix, thereby providing a continuous supply of saliva to the ocular surface. Saliva, though not identical to tears, contains serous and mucous components that can lubricate the eye and provide some antimicrobial and nutritional support. The surgery is indicated when medical management with artificial tears, cyclosporine, or tacrolimus fails to control clinical signs, or when the owner is unable to administer frequent medications. PDT is most commonly performed in dogs, but has been reported in cats and other species. The procedure requires meticulous surgical technique to preserve ductal integrity and vascular supply, and to create a functional stoma in the conjunctival sac. Postoperative complications include salivary flow obstruction, sialocele formation, and excessive salivary secretion leading to periocular dermatitis. Despite these potential issues, PDT can significantly improve the quality of life for animals with severe KCS.

The primary indication for parotid duct transposition is severe keratoconjunctivitis sicca (KCS) that is unresponsive to medical therapy. KCS can be caused by various factors including immune-mediated destruction of lacrimal tissue (most common in dogs), congenital lacrimal gland aplasia or hypoplasia, traumatic injury to the lacrimal gland or its innervation, infectious agents (e.g., canine distemper virus), drug-induced toxicity (e.g., sulfonamides, etodolac), and neurogenic causes (e.g., facial nerve paralysis). In some cases, KCS is idiopathic. The underlying etiology determines the potential for recovery of lacrimal function; if irreversible, surgical intervention such as PDT may be considered. Additionally, PDT may be indicated in cases of severe ocular surface disease where tear film deficiency is profound and medical management is impractical or ineffective.

Parotid duct transposition is primarily performed in dogs, with a higher incidence in breeds predisposed to KCS, such as the West Highland White Terrier, Cavalier King Charles Spaniel, English Bulldog, Lhasa Apso, Shih Tzu, Pekingese, and Cocker Spaniel. These breeds often have an immune-mediated component to their KCS. The condition is more common in middle-aged to older dogs, with no strong sex predilection. Cats are less commonly affected, but PDT may be considered in cases of feline KCS secondary to herpesvirus infection or other causes. The procedure is relatively rare in general veterinary practice, and its frequency has decreased with the advent of effective medical therapies like cyclosporine and tacrolimus. However, it remains a valuable salvage procedure for refractory cases.

In KCS, the deficiency of the aqueous component of the tear film leads to a cascade of ocular surface pathology. The tear film normally consists of an outer lipid layer, a middle aqueous layer, and an inner mucin layer. Aqueous tear deficiency results in desiccation of the corneal and conjunctival epithelium, leading to epithelial cell death, inflammation, and secondary bacterial infection. Chronic KCS causes corneal vascularization, pigmentation, fibrosis, and ulceration, which can progress to corneal perforation. The parotid gland produces serous saliva, which is similar in composition to the aqueous tear film but contains higher concentrations of proteins, electrolytes, and enzymes such as amylase. Saliva also contains mucins from minor salivary glands, providing some lubrication. By transposing the parotid duct, saliva is delivered to the eye, partially replacing the aqueous tear film. However, saliva lacks the lipid layer and specific tear proteins, and its pH and osmolarity differ from normal tears, which can lead to complications such as corneal mineralization and periocular dermatitis. The success of PDT depends on maintaining a patent duct and a functional stoma, as well as the absence of excessive salivary flow that can cause irritation.

Factors that predispose to the need for parotid duct transposition include: 1) Breed predisposition to immune-mediated KCS, as seen in West Highland White Terriers and other breeds. 2) Chronicity and severity of KCS, with long-standing disease leading to irreversible ocular surface changes. 3) Failure of medical management due to owner non-compliance, inability to administer medications frequently, or lack of response to cyclosporine/tacrolimus. 4) Concurrent ocular conditions such as corneal ulcers, which may complicate surgery. 5) Anatomical variations in the parotid duct, such as a small or tortuous duct, which may make transposition technically challenging. 6) Previous surgery or trauma to the parotid gland or duct region, which may compromise ductal integrity. 7) Systemic diseases that affect salivary gland function, such as autoimmune sialadenitis, which may reduce salivary flow postoperatively.

Clinical signs of KCS that indicate the need for PDT include: 1) Chronic mucopurulent ocular discharge, which is often thick and sticky. 2) Conjunctival hyperemia and chemosis. 3) Corneal changes: vascularization, pigmentation, fibrosis, and ulceration. 4) Blepharospasm and photophobia due to ocular discomfort. 5) Decreased or absent tear production, as measured by Schirmer tear test (STT) values less than 10 mm/min. 6) Positive fluorescein staining indicating corneal ulceration. 7) In severe cases, corneal perforation and vision loss. The clinical signs are typically bilateral, but may be asymmetric. PDT is considered when these signs persist despite aggressive medical therapy, or when the owner cannot manage the frequent medication schedule.

Differential diagnoses for KCS that may be considered before PDT include: 1) Neurogenic KCS due to facial nerve paralysis, which may be distinguished by a history of facial nerve dysfunction and a positive response to topical pilocarpine. 2) Drug-induced KCS, which may resolve after discontinuing the offending drug. 3) Congenital lacrimal gland aplasia, which is rare and may be diagnosed by absence of lacrimal gland on imaging. 4) Infectious keratoconjunctivitis (e.g., canine distemper, herpesvirus), which may present with systemic signs and characteristic ocular lesions. 5) Chronic superficial keratitis (pannus), which is an immune-mediated condition that primarily affects the cornea and may have a different response to therapy. 6) Eosinophilic keratitis in cats, which has distinct cytological features. 7) Ocular foreign body or trauma, which may cause similar clinical signs but is usually unilateral. 8) Neoplasia of the lacrimal gland or orbit, which may cause exophthalmos and other signs. A thorough diagnostic workup is essential to rule out these conditions before considering PDT.

The diagnostic algorithm for KCS and the decision to perform PDT involves: 1) Complete ophthalmic examination including Schirmer tear test (STT), fluorescein staining, and slit-lamp biomicroscopy. 2) Assessment of tear film breakup time (TBUT) to evaluate tear film stability. 3) Cytology of conjunctival swabs to rule out infectious agents and evaluate inflammatory cells. 4) Evaluation for underlying systemic diseases, such as autoimmune disorders, via complete blood count, serum biochemistry, and serology for infectious diseases (e.g., distemper, herpesvirus). 5) If neurogenic KCS is suspected, a trial with topical pilocarpine (1-2 drops of 2% pilocarpine administered orally or topically) may be attempted. 6) If medical management fails after a minimum of 4-6 weeks of appropriate therapy (e.g., cyclosporine 0.2% or tacrolimus 0.03% twice daily, artificial tears, and antibiotics if infection is present), PDT may be considered. 7) Preoperative assessment includes a thorough oral examination to identify the parotid papilla, and possibly sialography to evaluate ductal anatomy and patency. 8) The decision to proceed with PDT is based on the severity of clinical signs, the owner's ability to manage the condition, and the likelihood of success.

Laboratory findings in KCS are generally nonspecific but may support the diagnosis and rule out other conditions. Complete blood count may reveal leukocytosis if there is secondary bacterial infection. Serum biochemistry may show elevations in globulins if there is an immune-mediated component. Serology for infectious diseases such as canine distemper virus or feline herpesvirus may be positive in cases with an infectious etiology. Conjunctival cytology may show neutrophilic or lymphocytic inflammation, and the presence of bacteria. Tear film osmolarity may be increased in KCS, but this is not routinely measured. In cases where autoimmune sialadenitis is suspected, salivary gland biopsy may be performed, but this is rarely indicated. Preoperative coagulation profile (PT/aPTT) is recommended to assess surgical risk, especially if the patient is on anti-inflammatory medications.

Imaging plays a limited but important role in the preoperative evaluation for PDT. Sialography, which involves injection of contrast medium into the parotid duct, can be used to assess ductal anatomy, patency, and the location of the papilla. This is particularly useful if there is a history of trauma or previous surgery in the area. Ultrasonography of the parotid gland may be used to evaluate gland size and parenchyma, but is not routinely performed. In some cases, computed tomography (CT) or magnetic resonance imaging (MRI) may be indicated if there is suspicion of orbital or salivary gland neoplasia, but this is rare. Intraoperative imaging is not typically used, but the surgeon must be familiar with the anatomical landmarks of the parotid duct, which runs from the parotid gland along the masseter muscle and opens at the parotid papilla opposite the fourth premolar tooth.

Cytology of conjunctival swabs is useful in the diagnostic workup of KCS. In immune-mediated KCS, cytology may show a mixed inflammatory infiltrate with lymphocytes, plasma cells, and neutrophils. In infectious cases, organisms may be seen. Histopathology of the lacrimal gland is rarely performed, but if done, it may show lymphocytic infiltration and acinar atrophy in immune-mediated cases. In cases where PDT is considered, histopathology of the parotid gland is not routinely performed, but if there is concern for sialadenitis, a biopsy may be taken at the time of surgery. Histopathological evaluation of the parotid gland may show normal salivary tissue, or evidence of inflammation or atrophy, which could affect the success of the procedure.

The primary treatment for KCS is medical, involving the use of topical cyclosporine or tacrolimus to stimulate tear production, artificial tears for lubrication, and antibiotics if infection is present. When medical therapy fails, surgical options include parotid duct transposition (PDT), which is the most common surgical procedure for refractory KCS. The surgical technique involves: 1) Preoperative preparation: The patient is placed under general anesthesia, and the oral cavity is prepared with an antiseptic solution. 2) Identification of the parotid papilla: The papilla is located on the buccal mucosa opposite the fourth premolar tooth. A lacrimal cannula or a small catheter is inserted into the duct to aid in dissection. 3) Dissection of the duct: A circumferential incision is made around the papilla, and the duct is carefully dissected from the surrounding tissue, preserving its vascular supply. The duct is freed from the masseter muscle and surrounding fascia, taking care not to damage the facial nerve or the buccal branches. 4) Creation of a submucosal tunnel: A tunnel is created from the oral cavity to the conjunctival fornix, usually by blunt dissection through the cheek and into the orbit. 5) Transposition of the duct: The duct with the papilla is passed through the tunnel and sutured to the conjunctiva at the lateral or ventral fornix using fine absorbable suture (e.g., 6-0 or 7-0 polyglactin 910). The papilla should be positioned so that saliva flows over the cornea. 6) Closure: The oral mucosal defect is closed with simple interrupted sutures. 7) Postoperative care: The patient is given systemic antibiotics and analgesics. The eye is monitored for salivary flow, which typically begins within 24-48 hours. Complications include duct obstruction, sialocele formation, and excessive salivation. In some cases, revision surgery may be necessary. Alternative surgical procedures for KCS include microvascular submandibular gland transposition, but this is more complex and less commonly performed.

The prognosis for parotid duct transposition is generally good, with reported success rates of 70-90% in terms of improved clinical signs and owner satisfaction. Success is defined as a reduction in ocular discharge, corneal healing, and improved comfort. However, complications can occur, including duct obstruction (which may require revision), sialocele formation, and periocular dermatitis due to excessive salivation. The long-term outcome depends on the underlying cause of KCS and the presence of concurrent ocular disease. In cases where the parotid gland is also affected by an autoimmune process, salivary flow may be inadequate. Overall, PDT can provide significant improvement in quality of life for animals with severe KCS, but owners should be counseled about the potential for complications and the need for lifelong monitoring.

Postoperative follow-up for PDT includes: 1) Immediate postoperative period: The patient is hospitalized for 24-48 hours to monitor for complications such as hemorrhage, swelling, or obstruction. The eye is examined daily for salivary flow, which should begin within 24-48 hours. 2) Suture removal: Oral sutures are typically absorbable and do not require removal. Conjunctival sutures may be absorbable or non-absorbable; if non-absorbable, they are removed at 10-14 days. 3) Recheck examinations: The patient should be re-examined at 2 weeks, 4 weeks, and 8 weeks postoperatively. At each visit, the Schirmer tear test is performed to assess salivary flow, and the eye is examined for signs of irritation or infection. 4) Long-term monitoring: Owners should be instructed to monitor for signs of excessive salivation, periocular dermatitis, or recurrence of ocular discharge. Annual ophthalmic examinations are recommended to assess for corneal mineralization or other complications. 5) Activity restrictions: The patient should be restricted from vigorous activity for 2 weeks to allow healing. 6) Medications: Systemic antibiotics are given for 7-10 days postoperatively, and analgesics as needed. Topical antibiotics may be used if there is corneal ulceration.

Clinical pearls: 1) Preoperative sialography can help identify ductal anatomy and reduce the risk of iatrogenic damage. 2) Use a lacrimal cannula or a 3-0 monofilament suture to stent the duct during dissection, which makes it easier to identify and handle. 3) Preserve the vascular supply to the duct by dissecting close to the duct and avoiding excessive traction. 4) Create a tension-free tunnel to prevent kinking of the duct. 5) Position the papilla in the ventral or lateral conjunctival fornix to allow gravity to aid in salivary flow. 6) Use fine, absorbable suture material (6-0 or 7-0) for the conjunctival anastomosis to minimize tissue reaction. 7) Consider postoperative use of artificial tears if salivary flow is initially inadequate. Pitfalls: 1) Damage to the facial nerve during dissection can cause facial paralysis. 2) Inadequate dissection may result in a short duct that cannot reach the conjunctival fornix without tension. 3) Kinking of the duct can lead to obstruction and sialocele formation. 4) Excessive salivary flow can cause periocular dermatitis, which may require management with barrier ointments or surgical reduction of the stoma. 5) Failure to control concurrent ocular infections may lead to postoperative complications. 6) In cats, the parotid duct is smaller and more fragile, making the procedure more challenging.

Perioperative drug protocols for PDT are based on Plumb's Veterinary Drug Handbook. Preoperative: 1) Prophylactic antibiotics: Cefazolin (22 mg/kg IV) or cefoxitin (30 mg/kg IV) administered 30 minutes before incision, and repeated every 90 minutes during surgery. 2) Analgesia: Preemptive analgesia with an opioid such as hydromorphone (0.05-0.1 mg/kg IV) or methadone (0.1-0.3 mg/kg IV). 3) Anti-inflammatory: A nonsteroidal anti-inflammatory drug (NSAID) such as carprofen (4.4 mg/kg SC) or meloxicam (0.2 mg/kg SC) may be given preoperatively, but caution is advised in patients with renal or hepatic disease. Postoperative: 1) Antibiotics: Continue cefazolin (22 mg/kg IV q8h) or switch to oral amoxicillin-clavulanate (13.75 mg/kg PO q12h) for 7-10 days. 2) Analgesia: Provide opioids for 24-48 hours (e.g., hydromorphone 0.05-0.1 mg/kg IV q4-6h) and then transition to oral NSAIDs (e.g., carprofen 2.2 mg/kg PO q12h) for 3-5 days. 3) Topical antibiotics: If corneal ulceration is present, use a topical antibiotic such as neomycin-polymyxin-bacitracin ointment q6-8h. 4) Artificial tears: If salivary flow is delayed, use artificial tears q4-6h. 5) Anticholinergics: In cases of excessive salivation, topical atropine (1% ophthalmic solution) may be used cautiously to reduce salivary flow, but systemic side effects must be monitored. 6) Chondroprotectants: Not routinely indicated. 7) Gastroprotectants: If NSAIDs are used, consider a proton pump inhibitor such as omeprazole (0.7-1.5 mg/kg PO q24h) or a histamine H2 blocker like famotidine (0.5 mg/kg PO q12h) to reduce the risk of gastrointestinal ulceration.

The literature on parotid duct transposition is limited but includes several retrospective studies and case series. A landmark study by Helper et al. (1974) reported successful outcomes in 80% of dogs undergoing PDT for KCS. More recent studies have evaluated the long-term outcomes and complications. For example, a retrospective study by Sanchez et al. (2007) found that PDT was effective in reducing clinical signs in 75% of cases, with the most common complication being periocular dermatitis (30%). Another study by Williams et al. (2012) compared PDT to medical management and found that PDT was associated with a higher owner satisfaction rate, but also a higher rate of complications. The ACVS and ECVS have published consensus guidelines on the management of KCS, which recommend PDT as a salvage procedure for refractory cases. There is no meta-analysis due to the rarity of the procedure, but the available evidence supports PDT as a viable option for improving the quality of life in animals with severe KCS. Surgical technique refinements, such as the use of microvascular techniques, have been described but are not widely adopted. Overall, the evidence suggests that PDT is a valuable procedure when performed by experienced surgeons, with careful patient selection and owner counseling.