Other Names
- Parotid Duct Fistula
- Parotid Salivary Fistula
- Stensen’s Duct Fistula
What is Equine Parotid Duct Fistula?
An equine parotid duct fistula is an abnormal opening that forms in the skin of a horse’s cheek or jaw region, through which saliva leaks directly onto the skin surface rather than entering the mouth via the normal salivary duct. The parotid gland is the largest salivary gland in the horse, located near the base of the ear and along the angle of the jaw. Its secretions travel through the parotid duct (also called Stensen’s duct) into the mouth near the upper cheek teeth.
When this duct is damaged — typically by trauma — the wound may heal over the skin surface whilst the underlying duct remains disrupted. Saliva then tracks along the path of least resistance and discharges through a persistent opening in the skin. The condition is not life-threatening but causes significant ongoing discomfort, skin irritation, and cosmetic issues, and it will not resolve without targeted treatment.
Causes
The vast majority of equine parotid duct fistulae result from trauma to the cheek or jaw region. Common causes include:
- Bite wounds: Injuries from other horses biting over the parotid region
- Wire or fence injuries: Lacerations from sharp fencing materials
- Blunt trauma: Kicks, collisions with fencing or stable fixtures
- Poorly fitting tack: Pressure from cheekpieces, curb chains, or other tack components causing chronic irritation and eventual ulceration over the duct
- Surgical complications: Inadvertent damage to the duct during surgery in the region
In some cases, the original wound heals and appears resolved at the skin surface before the fistulous tract becomes apparent, which can delay diagnosis. The constant flow of saliva — particularly stimulated during eating — prevents the damaged duct from healing naturally.
Symptoms and Signs
Signs are generally straightforward and localised to the affected area:
- A persistent or intermittent weeping wound on the cheek, jaw, or parotid region that fails to heal
- Clear to slightly cloudy fluid discharge from the wound — saliva is thin, watery, and odourless
- Increased discharge during feeding — salivary flow is stimulated by eating and chewing
- Skin scalding or irritation around the opening from constant moisture
- The horse may show no pain or may resent handling of the area depending on surrounding tissue involvement
- A previous history of trauma or wound in the same region
The diagnosis is often clinched by noting that the discharge increases dramatically when the horse is fed — chewing triggers salivary production, which escapes through the fistula rather than entering the mouth.
Diagnosis
Diagnosis is generally clinical but can be confirmed by:
- Contrast fistulography: Injection of contrast medium into the fistulous tract followed by radiography to delineate the path of the fistula and its relationship to the parotid duct and gland
- Endoscopy of the duct: In some cases, endoscopic examination of the parotid duct from its oral opening can identify the site of disruption
- Fluid analysis: Amylase testing of the discharge; salivary fluid has high amylase activity, confirming the salivary nature of the discharge if in doubt
- Ultrasonography: To assess the parotid gland and identify any associated swelling, abscessation, or glandular involvement
It is important to distinguish a parotid duct fistula from a parotid gland fistula (where the gland itself is disrupted) as the treatment approach differs.
Treatment
Conservative management rarely achieves resolution. Treatment options include:
- Ligation of the parotid duct: The most commonly successful approach. The duct is surgically ligated (tied off) proximal to the fistula, allowing the distal section and fistula to close. The parotid gland subsequently atrophies as it can no longer drain — horses tolerate this well as the other salivary glands compensate for salivary function.
- Surgical excision and primary repair: In some cases, the damaged section of duct can be excised and the fistulous tract surgically closed. Success rates are lower than ligation due to the difficulty of creating a durable seal in a constantly mobile, salivary environment.
- Atropine injections: Occasionally used short-term to reduce salivary output and allow the area to dry, but not a curative treatment on its own.
- Wound management: Keeping the area clean and dry between treatments helps manage skin irritation and secondary infection.
Surgical ligation is the preferred and most reliable method. The procedure is typically performed under general anaesthesia by an equine surgeon.
Prevention
Prevention focuses on injury avoidance and prompt wound management:
- Check and maintain fencing to minimise sharp edges and protruding wire
- Ensure tack fits correctly and does not create pressure points over the parotid region
- Address bite wounds and lacerations over the jaw promptly — early, thorough wound management reduces the chance of fistula formation
- When suturing wounds in the parotid region, awareness of duct anatomy helps avoid inadvertent damage
Prognosis
The prognosis following surgical ligation is generally good to excellent. Most horses recover uneventfully after the ligation procedure, and the fistula closes within weeks as the gland atrophies. Horses experience no significant reduction in feed intake or wellbeing following loss of one parotid gland. Cases involving extensive glandular damage or infection may be more complex, but overall outcomes are positive with appropriate specialist surgical management.
When to Call the Vet
Contact your vet if:
- Your horse has a wound on the jaw or cheek area that discharges clear fluid, particularly if the discharge increases when eating
- A wound in the parotid region fails to heal despite treatment
- You notice a soft swelling near the base of the ear or along the angle of the jaw after any trauma to that area
Early assessment prevents months of unnecessary discharge, skin irritation, and frustration with a wound that simply will not resolve without targeted intervention.
Frequently Asked Questions
Will a parotid duct fistula resolve on its own?
Spontaneous resolution is rare. The constant flow of saliva through the tract prevents normal wound healing. While mild cases involving minimal duct damage occasionally close with strict rest and wound management, the majority require surgical intervention to achieve resolution.
Does tying off the parotid duct affect the horse’s ability to eat?
No. Horses have multiple salivary glands — submandibular, sublingual, and buccal glands compensate for the loss of one parotid gland. In practice, horses that undergo parotid duct ligation eat normally and maintain body condition without any dietary management changes required.
How long does recovery take after surgery?
Most horses show complete closure of the fistula within four to eight weeks of successful ligation. The parotid gland atrophies over several months, which is normal and expected. Full return to work is typically possible within four to six weeks of surgery, depending on the specific procedure performed and the horse’s individual healing.
Is the condition painful for the horse?
The fistula itself is often not acutely painful once established, though the surrounding skin may become sore from constant moisture exposure. Horses are usually more bothered by tack pressure on the area or by wound dressings than by the discharge itself. Pain management is generally straightforward during the surgical recovery period. See also: salivary gland anatomy for background on equine salivary structures.