CASE REPORTS

Surgical Excision of the Parotid Salivary Gland for Treatment of a Traumatic Mucocele in a Dog Kathleen M. Guthrie, DVM, Robert J. Hardie, DVM, DACVS, DECVS

ABSTRACT A 3 yr old spayed female mixed-breed German shepherd dog was presented with a right facial swelling that developed after fighting with another dog. A parotid salivary mucocele was diagnosed via physical examination, fine-needle aspirate, and sialography of the parotid and mandibular salivary glands. Surgical excision of the right parotid salivary gland and duct was performed along with drainage of the mucocele. Neither intraoperative nor postoperative complications occurred, and follow-up examination 4 mo later revealed no evidence of recurrence. Case outcome was considered excellent. Sialography was useful for confirming the parotid gland as the source of the mucocele. Surgical excision of the parotid salivary gland is technically challenging, but an effective treatment option for traumatic mucoceles in the dog. (J Am Anim Hosp Assoc 2014; 50:216–220. DOI 10.5326/JAAHA-MS-6002)

Introduction

mucoceles are rare.1–11 This report describes the successful diag-

Salivary mucoceles are the most common disease of the salivary

nosis, treatment and outcome of a parotid salivary mucocele of

glands in dogs, defined as an accumulation of saliva outside of the

traumatic origin in a dog.

salivary system arising from a disruption in either the duct or the gland.1 Salivary mucoceles are cystic in appearance; however, they

Case Report

are not true cysts because they do not possess an epithelial lining.

A 3 yr old spayed female mixed-breed German shepherd dog was

The salivary glands in the dog include the sublingual, mandibular,

presented to the University of Wisconsin Veterinary Medical

zygomatic, and parotid, and all have the potential to develop

Teaching Hospital for evaluation of a salivary mucocele on the right

a mucocele. Salivary mucoceles may occur in several locations,

side of the face. Approximately 1 mo prior to presentation, the dog

including the cervical region, sublingually, in the pharyngeal re-

was in a fight with another dog and was injured on the right side of

gion, and on the side of the face. Mucoceles of zygomatic origin

the face, resulting in an approximately 1 cm laceration in the skin

usually result in exophthalmos. Mucoceles typically are non-

ventral to the zygomatic arch. A few days later, a fluctuant sub-

painful and do not cause clinical signs unless they become either

cutaneous swelling developed at the site of the trauma. The re-

inflamed or infected; however, mucoceles in the pharyngeal re-

ferring veterinarian drained the swelling and diagnosed a mucocele

gion can cause potentially life-threatening respiratory distress.

based on gross appearance of the fluid. The facial swelling recurred

Potential causes for salivary mucoceles include sialoliths, neo-

after a few days, and the dog was referred to the University of

plasia, and trauma, but for the majority of dogs, a specific cause

Wisconsin Veterinary Medical Teaching Hospital.

cannot be identified. The sublingual salivary gland (and duct) is

On physical examination at the time of referral, a moderately

the most commonly affected gland, whereas reports of parotid

firm, nonpainful swelling measuring 4 cm in diameter was present

From the Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI.

CT computed tomography

Correspondence: [email protected] (K.G.)

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Surgical Excision of the Parotid Gland for Mucocele

on the right side of the face just ventral to the zygomatic arch. A 1 cm scar, consistent with the previous trauma, was present at the ventral aspect of the swelling. A fine-needle aspirate of the swelling was performed, and approximately 3 mL of slightly viscous, straw-colored fluid were removed. Cytologic examination of the fluid revealed a mostly acellular proteinacious background with rare macrophages and red blood cells. Based on the physical examination and cytologic examination of the fluid, a presumptive diagnosis of parotid salivary gland mucocele was made. To confirm the gland of origin of the mucocele, survey radiographs of the skull and contrast sialography were performed with the dog under general anesthesia. In preparation for anesthesia, blood was drawn for a serum biochemical analysis, packed cell volume, and total protein. Serum chloride concentration was slightly elevated at 120 mmol/L (reference range, 109–119 mmol/L), and all other values were within the reference ranges. The dog was premedicated with 1 mg of acepromazinea and 4 mg (0.17 mg/kg) of hydromorphoneb intramuscularly. Carprofenc was administered at a dose of 4.4 mg/kg subcutaneously prior to induction of anesthesia, and perioperative antibiosis was achieved with cefazolind at 22 mg/kg q 90 min for the duration of surgery. Anesthesia was induced with 110 mg (4.6 mg/kg) of propofole and maintained with inhaled isofluranef and 100% O2 via endotracheal intubation.6 A balanced crystalloid solution was administered perioperatively IV at a rate of 10 mL/kg/hr. Survey skull radiographs revealed the presence of a soft-tissue opacity ventrolateral to the right zygomatic arch. The right parotid

FIGURE 1

salivary gland papilla, located next to tooth 108 (using the modified

points to the contrast pooling at the site of the duct disruption, which

Triadan system, available at http://www.rvc.ac.uk/review/Dentistry/

is at the location of the mucocele. B: Lateral view of the normal

Basics/triadan/dog.html), was cannulated with a 24 gauge catheter,

mandibular sialogram. The arrow is pointing to the mandibular

and sialography of the right parotid gland was performed by in-

duct, and the asterisk is located over the mandibular gland. L, left;

g

jecting 3 mL of a contrast agent (300 mg/mL) into the catheter.

A: Lateral view of the parotid sialogram. The arrow

R, right.

Parotid sialography highlighted the distal portion of the duct as a thin line of contrast extending from the level of tooth 108

of contrast, consistent with a normal right mandibular salivary

caudally to the level of tooth 110, then the contrast coursed

gland (Figure 1B).

ventrally at a sharp angle, with pooling of contrast ventral and

Based on the results of the sialography, a right parotid

axial to the soft-tissue swelling. No contrast was identified in the

mucocele was diagnosed and parotid gland resection and drainage

caudal portion of either the duct or gland (Figure 1A). To rule

of the mucocele was performed. The dog was placed in left lateral

out involvement of the right mandibular gland, the right man-

recumbency and the right side of the face was clipped and asep-

dibular salivary gland papilla, located medial to tooth 407, was

tically prepared. After clipping the hair on the face, the scar on

cannulated with a 24 gauge catheter, and sialography of the right

the ventral aspect of the mucocele was more evident (Figure 2A).

mandibular gland was performed by injecting 3 mL contrast

A 10 cm incision was made, extending from the ventral aspect of

agent into the catheter. Mandibular sialography highlighted the

the vertical ear canal to the caudal extent of the ramus of the

duct as a thin line of contrast extending from the level of tooth

mandible coursing over the mucocele. The platysma and paroti-

407 to the caudal aspect of the ramus of the right mandible before

doauricularis muscles were incised over the parotid salivary gland

coursing ventrally to an ovoid structure with multiple thin lines

and reflected ventrally. Using a combination of blunt and sharp

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dissection, the parotid gland was dissected from the surrounding

in three layers, taking care to avoid the vessels and nerves ex-

tissue, taking care to avoid injury to the superficial temporal

posed after removal of the gland. Gauze sponges were applied

artery and the facial nerve and its branches (Figure 2B). The

to the exit site of the Penrose drain, and a stockinette was placed

glandular tissue was intimately associated with the surround-

over the head to hold the gauze in place.

ing musculature, making dissection laborious. With traction

Recovery from anesthesia was uneventful, and postoperative

on the parotid gland, the caudal portion of the duct (approxi-

analgesia (0.05 mg/kg hydromorphone intramuscularly) was ad-

mately 2 cm) was traced rostrally toward the caudal extent of

ministered q 4–6 hr pro re nata for 24 hr. Postoperative assessment

the mucocele, ligated with 3-0 glycomer 631h and transected.

of facial nerve function revealed normal palpebral reflex and

The mucocele was drained and flushed with sterile saline,

no other signs of facial nerve deficits. Based on minimal fluid

and a Penrose drain was placed within the subcutaneous space

production from the drain site, the Penrose drain was removed on

exiting ventral to the incision. The incision was closed routinely

day 1 postoperatively. No complications occurred, and the dog was discharged 48 hr postsurgically. Histopathology of the excised parotid gland revealed mild lymphoplasmacytic adenitis with duct ectasia. A section of the tissue surrounding the mucocele was also examined revealing fibrillar mucinous exudate with mild granulomatous response and early granulation tissue formation. No evidence of either neoplasia or sialolithiasis was evident. A follow-up phone call was made 4 mo after surgery. The owner reported no recurrence of the mucocele or other complications.

Discussion To the authors’ knowledge, this is the first report of a traumatic parotid salivary gland mucocele in a dog. Previously reported parotid mucoceles in dogs have been caused by either sialolithiasis or iatrogenic damage.6–10 Given the superficial location of the parotid salivary gland and duct, it is surprising that there are not more reports of traumatic parotid gland mucoceles in the literature.11 Based on the history of previous trauma to the face and the general location of the mucocele, the parotid gland was considered the most likely source; however, the zygomatic and mandibular glands could not be definitively ruled out. Therefore, sialography was performed to confirm the gland of origin. Cannulation of the parotid and mandibular papillae is very challenging and may not be feasible in all cases depending on the size of the dog and the individual anatomy. The interpretation of the sialograms was fairly straightforward in this case; however, because of the difficulty in FIGURE 2

A: Lateral preoperative view. The right side of the

dog’s face has been clipped, and the rostral direction is to the right.

performing sialography, a lack of a normal sialogram may not always indicate pathology.

The arrow points to the sialocele. Note the pink scar at the ventral

Computed tomography (CT) has also been used to identify

aspect. B: Lateral intraoperative view of the right parotid sialoade-

the parotid salivary gland as the source of a mucocele; however,

nectomy. Note the lack of distinction between the parotid gland and

in that case, the etiology of the mucocele was a sialolith, which

the surrounding tissue. The parotid gland is being retracted using

resulted in dilation of the duct, making the duct more identifiable

Babcock forceps. Rostral is to the right, and dorsal is to the top of the

with CT.9 For the case reported here, it is unlikely that CT would

photo.

have been useful for diagnosing the parotid gland as the gland of

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Surgical Excision of the Parotid Gland for Mucocele

origin because of the very small diameter of the duct and lack of

for treatment of keratoconjunctivitis. Ligation of the duct suc-

contrast within the caudal portion of the duct and gland. CT

cessfully led to atrophy of the gland and cessation of saliva

sialography, however, would have been a feasible diagnostic mo-

production.18

dality, and that technique has been described previously.12

Based on those reports, it follows that ligation of the duct of

Factors other than trauma, iatrogenic damage, or sialolithiasis

the offending salivary gland proximal to the disruption may be

may contribute to mucocele formation. Attempts to produce

a viable treatment option for mucoceles arising from any gland,

salivary mucoceles experimentally by either disruption or ligation

with the benefit being a less invasive surgical approach. How-

of the duct have been largely unsuccessful, which indicates that

ever, in dogs, most mucoceles occur in either the submandibular

13

a predisposition for mucocele formation may exist. Indeed, breed

or ventral cervical region and arise from either the mandibular or

predispositions have been reported in poodles, German shepherd

sublingual glands. In those cases, the mucocele typically sur-

dogs, greyhounds, Australian silky terriers, and dachshunds,

rounds both glands, making it impossible to determine what

suggesting a genetic predisposition.3 Mucoceles have also been

gland or duct is the source of leakage. Therefore, the most ef-

reported to occur in littermates, further supporting the hypothesis

ficient treatment option is to remove both glands and as much of

for a genetic predisposition.14 It is worth noting that the dog in

the duct(s) as possible.

this report is a mixed-breed German shepherd dog, which may

For the case reported herein, it is possible that the small

have predisposed the dog to mucocele formation following the

segment of the parotid duct caudal to the mucocele could have

traumatic injury to the face.

been identified and ligated as a simpler form of treatment given the

The current treatment of choice for a salivary mucocele of

technical challenge of excising the parotid gland, which required

mandibular and/or sublingual gland in origin is excision of the

meticulous and time-consuming dissection between the gland and

gland(s) and drainage of the mucocele.2,3 However, excision of the

surrounding tissue. Duct ligation would have also avoided the risk

salivary gland may not be necessary in all cases. Ligation of sali-

of iatrogenic injury to the facial nerve, which is intimately asso-

vary ducts generally results in atrophy of the respective glands,

ciated with the gland. However, based on the recent report of

13,15,16

One study describes an experi-

successful resolution of a parotid mucocele due to sialolithiasis

ment designed to create salivary mucoceles in dogs, by either

after parotid gland resection, the decision was made to resect the

without adverse effects.

ligating or longitudinally incising the ducts.

13

In dogs that had

gland as a more definitive treatment.9

the ducts ligated, the salivary glands atrophied within days, and no mucoceles were created in any of the dogs, regardless of

Conclusion

treatment. Another study describes attempts to experimentally

Although rare, parotid gland mucoceles should be considered as

create mucoceles in cats by ligating the mandibular, sublingual,

a differential for any swelling around the zygomatic region of the

and parotid ducts.15 For all three glands, atrophy occurred, with

face. A key reason for the success of this case was the correct

results most consistent in the parotid salivary gland. Mucoceles

identification of the gland of origin. The authors, therefore, rec-

formed only in glands where the duct had not been completely

ommend performing further imaging, such as sialography or CT, in

ligated, possibly from either lack of sufficient backpressure in the

any case where the location of the mucocele is either unusual or may

gland or potentially from lack of denervation that is accomplished

be associated with several glands. In the case reported herein, ex-

with complete duct ligation. In rats, ligation of the parotid duct

cision of the parotid gland was curative and resulted in an excellent

led to rapid atrophy of the glandular tissues and cessation of saliva

outcome for the dog, indicating that excision of the parotid salivary

16

production. Although ligation of the sublingual and mandibular

gland is a viable treatment option for parotid mucocele of traumatic

ducts has not been described as a treatment of mucoceles in dogs,

origin. However, further investigation of treatment options is in-

there are reports of successful treatment of parotid mucoceles by

dicated to compare the success rates of ligation of the duct proximal

ligation of the duct rather than sialoadenectomy.7,17,18 In two

to the disruption versus excision of the affected gland(s), as ligation

separate studies, Harvey described parotid duct ligation in one

of the duct may be associated with less morbidity.

cat and one dog for parotid salivary duct rupture, and in one dog for treatment of bilateral parotid gland enlargement. All three animals recovered uneventfully and presumably went on to develop atrophy of the parotid salivary glands.7,17 Kuhns et al. (1979) report ligation of the parotid duct in a dog following complications from a parotid duct transposition performed

FOOTNOTES a Phoenix Pharmaceuticals Inc., Burlingame, CA b Teva Parenteral Medicines Inc., Irvine, CA c Rimadyl; Pfizer Animal Health, New York, NY d Sandoz Inc., Princeton, NJ e Hospira Inc., Lake Forest, IL

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f g h

Isoflo; Abbott Animal Health, Abbott Park, IL Omnipaque; GE Healthcare, Waukesha, WI Biosyn; Syneture, Norwalk, CT

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