Salivary Mucoceles in Dogs: Cervical, Oral (rannula), and 1 type that causes airway obstruction

Anatomy

Fig. 1
(from: Manfra Marretta S. Dentistry and diseases of the oropharynx, in Birchard & Sherding (editors): Saunders Manual of Small Animal Practice, (3^rd ed.). St. Louis. Elsevier, 2006, pp 632-635.)

The mandibular salivary gland is located at the bifurcation of the maxillary and linguofacial veins. (Fig. 1) The duct empties at the sublingual papilla, which is lateral to the most rostral aspect of the frenulum of the tongue. The gland has a well-defined capsule. The sublingual gland has two distinct portions, the monostomatic portion, which is immediately adjacent and rostral to the mandibular gland, and the polystomatic portion, which are small islands of gland dispersed along the salivary duct. The sublingual salivary duct is closely associated with the mandibular duct. The parotid gland is located at the base of the ear canal. Its duct empties adjacent to the upper 4^th premolar. This is a wide, but thin gland; not globoid like the mandibular gland. The zygomatic gland is just ventral and medial to the zygomatic arch and the duct empties 1 cm caudal to the parotid duct.

Etiology of mucocele

 A salivary mucocele is the accumulation of saliva outside of the gland or duct system. The mucocele is not a true cyst since it does not have a secretory lining. It can be due to a variety of causes. Trauma to the head or neck that causes injury to either the gland or the duct can cause leakage of saliva. Oral mucocele (ranula) is a reported complication of mandibulectomy in dogs and cats. Infection or inflammation (sialadenitis) may cause enough tissue disruption to allow leakage. Histopathology of salivary tissue removed to treat mucoceles frequently reveals inflammatory changes. Although rare in dogs and cats but more common in humans, calculi can cause obstruction of the salivary duct with subsequent rupture of the duct and leakage. Rarely, neoplasia of the gland can cause disruption of glandular or ductal tissues.

Mucoceles are classified by their location. The cervical mucocele is the most common. A fluctuant mass is seen in the submandibular region and the leaking gland or duct is either the mandibular or the sublingual. If large, the mass may be mid-cervical or encompass the entire ventral aspect of the neck. An oral mucocele, also called a ranula, is due to leakage from the sublingual gland or duct and the swelling is intra-oral and lateral to the tongue. A pharyngeal mucocele is very similar to cervical but the fluctuant swelling is present in the pharynx, near the tonsil. Like the cervical mucocele, the pharyngeal is due to leakage from either the mandibular or sublingual salivary glands. Finally, the zygomatic mucocele can cause exophthalmus and/or peri-orbital swelling and is due to leakage from the zygomatic salivary gland.

Clinical Signs

Clinical signs of mucoceles vary according to their location.  The cervical mucocele causes a fluctuant, non-painful swelling in the cranial ventral cervical area. (Fig. 2)

Fig. 2: Cervical mucocele in a dog

 The mass usually lateralizes to the affected side. However, in some cases the mass is directly on midline making it difficult to determine whether the right or left salivary glands are causing the problem. 

The oral mucocele, or rannula, can cause dysphagia, anorexia, excessive salivation, abnormal movements or protrusion of the tongue. (See previous post on Ollie for a case example.) The ranula may be large enough to be visible by the owner. It appears cystic and can be large enough to deviate the tongue to the opposite side.

            Dogs with a pharyngeal mucocele (Fig. 3) can present for inspiratory stertor and dyspnea since the fluid filled mass causes a physical obstruction in the pharynx and upper airway.

Fig. 3: Pharyngeal mucocele (arrow) in a poodle

Difficulty swallowing can also be a sign of pharyngeal mucocele.

A mucocele of the zygomatic salivary gland can cause exophthalmus, divergent strabismus, and a fluctuant swelling in the orbital area.

Diagnosis

            In most cases, salivary mucoceles are not a diagnostic challenge. The animals have a history of an acute or chronic fluctuant swelling that is not painful. Aspiration of the mass typically reveals a straw colored, mucinous fluid that appears ropey when pushed through a needle and syringe onto a slide. (Fig. 4)

Fig. 4: FNA of a mucocele (www.acvs.org)

Cytology of the fluid reveals few cells unless the mucocele is very chronic or infected in which case more evidence of inflammation is seen.

            Diagnostic imaging is usually not necessary but may be indicated in complicated cases or ones in which the presentation is atypical. Ultrasound or computed tomography may be helpful in animals with zygomatic mucoceles to differentiate the mass from neoplasia or foreign body.

            In some animals, the cervical mucocele is difficult to lateralize because it is either directly on midline or very large. Simple methods to determine the affected side are to lay the dog on its back and see to which side the mucocele gravitates. (Fig. 5)

Fig. 5: Placing the dog in dorsal recumbency can help lateralize the mucocele.

Sometimes by pushing medially on the mucocele while doing an oral exam the clinician can see one side of the pharyngeal wall bulge inward. In the rare case where the affected side is still unclear after these manipulations, positive contrast sialography can be performed. Contrast material is injected into the salivary duct and the resultant images studied for evidence of leakage or obstruction.

Treatment

            Regardless of location, the definitive treatment of a salivary mucocele involves removal of the offending salivary glands. Performing only drainage of the mucocele will not result in long-term resolution.

Surgical excision of mandibular and sublingual glands is the treatment of choice for cervical mucoceles. (Fig. 6)

Fig. 6: Excised mandibular (large gland to the left) and sublingual (remaining glands extending
from left to right) salvary glands

The mandibular gland, and the monostomatic and polystomatic portions of the sublingual gland are removed as a unit since their ducts are closely associated. The surgical approach is directly over the mandibular gland that lies just cranial to the bifurcation of the jugular vein into the maxillary and linguofacial veins. The capsule of the mandibular gland is incised to allow dissection and removal of the gland. Dissection then proceeds cranially along the mandibular duct. (Fig. 7)

Fig. 7: Surgical excision of mandibular and sublingual salivary glands in a dog.
Retraction of the digastricus muscle (arrow) facilitates dissection.

The multiple portions of sublingual gland are removed with the mandibular gland and the ducts. Dissect the ducts as far cranially as possible, then ligate and remove the tissues. Take care to avoid injury to the lingual nerve which lies over the salivary duct and serves as the most rostral limit of the gland and duct excision. Place a pen-rose or closed suction drain in the mucocele and close the incision routinely.

                        The etiology of pharyngeal mucoceles is similar to cervical mucoceles since they are also caused by leakage from the mandibular or sublingual glands. Therefore, remove these glands as described under cervical mucoceles. In addition, excise the pharyngeal mucocele via an intra-oral approach. Make an elliptical incision at the base of the mucocele, and excise the redundant mucosa and underlying tissues to be sure that the interior of the mucocele has been exposed. Although marsupialization of the resultant pharyngeal defect has been described, the author simply leaves this incision open to heal by second intention.

                        An oral mucocele, or ranula, is treated by “deroofing” the mucocele, followed by marsupialization. (See previous post on Ollie.) Deroofing is performed by simply removing the mucosa over the dorsal portion of the swelling being sure to expose the inside of the mucocele. Marsupialization is performed by suturing the inner lining of the mucocele to the oral mucosa. This allows the mucocele to remain open and drain into the mouth. Suturing is usually done with an absorbable suture such as Monocryl or PDS. Removal of the mandibular and sublingual salivary glands on the affected side is also be performed to prevent recurrence.

                        The zygomatic mucocele is treated by removal of the zygomatic salivary gland, which is located just ventral to the eye and medial to the zygomatic arch. Removal of the gland can be performed by partial removal of the zygomatic arch, or by ventral orbitotomy. The zygomatic arch can also be temporarily removed to provide exposure, and then reattached with orthopedic wire. Be careful not to injure orbital structures during the dissection.          

Postoperative Care

            Submit removed tissues for histopathology and culture. If a pen-rose drain was left in the mucocele, remove it once drainage becomes minimal. If infection was suspected or documented by positive cultures, treat the dog with appropriate antibiotics for at least 7-10 days. After marsupialization of a ranula, feed the dog soft food for 2-3 weeks, and flush the mouth with water or oral antiseptic lavage after eating.

            Complications after treatment of a salivary mucocele are rare. A seroma can occur due to the dead space created by the mucocele. Conservative treatment with warm compresses is usually effective. Recurrence of mucocele is rare but may indicate incomplete removal of the affected salivary tissue, or that the incorrect gland was removed.

References

Bellenger CR, Simpson DJ. Canine sialocoeles – 60 clinical cases. J of Sm. An. Practice 33:376-380, 1992.

Schmidt GM, Betts CW. Zygomatic salivary mucoceles in the dog. J Am Vet Med Assoc 172:940-942, 1978.

Knecht CD. Diseases of the salivary glands in the dog. Comp Cont Ed II:932-938, 1980

Bartoe JT, Brightman AH, Davidson HJ. Modified lateral orbitotomy for vision-sparing excision of a zygomatic mucocele in a dog. Vet Ophthalmology10:127-131, 2007.

Manfra Marretta S. Dentistry and diseases of the oropharynx, in Birchard & Sherding (editors): Saunders Manual of Small Animal Practice, (3^rd ed.). St. Louis. Elsevier, 2006, pp 632-635.

Benjamino K, Birchard SJ, Niles JD, Penrod KD. Pharyngeal mucoceles in dogs: 14 cases. J Am Anim Hosp Assoc. 48(1):31-5, 2012

Outcome of Diagnosis and Treatment of "Ollie"

Fig. 1: FNA of the oral mass in Ollie

The gross appearance of the mass, its fluctuant nature, and the mucoid fluid that was aspirated (Fig. 1) were all suggestive of a rannula (oral mucocele). This is an accumulation of saliva from the sublingual salivary glands into the submucosal space in the mouth. 

The treatment for Ollie was marsupialization of the rannula (Fig. 2-3), and removal of the mandibular and sublingual salivary glands. (Fig. 4) 

Fig. 2: Completed marsupializaton of the rannula

Fig. 3: Close up of the marsupialized rannula showing the interior of the mucocele.

Marsupialization was performed by first incising over the dorsal aspect of the rannula with a scalpel. The saliva was evacuated from the cavity and the dorsal aspect of the rannula was debrided to make a large opening. The wall of the rannula was sutured to the inner tissue layer with 4-0 Monocryl in a simple continuous pattern. 

The right mandibular and sublingual salivary glands were removed in the standard fashion through a lateral cervical incision directly over the mandibular gland. (Fig. 4)

Fig. 4: Excised mandibular (yellow arrow) and sublingual (red arrows) salivary glands
in Ollie. Note the discolored areas of the sublingual glands. The salivary leakage was
likely originating from these glands.

Ollie was discharged the day after surgery with instructions to feed a soft diet and to flush the mouth with warm water after eating.

Ollie returned in 2 weeks for suture removal. The rannula had resolved and Ollie was eating and drinking normally and doing very well. 

In the next blog we will discuss salivary mucoceles in more detail.

Please post any questions you have about Ollie.

What's Your Diagnosis on "Ollie": A 5 year old Bichon with a huge oral mass?

Fig. 1

Ollie (Fig. 1) is a 5 year old male neutered Bichon who presented with a 5 day history of lethargy, discomfort, and excessive drooling. Oral exam revealed a large, soft mass just lateral to the frenulum of the tongue on the right side. (Fig. 2).

Fig. 2

Fine needle aspirate revealed a tan colored, thick, mucoid fluid. (Fig. 3)

Fig. 3

What is your diagnosis? What other diagnostic tests should be performed?
What is your recommended treatment?

Answer later this week!

Intestinal surgery quiz

1. True or False: Mortality rate associated with linear foreign bodies is the same as non-linear foreign bodies (such as a corn cob or ball).

2. In an intussuception, the section of intestine that is telescoped inside is called the:

            a. intussusceptum

            b. intussucipiens

            c. intussusinside

            d. dead part

            e. who cares?

3. What is the reported mortality rate for dogs having intestinal leakage after enterotomy or resection and anastomosis:

            a. 10%

            b. 30%

            c. 50%

            d. 75%

            e. 100%

  4. What is the “holding” or strongest histologic layer of the intestine:

a. serosa

b. muscularis

c. submucosa

d. mucosa

e. pseudostratified epithelium

  5. Intestinal anastomotic breakdown usually occurs:

            a. 1-2 days post-operatively

            b. 3-5 days post-operatively

            c. 5-7 days post-operatively

            d. 7-10 days post-operatively

            e. if you don’t sing “Kum-bi-ya”

 6. Which of the following is true about intussuception in dogs and cats:

a.     usually occurs at the ileo-ceco-colic junction in dogs

b.     is frequently not reducible

c.     is usually secondary to some primary disease process

d.     usually occurs in the jejunum in cats, and is associated with inflammatory bowel disease or lymphosarcoma in older cats

e.     all of the above are true

7. Name possible causes of ileus after intestinal surgery.

            a. pain (sympathetic stimulation)

            b. peritonitis

            c. hypokalemia

            d. mechanical obstruction

            e. All of the above

8. Name possible clinical signs of intestinal leakage after resection and anastomosis.

            a. fever

            b. abdominal pain

            c. anorexia

            d. vomiting

            e. all of the above

9. True or False: Linear foreign bodies sometimes cause full thickness perforation of the mesenteric aspect of the intestine.

10.  Which suture is best for closure of the intestine in a dog or cat:

            a. 2-0 catgut

            b. 3-0 polypropylene,  CA 2 needle

            c. 4-0 PDS, AR 1 needle

            d. 4-0 PDS, RB 1 needle

            e. 4-0 stainless steel

           

Answers: F, a, d, c, b, e, e, e, T, d

4 Ways to Avoid Leaving a Sponge in the Abdomen of a Dog, and Look What Else Someone Left In!

1. Count! Do a sponge count before and after the surgical procedure. If there is a discrepancy, search the surgical site for the sponge. If no sponge is found, obtain a postoperative radiograph to determine if a sponge is retained (see item #2).

 

Fig. 1: Ray-tek 4 X 4 sponges on the left have a radiopaque line in them (the blue material)
Larger laparotomy sponges on the right have a blue radiopaque ribbon on them. 

2. Use Ray-tek sponges. They have linear radiopaque material in them so that the sponge can be easily seen on radiographs. (Fig. 1)

 

Fig. 2: A sponge left in a dog during a spay. Bowel and mesentery are adhered to the sponge
making removal difficult.

3. Never pack an entire sponge in a body cavity. As the sponge absorbs blood and other fluids it blends in with the tissues and becomes almost invisible. (Fig. 2) Always leave part of the sponge outside of the cavity, or attach a forcep to it and keep the forcep outside of the cavity.

4. Use laparotomy sponges. (Fig. 1) These large, very absorbent sponges are a better choice than 4 x 4 sponges for packing off organs in the abdomen or thorax. A blue radiopaque ribbon is attached to them that can be left outside of the body cavity. Having said this, I have seen these left in the abdomen as well. Count them before and after the surgery also.

 

Fig. 3: Abdominal radiograph of a 4 year old female St. Bernard that was
spayed as a puppy.

Sponges are not the only things left in patients. (Fig. 3) The radiograph is a St. Bernard I operated many years ago at the Animal Medical Center in New York City. The dog had been spayed several years earlier. The dog presented to us for vomiting and abdominal pain. On abdominal exploratory, a section of bowel mesentery had become entrapped and strangulated in one of the rings of the forceps. The forceps were rusted and broken. Intestinal resection and anastomosis was necessary.

Establish protocols for all surgical procedures to prevent mistakes. Although they seem tedious, they are necessary to avoid complications and resultant patient morbidity.