By Colonel Stefanos Kladakis

Salivary mucoceles are a collection of saliva that has leaked from a damaged salivary gland or duct and they are surrounded by granulation tissue. They are not cysts. Cysts are cavities lined by epithelium, whereas the granulation tissue lining of a mucocele is produced secondary to inflammation caused by free saliva in the tissues. Saliva takes the path of least resistance, irritates tissue and causes inflammation. Granulation tissue forms in response to the inflammation and prevents saliva from migrating further. The cause of salivary mucoceles is rarely identified. The sublingual salivary gland is the most commonly involved. 

Dogs are more frequently affected than cats. Poodles, German shepherds and Dachshunds, are more commonly affected. An animal of any age may develop a mucocele but it’s more often in young male dogs. Clinical signs depend on the location of the mucocele. Most dogs have cervical or intermandibular mucoceles and are asymptomatic. These animals are usually presented for treatment of a gradually developing, fluctuant, painless mass. Patients with ranulas may present due to oral bleeding. Respiratory distress and dysphagia may be seen in patients with pharyngeal mucoceles. Swelling in the orbital area due to zygomatic mucoceles may cause exophthalmos. Most mucoceles are soft and fluctuant whereas tumors and abscesses are generally firm. It is sometimes difficult to identify the affected side when mucoceles are located on the ventral midline or intermandibular space. Palpation of cervical mucoceles may cause the sublingual tissues to bulge on the affected side. Concurrent sublingual and cervical mucoceles originate from the side where the sublingual mucocele is located. Survey radiographs rarely help, except in cases involving sialoliths, some foreign bodies, or neoplasia. Thoracic radiographs are indicated to evaluate for metastasis if neoplasia is suspected. Laboratory abnormalities are rare. Paracentesis of the mucocele should be performed aseptically to prevent infection. Aspiration of a clear, yellowish, or blood-tinged, mucoid fluid with a low cell count is consistent with saliva. Swellings in the same regions as mucoceles may be caused due to sialoadenitis, salivary neoplasia, sialoliths, cervical abscesses, foreign bodies, hematomas, cystic or neoplastic lymph nodes. Occasionally mucoceles may be difficult to distinguish from cysts or tumors. Salivary neoplasia, most commonly adenocarcinomas, affects older animals and may be associated with halitosis, weight loss, dysphagia, exophthalmos, Horner’s syndrome, sneezing, and dysphonia. 

Medical Management: Emergency aspiration of the mucocele may be necessary for animals presented with respiratory distress. Repeated drainage does not eliminate mucoceles and may complicate subsequent surgery by leading to abscessation or fibrosis. Mucoceles rarely resolve without surgery. 

Surgical Treatment: Complete excision of the involved gland-duct complex and drainage of the mucocele are curative. Resection, aspiration or drainage of the mucocele without removing the affected salivary glands will usually lead to recurrence. If you are having trouble identifying the affected side in an animal with a cervical mucocele, place the animal on its back. The contents of the mucocele often gravitate to the side of the affected gland. 

Surgical Anatomy: Dogs and cats have four major pairs of salivary glands. The parotid, mandibular, sublingual, and zygomatic glands. The mandibular gland is large and ovoid and lies within a fibrous capsule, caudal and ventral to the parotid gland. It is located between the linguofacial and maxillary veins as they merge to join the external jugular vein. The mandibular duct runs with the sublingual gland toward the floor of the mouth and opens on a small papilla lateral to the rostral border of the frenulum. The sublingual gland is divided into monostomatic and polystomatic portions. The monostomatic portion originates on the rostroventral border of the mandibular gland. The ducts from this portion of the sublingual gland course with the mandibular duct but often open on separate papillae. The polystomatic portion is divided into several lobules that surround the mandibular duct and lie immediately beneath the oral mucosa, secreting directly into the oral cavity. 

Surgical technique for Mandibular and Sublingual Salivary Gland Excision. How to? 

• Place the animal in dorsal recumbency for a ventral approach.

• A large area from the mid-cervical region to the most rostral portion of the ventral mandible is clipped and aseptically prepared (some are used to the lateral approach, an oblique positioning of the patient’s head and neck can also be used so that dissection can be extended from lateral to ventral when approaching rostral salivary tissue removal).

• An incision is made starting from a point 4-5 cm caudal to the ramus of the mandible on the affected side and extending rostrally toward the mandibular symphysis (if bilateral gland removal is to be performed, a midline incision can be made).

• The platysma muscle is incised to facilitate identification of the external jugular bifurcation. • The mandibular gland is located just cranial to this bifurcation.

• Tissues are bluntly dissected to expose the capsule covering the mandibular and sublingual salivary glands. The salivary glands must be differentiated from mandibular lymph nodes. The capsule over both glands is incised and bluntly dissected off the glandular tissue to facilitate ligation of vessels on the medial side of the mandibular gland.

• The gland complex is then retracted caudally to allow blunt dissection of the sublingual gland under the digastricus muscle. With an hemostat placed from rostral to caudal under the digastricus muscle, the ducts are clamped just rostral to the large glandular complex, and the mandibular and main sublingual gland are excised. The remaining ducts and sublingual glands are pulled under the digastricus muscle.

• Blunt and sharp dissection are continued rostrally to the level of the lingual nerve.

• The mylohyoideus muscle is incised for better exposure of the rostral glandular tissue and lingual nerve.

• Most intermandibular, cervical, or pharyngeal mucoceles resolve if duct and glandular tissue is removed up to the lingual nerve.

• If a ranula is present, dissection should continue rostral to the lingual nerve under the mylohyoideus to remove all of the glandular tissue up to the sublingual caruncle.

• The duct is ligated as rostrally as possible and transected.

• Lavage the surgical site before closure.

• The mylohyoideus, platysma muscle, and subcutaneous tissues are re-apposed with an synthetic absorbable monofilament suture material.

• Finally the mucocele is drained with an active or passive drain. 

Marsupialization for Arsupialization for Pharyngeal Mucoceles and Ranulas: Ventral recumbency and maximum opening of the mouth facilitates marsupialization of pharyngeal and sublingual mucoceles (ranulas). They are treated by marsupialization of the fluid-filled pocket and removal of the mandibular and sublingual salivary gland complex, including as much of the rostral submandibular glandular tissue as possible. For marsupialization, a large full-thickness oval area of the tissue overlying the mucocele is excised. The remaining external mucosa is sutured to the lining of the mucoceles with 4-0, synthetic, absorbable, monofilament suture material. 

Postoperative care and Assesment: Histologic assessment of the excised gland is useful to rule out neoplasia as a cause of the mucocele. Change bandages daily if a Penrose drain has been placed. Depending on the amount of drainage, remove the drain when drainage is minimal. Allow the drain site to heal by second intention. Soft food should be fed for 3-5 days after ranula marsupialization. 

Complications:

• Seromas can be formed in the dead space created after removal of the glands. They typically resorb and do not need aspiration or drainage.

• Infection is rare if aseptic technique is used.

• Recurrence of the mucocele may be due to the fact that original side of origin was misdiagnosed or if an inadequate portion of the gland was excised. Regional lymph nodes are sometimes mistaken for salivary glands. Dissection may be difficult if the mucocele was previously infected or drained. 

Prognosis: Very rarely mucoceles will resolve without surgery. The prognosis is excellent if the disease is accurately diagnosed and excision is complete. 

Useful tips:

• When in doubt, dorsal recumbency may help you identify the origin of the mucocele!

• Ventral or lateral approach? My preference is ventral because it provides much better exposure and should be definitely preferred for bilateral disease. Lateral approach may make your life more difficult if a most rostral excision has to be performed.

• Use a sterile marker pen for your anatomical landmarks!

• An assistant is not essential, but will make your life easier!

• Electrocautery is also not essential, but will make you sweat less! • For drainage you may use passive or active drains. Both are fine. If your choice is Penrose, remember that saliva is an irritant to the skin, so it is a good idea to place some lubricating jelly below the exit point to prevent local dermatitis.

• In cases of recurrence you may also need to consider oral approach to retrieve the remainder/ remnants of the sublingual salivary gland! 

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