Last month, I wrote about salivary gland anatomy. This time, we will look at conditions that may require salivary gland surgery and approaches to surgery of various salivary glands.
A sialocele is an abnormal accumulation of saliva resulting in a freely compressible swelling in the neck (Figure 1). Another term that has been used to describe this condition is salivary mucocele. However, as our veterinary patients produce a combination of mucous and serous salivary secretions, sialocele may be a more appropriate term.1 This disease occurs most commonly in dogs of all ages, and its etiology is thought to be a result of trauma to the duct of a monostomatic gland, resulting in extravasation of saliva into the subcutaneous and submucosal tissues with formation of a pseudocyst. However, ineffective attempts to surgically create sialoceles2 and breed predilections (poodles)1 suggest other factors, such as genetics, may play a role. Occasionally, especially if the sublingual gland is involved, a ranula (sublingual sialocele) may occur in conjunction with or in the absence of a cervical sialocele. Though palpation is a very helpful diagnostic tool, aspiration of the swelling can be done to obtain more information. Aspiration of a sialocele produces a straw-colored or blood-tinged viscous fluid. This fluid may be submitted for cytology, but the consistency and appearance of the fluid is very telling. Repeated aspiration in an attempt to drain the fluid is rarely beneficial and is not recommended since saliva is produced at such a rapid rate, any beneficial results of aspiration are transient.
Surgical approach to sialoceles
Sublingual sialocele (ranula). Surgical marsupialization of ranulas has been advocated historically for treatment of ranulas. However, as a sole procedure, this technique may be unable to resolve the problem. Marsupialization refers to removal of a full-thickness portion of sublingual mucosa to allow for continued intraoral drainage of accumulating fluid. The problem with relying on marsupialization lies in the fact the fluid-filled cavity is not lined by a cystic lining, but is rather a pseudocyst, so the potential for granulation and blockage of the drainage site is likely. Therefore, removal of the affected gland(s) is the treatment of choice.
Cervical sialocele with or without ranula. As the mandibular and monostomatic portion of the sublingual glands are intimately associated, they are removed together as one entity. Sometimes, the swelling can arise close to the midline, and it may be difficult to determine if the right or left mandibular/sublingual gland complex needs to be removed. In these cases, place the patient in exact dorsal recumbency, and the cervical swelling will fall toward the affected side.
A lateral or ventral approach can be pursued. A skin incision is made slightly medial to the body of the mandible, beginning at the caudal aspect of the mandibular gland, extending cranially to the mid-body of the mandible. The common capsule of the mandibular and sublingual glands is incised over the mandibular gland. The mandibular gland is mobilized after separation and ligation of vascular structures associated with the gland. Digital dissection is continued rostrally, allowing for exposure of the monostomatic portion of the sublingual gland. The gland/duct complex courses between the medial pterygoid and digastricus muscles. If the origin of the mucocele is identified, the ducts rostral to the origin can be ligated and the glands removed. If the digastricus muscle obscures visualization rostrally, it can be retracted or transected mid-body for greater visualization. The lingual nerve should be avoided, which is dorsal to the gland/duct complex. After removal of the glands, the digastricus may be reapposed if incised using 2-0 absorbable suture. Removal of the entire pseudocyst is not necessary; a Penrose drain may be placed to prevent accumulation of fluid postoperatively (Figure 2). Subcutaneous space is closed using 3-0 absorbable suture, followed by routine skin closure. The excised glands should be submitted for histopathological examination. The drain is left in place for approximately four days.
Zygomatic sialoceles may occur due to sialoliths, neoplasia, trauma to ducts/gland, or for idiopathic reasons. Exophthalmos is one of the most marked clinical sign with zygomatic sialoceles, along with ventral deviation of the pharyngeal and palatal mucosa ventrolateral to the eye. Access for removal of the zygomatic gland can prove quite challenging. Extraoral approach may involve temporary or permanent removal of a portion of the rostral zygomatic arch to obtain access from a lateral approach. The gland can then be removed from an intraoral approach during caudal maxillectomies.
Salivary gland neoplasia
In one study, salivary gland neoplasia was diagnosed in approximately 30 percent of salivary gland biopsies sent to pathologists.3 The most common type of neoplasia in both dogs and cats is salivary adenocarcinoma. The mandibular gland is the most commonly affected by neoplasia in cats and the parotid is the most commonly affected in dogs. Due to the fact salivary glands are surrounded by vital structures, complete removal of malignant salivary gland tumors with a wide margin of normal tissue may not be feasible. Unlike with sialoceles, dissection of a neoplastic mandibular gland is best done outside the capsule instead of within the capsule to try to obtain some semblance of margins. The combination of excision of the gland followed by radiation therapy may provide the best results with the least amount of problems.
Sialoliths have been documented to occur in all of the major salivary glands of the dog, and obstruction caused by a sialolith may result in formation of a sialocele. The obstructing stone may be located near the duct’s papilla, in which case it may be able to be grasped with small forceps. This may require enlarging the papilla’s opening. Incising over the duct to remove stones that are not at the papilla may be successful, but stricture or new stone formation may result in blockage. Sialoadenectomy is the most foolproof option, though removal of the parotid salivary gland without any complications can be challenging due to its diffuse nature and its intimate association with the facial nerve.
1 Lane JG. Surgical treatment of sialoceles. In: Verstraete FJM, Lommer MJ. Oral and Maxillofacial Surgery in Dogs and Cats. London: Saunders Elsevier; 2012. p 501-510.
2 DeYoung DW, Kealy JK, Kluge IP. Attempts to produce salivary cysts in the dog. Am J Vet Res. 1978;39:185-186.
3 Spangler WL, Culbertson MR. Salivary gland disease in dogs and cats: 245 cases (1985-1988). J Am Vet Med Assoc. 1991;198(3):465-9.
John Lewis, VMD, FAVD, DAVDC, practices dentistry and oral surgery at NorthStar VETS in Robbinsville, N.J., and is the founder of Silo Academy Education Center in Chadds Ford, Pa.