Sialocele

The most common indication for salivary gland surgery in veterinary medicine is a salivary mucocele, which is also commonly referred to as a sialocele. For consistency, it will be referred to as a sialocele for the remainder of the chapter. A sialocele is defined as an accumulation of salivary fluid due to its leakage into the interstitial space.³ Although specific underlying causes have been reported, such as trauma, foreign bodies, sialoliths, neoplasia, and even heartworm infection,⁴ an underlying cause is rarely found. Thus, an idiopathic sialocele is the most common type seen in veterinary medicine.

Depending upon the gland affected and the deposition of saliva, a sialocele can manifest in different ways. The most common presentation of a sialocele is a submandibular swelling secondary to leakage from the mandibular and sublingual gland complex, which share a capsule.³ Alternative differential diagnoses for submandibular swellings include branchial cysts, foreign bodies, trauma, and neoplasia. Salivary mucoceles have also been reported in alternate locations, including in the nasopharynx,⁵ pharynx,⁶ side of the face,⁷ and periorbital region. Pharyngeal mucoceles are most commonly seen in miniature and toy poodles. Approximately 50% of patients with a pharyngeal sialocele present for dyspnea, and 43% have a concurrent cervical mucocele. The mandibular–sublingual complex is the most commonly implicated source of pharyngeal mucoceles. In one study, recurrence occurred only in one patient of 14 who had the associated mandibular and sublingual salivary glands excised.⁶

The location of the swelling is generally related to which salivary gland is affected. A mucocele underneath the tongue is also often referred to as a ranula, which is the result of a sublingual sialocele within the polystomatic portion. Sialoceles originating from the parotid salivary gland will typically present with swelling on the side of the face, near the ear canal.⁸ Further, sialoceles originating from the zygomatic salivary gland frequently result in exophthalmos; however, there is one report of a zygomatic sialocele resulting in submandibular swelling.³

Salivary Neoplasia

Salivary neoplasia can arise from any of the major or minor salivary glands. Approximately 88% of all salivary gland neoplasia are epithelial tumors.¹ The most commonly reported cancers are adenocarcinoma, mucoepidermoid carcinoma, acinar cell carcinoma, squamous cell carcinoma, and carcinosarcomas. Other reported tumors include extraskeletal osteosarcoma,⁹ sialolipomas,¹⁰ pleomorphic adenoma,¹¹ and basal cell carcinoma.¹² As with any neoplastic process, the workup should include FNA or biopsy of the area of concern, as well as appropriate staging. Staging should include thoracic radiographs, abdominal ultrasound, and FNA of the suspected draining lymph node. These diagnostics could also be supplanted by computed tomography (CT) of the thorax, abdomen, and ideally, the head and neck to evaluate the primary tumor and local lymph nodes. Surgical excision is the treatment of choice for most salivary gland tumors; however, due to the anatomic location of all salivary gland tissue, wide excision is not feasible. Therefore, owners should be counseled that radiation or other adjunctive therapy may be recommended after reviewing the histopathology results.

Sialoliths

Although uncommon, sialoliths have also been reported in the dog. The etiology is thought to be due to slow or obstructed salivary flow from a chronic sialocele or secondary to a previously performed parotid duct transposition. The stone composition is often calcium oxalate or calcium carbonate.¹³ Sialoliths can be incidental findings but can also obstruct salivary ducts and can be seen concurrently with a sialocele.¹⁴ Surgical excision of the affected salivary gland and duct is curative (Figure 13.1).

Sialoadenitis

Sialoadenitis, an immune‐mediated inflammatory condition, has been reported in dogs.¹⁵ The predominant clinical finding in this condition is enlargement of the affected salivary gland; however, dogs may also present with pain in the region of the gland, hypersialism, or nausea.¹⁵ Histopathological findings include inflammatory infiltrates of predominately neutrophils, which surround and can replace salivary acini and ducts. Necrosis can also occur, which may be due to pressure necrosis from inflammation within the inflexible capsule of the gland. This condition may respond to corticosteroids and can be differentiated from sialoadenosis on the basis of cytology or histopathology.¹⁵

Sialoadenosis

Sialoadenosis is a noninflammatory condition of the salivary glands. It is typically associated with bilaterally enlarged and uniform salivary glands that are non‐painful.¹⁶ Surgical excision is not helpful, but dogs will often respond to phenobarbital treatment.¹⁶ Confusingly, this condition has also been described in the literature as necrotizing sialometaplasia and hypersialism. The pathophysiology is poorly understood but thought to be related to a primary abnormality of sympathetic innervation to the associated salivary gland. Besides the palpably enlarged glands, patients can also present with retching, gulping, and vomiting. Cytology and histopathology can reveal inflammation or normal salivary tissue.¹⁶ In one study, all dogs had reported improvement in clinical signs within days of starting typical anti‐seizure doses of phenobarbital; however, treatment duration can be prolonged due to relapse of signs after less than a month of treatment.¹⁶ Sialoadenosis should be considered in dogs with bilaterally symmetrical salivary gland enlargement and concurrent gastrointestinal signs. Although cytology and histopathology are not definitive for the diagnosis of this condition, they may be able to rule out neoplastic or inflammatory salivary gland diseases.