Cervical Sialocele

A salivary mucocele, also known as a sialocele, is an accumulation of saliva that has escaped from a damaged salivary gland or salivary duct and collected within surrounding tissues. Clinically, it usually presents as a soft, fluctuant, painless swelling in the neck region or inside the oral cavity. Although often mistakenly referred to as a salivary cyst, a mucocele is not a true cyst. Mucoceles are lined by inflammatory (granulation) tissue that forms in response to irritation caused by free saliva within the tissues, whereas true cysts are lined by epithelial (glandular) tissue that actively produces fluid.

Salivary mucoceles are classified according to their location:

• Cervical mucocele: This is the most common form. Saliva accumulates in the upper cervical region, beneath the jaw, or within the intermandibular space between the mandibles (Figures 1 and 3).
• Sublingual mucocele (ranula): A frequent location is the floor of the mouth, adjacent to the tongue. This type commonly occurs in conjunction with a cervical mucocele (Figure 2).
• Pharyngeal mucocele: This is an uncommon form and is essentially a variant of the cervical mucocele, with saliva accumulating primarily within the pharynx (Figure 4).
• Zygomatic mucocele: This is a very rare condition in which saliva originates from the zygomatic salivary glands located just beneath the eye.

In most cases, the exact cause of salivary mucoceles is not identified. However, trauma—such as that caused by choke collars, bite wounds, or chewing foreign objects—is generally considered the most likely initiating factor. When saliva leaks from a ruptured salivary gland or duct, it accumulates in the surrounding tissues and triggers a marked inflammatory response. Over time, a connective tissue capsule forms around the saliva, preventing further spread.

Salivary mucoceles occur almost exclusively in dogs and are only rarely seen in cats. All breeds can be affected, although an increased incidence has been reported in Poodles, German Shepherds, Dachshunds, and Australian Silky Terriers. There is no age predisposition, and the condition may develop at any stage of life.

Cervical mucoceles typically appear as a slowly enlarging, soft, painless, fluctuant swelling in the upper neck or intermandibular region (Figure 1). In most dogs and cats, the mass itself does not cause significant discomfort or functional problems.

When the mucocele is sublingual (ranula) (Figure 2), affected animals may have difficulty eating and may experience bleeding due to repeated trauma to the mass during chewing. Pharyngeal mucoceles are generally not detected unless the oral cavity and pharynx are examined under sedation. Animals with pharyngeal mucoceles may develop respiratory distress as the expanding mass obstructs the airway. This represents a potentially life-threatening emergency, requiring prompt treatment, as affected pets may die from acute respiratory compromise. Difficulty swallowing may also be observed.

Diagnosis of a salivary mucocele is usually straightforward. Palpation of the salivary glands is typically easy, and—with the exception of pharyngeal mucoceles—the lesions are readily recognized as soft, non-painful, fluctuant swellings. Other conditions, such as tumors or abscesses, may appear similar but are usually firmer or painful.

Over time, cervical mucoceles may migrate toward the ventral midline, making it difficult to determine whether the left or right salivary glands are affected (Figure 1). Examining the patient in dorsal recumbency under sedation (Figure 3) often allows the swelling to shift back toward the affected side.

Routine laboratory tests are generally not helpful for diagnosing salivary mucoceles. When there is uncertainty regarding whether the mass represents a mucocele or an abscess, sterile aspiration of the swelling may be performed. Saliva typically appears as a clear to yellowish, sometimes blood-tinged, thick, ropy fluid with a low cellular content (Figure 5). An increased white blood cell count within the aspirated fluid suggests infection of the salivary gland (sialadenitis) or an abscess. In equivocal cases, specialized laboratory staining techniques may assist in identifying the nature of the fluid.

Radiographs are rarely required for diagnosis; however, if neoplasia is suspected, thoracic radiographs are indicated to assess for metastatic disease.

The only definitive and effective treatment for a salivary mucocele is surgical removal of the affected salivary gland or glands (Figure 6).

Repeated aspiration of the mucocele does not provide a permanent solution. Although aspiration may temporarily reduce the swelling for weeks or even months, recurrence is common. Additionally, aspiration carries a risk of introducing bacteria into the mucocele, potentially resulting in infection and making subsequent surgical treatment more difficult.

Standard surgical treatment involves removal of the mandibular and sublingual salivary glands on the affected side. These glands are excised together because the duct of the mandibular gland passes through the sublingual gland, and removal of one inevitably traumatizes the other. The mandibular gland lies adjacent to large veins that contribute to formation of the jugular vein, and careful surgical technique is required to avoid injury to these vessels and several critical nerves in the area.

Sublingual mucoceles (ranulas) (Figure 2) may also be treated with marsupialization, in addition to removal of the mandibular and sublingual glands, to allow continuous drainage into the oral cavity. Marsupialization involves excision of an elliptical portion of the sublingual mucosa overlying the mucocele, followed by suturing of the oral mucosal edges to the underlying connective tissue.

In many cases, a surgical drain is placed to permit continued drainage of fluid from the surgical site while healing occurs.

If a drain is placed, several days of postoperative drainage should be expected. When a bandage is applied, it must be changed frequently. If the wound is left unbandaged, warm compresses using a moist towel are recommended to clean the surgical site and encourage fluid drainage.

The prognosis following appropriate drainage and complete removal of the affected salivary glands is excellent, and most dogs go on to live normal lives. Dogs do not develop dry mouth following removal of the mandibular and sublingual glands, even when glands are removed bilaterally.

Postoperative complications are uncommon when surgery is performed by an experienced surgeon. Occasionally, a fluid-filled pocket (seroma) may form at the surgical site; this may be drained or allowed to resolve spontaneously. Infections are possible but rare. If salivary gland tissue is not completely removed, recurrence of the mucocele may occur.