Salivary Mucocele

Also known as: Sialocoele — Ranula

Introduction

Salivary mucocoele is a term used to describe the abnormal accumulation of saliva outside of a salivary gland. The cause of mucocoeles is often unknown but it may occur where there is a lesion of the sublingual or mandibular salivary duct, or in one of the small ducts of the polystomatic sublingual salivary gland. Saliva leaks out and is not absorbed - causing the formation of a pseudocyst.

Mucocoeles are not true cysts because they are not lined by a layer of epithelium but by inflammatory connective tissue. The sublingual and mandibular salivary glands are most commonly involved but any of the glands produce a mucocoele. The saliva accumulates in one of three places:

• Cervical mucoceles are the most common, developing caudal and ventral to the mandible. The swelling is usually to one side but may occur in the midline.
• A ranula is an elongated swelling on the floor of the mouth. They usually originate from the polystomatic sublingual glands and are therefore most often found beneath the tongue. Due to its location, it may interfere with mastication and swallowing.
• Mucocoeles on the pharyngeal wall are less common but they may interfere within respiration or swallowing.

Signalment

Salivary mucocoeles are not common but they occur mainly in dogs.

Diagnosis

Clinical Signs

Salivary mucocoeles may be asymptomatic but the following signs may be observed:

• Dysphagia with obvious gagging or pharyngeal retching.
• Dyspnoea or respiratory stridor.
• Initially painful swelling evolving to a non-painful, enlarging, fluctuant mass, usually in the cervical region.
• Mucocoeles originating from the zygomatic gland may cause exophthalmus or strabismus if they impinge on the orbit.
• If the structure becomes infected, pain and typical signs of infections (pyrexia, depression and anorexia) may be observed.

Laboratory Tests

A definitive diagnosis relies on fine needle aspiration of the structure and cytological examination of the fluid obtained. Typically, this reveals yellow/amber mucoid or blood-tinged material with evidence of mild inflammation. Periodic Acid Schiff (PAS) staining may be used to detect mucus in the fluid.

Diagnostic Imaging

An ultrasound scan may be performed over the area of swelling to discount other possible diagnoses (including neoplasia, abscesses or lymphadenopathy). This imaging modality can also be used to guide fine needle aspiration. Alternatively, any of the salivary ducts can be cannulated within the oral cavity and water soluble iodine-containing contrast medium can be instilled into the salivary gland (positive contrast sialography). Radiographs of the affected area will then show whether the mucocoele is associated with a particular gland. This technique is technically difficult to perform and care should be taken not to spill contrast material into the mouth, potentially confusing the radiographic image.

Treatment

Surgical drainage and removal of the damaged gland and duct is the treatment of choice. Many of the salivary glands lie in close association with major structures of the head (including the cranial nerves and major blood vessels) and it may be advisable to refer such cases to a specialist centre for surgical removal. If the mucocoele cannot be removed surgically, it may be drained periodically by percutaneous aspiration. However, mucocoeles managed in this way rapidly recur and surgical removal of the tissue responsible for production of the saliva is preferable.

Ranulas (which are within the buccal cavity) may be treated by marsupialisation, in which the wall of the ranula is incised to allow the contents to drain into the mouth. The rim of the ranula must then be sutured to the oral mucosa to hold the aperture open. Additionally, the monostomatic and polystomatic sublingual and mandibular salivary glands on the affected side can be surgically resected.

Pharyngeal mucocoeles require complete gland and duct removal to alleviate dyspnoea and a temporary tracheostomy tube may be required in severe cases.

Prognosis

The prognosis is good for complete recovery. Complications arise if the salivary glandular tissue is not completely removed (leading to recurrence of the mucocoele) or if major structures are damaged during the surgical procedure.

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References

Guilford, W.G., Center, S.A., Strombeck, D.R., Williams, D.A. and Meyer, D.J. (1996) Strombeck's Small Animal Gastroenterology (3rd Edition) W.B. Saunders Company

Hall, E.J., Simpson, J.W. and Williams, D.A. (2005) BSAVA Manual of Canine and Feline Gastroenterology (2nd Edition) BSAVA

Merck & Co (2008) The Merck Veterinary Manual

Verstraete, F. J. M. (1998) Self-Assessment Colour Review - Veterinary Dentistry Manson

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