January 2007
Dr Gerhard Steenkamp

A three year-old Border collie dog is presented with a fluid filled mass of the Right cheek. (DSC 02440). The dog is not painful when you touch the lesion, nor is there any history of anorexia, pawing at the face or any other behavioural indicator that this lesion may adversely affect the dog.

a. How would you make a diagnosis in this case?
b. What is the pathogenesis of this lesion?
c. Discuss treatment options for this case.

Memorandum

a. After the dog is aneasthetised a proper palpation of the mass as well as surrounding tissue and the regional lymph nodes.  When a cyst is confirmed on palpation, fluid can be extracted from the cyst for evaluation.  In this case a clear straw coloured fluid was seen (DSC 02443).  When placed between the thumb and index finger there is a strand of fluid forming when the fingers are drawn apart.  The fluid is low in cell numbers and may sometimes be blood tinged.  The mucin and amylase content is variable and therefore not a reliable indicator.

b. Saliva will leak from the salivary gland into the surrounding tissue and a cyst lined by epithelium can form (mucous extravasation cyst) or the cyst may not be lined by epithelium but rather granulation tissue and is then called an extravasation cyst.  Obstruction or trauma to the duct is the most plausible explanations for the development of these cysts.  In this case the salivary gland in question is probably one of the many accessory salivary glands located in the buccal mucosa, called buccal salivary glands

c. Complete resection of the mucous extravasation cyst together with the offending salivary gland is the only treatment option available (DSC 02446).  Submitting the tissue for histopathological examination post operative is highly advisable as this is often the only way of knowing if the cyst together with the salivary gland was removed.