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Zymbal’s glands are located beneath squamous epithelium at the anterior and posterior aspect of the ear canal, and as a single external gland that is located anterior and ventral to the base of the external ear canal. The external portion of the gland appears triangular in shape, pink to yellow in color and is 3 to 5 millimeters in diameter. The glands excretory duct passes between the temporal bone and the cartilaginous plates to enter the ear canal near the tympanic membrane (Mohr et al., 1994).
The morphology of the Zymbal’s gland appears to be typical of other sebaceous glands, and its size and microscopic appearance tend to remain the same in the adult rat throughout life. It is also believed that the production of the end secretory product connected with the sebaceous holocrine process, called sebum, continues throughout life as well. However, the specific function of the Zymbal’s gland remains unknown.
Age-related nonneoplastic changes can occur in the Zymbal’s gland. Ductal cysts have been known to form which may be empty or contain thick, dried material. Occasionally tumors may be found within these cystic areas.
Neoplastic changes can also occur as rats age. The spontaneous development of tumors tends to increase between 18 and 24 months of age (Mohr et al., 1994).
Neoplastic growths can range from being clinically inapparent to papillomatous growths within the ear canal (Seely, 1991; Mohr et al., 1994). They can present as subcutaneous nodules, or as ulcerated tumors on the side of the face near the ear. The majority of these tumors are found to be unilateral (occurring on one side only). Since in many cases these tumors can be found underlying an abscess or formed within a cyst, veterinarians need to pay special attention when attempting to excise and drain. Zymbal’s tumors that are aggressive often have a gritty texture to them. Local invasion by these tumors is common, and as many of these tumors are malignant, metastasis to the lungs is not unheard of.
Tumors of the Zymbal’s gland are believed to arise from glandular acini, or from dutal epithelium, (Seely, 1991; Mohr et al., 1994) and may be classified as adenomas or adenocarcinomas based on histology.
Most often tumors arising from the Zymbal’s gland, in rats, are found to be malignant. While these malignant tumors are often only locally invasive; for rats diagnosed with a Zymbal’s gland carcinoma the prognosis is poor. The treatment goal is primarily palliative, promoting quality of life as long as the rat is comfortable.
Additional case histories involving Zymbal’s gland
Veterinarians please note: tumors can be found underlying an abscess or formed within a cyst when occurring in the Zymbal’s gland. Use caution when attempting to excise and drain. The cut surface of tumor may appear gritty.
FNA (fine needle aspiration)
Histological examination or cytology for cell type.
It is not unusual to find the area overlying the tumor has abscessed. In this event, surgical drainage (lancing) and debridement may be performed by the veterinarian.
Euthanasia should be considered before condition adversely affects quality of life.
If infection is present, treatment with broad-spectrum antibiotics recommended.
For information regarding medications refer to the Rat Medication Guide.
Medication to be given by mouth or injection will be based on the severity, or if the rat is able or willing to take meds by mouth.
*Note: Always check with a veterinarian when giving any medications to determine appropriate use or contraindication.
Where malocclusion is present, trimming of the teeth may be necessary. In cases of malocclusion or distortion of the jaw a soft diet is required. Block food may be softened in soy baby formula or Ensure, baby foods may also be offered. Pureeing of foods in a blender is also another option. In addition, skin care may also be required in the presence of drooling or damp chin due to malocclusion.
Provide fluids to prevent dehydration. If the rat is willing to drink on its own or by syringe (using needless syringe), the following are suggested: fresh water, or a glucose mixture of 3 teaspoons of honey in 1 pint of warm water (be sure water is warm enough to dissolve honey and then cooled just enough so as not to burn rat’s mouth), or Jello water, or electrolyte replacement drinks such as Pedialyte or Gatorade which can be found in local grocery stores. Please note that Pedialyte is only good refrigerated for 24 hours after opened, but can be frozen as ice cubes and kept longer, and then thawed when needed. Care should be taken to prevent aspiration when giving fluids with an oral syringe.
Provide additional nutritional supplement, such as Soy baby formula, Ensure, Boost, NutriCal paste (for dogs and cats found in pet store), mashed avocado, and baby foods. If the rat is not willing to eat on its own it may be time to discuss humane euthanasia with veterinarian.
Posted on March 7, 2008, 13:08,
Last updated on December 9, 2012, 17:06