A Layman's Guide to the Health and Nursing Care of Rats
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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.
Photos and case studies in following links show tumor growth and ulceration as a result of squamous cell carcinoma.
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.
Wound drain placement for removal of pus or fluid build-up if determined to be beneficial.
If infection is present, treatment with broad spectrum antibiotics recommended.
See the Rat Medication Guide for a listing of drugs, dosages, and usage.
For milder form of pain control in the post recovery period:
Banamine (flunixin meglumine). Do not use if a corticosteroid has already been prescribed.
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.
Refer to Rat Medication Guide for listing of NSAIDs, Corticosteroids, and Analgesics.
*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 may be 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.
Euthanasia should be considered before condition adversely affects quality of life.
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. If the rat is not drinking discuss providing warmed SQ fluids with your vet.
For 24-48 hours post-op, feed iron-rich foods to prevent anemia (cooked liver, scrambled or hard-boiled eggs).
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, provide feeding in an oral needless syringe every 2 hours, being careful to prevent aspiration. Providing small amounts of food in this fashion will help to promote intestinal motility during illness. Include additional multi-vitamin supplement (can be found in pet store) if food intake is poor.
It may be necessary to provide softer or pureed foods, or baby foods for those rats with malocclusion or distortion of the jaw.
Assist rat with grooming and cleaning if needed.
Posted on March 7, 2008, 13:08,
Last updated on March 13, 2008, 19:39
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