Tumor originating from or arising from an auditory sebaceous (fatty) gland that opens into each external ear canal known as Zymbal’s gland.
The following clinical signs may be observed:
- Cyst(s) or abscess at or near mass.
- A unilateral firm mass seen or felt ventral to the ear (side of face).
- A papillomatous growth seen within the ear itself.
- An ulceration of the skin overlying the mass.
- Bleeding from the ear.
- Occasional repetitive shaking of the head.
- End stage head tilt.
- Distortion of the jaw.
- Accompanying signs of malocclusion (may be severe).
*Note: for additional information on recognizing various signs of pain or discomfort refer to: Signs of Pain In Rats.
The bilateral Zymbal’s glands are adjacent to the auditory canal and are made up of several lobules of modified sebaceous glands. They were first described independently by Zymbal and by Zawish-Ossenitz in 1933 (Pliss, 1990; Seely, 1991; Mohr et al., 1994).
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 ductal 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.
Case Histories of Zymbal’s Gland Tumor
- Fig. 1: Zymbal’s gland tumor in 18-month-old male rat (Joey)
Additional case histories involving Zymbal’s gland
- Fig. 2: Squamous ca involving Zymbal’s gland (Ramekin)
- Fig. 4a: Squamous ca of the inner ear canal with ulceration, abscess, and infection in female rat (Jet’s case history). Includes link to cleaning of wound and supplies used. *Note: this case is unverified histologically.*
- Fig. 5: Squamous ca involving Zymbal’s gland in female rat (Lauren). *Warning; graphic.*
A lesion or growth which may show biologic activity that includes a change in shape, size, and color, or a bleeding ulceration.
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.
Zymbal’s gland carcinomas are very invasive. This typically makes tumor removal impossible, and the accompanying necrosis does not, in most cases, make debulking the tumor an option.
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.
If infection is present, treatment with broad-spectrum antibiotics recommended.
For information regarding medications refer to the Rat Medication Guide.
Palliative Care (Hospice Care)
Provide pain medication when the rat exhibits signs of pain or lesion is in advanced stage. A nonsteroidal anti-inflammatory agent such as Banamine, Metacam or piroxicam, or a corticosteroid such as dexamethasone or prednisone may be included to help reduce inflammation and swelling of surrounding tissue.
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.
Euthanasia should be considered before condition adversely affects quality of life.
- Provide hospital cage during end stage of life.
- Provide clean bedding daily such as felt, soft t-shirt type material or ink-free paper towels. Avoid using material such as terry cloth type towels that can ravel. Also avoid litter-type bedding, post-op, until healed to prevent the chance of wound contamination or infection.
- Provide additional warmth to maintain body temperature within normal limits. It is essential that the rat does not become overheated or dehydrated. The rat should also be able to move away from the heat source if it becomes uncomfortable. If the rat is unconscious or immobile extreme care must be taken to keep the heat low and stable.
- You can use an isothermic product that is heated in the microwave such as SnuggleSafe®. Make sure to follow the product directions carefully and wrap in a towel before placing in the cage. SnuggleSafe® will provide heat for 12 hours before needing to be reheated. Other similar types of product may vary in re-heat time. Check directions for individual product.
- If using a heating pad (good for long term use) use only the low heat setting, put a thick towel in between the pad and the cage bottom, and place beneath a corner of the cage.
- If none of these options are available you can use a plastic bottle filled with hot water, and wrapped in a towel, in the corner of the cage.
- Give medications as prescribed by veterinarian.
- Provide wound care using warm water or sterile saline.
- Contact veterinarian if any of the following develop: swelling, redness ,increased signs of pain, signs of increased weight loss, lethargy or changes in habits.
- Assess nutritional status:
- 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 Jell-O 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.
- Assist rat with grooming and cleaning if needed.
- When condition deteriorates and precludes further comfort or quality of life discuss euthanasia with veterinarian.
- Medication helps to relieve pain.
- Malocclusion minimized so the rat is able to eat and drink.
- Preserve quality of life until time to euthanize.
- Comfort the owner when euthanasia is required.
- Even though there is no prevention for Zymbal’s gland tumors early detection may improve quality of palliative/hospice care.
- Boorman, G. & Everitt, J. (2005). Neoplastic disease: Specialized sebaceous glands. In Suckow, M., Weisbroth, S., & Franklin, C. (Eds.), The laboratory rat (2nd ed., p. 485). Toronto: Academic Press.
- RENI. (n.d.). Zymbal Gland. Retrieved March 10, 2008, from https://www.item.fraunhofer.de/reni/trimming/manus.php?mno=034.
- Seely, J. (1994). Auditory Sebaceous Glands (Zymbal’s Glands). Pathobiology of the Aging Rat, 2, 423-433.