Definition

Keratoacanthoma (KA): a low grade growth of the epidermis that originates in the hair follicle and progresses rapidly. Also referred to as: “self-healing,” or “pseudocarcinoma.”

Clinical Signs

KA presents with a characteristic appearance of a crateriform lesion, a central keratinous plug, and edges of normal skin extending over the central keratinous crater.

*Note: for additional information on recognizing various signs of pain or discomfort refer to: Signs of Pain In Rats.

Etiology

Keratoacanthoma is a typically benign epidermal tumor that may resemble squamous cell cancer both visually and histologically. But unlike squamous cell cancer, it is usually benign. This type of lesion often forms a keratin horn that gives it a characteristic appearance.

Factors that may contribute to KA include:

• Immunocompromised status
• Trauma
• Genetic predisposition

A keratoacanthoma may occasionally progress to multiple growths, may enlarge, may become aggressive locally. However, metastasis to distant organs is very rare.

The cause of keratoacanthomas is unknown.

Prognosis and outcome for a rat diagnosed with keratoacanthoma is good.

Figure

Case History of Keratocanthoma

• Fig. 1: Keratoacanthoma in 2-year-old hairless male rat

Diagnostics

Exact diagnosis can be performed by biopsy and pathological examination.

Treatment

Keratoacanthomas can be surgically removed, but is often known to involute and resolve spontaneously. While this type of tumor does tend to resolve on its own after several weeks to months (spontaneous involution), the resulting wound may sometimes require suturing, and may or may not leave a scar.

Although lotions and ointments do not help to resolve this growth, if surrounding tissue is cracked, irritated or inflamed, the vet may choose to treat with applications of an antimicrobial ointment.

If the decision is made for surgical intervention, the procedure may be one of surgical excision, cryosurgery (a controlled type of tissue freezing), or electrocautery, depending on the location and involvement of the growth.

In the event of surgery, the inclusion of a post-op broad-spectrum antimicrobial is encouraged. The vet may also consider providing post-op pain control with oral analgesic (e.g., Torbugesic or Metacam).

For more information on antimicrobials or analgesics refer to the Rat Medication Guide.

Nursing Care

• Keep the area of growth clean.
• Apply any ointments your veterinarian may prescribe.

If surgery is an option:

• Provide a hospital (small, one-level) cage during recovery, or if there are concerns that cagemates may groom sutures or wound site.
• 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.
• Medicate for post-op pain as needed.
• If prescribed, give antimicrobials as ordered.
• A body wrap may be required, if thread sutures are used.
• In the event there is dried or excess drainage, the incisional site may be cleaned with a moistened cotton swab using warm water or normal saline.
• For 24 to 48 hours post-op feed iron-rich foods to prevent anemia (e.g., cooked liver, scrambled or hard-boiled eggs).
• Contact veterinarian if any of the following are observed:
  • Swelling at the incision site.
  • Inflammation (redness) or pain at the incision site.
  • Signs of increased weight loss, lethargy, or a change in habits.

Outcome

• Resolution or removal of keratoacanthoma with minimal scarring.
• If KA reoccurs discuss additional treatment with your veterinarian.

Prevention

• There is no known prevention for keratoacanthomas.