What is cryosurgery?
Cryosurgery (also called cryotherapy) is a form of surgery that uses liquid nitrogen, nitrous oxide or argon (collectively called cryogens) gas to freeze and destroy abnormal or diseased tissue, thus eliminating the need to surgically cut the tumour out. Cutaneous and subcutaneous tumours are the second most common type of tumours in cats, 50-65% of which are cancerous.
Cryosurgery kills cells by freezing intracellular fluid (fluid within the cells), ice shards and crystals form which ruptures the cell membrane and destroys the cell. You can see this in action when you defrost a piece of steak; the liquid left behind is the intracellular fluid that has escaped due to damage to the cell walls by the formation of ice crystals.
Cryotherapy is of benefit when traditional surgery is not possible due to difficult anatomic locations, such as on the eyelids, mouth, nose and anal region. It can penetrate between 2-5mm deep into the skin.
Cats who are a surgical risk.
Where the caregiver would prefer to avoid permanent cosmetic changes from surgery such as on the nose or ears.
What can cryosurgery treat?
- Benign and cancerous tumours
- Rodent ulcer
- Retinal tears
Before surgery, the cat will have a complete physical examination and undergo several tests, including the following:
- Baseline tests: Biochemical profile, urinalysis, and complete blood count to evaluate the overall health of the cat.
- Imaging: To evaluate the chest and lymph nodes for signs of metastasis (the spread of a tumour to other locations of the body).
- Punch biopsy: To determine the depth of the lesion.
How does the veterinarian perform cryosurgery?
Cryosurgery for tumours/lesions:
- Premedication is given before the treatment to sedate and calm the cat.
- It will be necessary to shave the area before treatment to enable the veterinarian to target the area.
- The area is sterilised with an antiseptic such as chlorhexidine.
- The cat will receive a local or more often, a general anesthetic.
- There main methods of delivery are open spray, swab or cryoprobe. The surgeon sprays liquid nitrogen 1 cm from the surface of the skin for 15-60 seconds, and in some cases, this is followed by a thaw and repeat freeze. A healthy margin of tissue surrounding a malignant tumour will also be treated to ensure all cancerous cells are targeted.
- After treatment, an eschar (dead tissue which falls from the skin) will form over the treated area. This is completely normal.
Cyclocryotherapy for glaucoma:
The above describes the treatment of tumours (lesions); cryotherapy can also treat glaucoma, which is a build-up of intraocular pressure within the eyeball. The eye contains a transparent jelly-like fluid known as intraocular fluid or aqueous humour, which maintains the shape spherical shape of the eye and nourishes the tissues within the eye.
The ciliary body is continually producing intraocular fluid. It drains away at the angle where the iris and cornea meet, exiting via a series of drainage canals (trabecular meshwork) and is reabsorbed into the bloodstream. This fluid in/fluid out should occur at the same rate, to keep pressure within the eye stable.
Glaucoma occurs when fluid continues to be produced, but drainage slows down due to a partial or complete blockage. This impedes outflow which leads to a build-up of fluid in the eye and increased intraocular pressure. There are two types of glaucoma in cats, primary or secondary. It can affect one eye (unilateral) or both eyes (bilateral).
Cryotherapy can destroy part of the ciliary body to reduce the production of intraocular fluid.
Cryosurgery for retinal tears:
Cryopexy is a procedure in which the ophthalmologist uses extreme cold to freeze the retina around the tear. This causes the area to swell and forms scar tissue when it heals. It is this scar tissue that seals the retina to the wall of the eye.
- Blood blisters
- Hair loss (alopecia)
- Pigment changes
- Nerve damage
Follow up care
The veterinarian will prescribe painkillers and antibiotics post-surgery.
It will be necessary to clean the area with an antiseptic, watch for signs of infection of inflammation and contact your veterinarian if you have any questions or concerns.