Cryosurgery

Cryobiology

Cryosurgery destroys tissue through two main biological phases:

Direct Cellular Injury

When liquid nitrogen touches the skin, the tissue temperature drops abruptly and ice crystals form.

• Rapid freezing: Small ice crystals form inside the cells, tearing cell membranes, wrecking organelles, and denaturing proteins.
• Slow thawing: As ice crystals outside the cells melt, the surrounding fluid becomes hypertonic and draws water out of the cells, which distort and collapse.

Indirect Vascular Injury (Vascular Stasis and Ischemic Necrosis)

Freezing temperatures damage the endothelial cells lining blood vessels, leading to vasoconstriction, platelet clumping, and tiny clots in the capillaries. This local shutdown of circulation starves the tissue of blood, causing secondary necrosis of the entire target area within a few days of the procedure.

Cold Sensitivity of Different Cell Types

• Melanocytes (pigment cells): Highly sensitive to cold and destroyed completely at −4°C to −7°C. This is why loss of pigment is such a common side effect of cryotherapy.
• Benign keratinocytes: Require −20°C to −30°C to be destroyed.
• Skin cancer cells (BCC, SCC): More resistant, requiring temperatures of −40°C to −50°C.
• Collagen framework and connective tissue: Fairly resistant to cold, which helps preserve the skin's underlying structure once the treated area heals.

Clinical Cryotherapy Techniques

Open Spray Technique

A dedicated liquid nitrogen spray device (cryogun) is used. The physician holds the nozzle at 90 degrees to the skin, 1–1.5 cm from the lesion, and sprays continuously until a frozen halo (ice ball or ice front) covers the lesion and extends into the surrounding normal skin:

• Benign lesions: the ice halo extends 1–2 mm beyond the lesion edge.
• Precancerous or malignant lesions: the ice halo extends 3–5 mm beyond the lesion edge.

Cone Technique (Neoprene or Plastic Cone)

A cone sized to fit the lesion confines the liquid nitrogen spray. This focuses the cold so it penetrates deep into the lesion without damaging the surrounding healthy skin, which is especially useful in delicate areas such as near the eyes or on the ear.

Contact Probe Technique

Chilled metal tips (copper or gold) attached to the nitrogen unit are pressed directly onto the lesion. This technique suits raised lesions or those where mechanical pressure is needed to compress blood vessels during freezing.

Intralesional Cryosurgery

Used specifically for keloids. The physician passes a special needle through the center of the keloid and then circulates liquid nitrogen through it. The scar freezes from the inside out, destroying the excess fibrous tissue while sparing as much of the epidermis and surface pigment cells as possible.

Clinical Indications for Cryotherapy

Healing and Managing Complications

Normal Course of Healing

• First 0–24 hours: The treated area becomes red and swollen, and a blister forms (either clear or a dark purple, blood-filled blister).
• Days 3–5: The blister breaks, dries, and forms a dark crust.
• Days 10–21: The crust falls off on its own, leaving new, light pink skin.

Managing Complications

• Sharp local pain: Usually felt as the area thaws. Patients can take paracetamol or ibuprofen 30 minutes before the procedure.
• Hypopigmentation or depigmentation: Caused by destruction of melanocytes. The risk is reduced by avoiding overly deep freezing in patients with darker skin types (Fitzpatrick IV–VI).
• Depressed scars and tissue atrophy: Occur when freezing lasts too long (over 30 seconds) on thin skin.
• Superficial nerve injury: A risk with prolonged freezing on the sides of the fingers and toes or behind the ear. Patients may have tingling or temporary numbness for a few weeks.