The hazards and benefits of tissue injury from cold have been recognised for many years. Successful cryosurgery requires an understanding of the effects of freezing living tissue in order to optimise the therapeutic benefit.
Cellular injury following freezing may be brought about by intra and extra-cellular ice formation, hypertonic damage, disruption of cell membranes and changes in cutaneous circulation during freezing. Much cellular injury occurs during thawing. The critical determinants of the extent of this injury are the rate of freezing, the lowest temperature reached, the duration of the freeze and the rate of thawing. Repetition of the freeze-thaw cycle produces greater tissue destruction than a single freeze-thaw cycle. Temperatures necessary to produce cell death in skin vary according to cell morphology, but most cells are killed at -25°C to -30°C. This temperature can be readily achieved at 3-4 mm depth from the skin surface using appropriate Liquid Nitrogen spray techniques. In contrast, the cotton wool bud method tends to be less effective. Cotton wool buds vary in their volume and compactness; the pressure exerted by them cannot be controlled accurately and they need to be re-dipped frequently into the nitrogen.
These variables lead to a lack of precision and the cotton bud method gives less reproducible results except in very small lesions, e.g. warts.
Cryotherapy is well tolerated in adults. It is not usually suitable for children under ten years of age, although some young children over five years of age may tolerate single freeze times of 5-10 seconds to a few lesions only. Patients should be warned, before treatment, about post-operative effects (see complications). African races may be particularly susceptible to hypertrophic scarring after cryosurgery and anyone with dark skin may develop marked hypo pigmentation.
There are no absolute contraindications, but it would be best avoided in patients with cryoglobulins or cold urticaria.
Contraindications for Cryo-surgery
Cryosurgery should not be used to treat non-melanoma cancer in the following circumstances:
- Tumour tethered to underlying structures.
- Tumour margins indeterminate, e.g. morphoeic basal cell carcinoma.
- Deeply infiltrating tumour, for example squamous cell carcinoma of the lip or helix of the ear, basal cell carcinoma of the alar crease and basal cell carcinoma in the pre and post auricular area.
- Recurrent tumour after previous cryotherapy, X-irradiation or surgery.
The dipstick or cotton wool bud is the simplest method. Ideally an amount of liquid nitrogen should be decanted into a metal gallipot for each patient. This will prevent contamination of the main supply with HPV, which could occur if buds are repeatedly dipped into it. A cotton wool bud, not too tightly packed, is dipped in the nitrogen and applied firmly to the lesion. For larger lesions redipping and reapplication may be necessary.
Several models of spray equipment are available and this method is increasingly popular. The spray tip comes in several diameters to allow fine control when needed. The tip is held about 1 cm from the skin for treatment. There may be some surface splatter but important structures, e.g. the eye, can be shielded with a plastic spoon. A spray tip resembling a smoker’s pipe allows nitrogen to be delivered vertically upwards and is most useful under the chin amongst other sites.
Probes have their advocates and are very useful inside the mouth, pharynx, cervix, etc. For skin lesions it is usual to apply lubricant jelly first to obtain good contact.
Reproducible Treatment Schedules (FTC – Freeze Thaw Cycle)
When treating benign lesions most cryosurgeons simply apply the bud or spray until the ice field extends 1mm beyond the lateral margin of the lesion, and maintain it for a few seconds. If the patient has a huge reaction or conversely there is no benefit, the operator will have no accurate way of determining how to proceed at the next visit. It is useful therefore to record the treatment in the notes. One method of doing this is the spot freeze method, which is suitable for lesions up to approximately 1cm. The spray is applied to the centre until ice has developed within the desired field. This field is then maintained for a given number of seconds (usually for 5-30 depending on the pathology of the lesion) Counting begins only when the desired field has been achieved; not at the commencement of spraying. A 10 second FTC means
Treatment of Benign Lesions
The spray is directly at the centre of the lesion. The spray time begins when the ice ball has extended to the margin of the lesion. The freeze time used should be recorded in the notes for future reference. Freeze times up to 10 seconds are often tolerated without any local anaesthesia. For multiple lesions, e.g. digital warts, a ring-block with plain lignocaine anaesthesia may be a useful technique.
Cryosurgery For Benign Lesions Using Cry-Ac System (C Nozzle)
|Disease||Spray Time (seconds)
times counted after formation of ice field
|Molluscum contagiosum||Ice formation only||none|
|Myxoid cyst of finger||30||2mm|
Treatment of Pre Malignant and Malignant Lesions
Cryosurgery is not usually the modality of first choice for treating skin cancer. However, it leaves excellent scars, it can be performed in the patient’s home or a nursing home, it is particularly suitable for superficial truncal basal cell carcinomas and it avoids the trauma of surgery in those who find surgery unacceptable.
The diagnosis is usually confirmed histologically prior to treatment.
Just as in excisional surgery it is necessary to allow a margin of clinically normal skin to be included in the treatment field to allow for sub clinical extensions. In addition it is important to remember that the lateral margin of the ice ball is not cold enough to kill cells. The isotherms are close together but an additional 1-2mm of ‘normal’ skin should be included to allow for these temperature considerations. The skin surrounding the tumour is delineated with a skin marker pencil. The skin surrounding the lesion can be anaesthetized.
The spray tip is held 5 – 10mm from the skin and the spray is directed perpendicularly at the centre of the field. Spraying leads to a palpable ice ball of increasing diameter, which extends to the margin of the field previously outlined. The ice ball must be formed quickly to ensure an adequate depth of the – 25°C isotherm below the skin surface. It is wise to divide the treatment field into overlapping smaller areas, e.g. 1.5cm diameter and treating each of these in turn with a full freeze thaw cycle. Slight adjustment in the flow rate from the gun will prevent extension of the ice field beyond the margin outlined. If a second freeze is to be performed (see Table), it is essential to allow a slow thaw to body temperature before re-freezing. Much cellular injury occurs during the thaw time. Complete, not partial thawing, decreases cell survival.
Cryosurgery for Pre-malignant and Malignant Lesions
Using Cry-Ac System (B or C Nozzle)
|Disease||Spray Time (secs)
counted after ice field formed
|Squamous cell carcinoma||2 x 30||3mm|
|Basal cell carcinoma||2 x 30||3mm|
Complications of Cryosurgery
Pain, swelling and blistering frequently occur when longer freeze times are used. Hypo pigmentation of the treated area is seen in people with dark skin, but this may improve in time. Paraesthesia occurs but is usually temporary. Prolonged sensory abnormality is very rare indeed, even after using 30 second freeze times around the fingertips. Cryosurgery on the fingers can lead to nail dystrophy and to extensor tendon injury.
Milia formation is often seen two months post-operatively but resolves spontaneously. A thin hypertrophic scar is often seen across the treatment field two months post-operatively, but this will settle spontaneously in the following months. Wound healing usually takes place in 4 to 6 weeks after treatment of non-melanoma skin cancer around the head and neck and forearms and hands, but slow wound healing is commonly seen for lesions treated on the shin and calf. Patients on anticoagulants and corticosteriods tolerate cryosurgery very well.
A dressing is advisable for those lesions treated with longer freeze times. Some degree of exudation may be expected during the first few days and an antiseptic dressing such as Providone-Iodine helps prevent secondary infection. Wounds can be washed and it is important that crust and exudate is removed regularly. Adequate analgesics should be prescribed. Patients should be reminded that there would be some pain and discomfort and swelling initially. Swelling can be considerable in the first 48 hour, especially surrounding wounds on the upper face, and blistering is very variable in the first 24 to 48 hours. This should be explained to the patients in order to allay anxiety. Hands and feet will feel sore for several days after treatment of multiple viral warts and fingers may be rather clumsy for 7 to 10 days after treatment.
- Shepherd, J.P., Dawber, R.P.R. (1982) Cryosurgery: History and Scientific Basis. Clinical & Experimental Dermatology. 7:321-328
- Colver, G.B., Dawber, R.P.R. (1989) Cryosurgery – Principles and Simple Practice. Clinical & Experimental Dermatology. 14:1-6
- Holt, P.J.A (1988) Cryotherapy for Skin Cancer; Results Over a 5 Year Period Using Liquid Nitrogen Spray Cryosurgery. British Journal of Dermatology. 119:231-240.
Dawber, R.P.R., Colver, G.B., Jackson, A. Cutaneous Cryosurgery. Principles and Clinical Practice. Martin Duniz, London 1997.