Cryotherapy in otolaryngology
Rapid freezing of tissues to temperatures of -30 degrees centigrade and below and their slow thawing causes tissue destruction. This phenomenon is used in cryosurgery to abalate vascular lesions. This principle was first introduced by Arnott in 1851, when he irrigated superficial tumors with ice cold brine solutions. Later in 1961 liquid nitrogen was used by Cooper and Lee. Lewis and Cahan treated 5 tumors of the glomus jugulare successfully with cryosurgery in 1967. The changes that take place at tissue level following use of cryo is rupture of cell membrane followed by intracellular dehydration, protein denaturation and disruption of cell metabolism causing local ischaemia and microthrombosis.
The required temperature for cell death is -20 degrees centigrade. Further lowering of temperature does not increase the lethality to the cells. Cooling should infact be carried out rather rapidly followed by gradual thawing. Repeated freeze-thaw cycle makes this therapy very effective. Adjusting the probe temperature and application time controls the width of the lesion.
The freezing agent (Liquid nitrogen / carbondioxide) is delivered to the tissue either by open method or thorough a closed system using a cryoprobe. Design of cryoprobe is based on Joule-Thomson effect (rapid expansion of compressed gas through a small hole produces cooling). The currently used probes produce a tip temperature of -70 degrees centrigrade. Some probes are provided with thermocouples that can be inserted into the tissue to monitor the temperature. Currently available closed systems employ liquid nitrogen, nitrous oxide or cabon dioxide.
Mechanism of tissue destruction:
Freezing the tissue causes cell death through the following mechanism:
The water present inside and outside the cell crystalizes with consequent rise in concentration of electrolytes. The pH of the medium also changes as the buffering substances crystalize out. Ureaand dissolved gases reach toxic levels causing cell death.
Cell membranes are made up of lipoproteins. Their denaturation causes the cell membrane to become more permeable to cations. Gradual thawing of cells engorged with cations results in cell lysis.
Sudden freezing arrests the respiratory function of the cell.
Arterial and venous supply to tissues is occluded leading to ischaemic infarct. Microthrombosis of capillaries are seen within a few hours of cryo application. This effect makes cryo a most efficient tool in the management of vascular lesions.
Autoantibodies specific to the frozen tissues have been demonstrated experimentally. This provides tissue specific immunity preventing regeneration of ablated mass.
Cryotherapy can be appled under LA/GA. Sometimes anesthesia may not be needed at all as freezing itself causes numbness. A suitable sized cryoprobe is applied on to the tissues which are frozen quickly for 3-8 mins and then it is allowed to thaw slowly. This procedure may be repeated once / twice. The area frozen should include a margin of normal tissue. A thermocouple can be implanted to ensure freezing at an adequate depth. After cryotherapy the area is allowed to heal by secondary intention. The necrotic slough falls off in 3-6 weeks. Repeat cycles of cryotherapy may be required to achieve desired results.
Uses of cryotherapy:
1. To abalate benign vascular tumors
2. To abalate premalignant lesions like leukoplakia
3. To abalate malignant lesions especially skin cancers like Bowen disease, basal cell carcinoma etc. Cryo is very useful in managing tumors that overlie cartilage as freezing does not damage the cartilage.
4. Used ro reduce the size of nasal turbinates in patients with allergic rhinitis
Advantages of cryotherapy:
1. Useful in managing poor risk patients
2. Useful in managing tumors in patients with bleeding disorders
3. Can be used in palliation therapy
4. There is very minimal post treatment discomfort
5. There is very minimal tissuee scaring
6. Can be performed as an outpatient procedure
1. No tissue is available for biopsy
2. Not possible to assess clearance margins
3. No control of in depth freezing
4. When used in skin lesions it causes localized depigmentation and loss of hair follicles