Minimally Invasive Surgery

Both lasers and cryosurgery avoid the use of the scalpel and obviate the need for suturing . Certain laser wavelengths in the near and mid infra-red can be taken down fibres into body cavities such as the temporomandibular joint, allowing a link with endoscopy. Excision of tissue by lasers is characterised by minimal scarring, for example of the oral mucosa, thought to be due to inhibition of myofibroblasts. Heat coagulation of tissue by penetrating laser wavelengths (eg.Nd:YAG) and cold protein coagulation as by cryosurgery, leaves the body repair mechanisms to separate the devitalised tissue. In this process there tends to be a release of cytokimes encouraging regeneration and an enhancement of local immune mechanisms.

Both lasers and cryosurgery have effects on nerve fibres, particularly the finer non-myeleinated pain fibres, reducing pain by comparison with conventional surgery in general.

Lasers

Lasers may be classified under the following headings :

• High intensity laser therapy (HILT) - is used to cut or ablate tissue. For cutting a tissue a temperature of 100deg.C needs to be attained to boil the interstitial water, while for
  coagulation 60deg.C is necessary for full coagulation of proteins.
  Cutting abilities of lasers are most useful in mucosal sub-surfaces for the removal of pre-malignant and early malignant lesions with minimal scarring, pain and tethering. The coagulating capabilities are best employed for vascular lesions such as cavernous haemangiomata. Care must be taken in the vicinity of nerves which will be damaged and cryosurgery can be combined with lasers to allow nerve regeneration.
• Selective Laser Therapy (SELT) - in this situation, one cellular population is selectively destroyed, leaving adjacent cells intact. There are two main methods:

a.) selective photothermolysis - an example of which is the treatment of port wine stains of the face where a tunable dye laser may be used to produce yellow light in the 585 nanometer range. This will penetrate through the epidermis without significant absorption, to be taken up by the chromophore of oxyhaemoglobin in the capillary haemangioma, allowing selective damage to the intima.

b.) photodynamic therapy - which involves the administration of a light-sensitising drug which is then activated by light, usually monochromatic (eg. 630nm helium neon laser). The interaction in the presence of oxygen precipitates cell killing. This photo-chemical reaction can be used to treat malignancy and pre-malignancy at a number of sites within the body. In terms of head and neck oncology a variety of photo-sensitisers have been used, each of which has different characteristics.

For example, dysplasia can be managed using aminolaevulitic acid which produces a relatively superficial zone of tissue necrosis and leaves the patient photosensitive for a short period of only 24 hours. Healing is uneventful and takes place without any scarring. Invasive tumours can be treated with a more powerful sensitiser, such as foscan which produces a depth of necrosis up to 1cm with surface illumination. This allows early invasive squamous carcinoma to be treated and the method is of particular use with field change disease and multifocal squamous cancer.

In addition to surface illumination, photodynamic therapy can be carried out by intralesional implantation of laser fibres with up to four point sources being treated at one time, producing necrosis with a radius of about 1cm. The disadvantage of this treatment is that the patient may remain sensitive to light for about three weeks and, because of the more powerful nature of the effect, there does appear to be some post-operative scarring.

The only drug that is currently licensed for treatment on a world wide basis is photofrin which is a dihamatoporphyrin ether / ester mixture. This produces an intermediate range of necrosis down to about ½ cm with quite a prolonged period of photo-sensitivity, up to six-eight weeks. Healing takes place with virtually no scarring. It should be emphasised that at present, though this treatment offers great potential, the only routine services are being offered on study protocols. There are currently about 14 units in the United Kingdom carrying out PDT on a regular basis with some units having extensive experience with numbers in excess of 200 patients treated.

• Low Intensity Laser Therapy (LILT) - low power lasers in milliwatt
  ranges rather than the range of watts for HILT are used in the augmentation of healing, such as intractable orofacial ulcers, using a visible red light at 630 or 660nm or near infrared irradiation around 830nm singly or in combination, and in pain control. Using the near infrared irradiation of a gallium aluminium arsenide laser at 820-830nm which penetrates at high energy densities, pain alleviation appears to be due to direct effects on fine nerve fibres, augmentation of cellular enzyme systems important in repair, and in some instances endorphin release.

Cryosurgery

For destruction of normal tissue, the attainment of a temperature of at least -15°C is necessary to produce intra-cellular ice formation, although for the destruction of malignant neoplasms -50°C is advocated. The normal ice ball shows the -2°C isotherm. The most potent method of freezing is by the use of phase change apparatus employing liquid nitrogen, where probes reach a temperature of approximately -180°C and a spray -198°C. Lesser potency may be obtained by the throttled gas method, classically employing nitrous oxide under pressure. In general, liquid nitrogen apparatus is indicated for the management of malignant disease and for lesions of bone, in view of its greater potency of effect. The main uses for cryosurgery in the orofacial region are :

• Soft tissue ablation : cold necrosis may be produced in such lesions as haemangiomas or exophytic T1 carcinomas. Care should be taken in treating large areas of leukoplakia as a stimulant effect can be produced in peripheral zones.
• Pain Control : temporary anaesthesia may be produced for about 6 months by freezing peripheral branches of the trigeminal nerve, which may be useful in certain cases of trigeminal neuralgia.
• Bone may be frozen to remove residual abberant tissue. At least -15°C needs to be obtained and liquid nitrogen spray is most applicable to uneven bone cavities. A pressure of between 8-10 lbs per square inch is indicated and cell ethal penetration occurs at a rate of approximately 3mms per minute, ie. about 3 minutes to freeze 1cm in depth. The method is particularly useful for keratocysts and benign neoplasms of bone, such as ameloblastoma. The lesion should be curetted and then freezing carried out for a suitable time, depending on the lesion. If the mandible is already significantly weakened by tumour, there is a risk of pathological fracture in the third month after freezing, when re-modelling takes place. This can be offset by inserting a cancellous bone graft at the time of the original operation.

Both lasers and cryosurgery present a spectrum of exciting methods which result in a new concept of conservative surgery, augmentation and biomodulation. It is anticipated that they will find a special role in combination with gene therapy in the future, in relationship to orofacial malignant disease. Lasers lend themselves to gentle ablation of tissue with lack of bleeding and pain, while cryosurgery has special merits in relationship to nerve and bone which may regenerate after therapy. Both modalities of treatment are extremely important in the practice of oral & maxillofacial surgery