The Nd:YAG laser in neurosurgery

Use of Laser in Arteriovenous Malformation Surgery

BACKGROUND

Arteriovenous malformation surgery is particularly demanding owing to the need to control bleeding of small, deep white matter vessels during and after removal of the nidus; this is probably one of the most critical moments of arteriovenous malformation surgery. The aim of this article is to describe a useful technique based on the use of tweezers to temporarily stop the blood flow followed by coagulation with the thulium laser.

METHODS

Surgery was performed in 20 patients with unruptured cerebral arteriovenous malformations. In each case, the superficial feeder vessels were easily coagulated with nonstick bipolar tips. The finer and deeper feeder vessels were coagulated with use of tweezers and thulium laser.

RESULTS

All patients were treated successfully. Optimal intraoperative hemostasis was achieved.

CONCLUSIONS

Results were good with no postoperative complications. Our results could encourage a more standardized use of the described technique.

Effect of CO2 milliwatt laser on peripheral nerves: Part I. A dose-response study

In order to explore further the role of laser for microneural repair, the effect of CO2 laser irradiation on intact rat sciatic nerves was investigated. In total 40 rat sciatic nerves were exposed to 12 different combinations of laser power (50, 100, and 150 mW) and pulse duration (0.1 to 3 s) normally used for CO2 laser-assisted nerve repair. The results were evaluated 24 hr after surgery with functional toe-spreading test and light microscopy. Irradiations of 50 and 100 mW for up to 1 s exposure time per pulse resulted in almost no deficit in motor function, while 100 mW power with prolonged exposure times and 150 mW power resulted in a significant decrease in motor function. Light microscopy showed significant focal injury to the epi/perineurium and the subepineunal nerve fibres proportional to the laser energy applied to the nerve, consisting of Wallerian degeneration and thrombosis of blood vessels. In conclusion, a power of 50-100 mW in combination with a pulse duration of 0.1-1 s produced no or minimal thermal damage with no or a negligible loss of motor function. Therefore, combinations of power and pulse duration above these thresholds are considered less suitable for CO2 laser nerve repair.

Study into penetration speed during laser cutting of brain tissues

The applications of CO2 continuous-wave lasers in neurosurgery have become important in recent years. Theoretical considerations of laser applicability in medicine are subsequently confirmed experimentally. To obtain precision operation in the laser cutting process, further theoretical developments and experimental studies need to be conducted. Consequently, in the present study, the heat transfer mechanism taking place during laser-tissue interaction is introduced using Fourier theory. The results obtained from the theoretical model are compared with the experimental results. In connection with this, an experiment is designed to measure the penetration speed during the laser cutting process. The measurement is carried out using an optical method. It is found that both results for the penetration speed obtained from the theory and experiment are in a good agreement.

Experimental and clinical standards, and evolution of lasers in neurosurgery

From initial experiments of ruby, argon and CO2 lasers on the nervous system so far, dramatic progress was made in delivery systems technology as well as in knowledge of laser-tissue interaction effects and hazards through various animal experiments and clinical experience. Most surgical effects of laser light on neural tissue and the central nervous system (CNS) are thermal lesions. Haemostasis, cutting and vaporization depend on laser emission parameters--wavelength, fluence and mode--and on the exposed tissues optical and thermal properties--water and haemoglobin content, thermal conductivity and specific heat. CO2 and Nd-YAG lasers have today a large place in the neurosurgical armamentarium, while new laser sources such as high power diode lasers will have one in the near future. Current applications of these lasers derive from their respective characteristics, and include CNS tumour and vascular malformation surgery, and stereotactic neurosurgery. Intracranial, spinal cord and intra-orbital meningiomas are the best lesions for laser use for haemostasis, dissection and tissue vaporization. Resection of acoustic neuromas, pituitary tumours, spinal cord neuromas, intracerebral gliomas and metastases may also benefit from lasers as accurate, haemostatic, non-contact instruments which reduce surgical trauma to the brain and eloquent structures such as brain stem and cranial nerves. Coagulative lasers (1.06 microns and 1.32 microns Nd-YAG, argon, or diode laser) will find an application for arteriovenous malformations and cavernomas. Any fiberoptic-guided laser will find a use during stereotactic neurosurgical procedures, including image-guided resection of tumours and vascular malformations and endoscopic tumour resection and cysts or entry into a ventricle. Besides these routine applications of lasers, laser interstitial thermotherapy (LITT) and photodynamic therapy (PDT) of brain tumours are still in the experimental stage. The choice of a laser in a neurosurgical operating room implies an evaluation of the laser use (applications, frequency), of the available budget and costs--including purchase, maintenance and staff training--, and material that will be necessary: unit, peripherals, safety devices and measures, training programme. Future applications of lasers in neurosurgery will come from technological advances and refined experimental applications. The availability of new wavelength, tunable, small sized and "smart" laser units, will enlarge the thermal and non-thermal interactions between laser energy and neural tissue leading to new surgical applications. Tissue photo-ablation, photohynamic therapy using second generation of photosensitizers, updated thermotherapy protocols, are current trends for further use of lasers in neurosurgery.

Lasers in neurosurgery

Lasers have been used in neurosurgery for the past 25 years, undergoing modifications to suit the specific needs of this medical discipline. The present report reviews the current use of lasers in neurosurgical practice and examines the pros and cons of lasers in specific neurosurgical applications. In spite of their advantages, laser use is still not widespread in neurosurgery. One reason is the continued lack of complete control over real-time laser interactions with neural tissue. A greater acceptance and use of lasers by neurosurgeons will depend upon automated control over defined specific parameters for laser applications based upon the type of tissue, the desired effect on tissue, and application to the clinical situation without loss of precision and a lot of expense. This will require the integration of newer lasers, computers, robotics, stereotaxy, and concepts of minimally invasive surgery into the routine management of neurosurgical problems.

1.32 microns Nd:YAG laser during neurosurgical procedures experience with about 70 patients operated on with the MC 2100 unit

The authors present their clinical experience with 1.32 microns Nd-YAG Laser. After a series of experimental studies which demonstrated the adaptability of such a wavelength to central nervous surgery, they used such a Laser during current neurosurgical procedures. The MC 2100 unit combines two wavelengths 1.32 microns and 1.06 microns, and two emission modes: continuous wave (c.w.) and pulsed. This Laser has been used during 70 procedures: 54 supra-tentorial, 8 infra-tentorial, 5 intra-spinal, 3 intra-orbital, 600 microns and 400 microns fibers were preferred in most cases, either with a telescopic light handpiece or- less often--with a focussing handpiece. The quality of vaporization--close to that of CO2 Laser- and of haemostasis-close to that of 1.06 microns Nd-YAG Laser-makes this 1.32 microns wavelength very suitable for neurosurgery. The manoeuverability due to the optic fibers is most interesting. Furthermore, such a Laser should have in the near future large applications in stereotactic and/or endoscopic neurosurgery.

The use of 1.32 Nd:YAG laser in neurosurgery: experimental data and clinical experience from 70 patients

The authors present their experience with the 1.32 mum Nd:YAG laser in neurosurgical procedures. In a first step, they conducted experiments on rat cortex. The thermic data and histologic results confirmed that the 1.32 Nd:YAG laser has physical properties quite close to the CO2 laser. Furthermore, the fact that the 1.32 mum wavelength can be conducted through optic fibers makes it well adapted to neurosurgery. The authors present experimental data (50 rats) and comment on their surgical experience with such a wavelength (70 patients). In the future, this laser should see its indications broadened in conventional neurosurgical procedures as well as in endoscopic and stereotactic neurosurgery.

Argon laser-induced arterial photothrombosis. Characterization and possible application to therapy of arteriovenous malformations

The common carotid, femoral, and middle cerebral arteries in the rat have been occluded thrombotically by means of a rose bengal dye-sensitized photochemical reaction initiated in vascular endothelium by the 514.5-nm beam of an argon laser, focused for maximum excitation efficiency of the photosensitizer according to a derived criterion. The total energy required for vessel occlusion was approximately 1 joule (J) for the middle cerebral artery and 140 to 180 J for the femoral and carotid arteries. At energy fluences (energy deposited per unit area) of 3.5 kJ/sq cm for the middle cerebral artery and 35 kJ/sq cm for the larger arteries, occlusion was observed within 3 minutes. The middle cerebral artery thrombus consisted entirely of aggregated platelets; in the larger arteries the thrombi were composed of platelet aggregates and groups of red blood cells interspersed within a matrix of coagulum. Vessels irradiated similarly in the absence of rose bengal dye displayed no morphological or functional damage. Because the photochemical reaction is mediated by electronic-state transitions, the process of photothrombosis (as opposed to photocoagulation) can be initiated in vessels with high flow rates without the requirement of increased temperature. The photothrombotic technique may be useful in the treatment of arteriovenous malformations owing to its significant enhancement of the efficiency and permanency of vessel occlusion.

Arteriovenous malformations of the lateral ventricle

Nine cases with arteriovenous malformations (AVM's) predominantly involving the lateral ventricle are presented. All the AVM's were small, but caused intraventricular hemorrhage in eight cases. Only two patients had an intracerebral hemorrhage large enough to warrant evacuation. Eight patients were under the age of 40 years at the onset of their disease. Computerized tomography demonstrated intraventricular hemorrhage in eight patients, and after intravenous administration of contrast medium a small area of enhancement with dilated subependymal draining veins was seen in seven. The lateral ventricles were of normal size in seven cases, and only two patients required a shunting procedure. Angiography demonstrated that the lesion was an AVM in eight patients, and did not visualize the lesion in the ninth. One patient suffered a recurrent intraventricular hemorrhage when the AVM was demonstrated, although repeated angiography had failed to disclose a vascular lesion at his first intraventricular hemorrhage 14 months before. All nine lesions were resected by microsurgical techniques, and the results were excellent in eight patients. Of four caudate lesions, three were resected through a frontal transcortical approach and the other was operated on through an anterior transcallosal approach; the results were excellent in three of these patients. Only one (Case 4) was left with neurological deficits; he had confusion and disorientation following a right frontal transcortical approach. Even in the dominant hemisphere, lesions in the head of the caudate nucleus could be safely resected by an anterior transcallosal approach. Two choroidal lesions located in the temporal horn and trigone on the dominant side were resected through a middle temporal gyrus approach, and three thalamic lesions through a posterior transcallosal approach, all with excellent results. In all cases the brain opening required was about the width of the retractor (maximum 2.0 cm, average 1.5 cm).