New long-wavelength Nd:YAG laser at 1.44 micron: effect on brain

Pulsed thulium laser blood vessel haemostasis as an alternative to bipolar forceps during neurosurgical tumour resection

Due to wavelength-specific water absorption, infrared lasers like the thulium laser emitting at 1940 nm wavelength proved to be suitable for coagulation in neurosurgery. Commonly bipolar forceps used for intraoperative haemostasis can cause mechanical and thermal tissue damage, whilst thulium laser can provide a tissue-gentle haemostasis through non-contact coagulation. The aim of this work is a less-damaging blood vessel coagulation by pulsed thulium laser radiation in comparison to standard bipolar forceps haemostasis. Ex vivo porcine blood vessels in brain tissue (0.34 ± 0.20 mm diameter) were irradiated in non-contact with a thulium laser in pulsed mode (1940 nm wavelength, 15 W power, 100-500 ms pulse duration), with a CO2 gas flow provided simultaneously at the distal fibre tip (5 L/min). In comparison, a bipolar forceps was used at various power levels (20-60 W). Tissue coagulation and ablation were evaluated by white light images and vessel occlusion was visualised by optical coherence tomography (OCT) B-scans at a wavelength of 1060 nm. Coagulation efficiency was calculated by means of the quotient of the difference between the coagulation and ablation radius to the coagulation radius. Pulsed laser application achieved blood vessel occlusion rate of 92% at low pulse duration of 200 ms with no occurrence of ablation (coagulation efficiency 100%). Bipolar forceps showed an occlusion rate of 100%, however resulted in tissue ablation. Tissue ablation depth with laser application is limited to 40 μm and by a factor of 10 less traumatising than with bipolar forceps. Pulsed thulium laser radiation achieved blood vessel haemostasis up to 0.3 mm in diameter without tissue ablation and has proven to be a tissue-gentle method compared to bipolar forceps.

Theranostic OCT microneedle for fast ultrahigh-resolution deep-brain imaging and efficient laser ablation in vivo

Current minimally invasive optical techniques for in vivo deep-brain imaging provide a limited resolution, field of view, and speed. These limitations prohibit direct assessment of detailed histomorphology of various deep-seated brain diseases at their native state and therefore hinder the potential clinical utilities of those techniques. Here, we report an ultracompact (580 μm in outer diameter) theranostic deep-brain microneedle combining 800-nm optical coherence tomography imaging with laser ablation. Its performance was demonstrated by in vivo ultrahigh-resolution (1.7 μm axial and 5.7 μm transverse), high-speed (20 frames per second) volumetric imaging of mouse brain microstructures and optical attenuation coefficients. Its translational potential was further demonstrated by in vivo cancer visualization (with an imaging depth of 1.23 mm) and efficient tissue ablation (with a 1448-nm continuous-wave laser at a 350-mW power) in a deep mouse brain (with an ablation depth of about 600 μm).

Electromagnetic field system for transsphenoidal surgery on recurrent pituitary lesions - technical note

BACKGROUND

Post operative scar tissue makes transsphenoidal surgery for recurrent pituitary lesions very difficult. However, with the use of a new cautery system, known as the EMF system, we were able to perform the surgical procedures with relative ease. In this article, we report the advantages and clinical applications of this new instrument in transnasal reoperation.

METHODS

The EMF system generates a high frequency current of 13.56 MHz that is focused on the target. This enables it to coagulate, cut, and vaporize tissue in a pinpoint fashion. The bayonet and pencil-type hand pieces of the EMF system are slim, and the tips of the probe are flexible. This enables the surgeon to easily reach deep narrow spaces. We have used the EMF system for transsphenoidal surgery on recurrent pituitary lesions in 18 patients. The system was used to cut and vaporize scar tissue and vaporize firm and fibrotic tumor tissue.

RESULTS

During surgery, the system could easily cut and vaporize scarred tissues in the nasal cavity, the sphenoid sinus, and the sella, without damage to the surrounding tissue. In addition, in 3 patients who had extremely fibrotic and firm tumors, we were able to easily vaporize the tumor with safety.

CONCLUSIONS

The EMF system enables the surgeon to cut and vaporize tissue with ease and with minimal injury to the surrounding structures. It was particularly valuable in the resection of firm tumors. It may also shorten the operating time because of quick vaporization of the firm tissue.

[Cartilage reshaping by laser in stomatology and maxillofacial surgery]

The restoration of congenital and traumatic malformations of the head and neck, together with the defects resulting from the trauma of ablative surgery, continue to pose significant problems to surgeons. The post-operative results are not always satisfactory because of the difficulty of shaping the cartilage and because of the tendency of cartilage to return to its original shape. Better understanding of laser-cartilage interaction and the development of a specific instrumentation Lasers (CO2, Nd: YAG, Ho: YAG) has enabled ex situ and in situ cartilage reshaping. A recent clinical study has demonstrated that nondestructive laser irradiation can reshape septal deviations

Optical coherence tomography monitoring for laser surgery of laryngeal carcinoma

BACKGROUND AND OBJECTIVES

The goal of this study is to apply a new bioimaging modality, the Optical Coherence Tomography (OCT), for intraoperative control in laser surgery of laryngeal carcinoma.

STUDY DESIGN/MATERIALS AND METHODS

We studied 26 patients with laryngeal carcinoma in situ and in T(1), T(2) stage. We used an endoscopic OCT device for imaging at a wavelength of 0.83 microm with the acquisition rate of approximately 0.5 frames/s for a single (200 x 200 pixel) tomogram. All patients were operated with a surgical YAG:Nd laser at two switchable wavelengths of 1.44 microm and 1.32 microm by laryngofissure, direct microlaryngoscopy, and fibrolaryngoscopy.

RESULTS

Information on structural alterations in laryngeal mucosa to the depth of 2 mm, obtained by OCT, makes it possible to precisely locate tumor borders, thus giving an opportunity to control the surgical treatment of laryngeal carcinoma. The YAG:Nd laser scalpel with wavelengths of 1.32 microm and 1.44 microm is successful in surgical procedures both in open and closed larynx due to efficient coagulation and minimization of collateral tissue damage area. Combination of the two wavelengths in the single laser unit and intraoperative OCT monitoring result is a new modality for minimally invasive larynx surgery.

CONCLUSIONS

OCT is promising to become a new diagnosing method of laryngeal carcinoma and a tool for laser treatment monitoring.

Effect of CO(2)-Milliwatt laser on peripheral nerves: part II. A histological and functional study

In order to further explore the role of laser for microneural repair, the early and late effects of CO(2) laser irradiation on intact rat sciatic nerves were investigated. A total of 48 rat sciatic nerves were exposed to 100-mW laser power with a pulse duration of 1.0 s and a spot size of 320 microm. In one-half of the nerves, albumin solder was applied to the nerve followed by laser irradiation. The results were evaluated up to 94 days after surgery with functional toe-spreading test, and light and transmission electron microscopy. Irradiation of the nerve resulted in almost no deficit in the motor function. A subperineurial degeneration of myelinated and unmyelinated axons is observed in the first 2 weeks after laser irradiation, while the central part of the nerve remains undamaged. The degeneration is followed by axonal regeneration with subsequent maturation of nerve fibres in time. No excessive intraneural or extraneural scarring was seen. In the soldered nerves, the solder elicits an inflammatory reaction upon the epineurium in the first week after irradiation. By week 1, the solder is completely absorbed. After 2 weeks, the inflammatory reaction ceases and by week 4, no residual reaction is seen. At 12 weeks, only minimally disarranged epineurium is seen with otherwise normal neural architecture. In conclusion, CO(2) laser irradiation at 100 mW with pulses of 1.0 s has no long term negative effects on nerve function and morphology. Therefore, these laser settings can be safely applied for laser-assisted nerve repair.

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.

Intracranial pressure waves generated by high-energy short laser pulses can cause morphological damage in remote areas: comparison of the effects of 2.1-micron Ho:YAG and 1.06-micron Nd:YAG laser irradiations in the rat brain

BACKGROUND AND OBJECTIVE

Histological effects of 2.1-micron Ho:YAG and 1.06-micron Nd:YAG laser pulses were compared in the rat brain, with special regard to areas remote from the irradiated site.

STUDY DESIGN/MATERIALS AND METHODS

Laser pulses were delivered through a 0.6-mm glass fiber, the tip of which was either introduced into the caudate nucleus (application mode I), or held at a 2-mm distance above the exposed intact dura. In the latter case, the space between the dura and the fiber tip was filled either with physiological saline (application mode II) or with air (application mode III).

RESULTS

In application modes I and II, but not in application mode III, Ho:YAG laser pulses of 1.5 J and 200 microseconds, but not Nd:YAG laser pulses with the same parameters, immediately caused morphological damage to a considerable number of neurons and axons randomly distributed among apparently normal ones in certain areas remote from the irradiated site. A decrease in the energy and an increase in the length of the pulses lowered the incidence of the remote morphological damage.

CONCLUSION

This novel finding may impose limits on the application of Ho:YAG lasers in human endoscopic neurosurgery.

New laser techniques for diagnosis and treatment of deep-seated brain lesions

The five years survival rate of deep-seated malignant brain tumors after surgery/radiotherapy is virtually 100% mortality. Special problems include: (1) lesions often present late; (2) position: lesions overlies vital structures, so complete surgical/radiotherapy lesion destruction can damage vital brain-stem functions; and (3) difficulty in differentiating normal brain from malignant lesions. This study aimed to use the unique properties of the laser: (a) to minimize damage during surgical removal of deep-seated brain lesions by operating via fine optic fibers; and (b) to employ the propensity of certain lasers for absorption of (nontoxic) dyes and absorption and induction of fluorescence in some brain substances, to differentiate borders of malignant and normal brain, for more complete tumor removal. A fine laser endoscopic technique was devised for removal of brain lesions, which minimized thermal damage and shock waves. A compatible endoscopic fluoroscopic laser technique was developed to differentiate brain tumor from normal brain.

High-power diode laser in neurosurgery: clinical experience in 30 cases

BACKGROUND

High-power semiconductor diode lasers were recently introduced and have been tested in ophthalmology and general surgery. These lasers are attractive from the practical and economical standpoint, and have enough power to perform most surgical procedures. They could replace other surgical lasers such as CO2, argon, 1.06 microm, and 1.32 microm Nd-YAG lasers for many applications in neurosurgery. We report our initial experience with the first available 0.805-microm surgical diode laser, the Diomed 25 (Diomed, Ltd, Cambridge, U.K.) in a series of 30 patients.

METHODS

The diode laser was evaluated during surgical resection of various types of central nervous system tumors in 30 patients. It was used free-hand in 27 patients in contact and non-contact, continuous wave (cw) and pulsed modes, and during ventricular endoscopy in three patients. Average time of laser use during a procedure was 248 seconds. Output power ranged from 1 to 25 watts, with an average power per patient of 2.64 to 15.5 watts (mean, 8.78 watts). Total energy delivered ranged from 65 to 11,051 joules per patient.

RESULTS

Using 600- or 400-microm non-contact optic fiber, well pigmented tumor tissue hemostasis was obtained at cw 3 to 10 watts with a defocused beam, whereas vaporization required 10-25 cw or pulsed watts with a focused beam. Soft and tough tissue section could be obtained using a sculpted cone-shaped (600-300 microm tip) contact fiber at 7-10 cw watts after fiber tip charring. Because of the deeper penetration of 0.805-microm light in non-pigmented tissues, non-contact mode is not recommended for white matter or poorly vascularized tumors. The contact mode was not efficient on very soft tissues such as edematous brain parenchyma. The contact fibers proved to be very fragile because of heat generation.

CONCLUSIONS

The high power diode laser proved to be efficient for hemostasis, section and vaporization, using contact and non-contact modes, at different output powers. Economical and ergonomical advantages of this new generation of surgical lasers may cause them to replace other surgical lasers such as argon, CO2, and Nd-YAG lasers, mostly for tumor surgery.

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.

Development of an avian model for restenosis

Recurrence of atherosclerotic plaque growth after interventional therapy, restenosis, is a significant clinical problem occurring in 20%-50% of cases. We have developed a new avian model for the investigation of restenosis after arterial injury in cholesterol fed White Leghorn roosters. Atherosclerotic plaque growth 1-30 weeks after angioplasty balloon mediated endothelial injury in the abdominal aorta was studied in 37 roosters. Roosters were maintained on either normal poultry diet or high cholesterol diet. Twelve cholesterol fed roosters were also fed a hormone supplemented diet in order to modify plaque morphology. The procedural success rate was high. Angiographic stenoses (mean 36% with maximum of 74%) were detectable in cholesterol fed roosters after balloon angioplasty with associated histological evidence of plaque growth (P < 0.017). Cholesterol feeding enhanced fatty plaque growth; hormone manipulation increased calcific and ulcerated plaque but with high associated morbidity. Three interventional devices were subsequently examined in 32 roosters (16 laser angioplasty, 7 atherectomy, and 9 stent implant). Plaque development was again assessed by contrast angiography and histological analysis. We conclude that balloon mediated arterial injury in cholesterol fed roosters produces early proliferative and late, complex atherosclerotic lesions providing an inexpensive model for plaque development after intimal injury.

Comparative study of Nd:YAG laser angioplasty at 1.06 microns, 1.32 microns, and 1.44 microns wavelengths: decreased vascular spasm and early mortality with 1.44 microns laser ablation

BACKGROUND AND OBJECTIVE

Although laser angioplasty has been demonstrated to be effective for the treatment of long, complex coronary arterial atherosclerotic stenoses, there is an associated risk of acute arterial spasm, dissection, and perforation as well as a significant restenosis rate. It has been postulated that the use of lasers emitting at wavelengths designed for radiation absorption by water would decrease local tissue trauma.

STUDY DESIGN/MATERIALS AND METHODS

We have examined the use of a Nd:YAG laser designed to emit at 1.44 microns, an absorption peak for water, and compared the results of laser ablation at 1.06 microns, 1.32 microns, and 1.44 microns wavelengths. Nd:YAG laser angioplasty was performed in the abdominal aorta of White Leghorn roosters. Acute and chronic vascular trauma was assessed by contrast angiography and histological analysis.

RESULTS

There was a significant decrease in early mortality with 1.44 microns laser ablation. This decreased mortality after 1.44 microns ablation was associated with a decrease in vascular spasm, perforation, and thermal damage. Atherosclerotic plaque development at follow up was decreased with 1.44 microns ablation but this was not significant.

CONCLUSION

1.44 microns laser ablation decreases early vascular trauma and mortality and may decrease subsequent atherosclerotic plaque development.

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.

The histopathological effects of the CO2 versus the KTP laser on the brain and spinal cord: a canine model

Because no data are available concerning the histopathological effects of the potassium titanyl phosphate (KTP) laser on central nervous tissue, a study was performed using a canine model to compare the histopathological effects of a commonly used laser (CO2) and the KTP laser on brain and spinal cord tissue. Exposed brain and spinal cord tissue were irradiated with 0.1-s pulses (x10), with spot sizes of 1 mm (in focus) over a range of 1 to 10 W. Wedge-shaped lesions were produced with the CO2 laser, while more blunt, semilunar-shaped lesions were produced by the KTP laser. The depth and width of the lesions were proportional to the energy applied. The lesions ranged in surface diameter from 0.6 to 1.3 mm for CO2 and 0.8 to 1.6 mm for KTP lasers, respectively. The depth of the lesions varied from 0.4 to 2.0 mm for CO2 and 0.3 to 1.1 mm for KTP lesions. Histopathologically, a central zone of tissue destruction and vaporization was surrounded by a zone of coagulative necrosis, in turn surrounded peripherally by a zone of pallor. CO2-induced lesions were histologically more hemorrhagic than KTP-induced lesions. In view of the histopathological findings, the KTP laser appears as safe as the CO2 laser in terms of tissue lateral thermal change (penetration) and tissue absorption. The additional hemostatic advantage observed clinically for the KTP laser is demonstrated histologically as well. Although the wavelength of the KTP and argon laser light are similar, the histopathological effects seem to be less pigment dependent. The KTP laser seems well suited for neurosurgery and has the versatility provided by a fiberoptic delivery system.

Current status of lasers in neurosurgical oncology

During the past decade and a half, the photothermal and photochemical effects of several medical lasers have been studied for the clinical treatment of benign and malignant, primary and secondary central nervous system tumors. Increased precision and hemostasis during tumor excision while limiting manipulation and retraction of nervous tissues are possible with the microsurgical carbon dioxide, argon, and frequency doubled neodymium:YAG lasers. Computerized tomography and magnetic resonance imaging-directed volumetric tumor removal by laser is feasible with computer-generated visual displays referenced to the patient's anatomy using stereotactic instrumentation. Photodynamic therapy with hematoporphyrin derivative as the photosensitizer and neodymium:YAG laser hyperthermia are currently under evaluation for the treatment of residual and recurrent malignant tumors. Encouraging results have been reported for each of these nonablative forms of laser use.

Acute effect of neodymium yttrium aluminium garment laser on the cerebral cortical structure, blood-brain barrier, and pial vessel behaviour in the cat

Experimental brain lesions were created by Nd:YAG laser (wave length 1.06 microns) irradiation on the cerebral cortex of anaesthesized adult cats with 20 Watts impacts of 0.5, 1.0, 2.5, and 5.0 seconds exposure time through cranial windows. Histological changes, disruption of the blood-brain barrier (Evans blue extravasation) and pial vessel reaction (large vessels more than 100 microns and vessels smaller than 100 microns) were studied under constant PaCO2, blood pH, and mean arterial pressure. Histological changes of the lesions consisted of a zone of dense coagulation, a pale zone of homogeneous coagulation and an oedematous zone. Evans blue extravasation was uniformly seen extending from the histologically changed area into the surrounding tissue in all experiments. Pial arteries in the area with morphological changes showed pronounced dilatation (100.0 +/- 7.2%) and one third of these arteries were closed by thrombi. Pial arteries in the area of Evans blue extravasation but outside of histological changes also dilated (large arteries 60 +/- 4.1%, small arteries 77 +/- 5.9%). Pial arteries outside of the Evans blue extravasation were affected transiently and only in a very small zone: Within a distance of 200 microns from the Evans blue extravasation, large arteries initially dilated by 41 +/- 8.3%; small arteries dilated within 400 microns (42 +/- 3.7%). Within 4 minutes after irradiation arterial dilatation was again significantly reduced (p less than 0.01). It is concluded that no important vascular changes occur beyond the zones of histologically altered brain tissue.

Cortical microcirculation in a new model of focal laser-induced secondary brain damage

To study the causes of spatial and temporal evolution of progressive neuro-injury in focal brain ischemia, models with consistent lesion topography are required. In such models, continuous monitoring of the microcirculation in a penumbral area undergoing progressive damage could be possible. We used a fixed-pulse (1.0 s, 40 W) Nd-YAG laser (NYL) to produced discrete brain lesions in rats and monitored the cerebral blood flow (CBF) with laser-Doppler flowmetry (LDF) in nonirradiated areas directly adjacent to the maturing lesion. We also examined the time evolution of the lesion topography over a 4 day period. The lesion volume determined by histopathological methods increased from 3.1 +/- 0.5 to 4.5 +/- 0.5 mm3 (p less than 0.05) during the first 2 h. Simultaneously, LDF indicated severe hypoperfusion (-60 +/- 21%, p less than 0.01) at a zone (1 mm distance from the laser lesion) where progressive neuronal degeneration and increased tissue water content (80.0 +/- 3.3% versus 76.8 +/- 2.1% in normal tissue, n = 7, p less than 0.05) were also observed. At a 4 mm distance from the lesion, hyperemic CBF responses were observed, but no histopathological signs or edema. Secondary brain damage progressed up to 4 days (lesion volume of 6.0 +/- 0.7 mm3). The NYL-induced brain lesion produced a highly reproducible focal injury and progressive neuronal death in a spatial relationship with microcirculatory failure and edema formation. The model allows prospective study of tissue state at a discrete zone, which is separate from the initial injury, but susceptible to secondary brain damage.

Effects of 1.32-micron Nd-YAG laser on brain thermal and histological experimental data

Considering that the 1.32-microns Nd-YAG laser should have physicothermal properties close to those of the CO2 laser, a series of experiments were conducted on rat cortex (N = 51). Three laser wavelengths were compared: CO2 laser (10.6 microns), 1.06-microns Nd-YAG, and 1.32-microns Nd-YAG lasers. For each shot, temperature measurements were recorded with an infrared thermographic videocamera. The digitized signals were figured as thermal profiles and temperature developments. Ninety-five shots were correctly studied and analyzed: CO2, N = 29; 1.06-microns Nd-YAG, N = 20; 1.32-microns Nd-YAG, N = 46. The histological lesions produced by these three lasers were compared on animals killed 24 hours (N = 20), 8 days (N = 20), and 30 days (N = 5) after the laser impacts. For equivalent densities of energy, the depth of cortical necrosis was comparable for the CO2 laser (200-250 microns) and the 1.32-microns Nd-YAG laser (210-260 microns) whatever the date of death; the 1.06-microns Nd-YAG laser shots were responsible for much more important damage (400-550 microns). Because of its important absorption in water and nervous tissue, the authors consider the 1.32-microns Nd-YAG laser most suitable for neurosurgery, particularly because it is conducted through optic fibers, and therefore is easy to handle during neurosurgical procedures.

Platelet-activating factor and progressive brain damage following focal brain injury

The effects of a platelet-activating factor (PAF) antagonist on brain edema, cortical microcirculation, blood-brain barrier (BBB) disruption, and neuronal death following focal brain injury are reported. A neodymium:yttrium-aluminum-garnet (Nd:YAG) laser was used to induce highly reproducible focal cortical lesions in anesthetized rats. Secondary brain damage in this model was characterized by progressive cortical hypoperfusion, edema, and BBB disruption in the vicinity of the hemispheroid lesion occurring acutely after injury. The histopathological evolution was followed for up to 4 days. Neuronal damage in the cortex and the hippocampus (CA-1) was assessed quantitatively, revealing secondary and progressive loss of neuronal tissue within the first 24 hours following injury. Pretreatment with the PAF antagonist BN 50739 ameliorated the severe hypoperfusion in 12 rats (increasing local cerebral blood flow from a mean +/- standard error of the mean of 40.5% +/- 8.3% to 80.2% +/- 7.8%, p less than 0.01) and reduced edema by 70% in 10 rats (p less than 0.05) acutely after injury. The PAF antagonist also reduced the progression of neuronal damage in the cortex and the CA-1 hippocampal neurons (decrease of neuronal death from 88.0% +/- 3.9% to 49.8% +/- 4.2% at 24 hours in the cortex and from 40.2 +/- 5.0% to 13.2% +/- 2.1% in the hippocampus in 30 rats; p less than 0.05). This study provides evidence to support progressive brain damage following focal brain injury, associated with secondary loss of neuronal cells. In this latter process, PAF antagonists may provide significant therapeutic protection in arresting secondary brain damage following cerebral ischemia and neurological trauma.