Use of the Nd-YAG laser in neurosurgery

Summary After many years of experience, in general we prefere the Nd-YAG laser, although the CO₂ laser is an advantage in a few specific cases (lipomas, cranial synostosis). While the focused CO₂ laser may be used as a cutting instrument in less vascular tissue with little trauma to the surroundings, the Nd-YAG laser produces a homogeneous coagulation with an energy dependent depth effect. Thus, with the Nd-YAG laser residual tumour tissue can be selectively and with a predictable depth effect thermally destroyed. Because of its excellent coagulation property, the use of the Nd-YAG laser is particularly indicated in highly vascular meningeal tumours. The shrinkage of a tumour and its demarcation which is due to the varying absorption properties facilitates the dissection and allows in addition the preservation of normal tissue.     

Percutaneous peripheral laser angioplasty with a pulsed Nd-YAG laser and sapphire tips

Percutaneous transluminal laser angioplasty with a pulsed Nd-YAG laser (1064 nm wavelength, 100s pulse duration, up to 0.4 J per pulse, 10 Hz repetition rate) coupled to optical fibres with sapphire tips of 1.8 and 2.2 mm diameter was performed under experimental conditions and then in 30 chronic occlusions of femoral and popliteal arteries in 22 patients.The experimental study in 11 human cadaverous arteries revealed that this laser system was effective in the recanalization of seven femoropopliteal occlusions, but the relative rigidity of the sapphire-tipped contact probe prevented its access to two infrapopliteal vessels. Two perforations occurred after the recanalization of 18 and 15 cm, respectively.Clinically the procedure was successful in 17 out of 25 sessions (68%). The probe formed a primary channel of at least 2.0 mm width which was further dilated by conventional balloon catheter. Ankle/brachial systolic pressure index (ABPI) increased from 0.43±0.13 to 0.79±0.21 after the procedure. In eight cases complications occurred. Two reocclusions were treated by Streptokinase infusion, two procedures were repeated 2 months later, one patient was referred to elective bypass surgery, and three patients were treated conservatively. Six patients were followed-up for more than 6 months. In one patient claudication of 400 m reappeared. ABPI showed a moderate decrease from 0.84±0.20 to 0.69±0.19.These first results are encouraging and it is likely that this method could become an important adjunct to balloon angioplasty.     

The role of pulse length in limiting distant damage to vascular tissue caused by the Nd-YAG laser

The total damage caused by equivalent doses of energy given to human cadaver vascular tissue over the same time scale from three Nd-YAG lasers of different pulse lengths is quantified. The continuous wave (c.w.) laser produces vacuolation and coagulation around a vaporized crater; the 100 μs pulsed laser produces less surrounding damage and the 10 ns pulsed laser none at all. The areas of damage in five craters made with 10 J energy were measured from histology slides using a digitising platten, and it was found that in each case the total amount of damage was the same, even though the depth of the craters made varied. The dose response for vaporization of the 10 ns pulsed laser was the greatest at 35 μm/J and that of the c.w. laser was least at 8 μm/J. A pulse length of 100 μs may not be the optimum for limiting surrounding tissue damage during laser angioplasty but it produces much less damage than a c.w. laser and unlike the 10 ns pulses is easily transmissible down an optical fibre.     

连续Nd:YAG激光治疗皮肤血管瘤的疗效观察

目的观察连续Nd:YAG激光(1064nm)治疗皮肤血管瘤的疗效。方法根据不同血管瘤的类型,选用适当的照射功率、照射时间和照射方式。蜘蛛痣、化脓性肉芽肿和较浅的草莓状血管瘤选用扫描式照射,输出功率为15~30W,直到病灶变为灰白色或轻微凹陷;较深的海绵状血管瘤和混合型血管瘤将光纤插入瘤体内并作扇形推进照射,输出功率为30~50W,每个方向照射2~3s,直到瘤体凹陷变平。结果139例患者经过1~5次治疗后,病灶消失,无明显的瘢痕形成。其中草莓状血管瘤59例,治愈39例,有效19例,无效1例;海绵状血管瘤28例,治愈8例,有效19例,无效1例;蜘蛛痣25例,全部治愈;化脓性肉芽肿17例,全部治愈;混合型血管瘤10例,治愈1例,有效6例,无效3例。随访2年,无复发。结论连续Nd:YAG激光是治疗除鲜红斑痣外各种血管瘤的一种有效方法。     

Histological changes in human breast cancer after interstitial irradiation with a pulsed Nd-YAG laser

This is a clinical study of the histological changes induced in human primary breast cancer by single-session pre-operative interstitial irradiation using a medium-power Nd-YAG laser (1064 nm, 1–6 W, 20 pulse s^-1, 100 Μs). Changes were studied in 15 tumours resected at an interval of 1–11 days after laser treatment, and in four biopsy samples from three tumours treated conservatively and biopsied for suspected recurrence 1–3 months after laser treatment. All foci of laser-induced destruction consisted of a sphere-shaped infarction 0.5–2.5 cm in diameter which enclosed a small evaporation cavity within carbonized walls. Vapour separation occurred in two tumours and gaseous rupture was seen in one tumour. Extensive vascular damage was seen inside the damaged area; damage to cancer cells was manifested by diminished size, vacuolization, cytoplasmic turbidity, pyknosis, disruption of the nuclear membrane and nuclear homogeneity. No clear morphological signs of damage could be seen in a significant percentage of cancer cells on short-term inspection (35–80%). Long-term histological study revealed a central necrotic area of diameter 1–1.2 cm in the laser-treated tumours, containing no viable cancer cells. In inadequately treated carcinomas, regrowth of tumour was seen at the periphery of this zone.     

Nd-YAG laser ablation of arteriosclerotic obstructions: Clinical long-term results in femoropopliteal artery occlusions

Laser recanalization of peripheral artery occlusions was performed in 338 patients. A continuous wave Nd-YAG laser was used in combination with sapphire-probe laser catheters. The initial recanalization rate was 85%. Complications such as dissections, perforations, emboli and spasm were observed in 14%. The cumulative patency rate after 3 years was 48%.     

The use of Nd-YAG laser in the treatment of malignant tumours of the oral and maxillofacial regions

Thirty cases with malignant neoplasms of the oral and maxillofacial regions treated by Nd-YAG laser are presented. All of them have been followed-up for 2–4 years, and the results are satisfactory. In 26 cases, the tumours disappeared clinically, were negative in pathological examination, and no recurrence was found in the 2–4 year follow-up period.     

Nd-YAG laser thermal effect: Comparative study of coagulation in rat liver in vivo by continuous wave and high power pulsed lasers

The coagulation effect of a continuous-wave neodymium-YAG (Nd-YAG) laser and of a high-power (500 W) pulsed (3–500 ms) microcomputer-controlled Nd-YAG laser are compared in rat liver in vivo. In a series of 68 animals, surface temperature was measured with an infrared camera, and necrosed volume was assessed histologically 24 h after laser irradiation. The high-power pulsed Nd-YAG laser presents two interesting features. First, it gives a better control of surface temperature. Second, a controlled sequence of high-power short pulses produces a predictable coagulated volume which can be comparable to that obtained with continuous-wave Nd-YAG or argon lasers.     

The use of the Nd-YAG and the CO2 laser in neurosurgery

Summary Over the last 3 years 120 patients have been operated on using laser techniques. This technique was chosen where technical difficulties were anticipated due to the size, the vascular supply or the localization of the process. Although the use of laser technique requires experimental work, before it can be applied clinically some distinct advantages could be demonstrated when compared with the use of the bipolar cautery.Due to its shrinking effect the laser beam is target oriented and makes the surgical procedure safe without the use of additional instruments. The Nd-YAG laser was preferred in tumors with a rich vascular supply. Thus there was a definitely decreased need for blood transfusions in patients operated on with the laser. Even those parts of the tumors that can not easily be reached, using conventional techniques can now be eliminated by laser irradiation.The variable distance between the handpiece of the laser instrument and the target organ allows a pin point as well as a more diffuse irradiation. Since it is not necessary to touch the tissue, laser techniques are particularly useful in critical areas, e. g. close to the brainstem or the spinal cord, because they make it unnecessary to touch the tissue.The question as to whether the use of laser technique will reduce the rate of recurrent tumor growth needs further studies based on longer follow-up periods. Further technical improvements are needed to make the laser device a true microinstrument. Finally a combination of both laser types — that is the Nd-YAG laser for coagulation and the CO₂ laser for cutting -might be a definite advantage.Dedicated to Prof. Dr. Dr. h. c. K. J. Zülch on occasion of his 70th birthday.     

Effects of super-pulsed Nd-YAG laser on arterial tissue: comparison with continuous wave

The effects of a super-pulsed Nd-YAG laser at 1.32 μm wavelength on normal or atherosclerotic human arterial tissue were evaluated and compared with those obtained with continuous wave. One joule per pulse was delivered through a 0.2 mm optical fibre with a pulse width of 10 ms at 10 Hz (super-pulse), or 10 W (10 J) were delivered at continuous wave in saline or blood. Ten joules were delivered with super-pulse or continuous wave for each tissue specimen. The aortic specimens were lased either by continuous wave or super-pulse. At super-pulse mode, ablation efficiency (mm³ J⁻¹) was 0.0149±0.0044 for normal tissue in saline, 0.0148±0.0043 for atheroma in saline, 0.0138±0.0062 for normal tissue in blood, and 0.0146±0.0049 for atheroma in blood. There was no significant difference between the groups. At continuous wave mode, ablation efficiency was 0.0507±0.0299 for atheroma in blood (p<0.001 vs super-pulse). However, extensive charring was observed with continuous wave lasing (41% with continuous against 14% with pulsed mode,p<0.001). Heavily calcified plaques were also ablated at 1.5 J per pulse and 15 W (continuous wave), resulting in extensive charring with continuous wave (77% vs 18% with super-pulse,p<0.01). In conclusion, at super-pulse mode, 1.32 μm Nd-YAG laser has neither the selectivity for atheroma nor influence of blood, thermal injury induced by super-pulse is less than that induced by continuous wave (cw), calcified plaques can be ablated by super-pulse, and super-pulsed Nd-YAG laser angioplasty is safer to use than continuous wave.     

Fibrescopic Nd-YAG laser treatment of superficial bladder tumours in outpatients

The neodymium-YAG (Nd-YAG) laser has been used via a flexible cystoscope to treat 48 superficial bladder tumours in 39 patients. The procedure can usually be performed with minimal discomfort under topical urethral anaesthesia alone or supplemented by a small dose of benzodiazepine. It is therefore suitable for use in ambulant outpatients. Local tumour clearance can be expected when this method is used. The savings in hospital admission costs and general anaesthesia may justify the comparatively high capital cost of the laser.     

Endoscopic Nd-YAG laser therapy of gastric polyposis

Thirteen patients with gastric polyposis (113 polyps) were treated by endoscopic Nd-YAG laser irradiation. Among them there were five cases with adenomas, six with hyperplastic polyps and two with inflammatory polyps. Ninety-six polyps were <1 cm, 13 polyps were 1 cm, and four polyps were 2 cm. In the patient who had the largest number of lesions, 22 polyps were found at endoscopic examination. All but two patients were regularly followed up endoscopically for 2–5 years after treatment and showed no sign of recurrence. Mild bleeding occurred in three cases. No perforation or any other serious complications occurred. The results were encouraging. It is concluded that endoscopic Nd-YAG laser ablation of gastric polyposis is effective, simple to perform, safe and deserves recommendation.     

Hysteroscopic treatment of uterine bleeding with the Nd-YAG laser

This preliminary study involves 45 patients, referred to us for hysterectomy, who complained of uterine bleeding that was resistant to conventional treatment. Prior to surgery, these patients had a diagnostic hysteroscopy which showed that the bleeding was due to submucosal fibroids, to intrauterine or cervical polyps, either alone or in association with adenomyosis, or to adenomyosis alone. These patients were treated as outpatients with the Nd-YAG laser, by using paracervical anaesthesia. In 80%, the menstrual cycle has returned to normal after a short follow-up (four cycles). Three patients required hysterectomy because hysteroscopy was impossible owing to multiple fibroids. Two patients have been lost to follow-up observations. In addition, there was a beneficial result on secondary dysmenorrhoea. Wherever necessary, uterine septa and synechiae were divided. Between six and 10 weeks after treatment, a follow-up hysteroscopy was performed. This confirmed that there was no recurrence of the underlying lesion, that the treated areas were scarred and that the endometrium in these areas was functional. Longer follow-up is necessary to assess the precise proportion of hysterectomies that can be avoided by using this technique.     

The use of the Nd-YAG laser in neurosurgery

Whereas the focused CO2 laser may be used as a cutting instrument in less vascularized tissue with limited trauma to the surrounding tissue, use of the defocused Nd-YAG laser results in homogeneous coagulation with an energy-dependent depth effect. Thus, residual tumor tissue may be cauterized selectively with a depth effect which can be predicted with satisfactory precision. Tumor shrinkage and demarcation based on different absorption properties facilitates dissection and, moreover, allows the preservation of healthy tissue. The excellent coagulating properties of the Nd-YAG laser render it especially effective in cases of highly vascularized meningeal tumors.     

Extent of thermal penetration of Nd-YAG laser — histological considerations

Summary The extent of thermal penetration of Nd-YAG laser was studied histologically. The material was obtained from seven cases of various types of intracranial and extracranial tumours and normal temporal muscle obtained at operation. After irradiation of the tumour surface with the laser, the tumours were removed and depth and width of pathological changes caused by heat were studied. Histologically, materials consisted of a vaporized surface, carbonized, vesicular, necrotic, oedematous layers and surrounding intact brain tumour tissue. There was a direct relationship between the thermal effect and the irradiated thermal energy (watt × exposure time × pulse number). The results showed that the thermal effect was limited to a depth of 6 to 10 mm from the irradiated surface when irradiated 4 times at the power of 90 watts for 2 seconds.     

Histological studies of myocardium zones irradiated with Nd-YAG laser

Histological investigation of the dog's myocardium performed 7 and 25 days after irradiation with different doses of Nd-YAG laser show that the damage zone has the shape of a hollow sphere with minor changes in cardiomyocytes in the central part of the sphere. The small blood vessels in the irradiated zone remained undamaged as well. A tentative explanation of the physical process that leads to this type of coagulation zone is given.     

Contact Nd-YAG laser in mastectomy and axillary evacuation: a prospective randomized study

Thirty patients underwent modified mastectomy for breast cancer. They were allocated into three operation groups. Group A (n=10) underwent conventional operation, group B (n=10) contact Nd-YAG laser operation, and group C (n=10) conventional mastectomy with laser evacuation of the axillary lymph nodes. The operation with contact Nd-YAG laser was slower (p<0.05) than the conventional operation. Laser significantly reduced pre-operative bleeding (p<0.01), but there were post-operative wound seromas in 50% of the cases. No other complications occurred. It is concluded that contact Nd-YAG laser is safe and reduces bleeding by sealing small vessels. However, there seems to be a risk for post-operative wound seromas particularly after radical axillary lymph node dissection.     

Low power interstitial Nd-YAG laser photocoagulation in normal rabbit brain

The safe, effective, clinical application of interstitial laser irradiation to destroy brain tumour tissue requires a knowledge of the relation of the extent of laser-induced (thermal) necrosis to the delivered laser power and total energy, and to time post-irradiation. We have conducted experiments to determine these relationships in normal rabbit brain. Irradiation by a Nd-YAG laser (1064 nm), at powers of 0.5–3.0 W and exposures of 200–1333 s produced well-defined necrotic lesions whose size increased with both the power and the total energy delivered. Lesions of 6 mm diameter made by 0.75 W for 1000s were well tolerated by animals allowed to recover from anaesthesia following irradiation. The diameter of the lesion was greatest at 48 h after irradiation. Following evolution of a characteristic healing response to necrosis in brain, the residual damage at 4 weeks was no greater in volume than that of the acute lesion. The results suggest that low power interstitial Nd-YAG laser photocoagulation in brain can be reliably and safely effected.     

Stretched nanosecond pulses of a Q-switched Nd-YAG laser: Transmission through optical fibres and in vitro effects on human calcified tissues

Using a new Q-switched Nd-YAG laser prototype (1064 nm), every initial pulse (15 ns or 33 ns duration, 10 Hz repetition rate, 2×E energy, Pmax power) was transformed into two successive pulses (each one with 15 or 33 ns duration, 1×E energy) delayed by 27 ns. With a 15 ns initial pulse, the two 15 ns components (each one with Pmax/2) were well separated and called a 15 ns double pulse. When the duration of the initial pulse was stretched to 33 ns, the overlapping of the two 33ns components (each with Pmax/4) produced only one pulse trapezoidally shaped, of 60 ns duration and called 60 bi-pulse. With double pulses, it was possible to transmit 100 mJ through a silica-silica optical fibre of 400 μm diameter, whereas 155 mJ were transmitted with bi-pulses. Human calcified atheromatous tissues were irradiated with bi-pulses through a 200 μm diameter optical fibre. Craters (0.6–0.7 mm in diameter) were easily obtained in atheromatous aortic segment with 40 mJ energy per bi-pulse. No trace of carbonization was noticed. Fragmentation of urinary and biliary calculi was also obtained.     

Endobronchial hamartoma treated by an Nd-YAG laser: Report of a case

Endobronchial hamartomas are only rarely encountered. They cause irreversible lung damage due to bronchial obstruction if not diagnosed early and treated properly. Among the various treatments for this rare disease, a surgical resection remains the most popular. We herein report a case of a 53-year-old man presenting with an endobronchial hamartoma which was successfully excised by laser irradiation via a rigid bronchoscope, along with a review of 113 patients with this disease reported in the literature.