Laser-assisted neuroendoscopy using a neodymium yttrium aluminum garnet or diode contact laser with pretreated fiber tips

Transcription

1 J Neurosurg 88:82 92, 1998 Laser-assisted neuroendoscopy using a neodymium yttrium aluminum garnet or diode contact laser with pretreated fiber tips WILLIAM P. VANDERTOP, M.D., PH.D., RUDOLF M. VERDAASDONK, PH.D., AND CHRISTIAAN F. P. VAN SWOL, M.SC. Departments of Neurosurgery and Clinical Technology and Physics, University Hospital, Utrecht, The Netherlands; and Wilhelmina Children s Hospital, Utrecht, The Netherlands Object. Although lasers have proved to be valuable in neuroendoscopy, surgeons are still not comfortable using highenergy laser endoscopic probes in proximity to vital structures such as the basilar artery in third ventriculostomy. The authors have developed a special laser catheter for use in neuroendoscopy; the object of this paper is to present their experimental and clinical experiences using the catheter. Methods. This laser catheter is fitted with an atraumatic ball-shaped fiber tip that is pretreated with a layer of carbon particles. These carbon particles absorb approximately 90% of the energy emitted, which is very effectively converted into heat. As the heat is generated in this very thin layer of carbon coating, the temperature at the surface of the ball-shaped tip reaches ablative temperatures instantly at powers of only a few watts per second, which has enabled the authors to limit drastically the amount of laser light used and the length of exposure needed, thereby increasing safety even around critical structures. Conclusions. The authors present experimental data and their clinical experience using these pretreated fiber tips with a neodymium yttrium aluminum garnet contact laser or a diode contact laser in 49 patients (22 males and 27 females) and a variety of procedures: third ventriculocisternostomy (33 patients), cyst fenestration (nine patients), colloid cyst resection (six patients), and fenestration of the septum pellucidum (one patient). There was no instance of mortality or increased morbidity. To date, the procedure success rate is 100% and the overall outcome success rate is 86%. The authors conclude that pretreated atraumatic ball-shaped fiber tips now make laser application safe and effective in a variety of neuroendoscopic procedures. Because of their low power range (only several watts), compact diode lasers will be the energy source of first choice. KEY WORDS neurosurgical endoscopy endoscopic surgery laser surgery diode laser Nd-YAG laser laser fiber tips contact laser E NDOSCOPIC intracranial surgery has gained rapidly increasing popularity because a wide variety of commercially available endoscopic tools has broadened the diagnostic and therapeutic options. 4,6,18 Although neuroendoscopy is considered a safe technique, the overall rate of clinically significant complications is reported to be approximately 7%. 19 Because blunt perforation of a membrane or cyst wall can be hazardous, especially when vital structures are obscured, several methods and instruments have been described and used. 18 A gentle thrust of the endoscope itself is simplest, but certainly not without danger. 8 A puncturing needle can be adequate, allowing the introduction of a balloon catheter to dilate the orifice of a ventriculostomy safely. In addition to monopolar coagulation wires and radiofrequency dissectors, laser assistance has also proved to be valuable in neuroendoscopy. 14,15 To date, the neodymium yttrium aluminum garnet (Nd- YAG) laser (1064 nm) has been used most frequently, both in contact and noncontact modes, for coagulation of 82 the choroid plexus blood vessels and for tumor resection. 24 Noncontact Nd-YAG laser light is not really suitable because the laser light is readily absorbed by cerebrospinal fluid (CSF), leading to wide scattering and possible thermal damage to surrounding tissue. The contacttipped Nd-YAG laser partly overcomes this problem because 10 to 20% of the laser energy is absorbed at the tip, but many surgeons are not comfortable using highenergy laser endoscopic probes in proximity to vital structures such as the basilar artery (for example, in third ventriculostomy). 7 We have developed a special laser catheter with an atraumatic ball-shaped fiber tip that is pretreated with a layer of carbon particles. This layer absorbs approximately 90% of the laser light, which is very effectively converted into heat. 23 This has enabled us to limit drastically the amount of laser light used and the length of the exposure needed, thereby increasing safety even around critical structures. In this paper we present our clinical experience, based on experimental studies, using these pre-

2 Laser-assisted neuroendoscopy with pretreated fiber tip TABLE 1 Clinical characteristics of 49 patients who underwent laser-assisted neuroendoscopy* Case Age, No. Sex Signs & Symptoms Medical History 1 5 mos, M bilat miosis, developmental delay, & eye movement disturbances pontine ischemic infarctions 2 4 mos, F bulging fontanelle, suture diastasis, & distended scalp veins 3 11 mos, M progressive increase in skull circumference; unilat shunting VP shunt 3 mos earlier for raised ICP 4 21 mos, M motor retardation, hypertonia in legs, & gait disturbance VP shunt 5 mos earlier for raised ICP 5 30 yrs, M generalized seizure depression, memory & concentration deficits 6 20 yrs, M headaches, vomiting, loss of consciousness, & diplopia postmeningitis hydrocephalus & VP shunt 7 8 yrs, M growth hormone deficiency, short stature, & large head 8 12 mos, M convulsions, vomiting, lt hemiparesis, & herpes encephalitis 9 72 yrs, M dysarthria, nausea, vomiting, & depressed consciousness ischemic infarction, rt MCA territory yrs, F depressed consciousness VP shunt for hydrocephalus yrs, M disorientation, headaches, & memory deficits Grade IV astrocytoma, corpus callosum yrs, M gait disturbance, memory loss, & depression yrs, M gait disturbance, nocturnal headaches, & cognitive deficits depressive disorder yrs, F irritability, headaches, memory loss, & weak concentration VA shunt for hydrocephalus; radiotherapy for tectal mass yrs, M weak concentration, fatigue, emotionally unstable, headaches, & gait disturbance yrs, F memory loss, weak concentration, bradyphrenia, & incontinence partial complex seizures; aqueductal stenosis mos, F headaches, irritability, & depressed consciousness VP shunt for vein of Galen malformation yrs, F headaches, visual loss, bradyphrenia, & dizziness recurrent skull base meningioma yrs, M visual loss & gait disturbance light spastic paraparesis yrs, F headaches & choked optical discs 21 3 yrs, F headaches, drowsiness, bradyphrenia IVH yrs, F headaches, loss of consciousness, & bradyphrenia posterior fossa ependymoma yrs, M headaches, diplopia, & choked optical discs yrs, F frontal dementia yrs, F gait disturbance, diplopia, & dizziness yrs, F headaches yrs, F headaches, bradyphrenia, & depressed consciousness plexus papilloma resection 8 yrs earlier yrs, F bradyphrenia, visual disturbances, choked optical discs, & headaches yrs, F visual disturbances & headaches yrs, F headaches & visual disturbances yrs, F bradyphrenia & bulbar palsy exophytic brainstem tumor 1 yr earlier yrs, F bradyphrenia, headaches, memory disturbances, & cognitive deficits cerebellar gliosis 30 yrs earlier yrs, M disorientation & mental deterioration Grade IV astrocytoma, lt temporal lobe 34 3 wks, M progressive increase in skull circumference, vomiting, sunset, & bulging myelomeningocele fontanelle yrs, M headaches, bradyphrenia, & weak concentration yrs, F headaches, bradyphrenia, & drowsiness neurofibromatosis I yrs, F headaches & bradyphrenia skull base meningioma 38 7 yrs, F headaches, vomiting, nausea, & drowsiness myelomeningocele & 2 recent VP shunt revisions yrs, F headaches yrs, F headaches, vomiting, nausea, & depressed consciousness infantile encephalopathy 41 7 yrs, F headaches, neck pain, & nausea myelomeningocele yrs, M headaches, vomiting, & choked optical discs 43 6 yrs, F headaches, ataxia, & poor school results yrs, F headaches & bradyphrenia rt frontal Grade IV astrocytoma & radiotherapy 1 yr earlier yrs, F headaches & bradyphrenia tectal plate astrocytoma & radiotherapy 10 yrs earlier yrs, M headaches 3rd & 4th ventricle astrocytoma resected 6 yrs earlier yrs, M dementia & Korsakoff s syndrome alcohol abuse yrs, M headaches VP shunt for 22 yrs: multiple revisions 49 7 yrs, M ataxia & choked optical discs * ICP = intracranial pressure; IVH = intraventricular hemorrhage; MCA = middle cerebral artery; sunset = sunset phenomenon of the eyes caused by tectal pressure; VA = ventriculoatrial; = not relevant. treated fiber tips with a Nd-YAG contact laser and a new generation of diode lasers in a variety of procedures. Clinical Material and Methods Patient Population From November 1993 to March 1997, 52 consecutive patients underwent 53 endoscopic procedures at our institutions. All operations were performed by the same surgeon (W.P.V.). In two cases the procedures were performed merely for diagnostic purposes and did not require the use of the laser; in one case the floor of the third ventricle was fenestrated using only a guide wire and Fogarty balloon catheter. The clinical features of the 49 remaining patients who underwent a laser-assisted neuroendoscopic procedure are described in Table 1. Laser-assisted procedures were all attended by a clinical laser physicist. There were 22 males and 27 females with ages ranging from 3 weeks to 72 years. Signs and symptoms were usu- 83

3 W. P. Vandertop, R. M. Verdaasdonk, and C. F. P. van Swol FIG. 1. Left: Ball-shaped tip pretreated with a layer of carbon particles, which absorbs approximately 90% of the laser light. Right: Laser catheter consisting of an 800- m atraumatic ballshaped tip (uncoated) molded to a 400- m silica fiber core. FIG. 2. Left: Case 29. Sagittal MR flow study obtained 5 days after a third ventriculostomy was performed in a 15-year-old girl who presented with headaches, visual disturbances, and choked optical discs. The image shows flow void through the ventriculostomy in the conventional location between the basilar artery ally attributable to raised intracranial pressure caused by bifurcation and the clivus. Right: Case 21. Sagittal MR flow an obstruction of normal CSF flow. study obtained 3 months after a third ventriculostomy was performed in a 3-year-old girl who had presented with headaches and bradyphrenia. The image clearly shows flow void through the patent ventriculostomy located between the basilar artery bifurcation and the ventral pons. Sources of Equipment Endoscopic Equipment. A selection of different flexible and steerable fiberscopes was used: the 4-mm Neuroendoscope (Codman, Bracknell, UK), the 2.3-mm Neuroview endoscope (Neuro Navigational, Costa Mesa, CA), the 4.6-mm Neuroview endoscope (Neuro Navigational), and the 2.7-mm Neuroflex (Clarus Medical Systems, Minneapolis, MN). For each endoscope, designated fiberoptic cables and lighting equipment were used in combination with a standard camera and television monitor. The Malis irrigation module (Codman) was implemented for continuous irrigation by using either a physiological saline solution or Ringer s solution. Laser Equipment. A standard 1064-nm Nd-YAG laser (Medilas 4060; MBB/Dornier, Munich, Germany) was used as well as a new generation 810-nm diode laser (Diomed 25, Diomed, Cambridge, UK). Although these lasers are capable of generating 60 W and 25 W, respectively, only 1 to 5 W were used. A special laser catheter was developed by one of the authors (R.M.V.), which consisted of an 800- to m atraumatic ball-shaped tip molded to a 400- m core fiber; the ball-shaped tip was pretreated with a layer of carbon particles that absorb approximately 90% of the laser light (Fig. 1). In vitro and in vivo dosimetry studies have shown that an exposure of 1 to 3 W for 0.5 seconds will ablate a layer of tissue 0.3 to 0.5 mm thick at each pulse with a 0.2- to 0.3-mm zone of coagulation around the ablation crater. Extending the exposure time or increasing the power mainly contributes to a larger coagulation zone around the crater of ablation. Using energies that are too high or exposing the probe to air instead of water results in vaporization of the coating itself, making the probe less effective and comparable to normal contact probes. Results Third Ventriculocisternostomy The most frequent indication for a third ventriculostomy was a shunt dysfunction in nine patients and a tectal mass in six patients (Table 2). Of the remaining patients, four had an aqueductal stenosis; three, a pineal tumor; one, a thalamic tumor; five a cerebellar tumor; two, a skull base meningioma; one, a Chiari I malformation; one, a cerebellar hematoma; and one, hydrocephalus associated with myelomeningocele. In all 33 patients a wide hole measuring 4 to 7 mm was made. Patency was confirmed in all patients by using postoperative magnetic resonance (MR) images: the ventriculostomy success rate was 100% (Fig. 2). Twenty-seven patients (82%) were found to have a successful outcome: 24 patients improved clinically and three remained stable. Preoperatively, 10 patients required a shunt. Postoperatively, three of these 10 patients remained dependent on the shunt (Cases 10, 17, and 40). One patient with a skull base meningioma proved to have nonresorptive hydrocephalus because she did not respond favorably despite a patent ventriculostomy on repeated endoscopy; therefore, she received a lumboperitoneal shunt. The infant with a myelomeningocele developed progressive hydrocephalus despite an open ventriculostomy and a shunt was subsequently placed. Seven patients who were shunt dependent preoperatively became fully independent of the shunt. Cyst Fenestration The most frequent indication for cyst wall fenestration was a third ventricular arachnoid cyst or suprasellar cyst in four patients (Table 2). The remaining five patients had a choroid plexus cyst (two), a right frontal cyst (two), and an anterior interhemispheric cyst (one). Marsupialization of the cyst contents to the lateral or third ventricles by partially resecting the cyst wall was performed in all cases (Fig. 3). In eight cases a ventriculoperitoneal (VP) shunt (four cases) or a second shunt (four cases) was avoided. Colloid Cyst Resection In two patients with a colloid cyst a complete resection was possible. In the remaining four patients, only a sub- 84

4 Laser-assisted neuroendoscopy with pretreated fiber tip TABLE 2 Diagnosis, treatment, and outcome in 49 patients who underwent laser-assisted neuroendoscopy* Presence of Shunt Case No. Age, Sex Diagnosis Endoscopic Procedure Preop Postop Clinical Outcome 1 5 mos, M cyst 3rd ventricle cyst fenestration improved 2 4 mos, F interhemispheric cyst cyst fenestration improved 3 11 mos, M cyst 3rd ventricle cyst fenestration VP VP improved 4 21 mos, M cyst 3rd ventricle cyst fenestration VP VP improved 5 30 yrs, M tectal mass lesion 3rd ventriculostomy stable 6 20 yrs, M choroid plexus cyst cyst fenestration VP VP improved 7 8 yrs, M suprasellar cyst cyst fenestration improved 8 12 mos, M cyst rt frontal cyst fenestration improved 9 72 yrs, M lt cerebellar hematoma 3rd ventriculostomy improved yrs, F shunt dysfunction 3rd ventriculostomy VP VP shunt dependent yrs, M shunt dysfunction septum pellucidum fenestration & VP shunt VP stable yrs, M colloid cyst foramen of Monro cyst resection improved yrs, M colloid cyst foramen of Monro cyst resection improved yrs, F VA shunt dysfunction 3rd ventriculostomy & shunt removal VA improved yrs, M pineocytoma 3rd ventriculostomy & tumor biopsy improved yrs, F tectal mass lesion 3rd ventriculostomy improved mos, F shunt dysfunction 3rd ventriculostomy VP VP shunt dependent yrs, F skull base meningioma 3rd ventriculostomy LP shunt dependent yrs, M tectal mass lesion 3rd ventriculostomy improved yrs, F colloid cyst foramen of Monro cyst resection improved 21 3 yrs, F VP shunt dysfunction 3rd ventriculostomy VP VP improved yrs, F posterior fossa ependymoma 3rd ventriculostomy improved yrs, M thalamic tumor 3rd ventriculostomy improved yrs, F pineal tumor 3rd ventriculostomy & tumor biopsy improved yrs, F Chiari I malformation 3rd ventriculostomy no benefit yrs, F colloid cyst foramen of Monro cyst resection improved yrs, F choroid plexus cyst cyst fenestration VP VP improved yrs, F tectal mass lesion 3rd ventriculostomy improved yrs, F aqueductal stenosis 3rd ventriculostomy improved yrs, F meningioma, tentorial hiatus 3rd ventriculostomy improved yrs, F cerebellar peduncle tumor 3rd ventriculostomy stable yrs, F aqueductal stenosis ( web ) 3rd ventriculostomy improved yrs, M cerebellar & ependymal nodules 3rd ventriculostomy & nodule biopsy stable 34 3 wks, M myelomeningocele 3rd ventriculostomy VP shunt dependent yrs, M aqueductal web 3rd ventriculostomy improved yrs, F aqueductal stenosis & ventricle tumor 3rd ventriculostomy & tumor biopsy improved yrs, F skull base meningioma 3rd ventriculostomy improved 38 7 yrs, F shunt dysfunction & 2 loose catheters 3rd ventriculostomy & shunt removal VP improved yrs, F colloid cyst cyst resection improved yrs, F shunt dysfunction 3rd ventriculostomy VP VP shunt dependent 41 7 yrs, F shunt dysfunction 3rd ventriculostomy VP improved yrs, M germ cell tumor 3rd ventriculostomy & tumor biopsy improved 43 6 yrs, F tectal mass lesion 3rd ventriculostomy improved yrs, F rt frontal cyst cyst fenestration VP shunt dependent yrs, F tectal mass lesion 3rd ventriculostomy VP VP improved yrs, M shunt dysfunction 3rd ventriculostomy VP improved yrs, M colloid cyst cyst resection stable yrs, M shunt dysfunction 3rd ventriculostomy VP improved 49 7 yrs, M cerebellar tumor 3rd ventriculostomy improved * LP = lumboperitoneal; VA = ventriculoatrial; = not applicable. One shunt was adequate instead of two shunts. Death 4 months later due to Grade IV astrocytoma. Obstructed shunt not removed. total resection was achieved, but the contents were completely aspirated and the remaining cyst wall was vigorously coagulated. None of these patients required postoperative intensive care monitoring and all were discharged 4 to 6 days postoperatively. In all six patients the preoperative complaints either disappeared or drastically improved immediately postoperatively, and the hydrocephalus resolved without the need for VP shunting. However, two patients have since undergone an interhemispheric, transcallosal resection of the remaining cyst. Fenestration of the Septum Pellucidum Only one patient underwent fenestration of the septum pellucidum to prevent placement of a bilateral VP shunt. His condition had deteriorated because of obstructive hy- 85

5 W. P. Vandertop, R. M. Verdaasdonk, and C. F. P. van Swol wide variety of neurosurgical disorders; in this study the procedure success rate was 100% and the overall outcome success rate was 86%. FIG. 3. Transverse T 1 -weighted MR images. Upper Left: Case 4. Image obtained in a 16-month-old boy with motor retardation, hypertonia in both legs, and a gait disturbance showing obstructive hydrocephalus with transependymal cerebrospinal fluid absorption. Upper Right: Image obtained in the same patient 3 months after placement of a right occipital VP shunt showing adequate drainage of the right lateral ventricle, no decrease in size of the left lateral ventricle and an increase in a third ventricular cyst. Lower Left and Right: Images obtained in the same patient 2 months (lower left) and 2 years (lower right) after he underwent a cyst fenestration. One shunt (right occipital) adequately drains both lateral ventricles and the third ventricular cyst has collapsed. drocephalus, caused by a Grade 4 astrocytoma of the corpus callosum, which previously had been irradiated. The procedure successfully permitted unilateral shunting of both ventricles. Operative Complications There was no instance of mortality or increased morbidity. One patient (Case 24) had a clinically silent hemorrhagic contusion in the right frontal lobe, which resolved spontaneously. Seven patients did not benefit clinically from a technically successful endoscopic procedure for an overall patient outcome success rate of 86%. Discussion This report shows that laser-assisted neuroendoscopy, using an Nd-YAG or diode laser with pretreated atraumatic ball-shaped fiber tips, can be safe and effective in a Laser Equipment and Coated Fiber Tips The experience with lasers in neurosurgery is mainly focused on tumor resection. An excellent review article 10 on the use of lasers in specific neurosurgical applications has been published recently, which every neurosurgeon who wishes to start laser-assisted surgery is encouraged to consult. For neuroendoscopy, the CO 2 laser (10.6 m) is not suitable because the light is highly absorbed by water. 6 Furthermore, the CO 2 laser can only be used with rigid endoscopes because development of flexible fibers and fiber tips is still in its infancy. 10 The continuous wave (CW) Nd- YAG, argon, potassium-titanyl phosphate, and diode lasers have proved to be very effective for resecting highly vascularized tissues and their waves can be transported efficiently through fibers. However, the relatively nonpigmented target tissues in endoscopic procedures poorly absorb the light of these lasers. Nevertheless, argon laser light ( nm) delivered through optical fibers has been used for fenestration of intraventricular cysts, 16 and the potassium-titanyl phosphate laser (532 nm) has proved useful for coagulation and cutting of choroid plexus that is adherent to ventricular catheters and for cyst fenestration. 1,11 To date, the Nd-YAG laser (1064 nm) has been used most frequently. 24 Recently, diode lasers have been introduced as a potential replacement for, or addition to, the existing CW medical laser systems. Diode lasers are available in wavelengths of 780 to 980 nm with powers of up to 60 W. These systems are small compared with other lasers and, nowadays, they are as compact as a standard electrocautery apparatus. Because of the semiconductor technology involved they are reliable and expected to be free of maintenance. These characteristics of the new generation of diode lasers make them the first choice. Because only a few watts of power are needed to use our specially developed black fiber tips, battery-driven diode lasers that are the size of a flashlight might even be used in the future. The fibers used at present are custom made in the medical laser center of our hospital. The device consists of a 400- m silica fiber with a 800- to m ball tip. A coating of carbon particles is attached to the front surface of the ball-shaped tip. This layer absorbs over 90% of the laser light transmitted through the fiber. During an exposure of only a few watts, this layer reaches temperatures of a several hundred degrees Celsius within a few tenths of a second. To preserve the efficacy of the probe, the tips should only be used in a water environment. Higher power settings or exposure times will burn off the coating of carbon ( 2000 C), returning the tip to a clean probe that no longer ablates tissue effectively. The manufacturing process is quality controlled according to high standards (International Organization for Standardization 9001) and fiber characteristics are measured before they are sterilized with ethylene oxide. A technician can be trained to perform this process within 1 hour per fiber. As the length of the original fibers is usually several meters, the fibers can be easily be used tens of times, contributing to significant cost reduction. 86

6 Laser-assisted neuroendoscopy with pretreated fiber tip FIG. 4. Thermal images of an in vitro model showing uncoated (A, B, and C) and coated (D and E) laser fiber tips. The thermal imaging method is based on color Schlieren techniques described elsewhere: 19 small changes in the refractive index that are induced by a temperature gradient are color coded and represented in a color image. A transparent medium (10% polyacrylamide gel [PAG]) with thermal properties similar to biological tissue was used. To simulate optical properties, an infrared absorbing dye was dissolved in the PAG. A side view is presented of a m fiber tip in contact with the PAG submerged in water. A: Uncoated fiber tip set at 2.5 W for 1 second shows minimal heat generation at the tip or in the tissue phantom (PAG). B: Uncoated fiber tip set at 20 W for 1 second generates a heat bubble into the tissue phantom, reflecting the distance at which tissue can be affected by the dissipating heat of the laser beam. C: Uncoated fiber tip set at 20 W for 10 seconds generates an enormous heat wave into the tissue phantom, reflecting the distance at which tissue can be affected by the dissipating heat of the laser beam. D: Coated fiber tip set at 1 W for 1 second shows a high rise in temperature at the tip, with no effect in the deeper layers. E: Coated fiber tip set at 2.5 W for 1 second shows a high rise in temperature at the tip, with minimal effect in the deeper layers. Mechanism of Ablation and Control of Ablation Depth The tissue effects during laser applications depend on a combination of the wavelength, the exposure time, and the power density in the tissue. When laser light is delivered through a fiber in contact with tissue, the optical, thermal, and mechanical properties of the delivery system are important. 21 When using probes in combination with CW lasers, thermal interaction is dominant. 22 From studies on the basic ablation mechanism of CW lasers using contact probes, it is known that carbonization of tissue followed by efficient heat absorption and vaporization of that tissue is the main mechanism of ablation. 21 Using regular uncoated fiber tips, laser light is converted into heat by absorption in tissue only. During neuroendoscopy, the white (nonpigmented) ependymal tissues and arachnoid membranes poorly absorb visual and near-infrared laser light. The light is scattered and absorbed in a large volume of tissue and, therefore, a large amount of energy is needed for the tissue to carbonize (10 20 W for many seconds). The moment of carbonization depends very much on the optical properties of the tissue and the presence of blood, which can act as a catalyst for the carbonization process. This moment cannot be predicted. Once carbonization is followed by vaporization, the dispersion of heat from uncoated fiber tips will transgress far beyond the intended depth with possible damage to deeper structures (Fig. 4). To obtain better control over the ablation process and increase the speed of the ablation mechanism, the fiber tips used in this study were precarbonized. Because most of the light is readily absorbed in the coated fiber tip, heat is generated at the tip itself and conducted from the probe to the tissue, contributing to a very localized rise in temperature and causing tissue carbonization. After the tissue carbonizes, the absorption increases tremendously, and above carbonization temperatures ( 350 C) the tissue is vaporized effectively. This way, an absorbant coating on the probe is helpful to initiate tissue ablation when the wavelength of the laser light is poorly absorbed by the tissue itself. When the volume of coating is small, ablation temperatures can be reached at low power levels. The hot spots on the probe surface carbonize tissue in direct contact. From this moment on, the black carbonized tissue will drive the ablation process. Because of the high absorption of laser light in the thin layer of carbon, only a few watts of energy are necessary to reach ablative temperatures instantly at the ball-shaped fiber tip with virtually no heat effect on surrounding tissues or deeper structures (Fig. 4). Because the carbon particles absorb a broad range of wavelengths very efficiently, any CW laser source that can be transmitted by optical fibers is suitable for this application. In vivo experiments on the cortical surface of a rabbit s hemisphere clearly have shown the great advantage of our coated fiber tips over conventional uncoated fiber tips (Figs. 5 and 6). The precoated tip enables the surgeon to predict the depth of ablation and the extent of coagulation. The procedure is started using very low energies to ensure coagulation before perforation. After each pulse the lesion can be examined and the dosimetry can be adapted depending on the effect observed (Fig. 7A C). At the moment of perforation, the light emitted from the fiber is minimal and highly scattered; thus, no temperature increase can be created in distal structures (Fig. 7D). This combination of low energy and high absorption makes the application safe and controlled. Laser Energy Normally with uncoated tips, the energy required for vaporization resulting in perforation of a membrane is on the order of several hundreds of joules. Our in vitro exper- 87

7 W. P. Vandertop, R. M. Verdaasdonk, and C. F. P. van Swol FIG. 5. Surface image of the left cerebral hemisphere of a rabbit (in vivo) showing effects on the cerebral cortex after exposure to laser light at different power settings with the contact laser. A: Uncoated fiber tip set at 2.5 W for 1 second. At the surface no effect is visible. B: Effect of an uncoated fiber tip at 20 W for 1 second. At the surface a minimal blanching might be visible. C: Effect of an uncoated fiber tip set at 20 W for 10 seconds. A slight, but definite blanching can be seen at the surface. D: Effect of a coated fiber tip set at 1 W for 1 second. A clear zone of blanching can be seen at the surface. Centrally, the arachnoid and pial layers are disrupted. E: Effect of a coated fiber tip at 2.5 W for 1 second. A small crater of coagulation and ablation can be seen surrounded by a small zone of blanching. iments showed that the amount of laser energy needed for coagulation or perforation when using pretreated fiber tips can be so little (1 4 J) that very little risk of thermal injury exists (Fig. 4). 21 Even thin strands of arachnoid running diagonally across a newly created opening can be safely treated using a laser with no risk to underlying structures (Fig. 7D). In two cases, we perforated the floor of the third ventricle in a stepwise fashion and found ourselves between the brainstem and the basilar artery (Figs. 2 and 7E and F). With the basilar artery bifurcation in direct view, the ventriculocisternostomy was expanded anteriorly (Fig. 7E). It has been stated that the use of laser energy might dangerously elevate CSF temperatures. 20 Although we never measured CSF temperatures before, during, or after neuroendoscopy, the reduced amount of laser energy needed with our pretreated tip did not lead to any significant problems. Mechanical and Electrical Alternatives To perforate a tissue or membrane mechanically, one has to use either a sharp instrument or, in combination with more force, a blunt tip. The risk of mechanical damage several millimeters beyond the puncture site is significant and the risk of rupturing blood vessels is substantial. 8,18 The use of electrical currents to burn a hole through a tissue or membrane is also associated with several problems. The pathway of the currents flowing out of a tip cannot be controlled because the fluid in the ventricles is conductive and the current flows along the way of least resistance. As the leads delivering the current to the tip are small, energy losses caused by resistance in the leads makes them less efficient and increases the potential of heating the whole catheter. In addition, to heat the tip to ablative temperatures instantly, very high currents would be necessary. On the other hand, a heat-dissipating element with insulated coating would require a rather large tip and several seconds would be necessary to heat the probe, which automatically implies that the relaxation time will also be on the order of seconds. This not only makes the tip hazardous to the environment during the cooling phase, but the tip will have the potential of sticking to the tissue. Again, at the moment of perforation there will always be the additional risk of damage underneath the perforation site. Colloid Cysts Complete resection of a colloid cyst at the foramen of Monro by using open, microsurgical techniques virtually guarantees a complete cure of the patient with no chance 88

8 Laser-assisted neuroendoscopy with pretreated fiber tip FIG. 6. Photomicrographs of cross sections through the maximum lesions on the gyri of a rabbit cerebral hemisphere after exposure to laser light (Luxol fast blue and H & E staining; bar = 1 mm). A: Effect of an uncoated fiber tip at 2.5 W for 1 second. No tissue necrosis or coagulation is visible. At the surface as well as in the deeper layers a normal anatomy and distribution of gray and white matter can be seen. B: Effect of an uncoated fiber tip at 20 W for 1 second. At the surface the arachnoid layer is intact. Beneath the cortical surface, however, a pear-shaped area of coagulation and edema can be clearly seen. C: Effect of an uncoated fiber tip at 20 W for 10 seconds. Although at the surface the arachnoid layer is intact, it has somewhat loosened from the pia mater, hence explaining the visible slight blanching (Fig. 5C). Immediately adjacent to this contact area, a very extensive circular zone of coagulation and edema is visible, which extends subcortically beyond the lateral margins of the point of contact. D: Effect of a coated fiber tip set at 1 W for 1 second. Even this small amount of energy (1 J) creates an ablation crater with disruption of the arachnoid layer and a minimal zone of edema. In the deeper layers no effect is visible. E: Effect of a coated fiber tip at 2.5 W for 1 second. A small ablation crater with a very small zone of edema is visible. The arachnoid layer is coagulated (brown) and disrupted. In the deeper layers no effect is visible. of recurrence; however, the procedure remains major surgery. 3 Although complete removal of a colloid cyst by endoscopy can be difficult, it carries a negligible morbidity and mortality rate and significantly reduces time spent in the hospital. 11 Cyst wall remnants after open resection are said to be responsible for a recurrence rate of 10%, 5 whereas longterm follow-up reports of stereotactic aspiration show recurrence rates of 30% and higher. 9,13 We have chosen to cauterize/carbonize the remaining cyst wall vigorously after its contents have been completely aspirated. Whether this destruction of the secreting component of the cyst will prevent recurrence of the cyst in the future remains to be seen. Advantages of Laser-Assisted Neuroendoscopy In young patients or in patients with longstanding hydrocephalus, the floor of the third ventricle is usually very thin and transparent, allowing a variety of methods to be used safely to perform a ventriculocisternostomy. 4,8,18 89

9 W. P. Vandertop, R. M. Verdaasdonk, and C. F. P. van Swol FIG. 7. Endoscopic views showing consecutive steps in a laser-assisted third ventriculostomy in a 59-year-old woman with obstructive hydrocephalus due to a pineal tumor. A: Anterior to the mamillary bodies, the floor of the third ventricle is quite thin but still obscures the basilar artery bifurcation and dorsum sellae. B: The floor of the third ventricle is perforated in a stepwise fashion by using a pretreated fiber tip set at 1 W for 0.5 seconds. C: A second (partial) perforation is connected with the first for a larger fenestration. D: Once the final arachnoidal layer is vaporized, the basal cistern is opened and the basilar artery bifurcation becomes visible with a small perforating artery. A thin strand of arachnoid is safely ablated. E: The ventriculostomy has been expanded anteriorly over the basilar artery. F: Direct view into the interpeduncular cistern with the pons below and the basilar artery with its many small perforating branches located anteriorly. 90

10 Laser-assisted neuroendoscopy with pretreated fiber tip However, in older patients or in patients who have recently developed obstructive hydrocephalus (such as cerebellar hematoma), the floor of the third ventricle may be quite thick, obscuring the exact location of the basilar artery bifurcation and the dorsum sellae (Fig. 7A). 2 In these cases it has been recommended that attempts at fenestration be abandoned to prevent potential injury to the basilar trunk and perforating vessels. 17 By using our pretreated black fiber tips, we were able to perforate the floor of the third ventricle safely in a stepwise fashion in all of our cases of third ventriculocisternostomy, even when the patient s anatomy was highly abnormal or the ventricular floor was very thick, obscuring underlying vital structures (Fig. 7B and C). After a perforation has been successfully made, a larger fenestration is often required because wide fenestrations are necessary for long-term successful internal patency. 11,12 However, it can be quite troublesome to enlarge a hole once it has been made, as the floor of the third ventricle or cyst wall can be flapping due to CSF pulsations. A second perforation, even close to vital structures, can be easily made using the pretreated fiber tip. Both perforations can then be connected with each other creating the wide fenestration desired (Fig. 7C and D). Dilation with a balloon catheter can also expand a hole, but the edges remain ragged. These ragged edges can be easily coagulated or vaporized by the laser, creating a smooth edge with probably less chance of secondary closure (Fig. 7D). Bleeding, no matter how minute, rapidly obscures the surgeon s view and might even increase the risk of premature secondary closure of a fenestration. Relatively thick membranes often harbor tiny blood vessels that rupture easily. Using the pretreated laser fiber tip with various power levels, bleeding is prevented in most instances because the vessels can be coagulated prior to fenestration. Choroid plexus fronds easily give way to minor bleeding when touched by the endoscope; this can be prevented by coagulating the choroid plexus if it is blocking the entry into the third ventricle. If bleeding does occur despite these precautionary measures, it is usually easily controlled. 11 Disadvantages of Laser-Assisted Neuroendoscopy The fiber tip is hand made from fused silica and quite small (800 m). As a result of the manufacturing process, a few millimeters of the fiber support behind the ballshaped tip have been removed, leaving a 400- m fragile silica fiber core unprotected. Because the fiber tip can easily break at this point if lateral pressure is exerted, it must be very carefully introduced into the 1-mm working channel. Breakage occurred in some of the earlier patients when we tried to advance the laser tip through the Y- shaped introduction channel or the curved tip of a flexible endoscope. This problem can be avoided by advancing the laser fiber only when the endoscope is straight. No adverse effects have occurred in the few patients in whom a tip had been lost inside the ventricle and could not be retrieved. Although every neurosurgeon can undoubtedly be taught to operate laser equipment, the presence and expertise of a laser physicist greatly contributed to the successful outcome of our procedures. If one wants to perform an emergency endoscopic procedure, one must then decide whether to resort to alternative endoscopic methods, or to buy time, for example, by inserting an external drainage catheter so the laser-assisted procedure can be performed electively. As for any laser procedures, laser safety guidelines must be followed. All operating personnel are required to wear protective eyewear specific to the wavelength being used. 14 We recommend having a person present who has been trained in laser applications. Conclusions Neuroendoscopy is rapidly becoming an essential part of the neurosurgeon s repertoire. With the continuing expansion of indications for this procedure, reduction of complications may be achieved by using more precise methods than are commonly practiced to puncture the floor of the third ventricle or fenestrate a cyst wall. 19 For this reason we developed a special laser catheter that drastically limits the amount of laser energy needed. In conjunction with the new generation of diode lasers safety is thereby greatly increased. Although the overall results of neuroendoscopic treatment are closely related to the experience of the surgeon and the selection of patients for these procedures, our short-term results are very promising. However, long-term results for many of these procedures must be awaited. Acknowledgments The authors would like to thank Drs. Nicolette C. Notermans for her critical review of the manuscript, Peter W. A. Willems for his help with the animal experiments, and Gerard H. Jansen for the histopathological assessments. References 1. Crone KR: Endoscopic technique for removal of adherent ventricular catheters, in Manwaring KH, Crone KR (eds): Neuroendoscopy. New York: Mary Ann Liebert, 1992, Vol 1, pp Decq P, Brugières P, Le Guerinel C, et al: Percutaneous endoscopic treatment of suprasellar arachnoid cysts: ventriculocystostomy or ventriculocystocisternostomy? Technical note. J Neurosurg 84: , Deinsberger W, Böker DK, Samii M: Flexible endoscopes in treatment of colloid cysts of the third ventricle. Minim Invasive Neurosurg 37:12 16, Drake JM: Ventriculostomy for treatment of hydrocephalus. Neurosurg Clin North Am 4: , Ehni G, Ehni B: Considerations in transforaminal entry, in Apuzzo MLJ (ed): Surgery of the Third Ventricle. Baltimore: Williams & Wilkins, 1987, pp Grotenhuis JA: General principles of neuroendoscopy, in Grotenhuis JA (ed): Manual of Endoscopic Procedures in Neurosurgery. Nijmegen: Machaon, 1995, pp Jones RFC, Brazier DH, Kwok BCT, et al: Neuroendoscopic third ventriculostomy, in Cohen AR, Haines SJ (eds): Minimally Invasive Techniques in Neurosurgery. Baltimore: Williams & Wilkins, 1995, pp Jones RFC, Teo C, Stening WA, et al: Neuroendoscopic third ventriculostomy, in Manwaring KH, Crone KR (eds): Neuroendoscopy. New York: Mary Ann Liebert, Inc., 1992, Vol 1, pp Kondziolka D, Lunsford LD: Stereotactic management of col- 91

11 W. P. Vandertop, R. M. Verdaasdonk, and C. F. P. van Swol loid cysts: factors predicting success. J Neurosurg 75:45 51, Krishnamurthy S, Powers SK: Lasers in neurosurgery. Lasers Surg Med 15: , Lewis AI, Keiper GL Jr, Crone KR: Endoscopic treatment of loculated hydrocephalus. J Neurosurg 82: , Manwaring KH: Endoscopic ventricular fenestration, in Manwaring KH, Crone KR (eds): Neuroendoscopy. New York: Mary Ann Liebert, Vol 1, 1992, pp Mathiesen T, Grane P, Lindquist C, et al: High recurrence rate following aspiration of colloid cysts in the third ventricle. J Neurosurg 78: , Miller MN: Organization of the neuroendoscopy suite, in Manwaring KH, Crone KR (eds): Neuroendoscopy. New York: Mary Ann Liebert, 1992, Vol 1, pp Oka K, Tomonaga M: Instruments for flexible endoneurosurgery, in Manwaring KH and Crone KR (eds): Neuroendoscopy. New York: Mary Ann Liebert, Inc., 1992, Vol 1, pp Powers SK: Fenestration of intraventricular cysts using a flexible, steerable, endoscope and the argon laser. Neurosurgery 18: , Rhoten RLP, Luciano MG, Barnett GH: Computer-assisted endoscopy for neurosurgical procedures: technical note. Neurosurgery 40: , Sainte-Rose C: Third ventriculostomy, in Manwaring KH, Crone KR (eds): Neuroendoscopy. New York: Mary Ann Liebert, 1992, Vol 1, pp Teo C, Rahman S, Boop FA, et al: Complications of endoscopic neurosurgery. Childs Nerv Syst 12: , Verdaasdonk RM, Borst C: Optical technique for color imaging of temperature gradients in physiological media: a method to study thermal effects of CW and pulsed lasers. Proc SPIE 1882: , Verdaasdonk RM, Borst C: Optics of fibers and fiber probes, in Welch AJ, van Gemert MJC (eds): Optical-Thermal Response of Laser Irradiated Tissue. New York: Plenum Press, 1995, pp Verdaasdonk RM, van Swol CFP: What makes a fiber tip do the job: an optical and thermal evaluation study. Proc SPIE 2396:37 45, Verdaasdonk RM, Vandertop WP: Endoscopic ventricular fenestration and choroid plexus coagulation using diode and ND:YAG contact laser ablation with pretreated fiber tips. Lasers Surg Med (Suppl 7):26, 1995 (Abstract) 24. Yamakawa K: Instrumentation for neuroendoscopy, in Cohen AR, Haines SJ (eds): Minimally Invasive Techniques in Neurosurgery. Baltimore: Williams & Wilkins, 1995, pp 6 13 Manuscript received September 23, Accepted in final form August 8, Address reprint requests to: William P. Vandertop, M.D., Ph.D., Department of Neurosurgery, University Hospital, G , P.O. Box 85500, NL-3508 GA Utrecht, The Netherlands. P.Vandertop@neuro.azu.nl. 92