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Use of the Laser in Neurosurgery
Symposium on Laser Surgery
Use of the Laser in Neurosurgery
Leonard]. Cerullo, M.D.,* and Leonard P. Burke, M.D.t
Each surgical specialty that has realized benefits of the laser in its particular area has capitalized on one or more of the unique features offered by the use of light energy, with its resultant conversions, in incising, denaturing, or removing tissue. In neurosurgery, the single most important attribute is the ability to precisely vaporize tissue with minimal mechanical and thermal damage to the surrounding sensitive structures. Ample laboratory evidence indicates that the thermal lesion produced by the laser is more readily controlled and offers less histologic, physiologic, and paraphysiologic damage to surrounding structures than any other form of thermal energy, including the finest bipolar cautery. Although the neodymium:YAG (yttrium-aluminum-garnet) laser has been appreciated for its coagulative properties, particularly in dealing with vascular tumors and malformations, and although argon has been demonstrated to produce clean, precise lesions, the workhorse of neurosurgery has been the CO 2 laser. This is due to its immediate absorption in water, with resultant minimization of scatter and spread to surrounding and deeper tissue. It is this wavelength, then, that is the focus of this article. When the inherent precision and gentleness of laser vaporization to effect tissue incision or removal is considered, one wonders why laser has become a neurosurgical tool only in the 1980s. In fact, as early as 1964 earlier investigators were exploring the use of various wavelengths-which they found to be either too destructive or too difficult to control. In 1965, Stellar appreciated the inherent gentleness of the use of an immaterial beam, but the neurosurgical community at large awaited the work of Takizawa and Ascher for the "reintroduction" of the instrument. Scattered investigators, including Lahita and Beck in Munich working with the Nd:YAG laser, and Pimenta in Brazil utilizing the CO 2 laser, were reported. Meanwhile, several neurosurgeons throughout the United States enjoyed anecdoctal experiences, positive or negative, using the instruments available From the Department of Surgery, Northwestern University Medical School, Chicago, Illinois *Assistant Professor of Surgery (Neurosurgery) tResident in Neurosurgery
Surgical Clinics of North America-Vol. 64, No.5, October 1984
995
996
LEONARD
J.
CERULLO AND LEONARD
P.
BURKE
to their gynecologic and otolaryngologic colleagues. By 1981, there was enough experience and interest generated to offer the First Congress on Laser Neurosurgery, which was held at Northwestern University in Chicago. The meeting featured extensive contributions from basic scientists and technologists, and presented the sparse available clinical experience (of such workers as Kelly, Robertson, Ascher, Cerullo, Brown, and Takizawa, among others). Although various explanations for the late arrival of the laser in neurosurgery have been offered, most likely it is because the development of microsurgery and appreciation of microsurgical techniques was a necessary precursor for the advent of laser, a further refinement on "micro" surgery. Although acoustical and photochemical effects of laser have been exploited in various clinical situations, to date these uses have been largely undiscovered for the neurosurgical community. By far, it is the precise and controllable thermal conversion currently utilized by the majority of clinical neurosurgeons at the time of this writing. Most would agree that the primary use for the laser as an instrument for vaporization is in the removal of extra-axial tumors considered hazardous by their proximity to vital neurologic or vascular structures. Certainly, meningeal tumors of the midline base, including tuberculum sellae, medial sphenoid wing, clivus, petrous apex, foramen magnum, and spinal canal, are included in this category. Nerve sheath tumors, unusual metastatic deposits, and lipomatous tumors of brain and spinal cord are similarly considered. Concomitant with the use of microsurgical techniques and laser technology has been an increasing bravado on the part of neurosurgeons, often in conjunction with head and neck surgeons, to approach the skull base in a more aggressive and innovative manner. Thus, the limits of operability have been extended and the surgical results improved. As this group of patients would have a normal life expectancy were it not for their preoperative or postoperative morbidity, it appears that this, the extra-axial tumor removal, is the area of greatest impact of the laser on neurosurgery. The technique for the removal of extra-axial tumors, regardless of location, is similar. Generally, the surgical exposure requires less wide uncovering of the neoplasm than with techniques that require removal of brain from the pathologic process, rather than the reverse. Following this rather limited uncapping, the CO 2 laser, at low energy and in defocused mode, is used to enter the capsule of the tumor. Surrounding sensitive structures are protected by moist cotton, as water immediately absorbs the energy of the CO 2 laser. As an appreciation of the consistency and vascularity of the tumor is gained, longer applications of higher powered lasers can be utilized; the limit depending on the experience and particular preference of the surgeon. As the interior of the neoplasm is evacuated, the lesion will be noted to be compressed by the surrounding neural structures, which already begin to assume a more normal anatomic position. When an appreciable portion of the tumor has been evacuated, attention may be paid to the capsule. It is important to recognize and preserve the arachnoidal interface between tumor and surrounding brain. In meningiomas, this is a single layer; in acoustic and other nerve sheath tumors, this may be two layers. Failure to respect this interface will result in bonding of the arachnoid to
USE OF THE LASER IN NEUROSURGERY
997
the tumor capsule, with resultant difficulty in appreciating the true delineation of tumor from brain. Normally, moist cotton is placed between the brain arachnoid and the tumor capsule. At this point, the defocused laser is used to shrink the capsule, allowing the tumor to dissect itself from surrounding neural structures, parachymal or vascular. The degree of shrinkage will be a function of the collagen content of the tumor and will vary from neoplasm to neoplasm, regardless of histology. By avoiding too great a depth of penetration into the corpus of the tumor before shrinking the capsule, overpenetration into surrounding vessels, cranial nerves, and brain structures can be avoided. Eventually, the tumor can be delivered through the operative exposure, or it can be entirely vaporized in situ. It should be remembered that the removal of the great mass of the tumor need not be by total vaporization, which may be too time-consuming and unnecessary. Rather, the laser can be used in a more focused mode to offer tumor morsilation in a hemostatic manner. Similarly, alternate methods of tissue removal, such as ultrasonic aspiration and regulated suction, can be used for this purpose, depending on the consistency of the lesion. Unquestionably, however, the more sensitive attachments of the tumor to cranial nerve, vessel, midbrain, and brain stem structures require gentle and precise vaporization offered by the laser. Appreciation of the relative hemostasis, even of the CO 2 laser, is realized when this form of tissue removal is compared with conventional methods. Likewise, the ability to continually monitor electrophysiologic parameters, such as evoked response testing, offers increased proof of the atraumatic nature of the technique. The second area where the inherent gentleness in containment of tissue destruction is appreciated is in the transgression of normal central nervous tissue to arrive at deeper, pathologic tissue. Examples include cerebrotomy and myelotomy for deep lesions, the actual removal of which may be laser vaporization or other techniques. The CO 2 laser can be used as a valuable coagulating instrument if a sharp area of demarcation is protected with moist cotton and the laser is used at low power. On the creation of a narrow band of coagulated tissue, the laser can then be used at higher power and sharp focus to incise along the coagulated strip. It is immediately apparent to the surgeon that surrounding tissues, within fractions of a millimeter, are healthy and well vascularized. The technique for removal of the gliomatous tumor within will depend on histology, consistency, and vascularity, as well as a surgical objective. Intramedullary lesions of the spinal cord are ideal candidates for total vaporization, while glioblastomas of the cerebrum are generally less suitable. A notable exception is the use of laser, coupled with a stereotactic computed tomographic guided apparatus of real-time ultrasonography, to vaporize deep lesions with minimal damage to surrounding nuclear structures. Should the lesion lie within the ventricular system, elimination of spinal fluid will allow carbon dioxide vaporization. Alternately, the use of another wavelength, such as Nd:YAG or argon, will allow denaturization and vaporization through the ventricular liquid. The increasing use of endoscopy in this regard will certainly impact on surgical results. Vaporization of gliomatous lesions has not been proven to offer increased longevity but is felt by many to improve surgical success by lowering morbidity.
998
LEONARD
J.
CERULLO AND LEONARD
P.
BURKE
Other incisional uses for the laser include myelotomy for pain or spasticity and lobectomy for tumor and epileptogenic focus ablation. The minimization of edema formation and negligible current of injury associated with incision of neural tissue in this manner have been demonstrated in the laboratory and are presently being investigated clinically; the early results are quite encouraging. The technique is the same as that for cerebrotomy, except that the moist cotton protection need be offered only to the tissue that will remain, allowing the surgeon a greater latitude in wider coagulation and more effective hemostasis in the tissue being removed. Whether this will translate to a lower rate of postoperative epilepsy is yet to be seen. Spinal syrinx fenestration and the creation of DREZ lesions for intractable pain also capitalize on the strict containment of damage offered by both CO 2 and argon lasers in sharp focus. Claims of reduced rate of neuroma formation and reduced pain following neuroma amputation have been ascribed to the CO 2 laser. At present, these have not been substantiated in laboratory investigations, though the data are somewhat contradictory. Although considered a rather pedestrian use, the ability of the CO 2 laser to hemostatically incise skin and muscle has been exploited in a number of neurologic operative procedures. Reduction of tetanic contraction of muscle, such as the paraspinal muscle, is noted to occur when laser dissection is compared with Bovie knife incision. The reduction of tetanic contractions may translate to reduced postoperative pain. Certainly, when the unstable spine is approached through a posterior route, minimization of violent contractions may be advisable in preventing free bony elements from being pulled and twisted onto the underlying dura and cord. Claims of reduced rate of scar formation and improved success following postoperative scar excision are yet to be substantiated. The CO 2 laser has been shown experimentally to be as effective in completely extirpating disk material, without creation of histologic diskitis, as currently effective mechanical means. The reduced area of exposure, secondary to freedom from visual impediment by instrumentation, may offer a further refinement to the microdiskectomy procedure. Similarly, the use of laser, either CO 2 or Nd:YAG, to open the sellar floor and sellar dura in trans-sphenoidal pituitary surgery have been applauded. Again, the emphasis is on the ability to work through a limited exposure on a deep structure without visual compromise by instrumentation. Recently, the Nd:YAG laser has begun to enjoy increasing acceptance in neurologic surgery. Histologic studies have confirmed the increased depth of penetration and lateral spread of distribution associated with this wavelength. On the other hand, the improved hemostasis and ability to work on the other side of an intact structure, such as the sinus dura, offers intriguing possibilities for the future. Ascher and co-workers have demonstrated the ability to denature pituitary tissue without opening the dura through a trans-sphenoidal approach. Similarly, Beck and Ascher have claimed to denature meningiomatous tumor, which has entered but not obliterated major venous sinuses, without physically opening the structure. Corroboration of these claims awaits further experience in a more controlled situation. Tew at the University of Cincinnati and Sundt at the Mayo Clinic
USE OF THE LASER IN NEUROSURGERY
999
have demonstrated the use of Nd:YAG laser for coagulation of the racemous portion of arteriovenous malformations and have indicated that the instrument may be very effective in dealing with the residual periphery of these lesions, particularly when located in very sensitive areas. Takeuchi, Handa, and others have showed the effectiveness of the Nd:YAG laser in the coagulation of large and small highly vascular tumors, whether intra-axial or extra-axial. The probability for the future is that the combination of Nd: YAG for coagulation and carbon dioxide for vaporization will allow more effective tumor removal with fewer high-energy requirements from either wavelength. Fasano and his co-workers have demonstrated the differing effects of argon, CO 2 , and Nd:YAG on various elements of vessel walls. Hypotheses regarding treatment of intracranial aneurysms and arteriovenous malformations have been made. Again, wide clinical use demands further laboratory confirmation. The use of various wavelengths, including argon and CO 2 , for tissue bonding has recently gained great popularity. Small vessels, nerves, dura, and hollow viscera have been so treated. The technique appears to offer advantages over the use of suture in preventing granuloma formation along the suture line and allowing unrestricted dilation at the anastomosis site. Others including Edwards have suggested the possibility for aneurysm formation at the anastomosis site and caution against the use of the procedure on that basis. Jain has used Nd:YAG laser for the same purpose but did not report the aneurysmal formation described by Edwards. However, he described aneurysm formation at the anastomosis site. Intravascular navigation with direct visualization and treatment either by photochemical reaction (excimer laser) or direct vaporization (argon, Nd:YAG, CO 2 ) are presently underway. Vessels ranging from the aorta to the mediumsize cerebral vessels have been treated. Results appear promising, but as yet no long-term animal studies are available to demonstrate the efficacy and/or safety of thse techniques. The fact appears to have been established that the laser has become the neurosurgical tool of the 1980s. The remaining question is to what degree this modality will augment, or replace, conventional technique. It now appears that the future of lasers in surgery, and particularly in neurosurgery, is limited only by the imagination of the surgeons.
BIBLIOGRAPHY Ascher, P. W.: Newest ultrastructural findings after the use of CO 2 laser on CNS tissue. Acta Neurochir. [Suppl.] (Wein), 28:572-581, 1979. Ascher, P. W.: Horizons in neurosurgery. Presented at the Meeting of Laser Association of Neurological Surgery International, Houston, May 1, 1983. Ascher, P. W., and Cerullo, L. J.: Laser use in neurosurgery. In Dixon, J. (ed.): Surgical Applications of Lasers. Chicago, Year Book Medical Publishers, 1983. Beck, 0. J.: The use of the Nd- YAG and the CO 2 laser in neurosurgery. Neurosurg. Rev., 3:261-266, 1980. Beck, 0. J., and Ascher, P. W.: Different lasers in neurosurgery. Presented at the Third Annual Meeting for American Society of Laser Medicine and Surgery, New Orleans, January 10-12, 1983.
1000
LEONARD
J.
CERULLO AND LEONARD
P.
BURKE
Bellina, J.: Connective tissue effects of CO 2 and argon lasers. Presented at the II Congress on Laser Neurosurgery, Chicago, September 23-25, 1982. Bellina, J. H., Sterjnoiholm, R., and Kurpel, J.: Biochemical analysis of carbon dioxide plume emission from irradiated tumors. In Bellina, J. H. (ed.): Gynecologic Laser Surgery. New York, Plenum Press, 1981. Boggan, J. E., et al.: Comparison of the brain tissue response in rats to injury by argon and carbon dioxide lasers. Neurosurgery, 11(5):609-616, 1982. Brown, J. T.: Laser fenestration for syringohydromyelia. Presented at the II Congress on Laser Neurosurgery, Chicago, September 23-25, 1982. Brown, T. E., True, C., McLaurin, R. L., et al.: Laser radiation: Long term effects of laser radiation on certain intracranial structures. Neurology, 17:78~796, 1967. Burke, L., Rovin, R. A., Cerullo, L. J., et al.: Nd:YAG laser in neurosurgery. In Joffee, S. N. (ed.): Nd:YAG Laser in Medicine and Surgery. New York, Elsevier Publishers, 1983. Cerullo, L. J.: CO 2 laser surgery in acute spinal cord injury. Presented at the Sixth Annual Scientific Meeting of the American Spinal Injury Association, Anaheim, California, May 8-11, 1980. Cerullo, L. J.: Acoustic nerve tumor removal with CO 2 laser: Technique and results. Presented at the II Congress on Laser Neurosurgery, Chicago, September 25, 1982. Cerullo, L., and Koht, A.: Anesthesiologic considerations in laser neurosurgery. Laser Med. Surg., 3(1):35-38, 1983. Cozzens, J.: Evans blue brain edema model for comparison of CO 2 and bipolar lesions. Presented at the First American Congress on Laser Neurosurgery, Chicago, October 1-3, 1981. Dixon, J. A.: General surgical and endoscopic applications of lasers. In Dixon, J. (ed.): Surgical Applications of Lasers. Chicago, Year Book Medical Publishers, 1983. Dwyer, R. M., et al.: Laser induced hemostasis in the canine stomach. Use of flexible fiberoptic delivery system. J.A. M.A., 231:486, 1975. Einstein, A.: Zur quantum Theorie des Strahlung. Phys. Z., 18:121-128, 1917. Fasano, V. A.: The treatment of vascular malformation of the brain with laser surgery. Presented at the II Congress on Laser Neurosurgery, Chicago, September 23-25, 1982. Fasano, V. A.: Effect of different laser sources on vessel wall. Presented at the Meeting of Laser Association of Neurological Surgery International, Houston, May 1, 1983. Fuller, T. A.: The physics of surgical lasers. Laser Surg. Med., 1:5-14, 1980. Goldman, L.: The argon laser and the portwine stain. Plast. Reconstr. Surg., 65(2):137-139, 1980. Kelly, P. J., et al.: Computer-assisted stereotactic laser microsurgery for the treatment of intracranial neoplasms. Neurosurgery, 10(3):324-331, 1982. Krasnov, M. M.: Q-Switched laser iridectomy and Q-Swithched laser goniopuncture. Adv. Ophthalmol., 34:192-196, 1977. Laws, E. R., Jr., et al.: Photoradiation therapy in the treatment of malignant tumors: A phase I (feasibility) study. Neurosurgery, 9(6):672-678, 1981. Neblett, C. R.: Reconstructive vascular surgery with use of the CO 2 laser. Presented at the II Congress on Laser Neurosurgery, Chicago, September 23-25, 1982. Rockwell Associates, Inc.: Laser Safety in Surgery and Medicine. Cincinnati, 1983. Saunders, M. L., Young, M. F., Becker, D. P., et al.: The use of the laser in neurological surgery. Surg. Neurol., 14:1-10, 1980. Taki, W., Takeuchi, J., Yonekawa, Y., et al.: Advance in laser microsurgery in neurosurgical operation with special reference to Nd-YAG laser. Presented at the Fourth Congress of the International Society for Laser Surgery, Tokyo, 1981. Takizawa, T.: History: Medilaser-S, Model MEL-442. In: Takizawa, T.: Illustrated Laser Surgery, Fundamentals, No.2. Tokyo, Mochida Pharmaceutical Co., 1982. Treyve, E., et al.: Incendiary characteristics of endotracheal tubes with the carbon dioxide laser. An experimental study. Ann. Otol. Rhin. Laryngol., 9:328-330, 1981. Yokota, H., Hara, M., Okada, J., et al.: Malignant glioma laser surgery. Presented at the V International Congress of Laser Medicine and Surgery. Detroit, October 7-9, 1983. (Dr. Cerullo) 676 N. St. Clair Suite 1950 Chicago, Illinois 60611
Use of the Laser in Neurosurgery
Leonard]. Cerullo, M.D.,* and Leonard P. Burke, M.D.t
Each surgical specialty that has realized benefits of the laser in its particular area has capitalized on one or more of the unique features offered by the use of light energy, with its resultant conversions, in incising, denaturing, or removing tissue. In neurosurgery, the single most important attribute is the ability to precisely vaporize tissue with minimal mechanical and thermal damage to the surrounding sensitive structures. Ample laboratory evidence indicates that the thermal lesion produced by the laser is more readily controlled and offers less histologic, physiologic, and paraphysiologic damage to surrounding structures than any other form of thermal energy, including the finest bipolar cautery. Although the neodymium:YAG (yttrium-aluminum-garnet) laser has been appreciated for its coagulative properties, particularly in dealing with vascular tumors and malformations, and although argon has been demonstrated to produce clean, precise lesions, the workhorse of neurosurgery has been the CO 2 laser. This is due to its immediate absorption in water, with resultant minimization of scatter and spread to surrounding and deeper tissue. It is this wavelength, then, that is the focus of this article. When the inherent precision and gentleness of laser vaporization to effect tissue incision or removal is considered, one wonders why laser has become a neurosurgical tool only in the 1980s. In fact, as early as 1964 earlier investigators were exploring the use of various wavelengths-which they found to be either too destructive or too difficult to control. In 1965, Stellar appreciated the inherent gentleness of the use of an immaterial beam, but the neurosurgical community at large awaited the work of Takizawa and Ascher for the "reintroduction" of the instrument. Scattered investigators, including Lahita and Beck in Munich working with the Nd:YAG laser, and Pimenta in Brazil utilizing the CO 2 laser, were reported. Meanwhile, several neurosurgeons throughout the United States enjoyed anecdoctal experiences, positive or negative, using the instruments available From the Department of Surgery, Northwestern University Medical School, Chicago, Illinois *Assistant Professor of Surgery (Neurosurgery) tResident in Neurosurgery
Surgical Clinics of North America-Vol. 64, No.5, October 1984
995
996
LEONARD
J.
CERULLO AND LEONARD
P.
BURKE
to their gynecologic and otolaryngologic colleagues. By 1981, there was enough experience and interest generated to offer the First Congress on Laser Neurosurgery, which was held at Northwestern University in Chicago. The meeting featured extensive contributions from basic scientists and technologists, and presented the sparse available clinical experience (of such workers as Kelly, Robertson, Ascher, Cerullo, Brown, and Takizawa, among others). Although various explanations for the late arrival of the laser in neurosurgery have been offered, most likely it is because the development of microsurgery and appreciation of microsurgical techniques was a necessary precursor for the advent of laser, a further refinement on "micro" surgery. Although acoustical and photochemical effects of laser have been exploited in various clinical situations, to date these uses have been largely undiscovered for the neurosurgical community. By far, it is the precise and controllable thermal conversion currently utilized by the majority of clinical neurosurgeons at the time of this writing. Most would agree that the primary use for the laser as an instrument for vaporization is in the removal of extra-axial tumors considered hazardous by their proximity to vital neurologic or vascular structures. Certainly, meningeal tumors of the midline base, including tuberculum sellae, medial sphenoid wing, clivus, petrous apex, foramen magnum, and spinal canal, are included in this category. Nerve sheath tumors, unusual metastatic deposits, and lipomatous tumors of brain and spinal cord are similarly considered. Concomitant with the use of microsurgical techniques and laser technology has been an increasing bravado on the part of neurosurgeons, often in conjunction with head and neck surgeons, to approach the skull base in a more aggressive and innovative manner. Thus, the limits of operability have been extended and the surgical results improved. As this group of patients would have a normal life expectancy were it not for their preoperative or postoperative morbidity, it appears that this, the extra-axial tumor removal, is the area of greatest impact of the laser on neurosurgery. The technique for the removal of extra-axial tumors, regardless of location, is similar. Generally, the surgical exposure requires less wide uncovering of the neoplasm than with techniques that require removal of brain from the pathologic process, rather than the reverse. Following this rather limited uncapping, the CO 2 laser, at low energy and in defocused mode, is used to enter the capsule of the tumor. Surrounding sensitive structures are protected by moist cotton, as water immediately absorbs the energy of the CO 2 laser. As an appreciation of the consistency and vascularity of the tumor is gained, longer applications of higher powered lasers can be utilized; the limit depending on the experience and particular preference of the surgeon. As the interior of the neoplasm is evacuated, the lesion will be noted to be compressed by the surrounding neural structures, which already begin to assume a more normal anatomic position. When an appreciable portion of the tumor has been evacuated, attention may be paid to the capsule. It is important to recognize and preserve the arachnoidal interface between tumor and surrounding brain. In meningiomas, this is a single layer; in acoustic and other nerve sheath tumors, this may be two layers. Failure to respect this interface will result in bonding of the arachnoid to
USE OF THE LASER IN NEUROSURGERY
997
the tumor capsule, with resultant difficulty in appreciating the true delineation of tumor from brain. Normally, moist cotton is placed between the brain arachnoid and the tumor capsule. At this point, the defocused laser is used to shrink the capsule, allowing the tumor to dissect itself from surrounding neural structures, parachymal or vascular. The degree of shrinkage will be a function of the collagen content of the tumor and will vary from neoplasm to neoplasm, regardless of histology. By avoiding too great a depth of penetration into the corpus of the tumor before shrinking the capsule, overpenetration into surrounding vessels, cranial nerves, and brain structures can be avoided. Eventually, the tumor can be delivered through the operative exposure, or it can be entirely vaporized in situ. It should be remembered that the removal of the great mass of the tumor need not be by total vaporization, which may be too time-consuming and unnecessary. Rather, the laser can be used in a more focused mode to offer tumor morsilation in a hemostatic manner. Similarly, alternate methods of tissue removal, such as ultrasonic aspiration and regulated suction, can be used for this purpose, depending on the consistency of the lesion. Unquestionably, however, the more sensitive attachments of the tumor to cranial nerve, vessel, midbrain, and brain stem structures require gentle and precise vaporization offered by the laser. Appreciation of the relative hemostasis, even of the CO 2 laser, is realized when this form of tissue removal is compared with conventional methods. Likewise, the ability to continually monitor electrophysiologic parameters, such as evoked response testing, offers increased proof of the atraumatic nature of the technique. The second area where the inherent gentleness in containment of tissue destruction is appreciated is in the transgression of normal central nervous tissue to arrive at deeper, pathologic tissue. Examples include cerebrotomy and myelotomy for deep lesions, the actual removal of which may be laser vaporization or other techniques. The CO 2 laser can be used as a valuable coagulating instrument if a sharp area of demarcation is protected with moist cotton and the laser is used at low power. On the creation of a narrow band of coagulated tissue, the laser can then be used at higher power and sharp focus to incise along the coagulated strip. It is immediately apparent to the surgeon that surrounding tissues, within fractions of a millimeter, are healthy and well vascularized. The technique for removal of the gliomatous tumor within will depend on histology, consistency, and vascularity, as well as a surgical objective. Intramedullary lesions of the spinal cord are ideal candidates for total vaporization, while glioblastomas of the cerebrum are generally less suitable. A notable exception is the use of laser, coupled with a stereotactic computed tomographic guided apparatus of real-time ultrasonography, to vaporize deep lesions with minimal damage to surrounding nuclear structures. Should the lesion lie within the ventricular system, elimination of spinal fluid will allow carbon dioxide vaporization. Alternately, the use of another wavelength, such as Nd:YAG or argon, will allow denaturization and vaporization through the ventricular liquid. The increasing use of endoscopy in this regard will certainly impact on surgical results. Vaporization of gliomatous lesions has not been proven to offer increased longevity but is felt by many to improve surgical success by lowering morbidity.
998
LEONARD
J.
CERULLO AND LEONARD
P.
BURKE
Other incisional uses for the laser include myelotomy for pain or spasticity and lobectomy for tumor and epileptogenic focus ablation. The minimization of edema formation and negligible current of injury associated with incision of neural tissue in this manner have been demonstrated in the laboratory and are presently being investigated clinically; the early results are quite encouraging. The technique is the same as that for cerebrotomy, except that the moist cotton protection need be offered only to the tissue that will remain, allowing the surgeon a greater latitude in wider coagulation and more effective hemostasis in the tissue being removed. Whether this will translate to a lower rate of postoperative epilepsy is yet to be seen. Spinal syrinx fenestration and the creation of DREZ lesions for intractable pain also capitalize on the strict containment of damage offered by both CO 2 and argon lasers in sharp focus. Claims of reduced rate of neuroma formation and reduced pain following neuroma amputation have been ascribed to the CO 2 laser. At present, these have not been substantiated in laboratory investigations, though the data are somewhat contradictory. Although considered a rather pedestrian use, the ability of the CO 2 laser to hemostatically incise skin and muscle has been exploited in a number of neurologic operative procedures. Reduction of tetanic contraction of muscle, such as the paraspinal muscle, is noted to occur when laser dissection is compared with Bovie knife incision. The reduction of tetanic contractions may translate to reduced postoperative pain. Certainly, when the unstable spine is approached through a posterior route, minimization of violent contractions may be advisable in preventing free bony elements from being pulled and twisted onto the underlying dura and cord. Claims of reduced rate of scar formation and improved success following postoperative scar excision are yet to be substantiated. The CO 2 laser has been shown experimentally to be as effective in completely extirpating disk material, without creation of histologic diskitis, as currently effective mechanical means. The reduced area of exposure, secondary to freedom from visual impediment by instrumentation, may offer a further refinement to the microdiskectomy procedure. Similarly, the use of laser, either CO 2 or Nd:YAG, to open the sellar floor and sellar dura in trans-sphenoidal pituitary surgery have been applauded. Again, the emphasis is on the ability to work through a limited exposure on a deep structure without visual compromise by instrumentation. Recently, the Nd:YAG laser has begun to enjoy increasing acceptance in neurologic surgery. Histologic studies have confirmed the increased depth of penetration and lateral spread of distribution associated with this wavelength. On the other hand, the improved hemostasis and ability to work on the other side of an intact structure, such as the sinus dura, offers intriguing possibilities for the future. Ascher and co-workers have demonstrated the ability to denature pituitary tissue without opening the dura through a trans-sphenoidal approach. Similarly, Beck and Ascher have claimed to denature meningiomatous tumor, which has entered but not obliterated major venous sinuses, without physically opening the structure. Corroboration of these claims awaits further experience in a more controlled situation. Tew at the University of Cincinnati and Sundt at the Mayo Clinic
USE OF THE LASER IN NEUROSURGERY
999
have demonstrated the use of Nd:YAG laser for coagulation of the racemous portion of arteriovenous malformations and have indicated that the instrument may be very effective in dealing with the residual periphery of these lesions, particularly when located in very sensitive areas. Takeuchi, Handa, and others have showed the effectiveness of the Nd:YAG laser in the coagulation of large and small highly vascular tumors, whether intra-axial or extra-axial. The probability for the future is that the combination of Nd: YAG for coagulation and carbon dioxide for vaporization will allow more effective tumor removal with fewer high-energy requirements from either wavelength. Fasano and his co-workers have demonstrated the differing effects of argon, CO 2 , and Nd:YAG on various elements of vessel walls. Hypotheses regarding treatment of intracranial aneurysms and arteriovenous malformations have been made. Again, wide clinical use demands further laboratory confirmation. The use of various wavelengths, including argon and CO 2 , for tissue bonding has recently gained great popularity. Small vessels, nerves, dura, and hollow viscera have been so treated. The technique appears to offer advantages over the use of suture in preventing granuloma formation along the suture line and allowing unrestricted dilation at the anastomosis site. Others including Edwards have suggested the possibility for aneurysm formation at the anastomosis site and caution against the use of the procedure on that basis. Jain has used Nd:YAG laser for the same purpose but did not report the aneurysmal formation described by Edwards. However, he described aneurysm formation at the anastomosis site. Intravascular navigation with direct visualization and treatment either by photochemical reaction (excimer laser) or direct vaporization (argon, Nd:YAG, CO 2 ) are presently underway. Vessels ranging from the aorta to the mediumsize cerebral vessels have been treated. Results appear promising, but as yet no long-term animal studies are available to demonstrate the efficacy and/or safety of thse techniques. The fact appears to have been established that the laser has become the neurosurgical tool of the 1980s. The remaining question is to what degree this modality will augment, or replace, conventional technique. It now appears that the future of lasers in surgery, and particularly in neurosurgery, is limited only by the imagination of the surgeons.
BIBLIOGRAPHY Ascher, P. W.: Newest ultrastructural findings after the use of CO 2 laser on CNS tissue. Acta Neurochir. [Suppl.] (Wein), 28:572-581, 1979. Ascher, P. W.: Horizons in neurosurgery. Presented at the Meeting of Laser Association of Neurological Surgery International, Houston, May 1, 1983. Ascher, P. W., and Cerullo, L. J.: Laser use in neurosurgery. In Dixon, J. (ed.): Surgical Applications of Lasers. Chicago, Year Book Medical Publishers, 1983. Beck, 0. J.: The use of the Nd- YAG and the CO 2 laser in neurosurgery. Neurosurg. Rev., 3:261-266, 1980. Beck, 0. J., and Ascher, P. W.: Different lasers in neurosurgery. Presented at the Third Annual Meeting for American Society of Laser Medicine and Surgery, New Orleans, January 10-12, 1983.
1000
LEONARD
J.
CERULLO AND LEONARD
P.
BURKE
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