Use of the argon surgical laser in neurosurgery

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✓ The argon surgical laser has been used in 68 neurosurgical procedures that included the removal of intracranial and intraspinal tumors, spinal cord fenestration for syringomyelia, and the production of dorsal root entry zone lesions. Characteristics that make the argon surgical laser a useful microneurosurgical instrument include the availability of a fiberoptic delivery system, a laser spot size that can be varied continuously between 0.15 and 1.5 mm, a single laser-aiming and treatment beam, the transmission of argon laser light through aqueous media such as irrigating or cerebrospinal fluids, and improved hemostasis compared to conventional techniques. The argon laser is limited primarily by its relatively low power output (less than 16 W), which makes the excision of large tumors difficult. However, even with these limitations, which can be used to advantage in the proper setting, the authors' laboratory and clinical experience suggests that the argon surgical laser may be useful in certain microneurosurgical operations.

Abstract

✓ The argon surgical laser has been used in 68 neurosurgical procedures that included the removal of intracranial and intraspinal tumors, spinal cord fenestration for syringomyelia, and the production of dorsal root entry zone lesions. Characteristics that make the argon surgical laser a useful microneurosurgical instrument include the availability of a fiberoptic delivery system, a laser spot size that can be varied continuously between 0.15 and 1.5 mm, a single laser-aiming and treatment beam, the transmission of argon laser light through aqueous media such as irrigating or cerebrospinal fluids, and improved hemostasis compared to conventional techniques. The argon laser is limited primarily by its relatively low power output (less than 16 W), which makes the excision of large tumors difficult. However, even with these limitations, which can be used to advantage in the proper setting, the authors' laboratory and clinical experience suggests that the argon surgical laser may be useful in certain microneurosurgical operations.

Surgical lasers, predominantly the carbon dioxide (CO2) laser, are being used with greater frequency in neurosurgical procedures. Uses of the surgical laser have included the operative removal of meningiomas,5,18,21 spinal cord tumors,6 and centrencephalic primary and metastatic tumors.14–16 Compared to conventional techniques, hemostasis is improved during tumor removal, less brain retraction and manipulation of normal structures are needed, and the precision is often improved compared with free-hand microsurgical technique. After sufficient experience with the use of surgical lasers has been gained, the time needed to perform some procedures is shortened. Lasers also probably reduce surgical trauma, especially when used with a micromanipulator and operative microscope.

We have evaluated the effects on neural tissue of CO2 and argon (Ar) surgical lasers, and found no significant difference in tissue injury to the brain or spinal cord of rats irradiated with equivalent energy density beams from each laser.7 The Ar laser appeared to produce better hemostasis than the CO2 laser.7 Because of these findings and the advantages offered by a fiberoptic micromanipulator delivery system, in June, 1981, we began using the Ar surgical laser for surgical procedures, after using the CO2 laser clinically for a year. Our experience with the Ar laser in 68 surgical procedures is reported here.

Clinical Material and Methods
Patient Population

Between June, 1981, and September, 1982, 68 patients were operated on at the University of California, San Francisco, or the San Francisco Veterans Administration Hospital using the Ar surgical laser (Table 1). Because these procedures were performed as part of an approved experimental protocol, all patients gave informed consent to be research subjects.

TABLE 1

Neurosurgical procedures performed with the argon laser

LocationLesionNo. of Cases
Cranial36
 supratentorialmetastases3
gliomas4
arteriovenous malformations2
craniopharyngiomas2
meningioma: torcular (1); tentorial (2); clival (1); parasellar (1)5
hemangioblastoma1
chromophobe adenomas2
choroid plexus carcinoma1
3rd ventricle ependymoma1
ganglioglioma1
 infratentorialmedulloblastomas4
4th ventricle ependymomas2
cerebellar astrocytoma1
acoustic neuromas4
5th nerve schwannoma1
jugular foramen schwannoma1
 transsphenoidalprolactinoma1
Spinal32
 intramedullaryhemangioblastoma1
ependymomas4
astrocytomas3
schwannoma1
metastasis1
 extramedullaryneuroblastoma1
 syringomyelia5
 dorsal root entry zone lesions16

Laser

The Ar laser was used when brain or spinal cord tumors were either growing in a location that presented a difficult surgical approach, such as at the base of the brain, or exhibited hypervascularity on preoperative radiographic studies. The Ar laser was used to make dorsal root entry zone (DREZ) lesions because we had found (unpublished results) that similar laser lesions in the cat spinal cord were more discrete than lesions made by the standard radiofrequency probe technique. Likewise, because experimental studies had shown that incisions made into the spinal cord with the Ar laser were less injurious than incisions made by routine methods, myelotomy for fenestration of syringomyelia was performed with the Ar laser.

A 16-W continuous-wave Ar ion surgical laser system was used in each procedure.* This laser operates in the blue-green portion of the visible spectrum at 488 nm and 514.5 nm; approximately 80% of the power output is available at these wavelengths. The laser is coupled to the operating microscope via a fiberoptic micromanipulator delivery system. After transmission through fiberoptic cables, a rather homogeneous distribution of energy within the laser beam results, which is a combination of TEM00- and TEM01-mode structure. The direction and spot size of the laser beam are controlled, respectively, by a “joy stick” and focus nob on the micromanipulator. The joy stick has the ability to decrease physiological tremor by a factor of 20:1. The laser beam spot size can be continuously varied between 0.15 and 1.5 mm. The power output, pulse duration, and repetition rate of the laser are controlled from the console.

Because the wavelength of the Ar laser is in the visible portion of the spectrum, operating room personnel must wear protective (tinted) eyewear when the laser is in use. An automatic shutter system is incorporated into the micromanipulator microscope attachment so that protective eyewear is not necessary for the surgeon or assistant when the surgical microscope is being used. The fact that the beam is visible, however, is advantageous. The CO2 laser beam is invisible, and a helium-neon laser is used as a visible aiming beam; in that case, to assure maximum precision of operation, the two beams must be critically aligned. With the Ar laser, this is not necessary, and the Ar laser is intrinsically more precise than the CO2 laser.

Technique and Operative Results
Intracranial Extra-Axial Tumors

The Ar laser was used in the resection of 16 extraaxial supra- and infratentorial lesions for which proximity or attachment to important neural structures necessitated a particularly gentle surgical technique. Our experience with the CO2 laser had suggested that there was no particular benefit compared to standard techniques for laser resection of large tumors in other locations, unless lesions were hypervascular. For some large tumors, the laser was used to resect only portions of the tumor involving delicate structures. In these instances, the laser produced essentially hemostatic vaporization of tumor tissue, made it possible to work within a cerebrospinal fluid (CSF)-containing space, minimized brain retraction, and decreased manipulation of vital structures.

The first step in the laser-aided excision of extra-axial tumors is the coagulation of the tumor surface with a low power density beam, which causes thrombosis of exposed vessels and shrinkage and retraction of the tumor capsule away from adjacent structures. Vaporization and debulking of the tumor is then performed using a high power density beam. It was possible to remove a tumor hemostatically by using either small laser spot sizes and high power densities to incise tumor and remove it in a piecemeal fashion, or by using large spot sizes and high power densities to vaporize tumor with a non-touch technique. By alternating between gutting of the interior of the tumor with high power densities and delivering the capsule of the tumor away from surrounding neural tissue by irradiating it with a low power density beam, these tumors could be removed readily with minimal manipulation and retraction of neural elements. Residual tumor attached to the facial or other cranial nerves was vaporized using short pulses and a small beam diameter, which avoided manipulation and traction injury to the nerve. A schwannoma of the trigeminal nerve was dissected away from the ipsilateral abducens nerve without injury to the nerve. The removal of large acoustic neurilemmomas was greatly improved by the laser; we were able to preserve facial nerve function in all patients in whom the laser was used.

During vaporization of tumor, a suction device that aspirates smoke is the only instrument necessary in the operative field. Thus, wide exposures and excessive brain retraction were generally avoided. Non-manipulative tumor removal is facilitated by the coagulative effect of the laser that causes retraction of tissue, which tends to deliver the tumor into the surgical field.

Two patients with craniopharyngiomas extending into the third ventricle were operated on through a transcallosal approach. The laser was used to make the callosal incision and to coagulate and vaporize tumor within the third ventricle. A portion of the septum pellucidum was excised to facilitate CSF flow between the two lateral ventricles. A large nonsecretory pituitary adenoma with intraventricular extension was also removed with the Ar laser. Because of the high transmission through water of light from the Ar laser, the presence of CSF does not affect use of the Ar laser for tumor removal.

One patient had a large recurrent fibrous prolactin-secreting pituitary adenoma with modest suprasellar extension that could not be aspirated; it was excised through a transsphenoidal approach. The Ar laser was used to cut through the bone of the sellar floor, to open the dura, and to coagulate and vaporize the tumor. Complete tumor removal was obtained without the use of multiple instruments, although this procedure could have been done with routine methods.

The laser was used in conjunction with standard surgical techniques for the excision of meningiomas that were in critical locations (Table 1). In the case of a torcular meningioma, remnants of tumor extending into the confluens of sinuses were coagulated and gently removed by vaporization without affecting venous drainage.

One tentorial meningioma that extended inferiorly into the cerebellopontine angle proved to be extremely vascular and, therefore, difficult to remove even with the aid of the Ar laser. This “sinusoidal-type” of tumor was tediously dissected by first using low power density to ensure coagulation of tumor vessels before the lesion was vaporized at a high power density. The Ar laser does not provide high power densities at spot sizes greater than 2 mm in diameter, which are necessary for the rapid vaporization of large or calcified tumors. However, a radical removal of these large lesions was accomplished in every patient with decompression of the adjacent brain stem, cranial nerves, and vascular structures. There was no morbidity or mortality among this group of patients.

The following case is an example of excision of an acoustic schwannoma with the Ar laser.

Case 1

This 28-year-old man noted the onset of tinnitus and decreased hearing in the right ear in August, 1981; at auditory evaluation a month later, a right sensorineural hearing deficit was noted. A computerized tomography (CT) scan of the posterior fossa in February, 1982, showed a 3.0-cm homogeneously contrast-enhancing mass in the right cerebellopontine angle that extended out of a widened internal auditory canal.

In March, 1982, the patient underwent the excision through a retromastoid approach of an acoustic schwannoma with the Ar laser. The tumor was gutted by laser vaporization and fragmentation, bipolar coagulation and suction, and sharp dissection. The tumor capsule easily separated itself from the brain stem. Attempts to remove adherent tags of tumor left on the facial nerve with sharp microdissection resulted in excessive manipulation of the nerve. Therefore, the laser was used to vaporize these fragments. The auditory nerve was sectioned with the remaining tumor at the internal auditory canal. Postoperatively, the patient had normal facial nerve function.

Intracranial Intra-Axial Tumors
Supratentorial Lesions

The decision to resect cerebral gliomas using the Ar laser was based on the appearance of tumor hypervascularity on preoperative angiograms. In general, blood vessels in these lesions are of small caliber (less than 2 mm in diameter) and therefore are readily coagulated with the Ar laser.

After selective laser coagulation of the pial surface vessels, a cortical incision was made with the laser using the smallest spot size (diameter 150 µ). Because of the large volume of tumor tissue that was usually present, the limited power output (approximately 10 W at the tissue surface), and the relatively small size of the largest Ar laser spot (1.5 mm), tumor excision by vaporization alone is impractical. Friable tumor is suctioned away and the laser is used to coagulate small bleeding vessels in the tumor bed, and to cut firm, fibrous portions of tumor; either suction or grasping forceps can be used to deliver, in a piecemeal fashion, tumor that is excised with the laser. Using this technique, relatively rapid tumor excision with minimal blood loss is possible. Hemostasis of the tumor bed is accomplished by using a large defocused laser spot size and low power density to coagulate tumor vessels under constant saline irrigation.

Other than the fact that it appeared that less manipulation of the surrounding brain was necessary during excision of tumor, we found that the laser provided no particular advantage for use in the excision of gliomas, nor did the laser affect long-term prognosis.

Infratentorial Lesions

Intra-axial infratentorial lesions either extended into the brain stem or occupied a position bordering the fourth ventricle. With the Ar laser, hemostatic tumor excision with decreased manipulation and tissue dissection around the brain stem could be accomplished. In each patient, blood loss during excision was judged to be less than would be expected using routine methods. The following is a description of such a case.

Case 2

This 18-year-old woman was evaluated at another hospital in July, 1981, for severe bitemporal headache and ataxia. A CT scan showed a cerebellar mass. She then underwent suboccipital craniectomy and partial removal of a Grade I astrocytoma. Her postoperative course was complicated by a wound infection that required a repeat operation 3 weeks later. She recovered, with return to essentially normal neurological function. She received 5700 rads to the posterior fossa, after which she did well except for the persistence of bitemporal headaches. However, a follow-up CT scan 10 months later showed that the tumor had recurred, and she was referred to our service for treatment.

The neurological examination was remarkable only for unsteadiness of tandem walking, with preferential leaning to the right. There was no other evidence of cerebellar or brain-stem dysfunction. A repeat CT scan showed an enhancing mass involving the vermis and extending into the right cerebellar hemisphere. The fourth ventricle was enlarged, but the lateral and third ventricles were of normal size. In June, 1982, the patient underwent reexploration through the previous suboccipital craniectomy. With the aid of bipolar coagulation and suction, the inferior vermis was opened down to firm grayish tumor tissue. The tumor was fibrous and could not be aspirated. The Ar laser was used to vaporize and excise the tumor. A saline-soaked cottonoid patty was placed into the fourth ventricle to protect the floor nuclei during removal of the tumor. Gross total removal was accomplished with very little bleeding.

Histologically, this was a low-grade astrocytoma with hyaline degeneration of many small blood vessels associated with areas of reactive glial changes, probably secondary to radiation therapy. No residual tumor was seen on a postoperative CT scan. The patient was discharged neurologically intact.

Miscellaneous Lesions

In two patients, solitary metastatic lung tumors in the dominant temporal lobe that had dense contrast enhancement on a CT scan and a tumor blush on a preoperative cerebral arteriogram were excised using the Ar laser. In each patient, the cortical incision over the tumor was made with the laser. Laser coagulation of the tumor pseudocapsule caused the tumor to shrink slightly, after which it retracted away from surrounding brain. By repeatedly using this technique and by debulking the central portion of the tumor using both routine techniques and the laser, complete excision was accomplished in each patient with minimal brain retraction and blood loss. In both patients, who were dysphasic preoperatively, normal speech returned within 1 week of surgery.

The Ar laser was helpful for the removal of a low-flow, partially calcified arteriovenous malformation (AVM) that was composed of small-caliber blood vessels, but it was not helpful in the removal of a large, high-flow AVM of the temporal lobe. In the first instance, the vessels of the AVM were coagulated by application of low-power laser beams to the surface of the lesion, which excluded blood from within the AVM and caused the lesion to shrink. In the latter patient, the temporal heating effect of the Ar laser, used in an attempt to induce vessel coagulation and thrombosis, was lost because of the transfer of heat away from the site of coagulation by the high blood flow. Another patient who harbored a solid hemangioblastoma of the right parietal lobe was successfully treated by coagulating the external surface of the tumor, which caused the tumor to shrink and allowed non-manipulative dissection of the tumor away from the surrounding brain.

The Ar laser was very helpful in the removal of two intraventricular lesions, a choroid plexus carcinoma of the lateral ventricle, and an ependymoma of the posterior third ventricle. The following report describes a patient with successful coagulation and resection of a parietal tumor.

Case 3

This 36-year-old woman with von Hippel-Lindau disease developed grand mal seizures in February, 1979. Initial electroencephalogram and nuclide brain scan studies were normal. However, because of persistent seizures in spite of diphenylhydantoin therapy, a CT scan was obtained in December, 1979, that showed a right parietal and bilateral cerebellar contrast-enhancing lesions. Cerebral arteriography showed highly vascularized tumors consistent with solid hemangioblastomas located in the deep right parietal area supplied by distal arterial branches of the middle cerebral artery, in the right inferior cerebellar hemisphere fed by branches of the right posterior inferior cerebellar artery, and in the left superior cerebellar hemisphere supplied by hemispheric branches of the superior cerebellar artery. The patient was followed for a year with adjustments in her anticonvulsant medication. Because of an episode of transient right arm numbness and right leg weakness after a seizure, a myelogram was obtained in December, 1980; no spinal lesion was seen. However, her seizures persisted and she was admitted to the hospital in October, 1981, for elective removal of the right parietal lesion.

The patient's neurological examination was normal. No further studies were performed. She had a right temporoparietal craniotomy. Ultrasonography was used intraoperatively to locate the tumor, which was found within the distal Sylvian fissure. The fissure was opened using standard microsurgical technique. The tumor, measuring 2.0 cm in diameter, was exposed on the surface of the island of Reil. With a low power output from the laser (1 to 2 W) and a diffused spot size (1.5 mm), the tumor was gradually coagulated (over approximately 15 minutes) under microscopic vision. The tumor shrank to approximately half its original size and pulled away from surrounding gliotic brain. The vascular pedicles were then coagulated with the laser and bipolar forceps, and the tumor was totally resected. The postoperative course was uncomplicated and the patient was discharged on the 8th postoperative day.

Intraspinal Tumors
Intramedullary Lesions

Ten patients underwent myelotomy and removal of an intramedullary spinal cord tumor. A gross total removal was obtained in all four patients with ependymoma, in one patient with a thoracic hemangioblastoma, in one patient with an exophytic cervical intramedullary schwannoma, and in one patient with a midthoracic astrocytoma. The other three patients, two with astrocytomas and one with metastatic squamous cell carcinoma, had subtotal resections performed. Patients either showed improvement or no change in neurological function immediately after surgery. One patient with metastatic squamous cell carcinoma to the midcervical cord did poorly because of preexisting lung disease and died of pneumonia on the 5th postoperative day. Somatosensory evoked potentials (SEP's) measured during surgery did not show amplitude or latency changes in the early waveforms derived from median nerve stimulation. Similar findings of preserved early potential waveforms of the cortical SEP's derived from stimulation of the median or posterior tibial nerves were seen in all patients in whom spinal cord tumor was exposed through a dorsal midline myelotomy with the Ar laser. This suggests that we were able to spare the posterior columns when myelotomy was performed with the Ar laser.

Pial surface vessels are quickly and efficiently coagulated with the Ar laser without affecting the underlying spinal cord. After this step, myelotomy is performed with the laser using the 150-µ spot diameter and between 3 and 5 W of laser power (recorded at the laser console).

After placement of pial retraction sutures at the edges of the dorsal myelotomy, further manipulation of the cord is seldom necessary. The Ar laser is used to vaporize and dissect tumor by using the tumor-edge coagulation technique. In patients in whom tumor was subtotally resected, it was difficult to establish a tumor-spinal cord interface either because of the infiltrative nature of the tumor or because the coagulation technique did not initiate formation of a tumor pseudocapsule. In these instances, excision was accomplished by vaporization alone. We are of the opinion that the Ar laser was especially helpful for removal of these lesions.

Case 4

This 36-year-old musician presented in 1975 with interscapular pain and shooting pains down his left leg. Myelography at that time demonstrated a widened cervical cord, and he underwent exploration through a C3–4 laminectomy. The operation was aborted because of heavy epidural bleeding. He was further evaluated for a possible AVM by selective spinal angiography, but no lesion was seen. Multiple myelographic studies performed between 1975 and 1980 showed progressive widening of the cervical cord at C1–7. In February, 1980, a C-6 laminectomy and biopsy of an intramedullary ependymoma was performed. Postoperatively, the patient received radiation therapy (5400 rads) to the cervical spine. Nonetheless, he had difficulty with writing and with fine motor movements of the hands, which interfered with his ability to perform as a computer musician. He also noticed intermittent tingling sensations in both legs that were associated with easy fatiguability in his legs when walking.

He was readmitted to the hospital in December, 1981. Neurological examination revealed mild to moderate bilateral weakness of the deltoids, biceps, triceps, wrist extensors, and intrinsic muscles of the hand accompanied by incoordination of hand movements. Mild spastic weakness and hyperreflexia were present in the lower extremities. Reflexes were absent in the upper extremities. Pin-prick sensation was absent between C-2 and T-4 on the left and between C-6 and T-4 on the right. There was normal sensation in the lower extremities. A Babinski sign was equivocal bilaterally.

In December, 1981, laminectomies were extended from C-2 to C-7, with total excision of the ependymoma. The majority of the tumor was solid, with a small cystic area along its inferior pole at the C-7 cord level. The Ar laser was used to make the dorsal midline myelotomy from C-3 to C-7. Intraoperative SEP's showed no change. The tumor was removed by the combination of internal decompression of tumor by laser vaporization and the surface coagulation technique. Bleeding points in the residual tumor bed were coagulated with the laser.

Postoperatively, the patient experienced a transient increase in left arm numbness, predominantly in the C-6 distribution, along with a diffuse increase in the numbness and weakness of his legs. However, when discharged on the 17th postoperative day, he was walking without difficulty and he noted improvement in his left arm weakness. Three months after surgery he was able to return to his work as a computer musician.

Dorsal Root Entry Zone Lesions

Lesioning of the DREZ of the spinal cord has been advocated by Nashold, et al.,17 as a means of producing pain relief in selected patients. Our results with the Ar laser will be mentioned here only briefly.

With the Ar laser, pial vessels are coagulated on the surface of the DREZ on the side(s) of the patient's pain, and a longitudinal series of craters is then made in the DREZ. In patients with pain secondary to dense arachnoiditis, the Ar laser was extremely helpful for incising fibrovascular bands that adhere the spinal cord to the dura, without cord manipulation or blood loss.

This treatment successfully relieved pain in 13 of 16 patients treated by this method, who had a mean follow-up period of 9 months. There were no complications, such as spread of injury into adjacent ascending or descending fiber tracts in these patients.

Syringomyelia

Based on our experience with laser myelotomy for spinal cord tumors and use of the laser for DREZ lesioning, we used the Ar laser to perform syringotomy in five patients. Fenestration of the syrinx cavity was made using the 150-µ laser spot size over a distance of 1.0 cm through the DREZ on the side of the patient's worse symptoms. All patients underwent shunting via a tube to either the ventral subarachnoid space or the peritoneal cavity. In one patient with thoracolumbar syringomyelia associated with a dense chronic constrictive arachnoiditis (idiopathic), the Ar laser was very helpful for dissection through a partially calcified arachnoid membrane and for lysing fibrovascular adhesions between the membrane and the dorsal surface of the cord. We have not performed laser syringotomy without the placement of a shunt tube. The use of the laser for syringomyelia seems to be of value only for the myelotomy, but is not a means of treatment in its own right.

Discussion

Because pigmented tissue readily absorbs light at the wavelengths at which the Ar laser emits, it has been used in dermatology and plastic surgery for removal of tattoos,2 cutaneous hemangiomas,3 telangiectasias, and other pigmented skin lesions,1 and its use for neovascular photocoagulation in diabetic retinopathy is well established.23,24 It has also been used for the treatment of gastrointestinal hemorrhage,8,22 bladder tumors (HD Noske, et al., and CF Rothauge: unpublished data, 1979), urethral strictures,20 and bronchial tumors10 through flexible endoscopes, procedures that are possible because of the fiberoptic delivery system of the Ar laser. Instruments such as the CO2 laser operate at wavelengths that, because of current technical limitations, preclude the use of fiberoptic delivery systems. The Ar laser has been particularly helpful in the surgery of the middle ear for tympanoplasty, stapedotomy, stapedectomy, ossicular sculpturing, myringotomy, and lysis of middle ear adhesions.9,11,13,19 We and others12 have found that lasers are advantageous for the removal of extra-axial tumors, particularly acoustic tumors.

The blue-green light of the Ar laser is in the visible portion of the spectrum and, characteristically, has high transmission through water and aqueous media such as CSF. Thus, the Ar laser's action on tissue is not significantly attenuated by CSF or standard irrigating solutions. Continuous irrigation can thus be used to cool delicate tissue such as cranial nerves when resecting small pieces of tumor from these structures; this is not possible with the CO2 laser. Moreover, because the beam is visible, a separate aiming device, such as the helium-neon laser beam needed with the invisible CO2 laser beam, is unnecessary. This greatly improves the precision of the laser as a microsurgical instrument. Pigments, in particular those colored red, have a high absorption coefficient and readily absorb light at the Ar laser wavelengths. Biological pigments such as melanin, hemoglobin, and cytochromes readily absorb Ar light energy and convert it into thermal energy.

Changes that may occur in the absorption coefficients and at tissue-tissue interfaces as a result of thermal injury will affect the reaction of tissues to continuous laser irradiation.7 This may explain the discrepancy between the predicted and the actual biological effects that are seen after laser applications in vivo.

Depending on the power densities used, the thermal effects of the laser can either vaporize or coagulate tissue. High power densities (greater than 1000 W/sq cm) produce rapid vaporization of biological tissues, and are therefore used to debulk tumors, create ablative lesions, or incise neural tissue. The diameter of the spot size is an important factor that determines the width of the area of laser injury. The smallest spot size is used to make neural incisions, such as myelotomy, or to remove tumor from adjacent critical structures such as the optic nerve or carotid artery. The smallest spot size of currently available CO2 lasers is larger than the smallest spot size of the Ar laser. Low power densities (100 to 500 W/sq cm) can coagulate vascular structures effectively. Thus, by manipulating the power output, duration of exposure, and spot size, the effects of the Ar laser on tissue can be changed.

At very low power densities (50 to 500 W/sq cm), the ability of the Ar laser to vaporize tissue is markedly decreased and its photocoagulation effect is increased. Coagulation of tissue is the result of the combination of the selective absorption of Ar laser light by hemoglobin and the scattering of laser light within the tissue, which decreases the power density per volume of tissue and thereby disperses the thermal effect of laser light over a larger volume of tissue. If the laser is operated at low power densities, scattering reduces the effective power density within tissue to a point at which no thermal reaction occurs. However, because the energy absorption of tissue becomes increasingly independent of the absorption coefficient and the beam wavelength at high power densities,4 application of the same beam spot size at high power densities rapidly vaporizes tissue at the point of impact and, because absorption characteristics of the adjacent tissue are changed, the amount of scattering is reduced. This effect may explain the similarity of lesions produced by Ar and CO2 lasers with respect to the depth of thermal effect in bordering neural tissue at high power densities.7

Our clinical experience with the Ar laser has been very similar to the experience with the CO2 laser reported by others. In addition to the advantages for tumor excision discussed above, we have found that the Ar laser has particular benefits for making fine incisions in neural tissue (myelotomy) and for making discrete, reproducible lesions in the DREZ of the spinal cord. Our case material is summarized in Table 2; we indicate there the lesions or procedures for which, in our opinion, the Ar laser was of value. This in no way indicates that the laser is superior to routine microsurgical techniques, but rather represents our personal experience.

TABLE 2

Experience with argon laser in 68 neurosurgical procedures*

ResultLesionNo. of Cases
very helpfuldorsal root entry zone lesions16
spinal intramedullary tumors10
medulloblastomas4
acoustic neuromas4
intracranial meningiomas4
4th ventricular ependymomas2
pituitary adenomas2
cerebral hemangioblastoma1
choroid plexus carcinoma1
3rd ventricular ependymoma1
cerebellar astrocytoma1
trigeminal schwannoma1
jugular foramen schwannoma1
helpfulsyringomyelia5
cerebral metastases3
intraventricular craniopharyngiomas2
tentorial meningioma1
arteriovenous malformation1
pituitary adenoma1
thoracic neuroblastoma1
ganglioglioma1
not helpfulmalignant gliomas4
arteriovenous malformation1

The argon laser was considered to be very helpful when the surgical result was judged to be better than that expected using standard microsurgical techniques (48 cases), helpful when the surgical result was equivalent to that expected using standard techniques (15 cases), and not helpful when the results with standard microsurgical techniques were judged to be superior to those obtained with the laser (five cases). (Reproduced, with permission, from Edwards MSB, Boggan JE, Fuller TA: The laser in neurological surgery. J Neurosurg 59:555–566, 1983.)

Our surgical experience suggests that, because of the available higher power densities, the CO2 laser is the superior instrument for debulking large, fibrous, relatively avascular tumors. However, for fine microsurgical work that does not require high power densities, the Ar laser has a slight advantage over the CO2 laser because of its maneuverability (fiber optic delivery system), smaller spot size, direct visual control of the beam that allows greater precision and hemostasis, and transmissibility through CSF. The differential absorption of laser light by pigmented and nonpigmented tissues can be used to advantage for the dissection of pigmented lesions in the central nervous system. Laser light directed on the edge of a tumor will be more thoroughly absorbed by the tumor with a greater thermal effect than on the nonpigmented (neural) side. The tumor-neural plane of dissection can be developed with precision and with decreased manipulation compared to standard techniques because of decreased physiological tremor. We have used this technique to excise tumors from the brain stem, spinal cord, and other critical neural locations.

Because technological advances are being made rapidly in medical laser research, it is likely that many more potential applications of lasers will be discovered. Each available laser system has unique characteristics that dictate its clinical use. More experimental work and clinical experience will be needed in order to fully understand the biological effects of these instruments so that they can be used for the maximum benefit of our patients.

Acknowledgment

We thank Neil Buckley for editorial assistance.

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    Bown SGStorey DWSwain Pet al: Controlled trial of argon laser photocoagulation for haemorrhage from peptic ulcers. Gut 22:A4141981 (Abstract)Bown SG Storey DW Swain P et al: Controlled trial of argon laser photocoagulation for haemorrhage from peptic ulcers. Gut 22:A414 1981 (Abstract)

  • 9.

    DiBartolomeo JREllis M: The argon laser in otology. Laryngoscope 90:178617961980DiBartolomeo JR Ellis M: The argon laser in otology. Laryngoscope 90:1786–1796 1980

  • 10.

    Dougherty TJ: Photoradiation therapy for bronchogenic cancer. Chest 81:2652661982Dougherty TJ: Photoradiation therapy for bronchogenic cancer. Chest 81:265–266 1982

  • 11.

    Escudero LHCastro AODrumond Met al: Argon laser in human tympanoplasty. Arch Otolaryngol 105:2522531979Escudero LH Castro AO Drumond M et al: Argon laser in human tympanoplasty. Arch Otolaryngol 105:252–253 1979

  • 12.

    Glasscock ME IIIJackson CGWhitaker SR: The argon laser in acoustic tumor surgery. Laryngoscope 91:140514161981Glasscock ME III Jackson CG Whitaker SR: The argon laser in acoustic tumor surgery. Laryngoscope 91:1405–1416 1981

  • 13.

    Hobeika CPRockwell RJ Jr: Argon laser microsurgery: its advantages and applications in otolaryngology. Laryngoscope 83:9609651973Hobeika CP Rockwell RJ Jr: Argon laser microsurgery: its advantages and applications in otolaryngology. Laryngoscope 83:960–965 1973

  • 14.

    Kelly PJAlker GJ Jr: A stereotactic approach to deep-seated central nervous system neoplasms using the carbon dioxide laser. Surg Neurol 15:3313341981Kelly PJ Alker GJ Jr: A stereotactic approach to deep-seated central nervous system neoplasms using the carbon dioxide laser. Surg Neurol 15:331–334 1981

  • 15.

    Kelly PJAlker GJ JrGoerss S: Computer-assisted stereotactic laser microsurgery for the treatment of intracranial neoplasms. Neurosurgery 10:3243311982Kelly PJ Alker GJ Jr Goerss S: Computer-assisted stereotactic laser microsurgery for the treatment of intracranial neoplasms. Neurosurgery 10:324–331 1982

  • 16.

    KellyPJAlker GJJrZoll JG: A microstereotactic approach to deep-seated arteriovenous malformations. Surg Neurol 17:2602621982Kelly PJ Alker GJ Jr Zoll JG: A microstereotactic approach to deep-seated arteriovenous malformations. Surg Neurol 17:260–262 1982

  • 17.

    Nashold BS JrOstdahl RH: Dorsal root entry zone lesions for pain relief. J Neurosurg 51:59691979Nashold BS Jr Ostdahl RH: Dorsal root entry zone lesions for pain relief. J Neurosurg 51:59–69 1979

  • 18.

    Nishiura IHanda HYamashita Jet al: Successful removal of a huge falcotentorial meningioma by use of the laser. Surg Neurol 16:3803851981Nishiura I Handa H Yamashita J et al: Successful removal of a huge falcotentorial meningioma by use of the laser. Surg Neurol 16:380–385 1981

  • 19.

    Perkins RC: Laser stapedotomy for otosclerosis. Laryngoscope 90:2282411980Perkins RC: Laser stapedotomy for otosclerosis. Laryngoscope 90:228–241 1980

  • 20.

    Rothauge CF: Urethroscopic recanalization of urethral stenosis using argon laser. Urology 16:1581611980Rothauge CF: Urethroscopic recanalization of urethral stenosis using argon laser. Urology 16:158–161 1980

  • 21.

    Strait TARobertson JHClark WC: Use of the carbon dioxide laser in the operative management of intracranial meningiomas: a report of twenty cases. Neurosurgery 10:4644671982Strait TA Robertson JH Clark WC: Use of the carbon dioxide laser in the operative management of intracranial meningiomas: a report of twenty cases. Neurosurgery 10:464–467 1982

  • 22.

    Swain CPBown SGStorey DWet al: Controlled trial of argon laser photocoagulation in bleeding peptic ulcers. Lancet 2:131313161981Swain CP Bown SG Storey DW et al: Controlled trial of argon laser photocoagulation in bleeding peptic ulcers. Lancet 2:1313–1316 1981

  • 23.

    Zweng HCFlocks M: Clinical experiences with laser photocoagulation. Fed Proc 24 (Suppl 14):65701965Zweng HC Flocks M: Clinical experiences with laser photocoagulation. Fed Proc 24 (Suppl 14):65–70 1965

  • 24.

    Zweng HCLittle HL: Argon laser photocoagulation in the treatment of disc new vessels in diabetic retinopathy. Aust J Ophthalmol 1:1011041973Zweng HC Little HL: Argon laser photocoagulation in the treatment of disc new vessels in diabetic retinopathy. Aust J Ophthalmol 1:101–104 1973

Cooper Medical Model 770 AMPL argon ion surgical laser system manufactured by Cooper Medical Corp., Lasersonics Division, 1255 Terra Belle Avenue, Mountain View, California 94043.

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Article Information

Address reprint requests to: Michael S. B. Edwards, M.D., % The Editorial Office, Department of Neurological Surgery, 350 Parnassus Avenue, Suite 807, San Francisco, California 94117.

© AANS, except where prohibited by US copyright law.

Headings

References

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Apfelberg DBKosek JMaser MRet al: Histology of port wine stains following laser treatment. Br J Plast Surg 32:2322371979Apfelberg DB Kosek J Maser MR et al: Histology of port wine stains following laser treatment. Br J Plast Surg 32:232–237 1979

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Apfelberg DBMaser MRLash H: Argon laser treatment of decorative tattoos. Br J Plast Surg 32:1411441979Apfelberg DB Maser MR Lash H: Argon laser treatment of decorative tattoos. Br J Plast Surg 32:141–144 1979

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Apfelberg DBMaser MRLash H: Extended clinical use of the argon laser for cutaneous lesions. Arch Dermatol 115:7197211979Apfelberg DB Maser MR Lash H: Extended clinical use of the argon laser for cutaneous lesions. Arch Dermatol 115:719–721 1979

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Bartal ADHeilbronn YDAvram Jet al: Carbon dioxide laser surgery of basal meningiomas. Surg Neurol 17:90951982Bartal AD Heilbronn YD Avram J et al: Carbon dioxide laser surgery of basal meningiomas. Surg Neurol 17:90–95 1982

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Beck OJ: The use of the Nd-YAG and the CO2 laser in neurosurgery. Neurosurg Rev 3:2612661980Beck OJ: The use of the Nd-YAG and the CO2 laser in neurosurgery. Neurosurg Rev 3:261–266 1980

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Boggan JEEdwards MSBDavis RLet al: Comparison of the brain tissue response in rats to injury by argon and carbon dioxide lasers. Neurosurgery 11:6096161982Boggan JE Edwards MSB Davis RL et al: Comparison of the brain tissue response in rats to injury by argon and carbon dioxide lasers. Neurosurgery 11:609–616 1982

8.

Bown SGStorey DWSwain Pet al: Controlled trial of argon laser photocoagulation for haemorrhage from peptic ulcers. Gut 22:A4141981 (Abstract)Bown SG Storey DW Swain P et al: Controlled trial of argon laser photocoagulation for haemorrhage from peptic ulcers. Gut 22:A414 1981 (Abstract)

9.

DiBartolomeo JREllis M: The argon laser in otology. Laryngoscope 90:178617961980DiBartolomeo JR Ellis M: The argon laser in otology. Laryngoscope 90:1786–1796 1980

10.

Dougherty TJ: Photoradiation therapy for bronchogenic cancer. Chest 81:2652661982Dougherty TJ: Photoradiation therapy for bronchogenic cancer. Chest 81:265–266 1982

11.

Escudero LHCastro AODrumond Met al: Argon laser in human tympanoplasty. Arch Otolaryngol 105:2522531979Escudero LH Castro AO Drumond M et al: Argon laser in human tympanoplasty. Arch Otolaryngol 105:252–253 1979

12.

Glasscock ME IIIJackson CGWhitaker SR: The argon laser in acoustic tumor surgery. Laryngoscope 91:140514161981Glasscock ME III Jackson CG Whitaker SR: The argon laser in acoustic tumor surgery. Laryngoscope 91:1405–1416 1981

13.

Hobeika CPRockwell RJ Jr: Argon laser microsurgery: its advantages and applications in otolaryngology. Laryngoscope 83:9609651973Hobeika CP Rockwell RJ Jr: Argon laser microsurgery: its advantages and applications in otolaryngology. Laryngoscope 83:960–965 1973

14.

Kelly PJAlker GJ Jr: A stereotactic approach to deep-seated central nervous system neoplasms using the carbon dioxide laser. Surg Neurol 15:3313341981Kelly PJ Alker GJ Jr: A stereotactic approach to deep-seated central nervous system neoplasms using the carbon dioxide laser. Surg Neurol 15:331–334 1981

15.

Kelly PJAlker GJ JrGoerss S: Computer-assisted stereotactic laser microsurgery for the treatment of intracranial neoplasms. Neurosurgery 10:3243311982Kelly PJ Alker GJ Jr Goerss S: Computer-assisted stereotactic laser microsurgery for the treatment of intracranial neoplasms. Neurosurgery 10:324–331 1982

16.

KellyPJAlker GJJrZoll JG: A microstereotactic approach to deep-seated arteriovenous malformations. Surg Neurol 17:2602621982Kelly PJ Alker GJ Jr Zoll JG: A microstereotactic approach to deep-seated arteriovenous malformations. Surg Neurol 17:260–262 1982

17.

Nashold BS JrOstdahl RH: Dorsal root entry zone lesions for pain relief. J Neurosurg 51:59691979Nashold BS Jr Ostdahl RH: Dorsal root entry zone lesions for pain relief. J Neurosurg 51:59–69 1979

18.

Nishiura IHanda HYamashita Jet al: Successful removal of a huge falcotentorial meningioma by use of the laser. Surg Neurol 16:3803851981Nishiura I Handa H Yamashita J et al: Successful removal of a huge falcotentorial meningioma by use of the laser. Surg Neurol 16:380–385 1981

19.

Perkins RC: Laser stapedotomy for otosclerosis. Laryngoscope 90:2282411980Perkins RC: Laser stapedotomy for otosclerosis. Laryngoscope 90:228–241 1980

20.

Rothauge CF: Urethroscopic recanalization of urethral stenosis using argon laser. Urology 16:1581611980Rothauge CF: Urethroscopic recanalization of urethral stenosis using argon laser. Urology 16:158–161 1980

21.

Strait TARobertson JHClark WC: Use of the carbon dioxide laser in the operative management of intracranial meningiomas: a report of twenty cases. Neurosurgery 10:4644671982Strait TA Robertson JH Clark WC: Use of the carbon dioxide laser in the operative management of intracranial meningiomas: a report of twenty cases. Neurosurgery 10:464–467 1982

22.

Swain CPBown SGStorey DWet al: Controlled trial of argon laser photocoagulation in bleeding peptic ulcers. Lancet 2:131313161981Swain CP Bown SG Storey DW et al: Controlled trial of argon laser photocoagulation in bleeding peptic ulcers. Lancet 2:1313–1316 1981

23.

Zweng HCFlocks M: Clinical experiences with laser photocoagulation. Fed Proc 24 (Suppl 14):65701965Zweng HC Flocks M: Clinical experiences with laser photocoagulation. Fed Proc 24 (Suppl 14):65–70 1965

24.

Zweng HCLittle HL: Argon laser photocoagulation in the treatment of disc new vessels in diabetic retinopathy. Aust J Ophthalmol 1:1011041973Zweng HC Little HL: Argon laser photocoagulation in the treatment of disc new vessels in diabetic retinopathy. Aust J Ophthalmol 1:101–104 1973

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