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Stephen K. Powers and Charles B. Wilson

✓ The case of a patient with two separate prolactin-secreting pituitary adenomas is presented. The importance of thorough inspection of the pituitary gland at operation is emphasized.

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Stephen K. Powers, Catherine A. Bolger and Michael S. B. Edwards

✓ Using a CO2 laser, discrete thoracic spinal cord lesions were made in cats anesthetized with ketamine and xylazine (Rompun). Differences in cortical somatosensory evoked potentials (SEP's) produced with high-intensity stimulation (20 times the motor threshold) of each posterior tibial nerve were determined for nine different combinations of unilateral spinal cord lesions.

The results of these studies show that nerve fibers in the ipsilateral dorsal column, the ipsilateral dorsal spinocerebellar tract, and the contralateral ventrolateral tracts with respect to the side of leg stimulation, contribute to cortical SEP's. A lesion of the dorsal spinocerebellar tract affected only the early waves (< 30 msec) of the SEP from leg stimulation ipsilateral to the side of the lesion, whereas a solitary lesion of the ventrolateral tract caused changes primarily in the amplitude of later waves (> 30 msec) of the SEP produced by contralateral leg stimulation. Lesions involving one-half of the dorsal column caused changes in the amplitude of both the early and late waves produced by stimulation ipsilateral to the side of the lesion. The effects of various combinations of lesions on the cortical SEP's were not additive, which indicates significant interaction between afferent pathways.

These findings suggest that high-intensity peripheral nerve stimulation, which activates both C and A fibers, could be used intraoperatively to assess spinal cord function with more accuracy than the current practice of using a stimulus strength of twice the motor threshold. The importance of using anesthetic agents that do not depress cortical activity (which may affect the later components of the SEP) is also emphasized.

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Stephen K. Powers, David Norman and Michael S. B. Edwards

✓ Nine patients with a peripheral nerve lesion (six intrinsic and three extrinsic) were evaluated with computerized tomography (CT). In all but one instance, the CT scans gave useful information regarding the anatomical location, size, and relationship of the lesion to surrounding structures. These cases illustrate the usefulness of CT as a diagnostic tool in the evaluation of peripheral nerve lesions.

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Stephen K. Powers, Michael S. B. Edwards, James E. Boggan, Lawrence H. Pitts, Philip H. Gutin, Yoshio Hosobuchi, John E. Adams and Charles B. Wilson

✓ 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.

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Stephen K. Powers, John E. Adams, Michael S. B. Edwards, James E. Boggan and Yoshio Hosobuchi

✓ Argon and carbon dioxide microsurgical lasers were used to produce lesions in the dorsal root entry zone (DREZ) experimentally in six cats and surgically in 21 patients who had denervation pain syndromes. The technique of producing lesions, the histological and physiological changes seen in the cat spinal cord, and the results of treatment in the clinical series are discussed. Lesions were produced within the DREZ without new involvement of the dorsal column system or corticospinal tract in all but one patient. Based on their subjective evaluation, two-thirds of the patients were relieved of more than 50% of their preoperative pain. These experimental results and clinical experience suggest that the argon and carbon dioxide lasers effectively produce localized microsurgical lesions in the DREZ. The concept that an abnormality involving either neurons in the substantia gelatinosa or internuncial fibers in Lissauer's tract is responsible for pain in patients with primary sensory nerve deafferentation is discussed.

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Stefan Pribil and Stephen K. Powers

✓ Microvascular end-to-end anastomoses of rat common carotid arteries measuring 0.6 to 0.7 mm in diameter were performed using an argon surgical laser system. Vascular bonding with the argon laser was accomplished in all cases. The anastomosed carotid artery segments were evaluated both angiographically and histologically at 1 day, 1 week, and 1 month after laser bonding. With increasing time after anastomosis, there was a trend toward increasing angiographically proven stenosis of the anastomotic segment and histologically demonstrated pseudoaneurysm formation of the vessel wall at the bonded site. Pseudoaneurysm formation was associated with a dense inflammatory response in the anastomotic vessel segment. In spite of excellent initial tissue bonding and vessel patency, the delayed results of progressive vessel wall disruption and segmental stenosis indicate that further experience in using the argon laser for vessel welding is needed before this method can be accepted as an alternative to current microvascular suture technique.

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Stephen K. Powers, Stefan Pribil, G. Yancey Gillespie III and Pamela J. Watkins

✓ The photochemotherapeutic effect of the mitochondria-specific dye rhodamine-123 (Rh-123) on human glioma cells in culture was studied. Cultured U-251MG glioma cells were incubated for 30 minutes in 10 µg/ml of Rh-123 and then exposed to blue-green light between 488 and 514.5 nm using a continuous-wave argon laser. Cells that were treated with Rh-123 and the argon laser at power densities less than 200 mW/sq cm demonstrated increasing tumor-cell killing with increasing time of exposure to laser light. Tumor-cell killing achieved with power densities of light less than 200 mW/sq cm was shown to be due solely to a photochemical effect and not to a direct (thermal) effect of the laser. The photochemical effect was dependent upon the intracellular concentration of Rh-123 and the length of light exposure, and not the intensity of light. The selective retention of Rh-123 by glioma cells and its exclusion from normal cells in conjunction with its photoactivated cytotoxicity suggest that Rh-123 may be a useful photosensitizing drug for the treatment of malignant gliomas in situ.

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Stephen K. Powers, William C. Beckman Jr., J. Tony Brown and Linda C. Kolpack

✓ The effect of interstitial laser photochemotherapy with the mitochondrial-specific intravital dye rhodamine-123 (Rh-123) was studied using a malignant rat glioma model system (RT2). Tumors were transplanted subcutaneously into the flank of athymic mice and into the cerebrum of adult rats. The Rh-123 photosensitization was produced by direct intratumoral injection of Rh-123 into the mouse RT2 flank tumors and by intravenous Rh-123 administration to adult rats with implanted RT2 intracerebral tumors. Intratumoral irradiation with 150 mW of argon laser light for an exposure time of 15 minutes was performed using a conical sapphire-tipped quartz optical fiber. Control groups of animals received either no treatment, Rh-123 injections, or administration of 150 mW of argon laser light for 15 minutes. Both flank and intracerebral tumors showed progressive diminution in size after treatment with Rh-123 photochemotherapy. There was no evidence of tumor recurrence in 60% of Rh-123 photochemotherapy-treated tumors. Recurrences in tumors treated with Rh-123 photochemotherapy usually appeared at the periphery of the original tumor at 10 days after treatment. Histologically, photochemotherapy-treated intracerebral tumors showed progressive shrinkage with increasing tumor necrosis over time. The finding of residual or recurrent tumor at the periphery of the original tumor mass suggests that the lack of penetration of the blue-green (argon) light was responsible for preventing complete tumor ablation. Our results suggest that Rh-123 photochemotherapy can destroy malignant gliomas in vivo; however, the poor penetrability of the photoactivating blue-green light may limit the effectiveness of this treatment for large or extensively invasive tumors.

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John J. Gartman, Thomas E. Melin, W. Thomas Lawrence and Stephen K. Powers

✓ The authors describe the case of a male infant who was diagnosed prenatally as having iniencephaly. Since birth, the child has grown, thrived, and undergone two successful operations to correct his cervical deformity. This case demonstrates that the iniencephaly defect is not uniformly fatal and that neurosurgical intervention may offer significant improvement in the cervical deformity.