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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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James E. Boggan, Catherine Bolger, and Michael S. B. Edwards

✓ Intracerebral tumors were produced in 99 rats by stereotaxic implantation of 9L gliosarcoma brain-tumor cells. Hematoporphyrin derivative (HPD), 10 or 20 mg/kg, was administered as an intravenous bolus 24 or 48 hours before irradiation of the tumor region with light from an argon pumped-dye laser (632 nm). Laser light, at a dose of 30, 60, or 200 joules/sq cm, was delivered through a craniectomy 10 or 13 days after tumor implantation. Survival times were significantly prolonged in rats exposed to laser light at a dose of 200 joules/sq cm 24 hours after administration of HPD, 20 mg/kg.

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Stanley Hoang, Omar Choudhri, Michael Edwards, and Raphael Guzman

A vein of Galen malformation is a rare intracranial vascular lesion affecting the pediatric population. Its poor prognosis has been significantly improved with the development of endovascular embolization. In this paper the authors review the developmental mechanisms, clinical pathophysiology, and the available data on the management and outcome of the disease.

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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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Brian T. Andrews, Michael S. B. Edwards, and Peter Gannon

✓ Spontaneous thrombosis of aneurysms occurs rarely in children, and, to our knowledge, there are no reports of aneurysms presenting as an embolic event in a child. We describe the case of a 3-year-old boy whose symptoms initially suggested an ischemic event to the dominant hemisphere. Initial computerized tomography scans indicated an intracranial hemorrhage. Subsequent radiographic study revealed evidence of emboli and, at exploration, a large acutely thrombosed aneurysm of the left middle cerebral artery associated with arterial occlusion was found. Entrapment of the aneurysm and thrombectomy provided excellent operative results.

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Stanley L. Barnwell and Michael S. B. Edwards

✓ The case of an 11-year-old boy is reported in whom two intramedullary lesions developed at the thoracic-cervical and thoracic-lumbar junctions 2½ years after resection and irradiation of a medulloblastoma in the posterior fossa. There was no evidence of subarachnoid spread of the tumor. Magnetic resonance imaging was used to localize these lesions, and provided much better diagnostic information than either computerized tomography scans or myelograms.

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Michael S. B. Edwards, James E. Boggan, and Terry A. Fuller

✓ The use of lasers in neurosurgical procedures has received a great deal of attention recently. Surgical use of lasers has been viewed with suspicion and skepticism, probably because of (justified) apprehensions about the misuse of lasers in early work and about the ways in which laser light affects tissues, and a lack of understanding of the basic physics and practical operation of lasers. The authors review the physics, biophysics, experimental findings, and operative use of lasers in current neurosurgical practice, and discuss briefly their experience gained in over 150 neurosurgical procedures using the carbon dioxide and argon surgical lasers.

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Griffith Rutherford Harsh IV, Michael S. B. Edwards, and Charles B. Wilson

✓ The clinical and radiographic findings, surgical treatment, and outcome in 16 pediatric patients with intracranial arachnoid cysts are reviewed. The clinical presentation reflected the anatomical location of the lesions. Computerized tomography or magnetic resonance imaging scans were diagnostic in all cases. Of the nine cysts treated primarily or secondarily by craniotomy for fenestration and drainage into the basilar cisterns, five recurred. Cyst-peritoneal shunting led to diminished cyst size and clinical improvement in all seven cases in which it was used as the initial treatment and in all four cases in which fenestration had been unsuccessful. The results in this series show that cyst-peritoneal shunting is the treatment of choice for most intracranial arachnoid cysts in children.