The Role of Endoscopic Assisted Microneurosurgery (Image Fusion Technology) in the Performance of Neurosurgical Procedures

The use of endoscopic techniques has gained significant popularity over the past decade. The potential advantages of angled lenses to visualize around tight corridors without retracting have proven to be an attractive feature. The limitation of endoscopy has been the inability to obtain a true three-dimensional perspective for which microscopy is ideal. Therefore we postulated that for complex intradural lesions the merger of the two technologies would prove to be ideal. In this paper we report our experience with simultaneous microscopy and endoscopy, using picture-in-picture technology, for intracranial vascular and oncological surgery. We have found it useful to offer enough visualization to allow for performing surgery and not just for inspection.

The role of somatosensory evoked potentials in the evaluation of spinal cord retethering

Early detection of clinically significant spinal cord retethering is of paramount importance for the preservation of neurologic function in patients with repaired spinal dysraphic lesions. We retrospectively analyzed 90 children who were followed with serial peroneal somatosensory evoked potentials (SEPs) after a repair of their spinal dysraphic lesions with the objective of evaluating whether SEPs were a useful way of monitoring these children to facilitate early detection of clinically significant retethering. Three hundred and nine studies were performed on these children yielding a mean of 3.4 studies per patient. The median time between SEP studies was 13 months. A clinical examination was performed at the time each SEP was done. Sixty-one patients (68%) had a myelomeningocele; 25 (28%) had a lipomyelomeningocele while other types of dysraphic lesions were found in the remaining 4%. Nineteen patients (21%) had no change in serial SEPs; 7 of these 19 (37%) had a deterioration in clinical status while the SEPs were stable. Twenty-six patients (29%) showed improvement in serial SEPs, however, 3 of the 26 had clinical worsening at the time SEPs improved. SEPs deteriorated in 45 patients (50%); 13 of the 45 had an associated clinical deterioration, and the remaining 32 were stable clinically. Twenty-three patients (26%) had a clinical deterioration; of these only 13 had a corresponding deterioration in SEPs, 7 patients had stable SEPs while 3 had improvement in SEPs at the time of clinical deterioration. This results in a false-positive rate of 71% and a false-negative rate of 43%. We conclude that serial SEPs do not correlate well with clinical status and are not a useful modality for monitoring patients at risk for retethering.

Radiobiologic models for radiosurgery

A series of initial radiobiologic investigations have been performed using three animal models. The baboon model proved to be a valuable technique to assess the in vivo radiobiologic response of single-fraction irradiation doses delivered to the primate brain stem. Multimodality neurodiagnostic testing, including CT, MR imaging, xenon-enhanced CT, evoked potential studies, and analysis of CSF myelin basic protein levels, all of which eventually were correlated with neuropathologic examination, enabled detection of lesions produced with high-dose (150 Gy) radiosurgery as early as 6 weeks. Within the first 6 months after radiosurgery, lower doses (20 Gy, 50 Gy) did not result in clinically or neurodiagnostically detectable lesions. The rat arteriovenous fistula model permits analysis of the delayed histopathologic effects of radiosurgery on an experimentally created fistula designed to mimic an AVM. The rat C6 glioma model is designed to evaluate the effect of radiosurgery in an infiltrative tumor that simulates a human malignant brain tumor. These studies are intended eventually to increase our knowledge about the safety and efficacy of radiosurgery in both the normal and tumor-implanted brains. We believe that such fundamental studies ultimately will improve our ability to reach the goals of radiosurgery: to destroy the target and spare the surrounding brain. Eventually, it may become feasible to achieve these goals by combining radiosurgical technique with both radiation sensitizers (for the treated volume) and brain protectors.

Recurrent spinal cord injury without radiographic abnormalities in children

Spinal cord injury without radiographic abnormality is a well-known entity in the pediatric age group. Age-related elasticity of the vertebral ligaments as well as immaturity of the osseous structures in the pediatric spine allow momentary subluxation in response to deforming forces. The resultant neurological injuries range from transient dorsal column dysfunction to complete cord transection. Between 1960 and 1985, 42 such injuries were treated at the Children's Hospital of Pittsburgh. Management of these radiographically occult spinal cord injuries consisted of cervical immobilization for 2 months in a hard collar and restriction of contact sports. Recurrent cord injury occurred in eight cases during the 2-month immobilization period. A clearly defined traumatic episode was identified in seven of the eight patients, although in four children the recurrent trauma to the spine was trivial. Five of the children removed their collars briefly before the second injury, and two children incurred reinjury with the hard collar in place. The remaining child was too young for hard-collar immobilization, and recurrent neurological deterioration occurred during sleep. Serial flexion-extension films failed to detect frank instability in any of the eight cases. The children most susceptible to reinjury were those who sustained mild or transient neurological deficits from an initial cord injury and who rapidly resumed normal activities. Radiographically occult spinal instability resulting from the initial injury to the vertebral and paravertebral soft tissues presumably made these children vulnerable to recurrent spinal cord injury, often from otherwise insignificant trauma. During the last 21 months, 12 additional children have been managed with a more stringent protocol combining neck immobilization in a rigid cervical brace for 3 months and restriction of both contact and noncontact sports, together with a major emphasis on patient compliance. With this new protocol, no recurrent cord injuries have been documented.

Sensory information processing in patients with nonalcoholic cirrhosis. Short-latency visual, auditory, and somatosensory event-related potentials

Visual, auditory and brainstem event-related potentials were obtained from patients with hepatocellular and cholestatic disease and a control group of normal subjects. The results did not reveal systematic neurophysiologic disturbances in persons with well compensated cirrhosis. It is concluded that short-latency event-related potentials are rather insensitive for detecting subclinical hepatic encephalopathy.