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Dudley S. Dinner, Hans Lüders, Ronald P. Lesser, Harold H. Morris, Gene Barnett and G. Klem

✓ The relationship of intraoperative monitoring of spinal cord somatosensory evoked potentials and postoperative deficit in 220 cases (121 with scoliosis, 41 with neoplasms, and 58 others) is reported. Bilateral posterior tibial nerve stimulation was used in 181 cases and unilateral median nerve stimulation in 39. Spinal cord (interspinous ligament needles), subcortical (neck surface), and cortical (scalp surface) SEP's were monitored. Seven patients had worsening of neurological function after surgery, three of whom demonstrated significant changes in SEP's monitored. In an additional four cases, there was more than a 50% decrease in amplitude of subcortical/cortical SEP's during monitoring, but no change in neurological status postoperatively. Combined monitoring of spinal cord, subcortical, and cortical SEP's enhanced the certainty of detecting spinal cord dysfunction even though there was a significant number of false-negative and false-positive results. A marked change in the SEP's indicated a high chance of developing a neurological deficit (three or 43% of seven cases), and if there was no change the chance of any neurological postoperative deficit was extremely low (four or 1.87% of 213 cases). These data justify the use of intraoperative SEP monitoring.

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Gene H. Barnett, Russell W. Hardy Jr., John R. Little, Janet W. Bay and George W. Sypert

✓ Hypertrophy of the posterior spinal elements leading to compromise of the spinal canal and its neural elements is a well-recognized pathological entity affecting the lumbar or cervical spine. Such stenosis of the thoracic spine in the absence of a generalized rheumatological, metabolic, or orthopedic disorder, or a history of trauma is generally considered to be rare. Over a 2-year period the authors have treated six cases of thoracic myelopathy associated with thoracic canal stenosis. In four patients the deficits developed gradually and painlessly. The three older patients had a clinical profile characterized by complaints of pseudoclaudication, spastic lower limbs, and evidence of posterior column dysfunction. Two patients were younger adults with low thoracic myelopathy associated with local back pain after minor trauma. Both patients also had congenital narrowing of the thoracic spinal canal.

Oil and metrizamide contrast myelography in the prone position were of limited value in diagnosing this condition; in fact, myelography may be misleading and result in erroneous diagnosis of thoracic disc protrusion, when the principal problem is dorsal and lateral compression from hypertrophied facets. Magnetic resonance imaging and computerized tomography sector scanning were more useful in the diagnosis of this disorder than was myelography. Thoracic canal stenosis may be more common than is currently recognized and account for a portion of the failures in anterior and lateral decompression of thoracic disc herniations.

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Gene H. Barnett, Allan H. Ropper and Keith A. Johnson

✓ Magnetic resonance (MR) imaging has been largely restricted to patients who are neurologically and hemodynamically stable. The strong magnetic field and radiofrequency transmissions involved in acquiring images are potential sources of interference with monitoring equipment. A method of support and physiological monitoring of critically ill neurosurgical and neurological patients during MR imaging using a 0.6-tesla MR system is reported. This technique has not caused degradation of the MR image due to electrical interference. Adequate preparation and precautions allow many critically ill neurosurgical and neurological patients to safely undergo MR imaging.

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Gene H. Barnett, Allan H. Ropper and June Romeo

✓ The relationship between intracranial pressure (ICP) and outcome was studied in 10 adults with encephalitis. Eight had biopsy-proven herpes simplex encephalitis, one had acute hemorrhagic leukoencephalitis, and in one case the cause of encephalitis was unknown. Monitoring of ICP was instituted because of clinical deterioration or computerized tomography evidence of brain swelling, and was begun a mean of 7 days after the orlset of symptoms and continued for a mean of 9 days.

All five survivors, but only one of the five fatalities, had an initial ICP of less than 12 mm Hg (p < 0.05). Four patients with a mean daily ICP of less than 20 mm Hg survived, whereas five of six patients with higher ICP's died (p < 0.05). Peak ICP did not occur until the 12th day of illness on average. The Glasgow Coma Scale score at the time the ICP monitor was inserted did not correlate with outcome. Intracranial pressure monitoring in severe encephalitis may be a useful adjunct for therapy and an indicator of prognosis.

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Jeffrey V. Rosenfeld, Gene H. Barnett, Cathy A. Sila, John R. Little, Emmanuel L. Bravo and Gerald J. Beck

✓ Atrial natriuretic factor (ANF) is a diuretic natriuretic peptide hormone produced by both the heart and brain which has been postulated to play a role in the hemodynamic and sodium instability that frequently follows subarachnoid hemorrhage (SAH). Levels of ANF were measured in 12 patients with nontraumatic SAH and nine control patients with unruptured cerebral aneurysms. At surgery, the mean plasma ANF level (± standard deviation) of the SAH group was significantly higher than that of the control group (158.1 ± 83.8 vs. 57.8 ± 45.3 pg/ml, respectively; p = 0.01). There was no significant difference in serum sodium concentration, blood pressure, or central venous pressure between these groups. Nine patients with SAH due to aneurysm rupture had plasma ANF levels similar to those in three patients with SAH due to other causes. Four patients with moderate to severe SAH had significantly higher mean cerebrospinal fluid (CSF) ANF values (17.7 ± 12.8 pg/ml) than five patients with minimal SAH (0.6 ± 0.9 pg/ml) or the control group of nine patients (3.7 ± 1.3 pg/ml) (p < 0.05). Five patients with moderate to severe SAH had significantly higher plasma ANF values (202.6 ± 72.2 pg/ml) than five with minimal SAH (86.8 ± 29.2 pg/ml) or the control group (57.8 ± 45.3 pg/ml) (p < 0.05). Plasma ANF values were substantially higher than CSF ANF content in the SAH group (p < 0.01) and in the control group (p = 0.05).

From these data it is concluded that: 1) plasma ANF is elevated significantly after SAH; 2) this rise appears unrelated to the cause of hemorrhage, serum sodium concentration, blood pressure, or central venous pressure, but is related to the extent of the hemorrhage; 3) ANF concentrations in the CSF are significantly lower than in plasma, and are elevated after moderate to severe SAH; and 4) the source of CSF ANF is probably the plasma, and the source of plasma ANF is likely the heart.

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Issam A. Awad and Gene H. Barnett

✓ The mechanism of nonhemorrhagic neurological deterioration from spinal arteriovenous malformation (AVM) and the role of acute surgical intervention in this setting are not well understood. The case is described of a 65-year-old man who presented with a 2-year history of mild gait spasticity and vague sensory complaints affecting both lower extremities. Following a diagnostic lumbar puncture, these symptoms progressed painlessly over a 4-day period to total motor paraplegia, urinary retention, and hypesthesia in all modalities with a midthoracic sensory level. Magnetic resonance imaging showed a probable spinal AVM but no evidence of hemorrhage or cord compression. Spinal angiography confirmed the diagnosis of spinal AVM fed by radicular branches of left T-7 and T-8 segmental intercostal arteries. Drainage was via long dorsal veins caudally. Emergency laminectomy with intradural exploration was performed. There was no evidence of prior hemorrhage or focal mass effect, although the cerebrospinal fluid pressure was elevated. The dural component of the spinal AVM was excised, and its communications with the spinal cord were disconnected intradurally. Neurological function started improving within 6 hours of the patient awakening from anesthesia. He had achieved antigravity strength in every muscle group of the lower extremities by the time of discharge to a rehabilitation center 10 days after surgery. Three months postoperatively, he was ambulating with a walker and was continent of urine and stool. Possible pathophysiological mechanisms are discussed in light of the favorable response to timely surgical intervention.

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Marc I. Chimowitz, Gene H. Barnett and Joann Palmer

✓ Of 165 consecutive patients undergoing computerized tomography- or magnetic resonance imaging-guided stereotactic brain biopsies at the Cleveland Clinic between June, 1987, and November, 1989, four patients (2.4%) developed arterial hemorrhage refractory to conventional efforts to secure hemostasis. Craniotomy was performed in one of these patients to control the hemorrhage; in the other three, 0.5 to 2 cc of thrombin (5000 U/cc) was slowly injected via the biopsy cannula, resulting in immediate control of bleeding in all three cases. Postoperatively, the first two patients treated with 1 to 2 cc of thrombin were slow to awaken; one had evidence of vasospasm by transcranial Doppler ultrasound studies and multiple infarcts on cranial computerized tomography, while the other had a moderate-sized frontal hematoma with intracranial hypertension. After prolonged recovery periods, only mild neurological deficits persisted in both patients. The third patient, treated with 0.5 cc of thrombin, had an uneventful postoperative course. Thrombin is highly effective for stopping intractable arterial hemorrhage during stereotactic brain biopsy; however, it is a vasospastic agent and may have been responsible for the cerebral infarctions in one patient. Therefore, thrombin should be used only as a last resort, short of craniotomy, to control intractable arterial hemorrhage during stereotactic brain biopsy.

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Gene H. Barnett, Donald W. Kormos, Charles P. Steiner and Joe Weisenberger

✓ A technique of “frameless” stereotaxy that allows real-time intraoperative neurosurgical localization is described. The system is composed of four components: a hand-held probe containing two ultrasonic emitters, a microphone array that is rigidly affixed to the operating table in proximity to the surgical field, hardware to control and detect timing of signal production and reception, and a color graphics computer workstation with software to calculate and present the location of the probe tip on reconstructed neuroimaging studies. Unlike previously reported mechanical or sonic navigational devices, this system is adaptable to a wide array of neurosurgical instruments, allows free movement of the operating table and conventional patient draping, and has accuracy in the hostile operating room environment that rivals that of frame stereotaxy.

In the operating room environment, using four pulse pairs with the wand positioned optimally, reproducibility of a point in space is ± 0.6 mm. The wand has a broad range of orientations that maintain error at or below 1.0 mm. The mean error when measuring distances within a 1000-cu cm cube is 1.1 ± 1.0 mm (1.0% ± 0.7%). The ability to localize a fourth point (a target) in space is typically within 1.5 mm (using computerized tomography scans with a 1-mm slice thickness) but is dependent on several variables. This technology provides a powerful yet flexible tool in the neurosurgical operating room.