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Thomas J. Croft, Jerald S. Brodkey, and Frank E. Nulsen

✓ Cortical evoked potentials in anesthetized cats were recorded by a noninvasive averaging technique as a means of estimating spinal cord damage. Graded pressure on the spinal cord produced reversible blocking of these potentials. With this type of trauma, block of motor transmission through the cord paralleled the block of sensory transmission, and each seemed to be a sensitive indicator of spinal cord function. The possible use of such monitoring in anesthetized patients undergoing spinal operations is discussed.

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Thomas L. Ellis, William A. Friedman, Frank J. Bova, Paul S. Kubilis, and John M. Buatti

Object. The aim of this study was to evaluate the causes of treatment failure in patients with arteriovenous malformations (AVMs) who underwent radiosurgery, which is increasingly used as a treatment method for selected, surgically high-risk AVMs. Unfortunately, radiosurgical treatment fails in a small but significant percentage of patients. In the time period covered in this study, 72 patients attained angiographically confirmed cures after radiosurgery and 36 were retreated after the initial radiosurgical treatment failed.

Methods. Using a computerized image fusion technique, the initial radiosurgical dosimetry plan was superimposed on the remaining AVM nidus at the time of retreatment. Twenty-six percent of the retreated cases were found to have AVM niduses outside the original treatment isodose line, which means that targeting error was a factor. The retreated group was also statistically compared with the cured group.

Conclusions. Multivariate analysis revealed that the following factors were statistically significant predictors of treatment failure: increasing AVM size, decreasing treatment dose, and increasing Spetzler—Martin grade.

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Aaron Mohanty, Thomas S. Frank, Sharif Mohamed, Kristalynne Godwin, and Gautam G. Malkani

OBJECTIVE

The advent of endoscopic synostectomy has enabled early surgery for infants with craniosynostosis. Even though diagnosis is often made at birth, endoscopic synostectomy has traditionally been delayed until the infant is 3 months of age. There have been very few published reports of this procedure being performed in the early neonatal period. The authors discuss their experience with ultra-early endoscopic synostectomy, defined as an operation for infants aged 8 weeks or younger.

METHODS

A retrospective analysis of infants who underwent operations at or before 8 weeks of age between 2011 and 2020 was done.

RESULTS

Twenty-five infants underwent operations: 11 were 2 weeks of age or younger, 8 were between 3 and 4 weeks of age, and 6 were between 5 and 8 weeks of age. The infants weighed between 2.25 and 4.8 kg. Eighteen had single-suture synostosis, and 7 had multiple sutures involved. Of these 7, 4 had syndromic craniosynostosis. The average operative time was 35 minutes, and it was less than 40 minutes in 19 cases. The estimated operative blood loss was 25 ml or less in 19 cases; 5 infants required an intraoperative blood transfusion. In 1 child with syndromic multisuture craniosynostosis, the surgery was staged due to blood loss. Two children experienced complications related to the procedure: one had an incidental durotomy with skin infection, and the other had postoperative kernicterus. All infants were fitted for cranial remodeling orthoses following surgery. Three of the 25 infants required reoperations, with 2 patients with syndromic craniosynostosis needing repeat surgery for cranial volume expansion and cosmetic appearance. Another child with syndromic craniosynostosis is awaiting cranial expansion surgery. Follow-up varied between 6 months and 8 years.

CONCLUSIONS

The data show that ultra-early synostectomy is safe and not associated with increased complications compared with surgery performed between 3 and 6 months of age. Infants with multisuture synostosis had increased operative time, required blood transfusion, and were more likely to require a second operation.

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Thomas J. Buell, Shay Bess, Ming Xu, Frank J. Schwab, Virginie Lafage, Christopher P. Ames, Christopher I. Shaffrey, and Justin S. Smith

OBJECTIVE

Proximal junctional kyphosis (PJK) is, in part, due to altered segmental biomechanics at the junction of rigid instrumented spine and relatively hypermobile non-instrumented adjacent segments. Proper application of posteriorly anchored polyethylene tethers (i.e., optimal configuration and tension) may mitigate adjacent-segment stress and help prevent PJK. The purpose of this study was to investigate the impact of different tether configurations and tensioning (preloading) on junctional range-of-motion (ROM) and other biomechanical indices for PJK in long instrumented spine constructs.

METHODS

Using a validated finite element model of a T7–L5 spine segment, testing was performed on intact spine, a multilevel posterior screw-rod construct (PS construct; T11–L5) without tether, and 15 PS constructs with different tether configurations that varied according to 1) proximal tether fixation of upper instrumented vertebra +1 (UIV+1) and/or UIV+2; 2) distal tether fixation to UIV, to UIV−1, or to rods; and 3) use of a loop (single proximal fixation) or weave (UIV and/or UIV+1 fixation in addition to UIV+1 and/or UIV+2 proximal attachment) of the tether. Segmental ROM, intradiscal pressure (IDP), inter- and supraspinous ligament (ISL/SSL) forces, and screw loads were assessed under variable tether preload.

RESULTS

PS construct junctional ROM increased abruptly from 10% (T11–12) to 99% (T10–11) of baseline. After tethers were grouped by most cranial proximal fixation (UIV+1 vs UIV+2) and use of loop versus weave, UIV+2 Loop and/or Weave most effectively dampened junctional ROM and adjacent-segment stress. Different distal fixation and use of loop versus weave had minimal effect. The mean segmental ROM at T11–12, T10–11, and T9–10, respectively, was 6%, 40%, and 99% for UIV+1 Loop; 6%, 44%, and 99% for UIV+1 Weave; 5%, 23%, and 26% for UIV+2 Loop; and 5%, 24%, and 31% for UIV+2 Weave.

Tethers shared loads with posterior ligaments; consequently, increasing tether preload tension reduced ISL/SSL forces, but screw loads increased. Further attenuation of junctional ROM and IDP reversed above approximately 100 N tether preload, suggesting diminished benefit for biomechanical PJK prophylaxis at higher preload tensioning.

CONCLUSIONS

In this study, finite element analysis demonstrated UIV+2 Loop and/or Weave tether configurations most effectively mitigated adjacent-segment stress in long instrumented spine constructs. Tether preload dampened ligament forces at the expense of screw loads, and an inflection point (approximately 100 N) was demonstrated above which junctional ROM and IDP worsened (i.e., avoid over-tightening tethers). Results suggest tether configuration and tension influence PJK biomechanics and further clinical research is warranted.

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Thomas H. Jones, Richard B. Morawetz, Robert M. Crowell, Frank W. Marcoux, Stuart J. FitzGibbon, Umberto DeGirolami, and Robert G. Ojemann

✓ An awake-primate model has been developed which permits reversible middle cerebral artery (MCA) occlusion during physiological monitoring. This method eliminates the ischemia-modifying effects of anesthesia, and permits correlation of neurological function with cerebral blood flow (CBF) and neuropathology. The model was used to assess the brain's tolerance to focal cerebral ischemia. The MCA was occluded for 15 or 30 minutes, 2 to 3 hours, or permanently. Serial monitoring evaluated neurological function, local CBF (hydrogen clearance), and other physiological parameters (blood pressure, blood gases, and intracranial pressure). After 2 weeks, neuropathological evaluation identified infarcts and their relation to blood flow recording sites.

Middle cerebral artery occlusion usually caused substantial decreases in local CBF. Variable reduction in flow correlated directly with the variable severity of deficit. Release of occlusion at up to 3 hours led to clinical improvement. Pathological examination showed microscopic foci of infarction after 15 to 30 minutes of ischemia, moderate to large infarcts after 2 to 3 hours of ischemia, and in most cases large infarcts after permanent MCA occlusion. Local CBF appeared to define thresholds for paralysis and infarction. When local flow dropped below about 23 cc/100 gm/min, reversible paralysis occurred. When local flow fell below 10 to 12 cc/100 gm/min for 2 to 3 hours or below 17 to 18 cc/100 gm/min during permanent occlusion, irreversible local damage was observed.

These studies imply that some cases of acute hemiplegia, with blood flow in the paralysis range, might be improved by surgical revascularization. Studies of local CBF might help identify suitable cases for emergency revascularization.

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Experimental cerebral oligemia and ischemia produced by intracranial hypertension

Part 1: Pathophysiology, electroencephalography, cerebral blood flow, blood-brain barrier, and neurological function

Lawrence F. Marshall, Felix Durity, Robert Lounsbury, David I. Graham, Frank Welsh, and Thomas W. Langfitt

✓ Cerebral blood flow, electrical activity, and neurological function were studied in rabbits subjected to either 15 minutes of oligemia (20 torr cerebral perfusion pressure) or complete cerebral ischemia produced by cisterna magna infusion. During oligemia, flow was reduced from 68.4 ± 4.2 ml/100 gm/min to 26.3 ± 4.4 (p < .01), and during ischemia animals had no proven flow. By 5 minutes after oligemia or ischemia significant symmetrical hyperemia occurred and there was no evidence of the no-reflow phenomenon. The electroencephalogram became isoelectric significantly later and returned significantly sooner in oligemia than in ischemia. Oligemic animals had earlier and better return of neurological function than their ischemic counterparts, although postinsult hypocapnia improved functional recovery in both groups. These experiments do not support the concept that oligemia is a more severe insult than complete ischemia. In intracranial hypertension produced by this model, the no-reflow phenomenon does not occur.

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Lawrence F. Marshall, Frank Welsh, Felix Durity, Robert Lounsbury, David I. Graham, and Thomas W. Langfitt

✓ The authors studied the effect on cortical metabolites of intracranial hypertension produced by the infusion of mock cerebrospinal fluid into the cisterna magna in rabbits subjected to 15 minutes of cerebral oligemia (20 torr) or 15 minutes of complete ischemia. In both groups high-energy metabolites were exhausted within the first 5 minutes of the 15-minute insult. Significant recovery of the high-energy intermediates occurred within 15 minutes of reperfusion, well before return of electroencephalogram (EEG) activity. Continued reperfusion, during which electrical activity and function were returning, brought only moderate improvement in energy metabolites. In contrast, severe lactic acidosis persisted at least 15 minutes after insult, but was reduced by the time EEG activity returned. At no time were there striking differences in metabolites between the oligemic and ischemic groups. These results indicate that recovery in general, and the significantly earlier recovery of oligemic as compared to ischemic animals, cannot be explained on the basis of energy supply. Whether the persistence of lactic acidosis is an important factor limiting return of function requires further study.

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Lawrence F. Marshall, David I. Graham, Felix Durity, Robert Lounsbury, Frank Welsh, and Thomas W. Langfitt

✓ The authors studied the morphological sequelae of 15 minutes of cerebral oligemia (20 torr cerebral perfusion pressure) and complete cerebral ischemia produced by raised intracranial pressure in rabbits. Ischemic cell change was present in five of seven ischemic animals; it was most extensive in the striatum and hippocampus, with only a few ischemic nerve cells in the thalamus and neocortex. The brains of control and oligemic animals were normal. These results indicate the following: 1) ischemia is a more severe insult than oligemia; 2) compression ischemia results in a pattern of damage that differs from that produced by other types of ischemia; and 3) the method used to reduce cerebral perfusion pressure is an important factor in determining the pattern and extent of brain damage produced.

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Christopher Nutting, Michael Brada, Lucy Brazil, Ahmen Sibtain, Frank Saran, Charlotte Westbury, Anne Moore, David G. T. Thomas, Daphne Traish, and Susan Ashley

Object. This study was undertaken to assess the long-term efficacy and toxicity of conventional fractionated external-beam radiation in the treatment of benign skull base meningioma.

Methods. This is a retrospective study of 82 patients with histologically verified benign skull base meningioma treated by surgery followed by fractionated external-beam radiation at the Royal Marsden Hospital between 1962 and 1992. The 5- and 10-year progression-free survival (PFS) rates were 92% and 83%, respectively, with the site of disease being the only independent prognostic factor for tumor control according to multivariate analysis. The 10-year PFS rate for patients with sphenoid ridge meningiomas was 69% compared with 90% for those with tumors in the parasellar region. The overall 10-year survival rate was 71%, with performance status and patient age found to be significant independent prognostic factors. Six patients had worsening vision, which was due to cataract in five cases and retinopathy in one. There were no recorded cases of cranial nerve neuropathy.

Conclusions. The excellent long-term tumor control and length of survival with minimal toxicity associated with conventional external-beam radiation should serve as a baseline for evaluation of new treatment strategies such as radiosurgery and skull base surgery.

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Edgar F. Fincher, Dr. Bronson S. Ray, Dr. Harold J. Stewart, Dr. Edgar F. Fincher, Dr. T. C. Erickson, Dr. L. W. Paul, Dr. Franc D. Ingraham, Dr. Orville T. Bailey, Dr. Frank E. Nulsen, Dr. James W. Watts, Dr. Walter Freeman, Lt. Col. C. G. de Gutiérrez-Mahoney, Dr. Frank Turnbull, Dr. Carl F. List, Lt. Comdr. William J. German, Dr. A. Earl Walker, Dr. J. Grafton Love, Dr. Francis C. Grant, Dr. I. M. Tarlov, Lt. Comdr. Thomas I. Hoen, and Dr. Rupert B. Raney