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Randolph George, Lyal Leibrock and Mel Epstein

✓ The authors have retrospectively analyzed 840 cerebrospinal fluid shunting procedures over a 25-year period to determine the relationships between infection rates and several possible influences on infection. Two-thirds of all shunt infections occurred within 1 month of surgery. The very young and very old had higher infection rates. Infections became less prevalent over the period of the study, and mortality from infection decreased from 35% to 6%. Successive shunts (revisions) were found to have progressively higher infection rates. Ventriculoatrial and ventriculoperitoneal silicone plastic shunts had similar infection rates (11.4% and 12.0%). The uncontrolled use of prophylactic antibiotics had no effect on shunt infections. Staphylococcus epidermidis became gradually more prevalent over the period of the study, and eventually caused one-half of all infections. Where infection occurred in the presence of prophylaxis, the infectious organism was usually sensitive to the antibiotic being used. The surgeon was found to be the largest single factor in the incidence of shunt infections. A 25-fold variance in infection rates among surgeons could be related to individual experience and technique.

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Neville W. Knuckey, Steven Gelbard and Mel H. Epstein

✓ Standard neurosurgical management mandates prompt evacuation of all epidural hematomas to obtain a low incidence of mortality and morbidity. This dogma has recently been challenged. A number of authors have suggested that in selected cases small and moderate epidural hematomas may be managed conservatively with a normal outcome and without risk to the patient. The goal of this study was to define the clinical parameters that may aide in the management of patients with small epidural hematomas who were clinically asymptomatic at initial presentation because there was no clinical evidence of raised intracranial pressure or focal compression. A prospective study was conducted of 22 patients (17 males and five females) aged from 1 to 71 years, who had a small epidural hematoma diagnosed within 24 hours of trauma and were managed expectantly. Of these, 32% subsequently required evacuation of the epidural hematoma 1 to 10 days after the initial trauma.

Analysis of the patients revealed that age, sex, Glasgow Coma Scale score, and initial size of the hematoma are not risk factors for deterioration. However, deterioration was seen in 55% of patients with a skull fracture transversing a meningeal artery, vein, or major sinus, and in 43% of those undergoing computerized tomography (CT) within 6 hours of trauma. In contrast, only 13% of patients in whom the diagnosis of a small epidural hematoma was delayed over 6 hours subsequently required evacuation of the epidural collection. Of patients with both risk factors, 71% required evacuation of the epidural hematoma. None of the patients suffered neurological sequelae attributable to this management protocol.

It was concluded that patients with a small epidural hematoma, a fracture overlaying a major vessel or major sinus, and/or who are diagnosed less than 6 hours after trauma are at risk of subsequent deterioration and may require evacuation. Conversely, patients without these risk factors may be managed conservatively with repeat CT and careful neurological observation, because of the low risk of delayed deterioration.

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Helen M. Haupt, John P. Kurlinski, Nancy K. Barnett and Mel Epstein

✓ Spinal cord infarction in association with pneumococcal meningitis has not been previously recognized. The case is reported of a 5½-year-old boy who had Streptococcus pneumoniae meningitis complicated by the sudden onset of flaccid paraplegia and loss of all sensory modalities below the level of T-2. At operation, the spinal cord was pale and enveloped by dense adhesions, suggesting compromise of the arterial vasculature with concomitant infarction.

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Neville W. Knuckey, Richard Haas, Ross Jenkins and Mel H. Epstein

✓ Patients with symptomatic aneurysms that are not excluded from the cerebral circulation have a poor prognosis. Standard treatment is surgical exploration with direct clipping of the aneurysm. Because of their large size or relationship to the base of the skull, some aneurysms may not be suitable for direct surgical clipping and may require alternative treatment modalities. A prospective clinical and radiological study of seven patients treated with the endovascular placement of platinum-Dacron microcoils to exclude the aneurysm from the cerebral circulation is reported.

The seven patients ranged in age from 37 to 63 years; four were women. At completion of the endovascular procedure, total occlusion of the aneurysm with preservation of the parent artery had been achieved in four patients and 90% occlusion of the aneurysm in two. In the seventh patient, occlusion of the internal carotid artery resulted in the patient's death. At the 6-month follow-up review, both patients with an aneurysm less than 20 mm in size had persistent aneurysm thrombosis; however, the two patients with giant aneurysms had partial recanalization. Both required repeat thrombosis of their aneurysm with the placement of additional microcoils, one at 6 weeks and one at 6 months. These two patients have persistent aneurysm thrombosis at 12 months following their second procedure. The patient mortality rate for this study was 14%, while the procedure mortality/morbidity rate was 9%. It is concluded that thrombotic aneurysm therapy of difficult aneurysms is a safe procedure and will have a place in the treatment of selected aneurysms.

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Neville W. Knuckey, Angela G. Fowler, Conrad E. Johanson, James R. B. Nashold and Mel H. Epstein

✓ Microdialysis is used in vivo for measuring compounds in brain interstitial fluid. The authors describe another application of this technique to the central nervous system, namely microprobe dialysis in the cisterna magna to study the dynamics of ion transport and cerebrospinal fluid (CSF) formation in the rat. The choroid plexus is the major source of CSF, which is produced by active transport of Na from blood into the cerebral ventricles. Formation of CSF is directly proportional to the blood-to-CSF transport of Na. By injecting 22Na into the systemic circulation and quantifying its movement into CSF by microdialysis, one can reliably estimate alterations in the rate of CSF formation. The sensitivity of this system was determined by administering acetazolamide, a standard inhibitor of CSF production. Because acetazolamide is known to decrease CSF formation by 40% to 50%, the cisternal microdialysis system in animals treated with this drug should detect a corresponding decrease in the amount of 22Na dialyzed. This hypothesis is supported by the 22Na uptake curves for control versus treated animals: that is, by the acetazolamide-induced average diminution of about 45% in both the rate and extent of tracer accession to dialysate. Bumetanide, a loop diuretic, reduced by 30% the 22Na entry into dialysate. Microprobe dialysis of fluid in the cisterna magna is thus a minimally invasive and economical method for evaluating effects of drugs and hormones on the choroid plexus-CSF system.

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Steven T. Cobery, Georg Noren, Gerhard M. Friehs, Prakash Chougule, Zhen Zheng, Mel H. Epstein and William Taylor

✓ The authors investigated the use of gamma knife surgery (GKS) in the treatment of central neurocytoma, a usually benign primary brain tumor of the lateral and third ventricles. Four patients with subtotally resected or recurrent central neurocytomas were retrospectively studied. The prescription isodose was 9 to 13 Gy to the 30 to 50% peripheral isodose line. Pre- and postoperative magnetic resonance (MR) images were compared to determine the volume reduction following GKS. Follow-up review included annual MR imaging and clinical evaluation by a neurosurgeon. Follow-up periods ranged from 12 to 99 months.

Marked reduction in tumor size was seen in all four patients; the decrease in tumor volume for each was 48%, 72%, 81%, and 77%, respectively, at the last follow-up review. None of the four patients required additional treatment and none experienced a decline in neurological function during the follow-up period. No complications have been noted in any of these patients to date. Even though there have been few observations and follow-up time has been limited, because of the consistency of the response and the lack of observed side effects, GKS may be the treatment of choice for subtotally resected and recurrent central neurocytomas.

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Douglas Kondziolka, L. Dade Lunsford, John C. Flickinger, Ronald F. Young, Sandra Vermeulen, Christopher M. Duma, Deane B. Jacques, Robert W. Rand, Jean Regis, Jean-Claude Peragut, Luis Manera, Mel H. Epstein and Christer Lindquist

✓ A multiinstitutional study was conducted to evaluate the technique, dose-selection parameters, and results of gamma knife stereotactic radiosurgery in the management of trigeminal neuralgia. Fifty patients at five centers underwent radiosurgery performed with a single 4-mm isocenter targeted at the nerve root entry zone. Thirty-two patients had undergone prior surgery, and the mean number of procedures that had been performed was 2.8 (range 1–7). The target dose of the radiosurgery used in the current study varied from 60 to 90 Gy. The median follow-up period after radiosurgery was 18 months (range 11–36 months). Twenty-nine patients (58%) responded with excellent control (pain free), 18 (36%) obtained good control (50%–90% relief), and three (6%) experienced treatment failure. The median time to pain relief was 1 month (range 1 day–6.7 months). Responses remained consistent for up to 3 years postradiosurgery in all cases except three (6%) in which the patients had pain recurrence at 5, 7, and 10 months. At 2 years, 54% of patients were pain free and 88% had 50% to 100% relief.

A maximum radiosurgical dose of 70 Gy or greater was associated with a significantly greater chance of complete pain relief (72% vs. 9%, p = 0.0003). Three patients (6%) developed increased facial paresthesia after radiosurgery, which resolved totally in one case and improved in another. No patient developed other deficits or deafferentation pain. The proximal trigeminal nerve and root entry zone, which is well defined on magnetic resonance imaging, is an appropriate anatomical target for radiosurgery. Radiosurgery using the gamma unit is an additional effective surgical approach for the management of medically or surgically refractory trigeminal neuralgia. A longer-term follow-up review is warranted.