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Guenther Christian Feigl and Gerhard A. Horstmann

determined for each patient (Table 2 ). Treatment and Follow-Up Protocol All radiosurgical procedures were performed using the Leksell Gamma Knife model C (Elekta Instruments, Stockholm, Sweden) with the automatic positioning system. 20 To reach a high conformity over irregular tumor volume shapes and to deliver a steep dose gradient to vulnerable surrounding structures a maximum number of isocenters was applied in each case. 21 Contrast-enhanced T 1 -weighted magnetization-prepared rapid- acquisition gradient-echo MR imaging was performed during each follow

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Mario Brock, Hans-Hermann Görge and Gabriel Curio

the intervertebral space. Direct pressure measurements within lumbar discs require highly specialized equipment and have not hitherto yielded reliable results. 3 It appeared more plausible to us that intradiscal compliance, rather than mere intradiscal pressure, is altered in the presence of disc degeneration. We therefore decided to test the pressure changes that occur following rapid volume loading by bolus injection of a small amount of a substance without inhibitory action on the enzyme chymopapain. The present paper reports the results of studies on the

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Jonathan M. Bledsoe, Michael J. Link, Scott L. Stafford, Paul J. Park and Bruce E. Pollock

preferred treatment when this can be accomplished safely, 18 but subtotal resection followed by fractionated radiotherapy or SRS is often performed when the risk of total removal is prohibitive. 6 , 10 , 12 , 16 , 19 The dose/volume relationship and how it relates to postradiosurgical complications has been well documented. 5 Nonetheless, the progressive trend to treat benign tumors with lower radiation doses theoretically permits patients with larger lesions to be considered for SRS. 7 In this study, we review the radiosurgical experience at our center for patients

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Roberto C. Heros

This is an excellent retrospective study of the relationship between hospital case volume and mortality rates in patients admitted through the emergency department of an acute-care hospital with the diagnosis of subarachnoid hemorrhage (SAH). The data are derived from records kept in 18 states representing 58% of the US population. Although my expertise with statistics in general and with this type of epidemiological research in particular is limited, the paper has been duly reviewed by an individual with such expertise who found no major flaws with the

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Barbara J. Fisher, Glenn S. Bauman, Christopher E. Leighton, Larry Stitt, J. Gregory Cairncross and David R. Macdonald

estimated by measuring the three largest tumor dimensions of the contrast-enhancing abnormalities or the low attenuation volume in nonenhancing lesions, in the anteroposterior (D 1 ), superoinferior (D 2 ), and transverse views (D 3 ). Tumor volumes on postoperative CT scans obtained before and after radiotherapy were compared to assess volume response to radiation (volume = π/6 D 1 D 2 D 3 ). Tumor volume response was classified as stable (< 25% decrease), minor (≥ 25% to < 50% decrease), major (≥ 50% decrease), or complete (no measurable tumor observed on follow-up scan

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Kenan AlKhalili, Nohra Chalouhi, Stavropoula Tjoumakaris, Robert Rosenwasser and Pascal Jabbour

tissue as much as possible. Both the radiation dose and the treatment volume have major roles that contribute to morbidity and mortality. Radiation dose must be decreased with increasing lesion volume to prevent normal tissue toxicity. 5 Consequently, larger AVMs have been associated with less successful obliteration rates. 18 , 49 To achieve higher obliteration rates with fewer radiosurgical side effects, the concept of staged-volume radiosurgery (SVR) has been introduced. 16 , 38 However, the treatment of large AVMs using SVR has been rarely reported. A number of

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Michael Kosteljanetz

following reasons: 1) the technique as described originally has not been evaluated in patients with communicating hydrocephalus, and 2) the method provides data on CSF resistance and pressure-volume relationships during the same test. The present study was only concerned with CSF dynamics as studied by quantitative techniques and did not employ radioisotopes or x-ray contrast medium. While most studies have been concerned with the selection of patients who will benefit from CSF diversion surgery, our investigation was exclusively concerned with a pathophysiological

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Roberto C. Heros

This is another excellent article relating outcome to hospital case volume; in this instance the number of operations performed for clipping of cerebral aneurysms is compared with outcome. Again, the authors have found a significant relationship between volume and outcome, as measured by mortality rates. I have just written an editorial on a similar article (Cross DT, Tirschwell DL, Clark MA, et al: Mortality rates after subarachnoid hemorrhage: variations according to hospital case volume in 18 states, J Neurosurg 99: 805–806, November, 2003) and many of the

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Pressure-volume index as a function of cerebral perfusion pressure

Part 2: The effects of low cerebral perfusion pressure and autoregulation

W. John Gray and Michael J. Rosner

P revious studies of the relationship of cerebral perfusion pressure (CPP) changes to “brain stiffness, ” whether measured by compliance, elastance, volume pressure response, or pressure-volume index (PVI), have suggested that at normal levels of intracranial pressure (ICP), “brain stiffness” does not change significantly when CPP is changed within the 50- to 160-mm Hg range. 1, 10, 18 Recent work by us in cats has shown that deep barbiturate anesthesia nearly obliterates the relationship between PVI and CPP, but under light anesthesia cats showed a

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Pressure-volume index as a function of cerebral perfusion pressure

Part 1: The effects of cerebral perfusion pressure changes and anesthesia

W. John Gray and Michael J. Rosner

M any authors have attempted to quantify the stiffness of the neuraxis in terms of the pressure change in response to a volume load, 22, 24, 25, 29 generating an exponential pressure-volume curve. Compliance, defined as the change in cerebrospinal fluid (CSF) volume per unit change in CSF pressure, is not constant but varies as a function of CSF pressure; thus, compliance is highest at low CSF pressures and decreases as CSF pressure increases. The pressure-volume curve can be transformed to a linear equation when the logarithm of the pressure is plotted