Search

BackgroundThe COVID-19 pandemic has disrupted established care paths worldwide. Patient awareness of the pandemic and executive limitations imposed on public life have changed the perception of when to seek care for acute conditions in some cases. We sought to study whether there is a delay in presentation for acute ischemic stroke patients in the first month of the pandemic in the US.MethodsThe interval between last-known-well (LKW) time and presentation of 710 consecutive patients presenting with acute ischemic strokes to 12 stroke centers across the US were extracted from a prospectively maintained quality database. We analyzed the timing and severity of the presentation in the baseline period from February to March 2019 and compared results with the timeframe of February and March 2020.ResultsThere were 320 patients in the 2-month baseline period in 2019, there was a marked decrease in patients from February to March of 2020 (227 patients in February, and 163 patients in March). There was no difference in the severity of the presentation between groups and no difference in age between the baseline and the COVID period. The mean interval from LKW to the presentation was significantly longer in the COVID period (603±1035 min) compared with the baseline period (442±435 min, PConclusionWe present data supporting an association between public awareness and limitations imposed on public life during the COVID-19 pandemic in the US and a delay in presentation for acute ischemic stroke patients to a stroke center.

Background and purposeWe previously reported a single-centre study demonstrating that smoking confers a six-fold increased risk for having an unruptured intracranial aneurysm (UIA) in women aged between 30 and 60 years and this risk was higher if the patient had chronic hypertension. There are no data with greater generalisability evaluating this association. We aimed to validate our previous findings in women from a multicentre study.MethodsA multicentre case-control study on women aged between 30 and 60 years, that had magnetic resonance angiography (MRA) during the period 2016–2018. Cases were those with an incidental UIA, and these were matched to controls based on age and ethnicity. A multivariable conditional logistic regression was conducted to evaluate smoking status and hypertension differences between cases and controls.ResultsFrom 545 eligible patients, 113 aneurysm patients were matched to 113 controls. The most common reason for imaging was due to chronic headaches in 62.5% of cases and 44.3% of controls. A positive smoking history was encountered in 57.5% of cases and in 37.2% of controls. A multivariable analysis demonstrated a significant association between positive smoking history (OR 3.7, 95%CI 1.61 to 8.50), hypertension (OR 3.16, 95% CI 1.17 to 8.52) and both factors combined with a diagnosis of an incidental UIA (OR 6.9, 95% CI 2.49 to 19.24).ConclusionsWomen aged between 30 and 60 years with a positive smoking history have a four-fold increased risk for having an UIA, and a seven-fold increased risk if they have underlying chronic hypertension. These findings indicate that women aged between 30 and 60 years with a positive smoking history might benefit from a screening recommendation.

Background Pedicle screw placement is the most common method of fixation in the thoracic spine. Use of the “superior facet rule” allows the operator to locate the borders of the pedicle reliably using posterior landmarks alone. This study investigated the ability of 3-dimensionally (3D)-printed thoracic vertebrae, made from combined thermoplastic polymers, to demonstrate pedicle screw cannulation accurately using the superior facet as a reliable landmark. Methods An anonymized computed tomography scan of the thoracic spine was obtained. The T1–T12 thoracic vertebrae were anatomically segmented and 3D-printed. The pedicle diameters and distance from the midpoint of the superior facet to the ventral lamina were recorded. A total of 120 thoracic pedicles in 60 thoracic vertebral models were instrumented using a freehand technique based only on posterior landmarks. The vertebral models were then coronally cut and examined for medial or lateral violations of the pedicle after screw placement. Results A total of 120 pedicle screws were placed successfully within the 3D-printed thoracic vertebral models. Average measurements fell within 1 standard deviation of previous population studies. There were no pedicle wall violations using standard posterior element landmarks for instrumentation. There were 3 lateral violations of the vertebral body wall during screw placement, all attributable to the insertion technique. Conclusions 3D-printed thoracic vertebral models using combined thermoplastic polymers can accurately demonstrate the anatomical ultrastructure and posterior element relationships of the superior facet rule for safe thoracic pedicle screw placement. This method of vertebral model prototyping could prove useful for surgical education and demonstrating spinal anatomy.

Multimodal CT scans, including non-contrast CT, CT perfusion, and CT angiography, are widely used in acute stroke diagnosis and therapeutic planning. While each imaging modality has its advantage in brain cross-sectional feature visualizations, the varying image resolution of different modalities hinders the ability of the radiologist to discern consistent but subtle suspicious findings. Besides, higher image quality requires a high radiation dose, leading to increases in health risks such as cataract formation and cancer induction. In this work, we propose a deep learning-based method Transfer-GAN that utilizes generative adversarial networks and transfer learning to improve multimodal CT image resolution and to lower the necessary radiation exposure. Through extensive experiments, we demonstrate that transfer learning from multimodal CT provides substantial visualization and quantity enhancement compare to the training without learning the prior knowledge.

Background and Purpose: Given the benign natural history of intracranial low-grade dural arteriovenous fistulas (dAVFs), their routine treatment remains controversial. The aim of this study is to compare the outcomes of low-grade dAVF treatment to conservative management. Methods: We performed a retrospective review of dAVF patients derived from 12 institutions participating in the Consortium for Dural Arteriovenous Fistula Outcomes Research (CONDOR). Patients with low-grade (Borden I) dAVFs were included and categorized into treatment and observation cohorts. Primary outcome was defined as modified Rankin Scale (mRS) score at final follow-up. Secondary outcomes were rates of excellent (mRS 0-1) and good (mRS 0-2) functional outcomes, symptomatic improvement, mortality, and obliteration at final follow-up. Results: The treatment and observation cohorts comprised 230 and 112 patients, respectively. At last follow up, no difference in primary or secondary outcomes was observed between the two cohorts, with the exception of obliteration, which was higher in the treatment cohort (79.3% vs. 28.2%, p Conclusions: Low-grade dAVF treatment was not associated with increased functional disability compared to conservative management. Although higher obliteration rates were achieved in the treatment cohort, rates of symptomatic improvement were similar between the two cohorts. This study did not provide evidence to support the routine treatment of low-grade dAVFs.

Objective To compare outcomes between patients who underwent mechanical thrombectomy for large vessel occlusion based on platelet count: low versus normal. Methods Three studies were included with a pooled cohort of 1125 patients. Data points were collected and pooled by meta-analysis of proportions via a logit transformation to provide a summary statistic. Both fixed-effect and random-effects models were recruited for the analysis. In this meta-analysis, risk of developing symptomatic intracranial hemorrhage, unfavorable clinical outcomes (modified Rankin Scale score >3), and mortality of patients with low platelet counts were compared with patients with normal platelet counts according to the criteria for inclusion used by each study. Results Of patients, 50 (4.7%) had low platelet count, and 1075 (95.3%) had normal platelet count. Patients in the low platelet count group had a substantially higher risk of mortality (risk ratio 1.93, 95% confidence interval 1.43–2.60, P Conclusions Patients with low platelet counts had increased mortality compared with patients with normal platelet counts following mechanical thrombectomy for large vessel occlusion.

Once the accepted norm during Harvey Cushing's time, the mantra of work to the exclusion of family and lifestyle is now recognized as deleterious to overall well-being. A number of neurosurgical residency training programs have implemented wellness programs to enhance the physical, mental, and emotional well-being of trainees and faculty. This manuscript highlights existing organized wellness education within neurosurgery residency programs in order to describe the motivations behind development, structure, and potential implementation strategies, cost of implementation, and identify successes and barriers in the integration process. This manuscript is designed to serve as a "how-to" guide for other programs who may identify a need in their own trainees and begins the discussion of how to develop wellness, leadership, grit, and resiliency within our future generation of neurosurgeons.

Background: Inflammatory myofibroblastic tumor is a rare, poorly understood tumor that has been found to occur in almost every organ tissue. Its location within the central nervous system is uncommon, and patients tend to present with nonspecific symptoms. Case Description: A female in her eighth decade presented to neurosurgery clinic with complaints of headache and dizziness. Initial imaging was consistent with a low-grade, benign brain lesion in the region of the left choroidal fissure. She was recommended for observation but returned 1 month later with progressive symptoms and doubling of the lesion size. She underwent surgical resection and was found to have an IMT arising from the wall of the left anterior choroidal artery. Conclusion: Intracranial IMT remains a rare and poorly understood entity. The present case demonstrates a novel presentation of IMT in an adult patient and exemplifies the heterogeneity of the disease presentation.

Background Endovascular mechanical thrombectomy (MT) performed with stent retriever devices have proven efficacious in the treatment of adult patients with acute cerebral ischemia resulting from large-vessel occlusion. Recently, reports describing the use of MT in pediatric large-vessel occlusion have increased. However, these case reports are generally limited to older children and teenagers. Case Description We report the use of a Solitaire (Medtronic, Minneapolis, Minnesota, USA) stent retriever for thrombectomy and revascularization of the right middle cerebral artery) in a 6-month-old patient. Conclusions To our knowledge, this is the youngest patient reported to be treated with MT using a stent retriever. This case adds to the growing literature that supports the use of MT as a stroke intervention in pediatric patients.

STUDY DESIGN A retrospective national administrative database study. OBJECTIVE Advances in treatment of traumatic cervical spinal cord injury with fracture (TCSCIF) have led to significant improvements in clinical outcomes; however, progress in healthcare is seldom ubiquitous across demographic groups. Therefore, we explored if disparities in treatment and outcome after TCSCIF exist across race and socioeconomic status. SETTING USA. METHODS We queried the Nationwide Inpatient Sample database from 1998 to 2009 for TCSCIF hospitalizations. Multivariate analysis was used to identify the correlation between socioeconomic status and race to injury, treatment type, and outcome. RESULTS There were 21,985 admissions for TCSCIF, 66.9% of whom had a favorable discharge disposition. In-hospital mortality rate was 12.5%. A total of 43.7% underwent surgery. Overall, surgery was associated with lower in-hospital mortality (OR 0.30, 95% CI 0.27-0.34, p

Background In some fluoroscopy machines, the dose-rate output of the fluoroscope is tied to a selectable patient size. Although patient size may play a significant role in visceral or cardiac procedures, head morphology is less variable, and high dose outputs may not be necessary even in very obese patients. We hypothesized that very small patient size setting can be used to reduce dose for cerebral angiography without compromising image quality. Methods Patients who underwent endovascular neurosurgical procedures during the 2015–2016 academic year were identified, and estimated procedural air kerma (AK) was tabulated retrospectively. Technologists were instructed to begin using the very small patient size setting for all procedures performed using our Philips Allura Xper FD20 biplane fluoroscopy system beginning in March 2016. No changes were made in a second procedure room using a Toshiba Infinix system. Student t tests and logistic regression models were used to compare radiation exposure before and after March 1, 2016, for both machines. Results For diagnostic cerebral angiograms performed on the Philips system (n = 302), AK was reduced by approximately 17% (1277 vs. 1061 mGy; P = 0.0006.) Changes in table height, total fluoroscopy time, patient weight, and body mass index did not contribute to this difference. No significant change was seen in total AK using the Toshiba system (n = 237). Blinded review by a neuroradiologist did not demonstrate any change in image quality. Conclusions Using the very small patient size reduces fluoroscopy dose by 17% for cerebral angiography without impacting image quality.

OBJECTIVEInhibition of platelet aggregation is vital to preventing thromboembolic complications related to stent placement in endovascular neurosurgery, but excessive inhibition potentiates hemorrhagic complications. Recent evidence suggests an ideal inhibition range of 70–150 P2Y12 response units (PRU) as measured on the VerifyNow assay, which relies on photometric measurements of platelet aggregation. Thromboelastography (TEG) with platelet mapping (PM) is an alternative assay that directly measures clot formation and mechanical strength. This study compares the results of PRU to TEG-PM.METHODSPatients with simultaneous or near-simultaneous PRU and TEG-PM results who underwent cervical carotid artery stenting, intracranial stent-assisted aneurysm coiling, or flow diversion at the authors’ institution between August 2015 and November 2016 were identified. PRU results were compared with the TEG maximal amplitude (MA) attributable to adenosine diphosphate (ADP) activity (MA-ADP) as measured by TEG-PM. Platelet inhibition was considered therapeutic for MA-ADP values < 50 mm or PRU < 194. The Pearson correlation coefficient was calculated, and the sensitivity and specificity of PRU were calculated assuming that the results of TEG-PM reflected the true degree of platelet inhibition.RESULTSTwenty-three patients were identified with a total of 37 matched sets of TEG-PM and PRU. Three of these pairs were excluded due to anemia outside of the PRU manufacturer’s recommended range. The Pearson correlation coefficient for these values was 0.50 (p = 0.0026). The prevalence of clopidogrel nonresponders determined by TEG-PM (9%) matched reported rates (5%–12%); PRU demonstrated much higher prevalence (39%). For detecting a therapeutic level of platelet inhibition, PRU demonstrated a sensitivity of 0.59, specificity of 0.50, positive predictive value of 0.95, and negative predictive value of 0.07. Ideal inhibition was concordant in only 25% of observations in which at least one of the results was ideal.CONCLUSIONSAgreement between TEG-PM and PRU regarding the degree of platelet inhibition is poor. PRU likely overestimates clopidogrel resistance, as 93% of patients with PRU > 194 demonstrate a therapeutic level of platelet inhibition on TEG.

Military neurosurgery has played an integral role in the development and innovation of neurosurgery and neurocritical care in treating battlefield injuries. It is of paramount importance to continue to train and prepare the next generation of military neurosurgeons. For the Army, this is currently primarily achieved through the military neurosurgery residency at the National Capital Consortium and through full-time out-service positions at the Veterans Affairs–Department of Defense partnerships with the University of Florida, the University of Texas–San Antonio, and Baylor University. The authors describe the application process for military neurosurgery residency and highlight the training imparted to residents in a busy academic and level I trauma center at the University of Florida, with a focus on how case variety and volume at this particular civilian-partnered institution produces neurosurgeons who are prepared for the complexities of the battlefield. Further emphasis is also placed on collaboration for research as well as continuing education to maintain the skills of nondeployed neurosurgeons. With ongoing uncertainty regarding future conflict, it is critical to preserve and expand these civilian-military partnerships to maintain a standard level of readiness in order to face the unknown with the confidence befitting a military neurosurgeon.

A 35-year-old male presented with headaches and was found to have a Spetzler-Martin grade 2 right occipital arteriovenous malformation (AVM) with single, superficial draining vein. The patient opted to undergo embolization for possible cure with resection scheduled in the event complete obliteration was not achieved. Three weeks later, angiography during his embolization procedure revealed that the AVM had spontaneously obliterated; no treatment was required. In conjunction with prior case reports/series, this patient highlights the need for current imaging prior to proceeding with intervention to confirm that spontaneous obliteration has not occurred between diagnosis and treatment.

Object Intraoperative fluoroscopy has long been used for anatomical localization in transsphenoidal pituitary surgery. More recently, frameless stereotaxy has been used to supplement 2D sagittal radiographs with 3D multiplanar reconstructions. Use of Arcadis Orbic allows both conventional fluoroscopic views and multiplanar reconstructions to be acquired intraoperatively without need for preoperative planning studies. The authors report their initial experience using Arcadis Orbic during transsphenoidal pituitary surgery. Methods To test the system, the authors placed a dehydrated human skull in a radiolucent head holder, and obtained standard 2D fluoroscopic images of the skull base and sella turcica. Arcadis Orbic was then used with frameless stereotaxy to register 3D multiplanar reconstructed images of skull base anatomy. The authors then used Arcadis Orbic in 26 transsphenoidal pituitary tumor resections and compared image quality, accuracy, and ease-of-use to standard techniques. Results Arcadis Orbic 2D fluoroscopic images matched or exceeded the quality of images acquired by standard C-arm machines. Arcadis Orbic multiplanar reconstructions provided excellent images of the skull base when compared with preoperative Stealth computed tomography (CT) studies. Intraoperative frameless stereotactic navigation using Arcadis Orbic was highly accurate and more reliable than registering preoperative CT images. Conclusions Arcadis Orbic provides excellent quality 2- and 3D images during transsphenoidal pituitary surgery, and intraoperative frameless navigation using these images is highly accurate. Arcadis Orbic is easy to use, even in patients with large body habitus, and image acquisition takes no longer than registration during a frameless stereotactic case. Based upon our preliminary experience, Arcadis Orbic precludes the need for preoperative CT studies in patients with pituitary lesions requiring frameless stereotactic navigation.

Background The Role III, Multinational Medical Unit at Kandahar Air Field, Afghanistan, was established to provide combat casualty care in theater for International Security Assistance Forces, Afghanistan National Security Forces, and local nationals during Operation Enduring Freedom–Afghanistan. The authors describe their experience of treating unstable lumbar spine fractures with orthopedic extremity instrumentation sets from January 2007 to January 2008 and November 2010 to May 2011. Methods During the study periods, 15 patients comprising Afghanistan National Security Forces and local nationals presented to the medical facility for treatment of unstable lumbar spine fractures. The patients underwent surgery for either anterior corpectomy and instrumented fusion ( n = 5) or posterior instrumented fusion ( n = 10). Because of periodic scarcity of spinal instrumentation sets, orthopedic extremity instrumentation sets were used (Synthes Large Fragment LCP Instrument and Implant Set) for spinal stabilization. Results Immediate postoperative standing and sitting plain radiographs demonstrated no evidence of fracture progression or immediate hardware failure. One patient was seen in follow-up at 4 weeks and demonstrated construct stability on follow-up radiographs. Conclusions In the combat environment with sparse resources, unstable spine fractures may potentially be treated using instrumentation not specifically designed for spinal implantation. This is an off-label use, and the authors do not recommend the use of these techniques as standard treatment in most medical environments.

We postulated that acute hypoxemia increases susceptibility to orthostatic hypotension by increasing the sensitivity of cardiovascular baroreceptors.Hemodynamics were measured noninvasively in 17 healthy, normotensive subjects while being subjected to decreasing venous return by exposure to lower body negative pressure (LBNP) and breathing either a normobaric normoxic (21% O2) or normobaric hypoxic (12% O2) gas mixture.Hypoxia variably decreased hemoglobin saturation (in percent+/-SEM, from 99%+/-1% to 87%+/-2%, P.01). Incremental increases in LBNP to -50 mm Hg significantly lowered systolic blood pressure (BP), pulse pressure (PP), forearm blood flow (FBF), and increased heart rate (HR). Hypoxia significantly increased baseline systolic BP, PP, and HR. The maximum change in HR in response to LBNP-induced reductions in PP increased during acute hypoxemia (maximum DeltaHR/DeltaPP, in +/-SEM) from 1.32+/-0.18 beats/min/mm Hg v 1.91+/-0.25 beats/min/mm Hg, P.05. Those subjects who had the most hemoglobin desaturation during hypoxia, when compared to those subjects who desaturated minimally, had greater systolic BP at rest (128+/-3 mm Hg v 114+/-3 mm Hg, P=.05) and during LBNP (115+/-4 mm Hg v 100+/-1 mm Hg, P=.01).Acute hypoxia increased compensatory HR responses to LBNP-dependent reductions in BP. Those normotensive individuals with higher BP at rest and during LBNP developed greater degrees of hypoxia-induced hemoglobin desaturation. Patients with sleep apnea with periods of hypoxemia are prone to hypertension; more important, patients with higher BPs also demonstrate greater degrees of hypoxia-induced desaturation of oxyhemoglobin.

A 33-year-old male presented for resection of an intracranial mass after 1 year of recurrent headaches and dizziness. Cerebrospinal fluid testing had shown a lymphocytic pleocytosis (163 cells/mm3, 59% lymphocytes, 20% neutrophils) with normal protein (42 mg/dL), glucose (54 mg/dL), cultures, and serologic testing. Multiple brain magnetic resonance imaging (MRI) studies showed enlarged ventricles but no masses. Immediately before surgery, a discrete cystic structure was visible on imaging (Figure 1 ). A large cyst consistent with neurocysticercosis was identified intraoperatively. No additional lesions were observed, and he had complete resolution of symptoms. He received 7 days of albendazole, dexamethasone, and levetiracetam per guidelines for a solitary lesion.1 Follow-up imaging using higher resolution (1 mm versus 6 mm planes) and volumetric sequencing displayed an extra-parenchymal cyst with a visible scolex lateral to the fourth ventricle (Figure 2 ). As a result of surgical excision, there was no evidence of a residual fourth ventricle cyst. His MRI spine was negative, and he received two additional months of therapy until radiographic resolution, per guidelines for extra-parenchymal lesions.1 This thin walled extra-parynchymal cyst was uncovered with higher quality imaging using both finer planes and an ultrafast MRI technique known as volumetric imaging (e.g., fast imaging employing steady-state acquisition [FIESTA] sequencing). Ideally, higher quality imaging would have revealed these cysts preoperatively. However, his films were suggestive of mass lesion and thus volumetric imaging was not performed until the surgical pathology provided a definitive diagnosis. This case displays the role that high quality volumetric imaging plays in the diagnosis of neurocysticercosis. Figure 1. (A) Gadolinium-enhanced magnetic resonance imaging (MRI) of the brain showing evidence of a fourth ventricular cystic structure. (B) Histopathology of a surgically removed cyst with i) cuticular layer with microvilli, ii) cellular layer, and iii) reticular ... Figure 2. Axial T2. Follow-up imaging 2 months post-surgical. (A) 1.2 cm cyst located at the right Foramen of Luschka (lateral recess of the fourth ventricle) consistent with neurocysticercosis cyst with internal scolex. (B) Post-surgical image displaying post-surgical ...

To follow the progression of neuroimaging as a means of non-invasive evaluation of mild traumatic brain injury (mTBI) in order to provide recommendations based on reproducible, defined imaging findings.A comprehensive literature review and analysis of contemporary published articles was performed to study the progression of neuroimaging findings as a non-invasive 'biomarker' for mTBI.Multiple imaging modalities exist to support the evaluation of patients with mTBI, including ultrasound (US), computed tomography (CT), single photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetic resonance imaging (MRI). These techniques continue to evolve with the development of fractional anisotropy (FA), fiber tractography (FT), and diffusion tensor imaging (DTI).Modern imaging techniques, when applied in the appropriate clinical setting, may serve as a valuable tool for diagnosis and management of patients with mTBI. An understanding of modern neuroanatomical imaging will enhance our ability to analyse injury and recognize the manifestations of mTBI.

The purpose of this study was to assess for peri-operative factors associated with brain shift following craniotomy for subdural grid electrode placement.A retrospective analysis of cases operated at a single institution was undertaken, examining 63 consecutive patients undergoing craniotomy for subdural grid placement for seizure monitoring between 2001 and 2007. Peri-operative records were reviewed in order to assess for intraoperative employment of osmotic duiresis. Postoperative MRI scans were analyzed for shift of the midline and brain displacement.One patient was excluded due to gross hemispheric atrophy confounding the midline, and four patients were excluded due to lack of available imaging. Hence 58 patients were radiographically reviewed. The employment of osmotic diuresis during grid placement appeared to be the most significant peri-operative factor influencing brain shift. Osmotic diuresis was administered in only 14 patients. Midline shift of the third ventricle was greater in the osmotic diuresis group (2.3 ± 0.3 mm vs. 1.5 ± 0.2 mm, p = 0.037). Moreover, the volume of shifted brain was significantly higher in the osmotic diuresis group (7.9 ± 0.5 cm(3) vs. 4.7 ± 0.5 cm(3), p = 0.003). There was no significant difference in the rates of neurological complications between patients who received osmotic diuresis and those who did not.Employment of osmotic diuresis during grid placement appears to be associated with a paradoxical increase in the volume of shifted brain. This may be due to a combination of the resultant "sagging" of the brain and the pressure exerted by the grid, suggesting that osmotic diuresis might not improve mass effect as intended when employed within this context.

OBJECTIVE: Antiplatelet therapy is critical to endovascular neurosurgical procedures. Some patients are aspirin-resistant nonresponders. We reviewed our endovascular neurosurgery patients who were premedicated with aspirin and clopidogrel and identified nonresponders to aspirin. Factors associated with aspirin resistance were determined. METHODS: Consecutive endovascular neurosurgery patients were identified who were treated by the senior author (BLH) from December 2006 to October 2007 and who were premedicated with aspirin (325 mg) and clopidogrel (75 mg) for 7 days before the procedure. We retrospectively reviewed values from the platelet function analyzer-100 test (Dade-Behring, Deerfield, IL) from 1 day before the procedures. The following factors were evaluated for association with aspirin drug resistance: age, sex, body mass index, and smoking history; patients with hypertension, diabetes, coronary artery disease/ peripheral vascular disease, or hypercholesterolemia; disease pathology (aneurysm, intracranial stenosis, or extracranial stenosis); patients taking statins, β-blockers, angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, or antidepressants; and white blood cell count, hemoglobin, hematocrit, and platelet levels. A stepwise logistic model selection was used to select important factors and their interactions. RESULTS: Eighty-one consecutive patients with the following interventions were included in the study: 35 aneurysm coilings (43%), 21 stent-assisted aneurysm coilings (26%), 13 carotid stent and angioplasties (16%), 7 intracranial stents and angioplasties (9%) , and 5 extracranial vertebral artery stents and angioplasties (6%). Seventeen patients (21 %) were nonresponders to aspirin. After model selection, the only factor associated with aspirin resistance was not taking an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker (P = 0.0348; odds ratio, 0.214; 95% confidence interval, 0.051-0.896). CONCLUSION: Twenty-one percent of patients premedicated with aspirin and clopidogrel dual therapy for 7 days before endovascular neurosurgical procedures were nonresponders to aspirin. Patients not taking an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker may be at higher risk for aspirin drug resistance.

The maintenance of excessively high peripheral blood flow through dilated blood vessels during immersion in cold water could explain some individuals' predisposition to hypothermia. We hypothesized that interpersonal differences in vascular reactivity could account for contrasting susceptibility to hypothermia.Twenty-two highly fit, volume replete subjects undergoing Navy SEAL training were recruited for this study. Vascular reactivity in these trainees was determined in a thermal-neutral environment by measuring changes in forearm blood flow (FBF) while decreasing their BP with the application of lower body negative pressure (LBNP). FBF was also measured during exposure of these subjects to ice cold water. BP, heart rate, stroke volume, and skin temperatures were also recorded.Changes in FBF induced by a fall in BP correlated with an individual's reduction in FBF caused by ice water immersion (n = 17, r = 0.84, p0.001). A subject's decrement in BP induced with LBNP correlated inversely with the fall in skin temperature in response to cold water immersion (n = 19, r = 0.70, p0.001). Finally, we found that sodium excretion also correlated with cold-induced decrements in peripheral blood flow (n = 7, r = 0.83, p0.05).It is suggested that contrasting cardiovascular baroreceptor sensitivity and vascular responsiveness contribute to individual differences in susceptibility to hypothermia. Furthermore, the trend toward dietary salt restrictions may not be salutary in the Navy SEAL who must frequently operate in cold ambient environments.