Predictors of Progression in a Series of 81 Adult Patients Surgically Managed for an Intracranial Hemangioblastoma: Implications for the Postoperative Follow-Up.

The aim was to identify predictors of progression in a series of patients managed for an intracranial hemangioblastoma, in order to guide the postoperative follow-up modalities. The characteristics of 81 patients managed for an intracranial hemangioblastoma between January 2000 and October 2022 were retrospectively analyzed. The mean age at diagnosis was of 48 ± 16 years. Eleven (14%) patients had von Hippel-Lindau disease. The most frequent tumor location was the cerebellar hemispheres (n = 51, 65%) and 11 (14%) patients had multicentric hemangioblastomas. A gross total resection was achieved in 75 (93%) patients. Eighteen (22%) patients had a local progression, with a median progression-free survival of 56 months 95% CI [1;240]. Eleven (14%) patients had a distant progression (new hemangioblastoma and/or growth of an already known hemangioblastoma). Local progression was more frequent in younger patients (39 ± 14 years vs. 51 ± 16 years; p = 0.005), and those with von Hippel-Lindau disease (n = 8, 44% vs. n = 3, 5%, p < 0.0001), multiple cerebral locations (n = 3, 17% vs. n = 2, 3%, p = 0.02), and partial tumoral resection (n = 4, 18% vs. n = 1, 2%, p = 0.0006). Therefore, it is advisable to propose a postoperative follow-up for at least 10 years, and longer if at least one predictor of progression is present.

Endonasal Endoscopic Optic Canal Decompression for Nontraumatic Optic Neuropathy: Long-Term Visual Outcomes in 36 Patients.

BACKGROUND: The management of compressive optic neuropathy (CON) arising from nontraumatic compression of the optic nerve within the optic canal (OC) remains a topic of controversy. In this study, our aim was to assess the effectiveness and safety of endonasal endoscopic optic nerve decompression (EEOND). In addition, we conducted an analysis of prognostic factors that could potentially influence visual outcomes. METHODS: This retrospective cohort study was conducted between January 2015 and December 2021, involving adult patients (age > 18) diagnosed with CON and treated with EEOND at our specialized skull base expert center. The study evaluated the impact of surgery on visual acuity (VA), mean deficit (MD), and foveal threshold (FT) of the visual field (VF). These parameters were assessed preoperatively and at 3- and 12-month postoperative follow-ups. The relationship between clinical variables and the differences in postoperative to preoperative VA, MD, and FT of the visual field was analyzed through univariate and multivariate approaches. RESULTS: Thirty-six patients (38 eyes) were included, with a mean age of 52 (±12) years, and a female predominance (78%). The mean ophthalmologic follow-up duration was 38 (±32) months. At the 12-month follow-up, 39% of the patients exhibited a VA improvement of ≥0.2 LogMAR. Partial VF improvement (MD improvement ≥25%) was observed in 55% of the patients, whereas 19% experienced complete recovery. In multivariate analysis, the presence of a type 4 OC was identified as the sole negative prognostic factor for visual improvement (VA and VF) at 12 months. Six patients (17%) encountered minor surgical complications, all of which were managed conservatively and had no impact on visual outcomes. CONCLUSIONS: Our study demonstrates that EEOND is a safe and effective procedure, even in cases of severe and long-lasting CON caused by nontraumatic compression of the optic nerve at the level of the OC.

Neuro damage control: current concept and civilian applications.

Damage control (DC) initially referred to abbreviated (<1 h) surgical procedures to control abdominal hemorrhage in severe trauma patients, to avoid the 'bloody vicious circle' of hypothermia-coagulopathy-acidosis-hypocalcemia. Progressively, the concept was extended to pre-hospital and peri-operative surgical and non-surgical trauma care. The DC strategy can be applied either in a single severe trauma patient at risk of progression toward the bloody vicious circle or in case of limited or overwhelmed health resources (deprived environment, mass casualties, etc.). DC strategies in neurological casualties have improved over the last decade in military neurosurgeons, but remain poorly codified in civilian settings. In this comprehensive review, we summarize the current concept of neuro-DC, which includes surgical and medical care for neurological injuries as part of a DC strategy. Neuro-DC basically consists in: (i) preventing secondary brain injury; (ii) controlling intracranial bleeding; (iii) controlling intracranial pressure; (iv) limiting contamination of compound wounds; and (v) achieving secondary anatomical restoration.

First evidence of anti-VEGF efficacy in an adult case of adamantinomatous craniopharyngioma: Case report and illustrative review.

BACKGROUND: Craniopharyngioma (CP) is a neurosurgical challenge, due to location and to the substantial risk of morbidity associated with surgical resection. Recent advances in molecular research have identified a mutation signature in papillary craniopharyngiomas: BRAF V600E. This has led to targeted therapy, yielding positive results. Despite numerous studies of the pathophysiology of adamantinomatous craniopharyngioma, treatment options for molecular-based therapy are still lacking. The objective of our study was to provide an illustrative review of the literature on possible molecular targets in adamantinomatous craniopharyngioma and to report the case of a patient harboring an adamantinomatous craniopharyngioma deemed unsuitable for surgical resection, in which an anti-VEGF antibody was used to achieve tumor control. CASE REPORT: An 84-year-old-man was referred to our department with a history of visual loss caused by recurrent infundibular adamantinomatous craniopharyngioma. A first surgical attempt to reduce the cystic portion of the tumor compressing the optic pathway failed. Due to rapid worsening of visual function, adjuvant therapy with bevacizumab was initiated before radiotherapy. RESULTS: Neuroradiological and ophthalmological follow-up showed a decrease in tumor volume and improvement in visual function as early as 6 weeks after commencing therapy. These results were confirmed 3 months after commencement of chemotherapy. Radiotherapy was scheduled for long-term tumor control. CONCLUSIONS: To the best of our knowledge, our case is the first in the literature in which targeted therapy using anti-VEGF was successfully used as a single agent to treat adamantinomatous craniopharyngioma, with favorable outcome in terms of tumor shrinkage and clinical improvement. These preliminary results may open new perspectives for the management of adamantinomatous craniopharyngioma. Validation of this approach requires additional clinical evidence.

Analysis of intracranial pressure pulse waveform in studies on cerebrospinal compliance: a narrative review.

Continuous monitoring of mean intracranial pressure (ICP) has been an essential part of neurocritical care for more than half a century. Cerebrospinal pressure-volume compensation, i.e. the ability of the cerebrospinal system to buffer changes in volume without substantial increases in ICP, is considered an important factor in preventing adverse effects on the patient's condition that are associated with ICP elevation. However, existing assessment methods are poorly suited to the management of brain injured patients as they require external manipulation of intracranial volume. In the 1980s, studies suggested that spontaneous short-term variations in the ICP signal over a single cardiac cycle, called the ICP pulse waveform, may provide information on cerebrospinal compensatory reserve. In this review we discuss the approaches that have been proposed so far to derive this information, from pulse amplitude estimation and spectral techniques to most recent advances in morphological analysis based on artificial intelligence solutions. Each method is presented with focus on its clinical significance and the potential for application in standard clinical practice. Finally, we highlight the missing links that need to be addressed in future studies in order for ICP pulse waveform analysis to achieve widespread use in the neurocritical care setting.

Managing Idiopathic Normal Pressure Hydrocephalus: Need for a Change of Mindset.

Idiopathic normal pressure hydrocephalus (iNPH) refers to a complex brain disorder characterized by ventricular enlargement and the classic Hakim's triad of gait and balance difficulties, urinary incontinence, and cognitive impairment. It predominantly affects older patients in the absence of an identified cause. As the elderly population continues to increase, iNPH becomes a growing concern in the complex spectrum of neuro-geriatric care, with significant socio-economic implications. However, unlike other well-structured management approaches for neurodegenerative disorders, the management of iNPH remains largely uncodified, leading to suboptimal care in many cases. In this article, we highlighted the challenges of current practice and identify key points for an optimal structuration of care for iNPH. Adopting a global approach to iNPH could facilitate a progressive shift in mindset, moving away from solely aiming to cure an isolated neurological disease with uncertain outcomes to providing comprehensive care that focuses on improving the daily life of frail patients with complex neurodegenerative burdens, using tailored goals.

Prognostic factors for significant 6-month recovery in dysthyroid optic neuropathy in a tertiary center: A series of 69 eyes in 38 patients.

PURPOSE: To identify initial features associated with significant recovery in patients with Graves' disease dysthyroid optic neuropathy (DON) treated according to EUGOGO guidelines by intravenous glucocorticoids (ivGC) and decompression surgery in first and second-line, respectively. PATIENTS AND METHODS: Consecutive patients referred to our expert multidisciplinary consultation over a 6-year period underwent systematic exploration: endocrine assessment, ophthalmic examination and radiological exploration. Visual recovery, based on best-corrected visual acuity (BCVA) and visual field (VF), were evaluated at baseline, 1week and 6months. Baseline parameters were then tested for prognostic value on univariate and multivariate analyses. RESULTS: Thirty-eight patients (69 eyes) with DON were included. Significant recovery at 6months was found in 48/69 eyes (70%), partial recovery in 18/69 (26%), and no recovery in 3/69 (4%). Fifty-one eyes (28 patients) required surgical decompression after ivGC. These patients showed more severe presentation at diagnosis, had received significantly less GC for Graves' orbitopathy before onset of DON, and showed greater fat prolapse on CT scans compared to non-operated patients. On multivariate analysis, male gender (P=0.001), cumulative GC dose>1g before DON diagnosis (P=0.048) and initial BCVA≤0.3 (P=0.004) were significantly associated with better outcomes, whereas Clinical Activity Score>5 (P=0.013) was associated with a poorer outcome. CONCLUSION: This study confirms a generally favorable 6-month recovery rate in DON treated according to EUGOGO guidelines and provides new information on baseline predictors of poor evolution. These results may help the respective indications for medical and surgical treatment to be more effectively combined in the future.

CSF dynamics in long-standing overt ventriculomegaly in adults.

OBJECTIVE: Long-standing overt ventriculomegaly in adults (LOVA) is a form of chronic hydrocephalus and its pathophysiology and treatment remain debated. An analysis of CSF dynamics in this condition has rarely been reported. The aim of this study was to analyze hydrodynamic characteristics of patients with suspected LOVA to discuss its pathophysiological mechanisms and the importance of CSF dynamics analysis for diagnosis and treatment of these patients. METHODS: This retrospective cohort study, conducted between May 2018 and October 2022, included adult patients aged > 18 years investigated in a department of neurosurgery through a lumbar infusion study for suspicion of LOVA (n = 23). These patients were then compared with a control cohort explored for suspicion of idiopathic normal pressure hydrocephalus (iNPH; n = 30). Clinical symptoms, radiological findings, and hydrodynamic parameters were analyzed. The authors specifically compared two hydrodynamic parameters: resistance to CSF outflow, or Rout, which relies on CSF resorption, and pressure-volume index (PVI), which reflect overall craniospinal compliance. The lumbar infusion study was considered pathological (confirming the diagnosis of chronic hydrocephalus) when at least one of these two parameters was altered. RESULTS: Rout was significantly less frequently increased (cutoff ≥ 12 mm Hg/ml/min) in patients with LOVA (52%) than in those with iNPH (97%; p < 0.001). In contrast, PVI was impaired (cutoff ≤ 25 ml) in both cohorts, i.e., in 61% of patients with LOVA and in 83% of patients with iNPH. Overall, the rate of pathological lumbar infusion study in LOVA (87%) was not statistically different than in iNPH (100%). However, PVI was the only impaired parameter most frequently found in those with LOVA (35%) compared with those with iNPH (3%; p = 0.002). CONCLUSIONS: This study suggests that there is a differential CSF dynamics pattern when comparing patients with LOVA versus those with iNPH. A higher proportion of patients with LOVA showed isolated compliance impairment. These findings highlight the utility of CSF dynamics analysis for the evaluation of patients with suspected chronic obstructive hydrocephalus such as LOVA. Future research with larger case series may help define diagnosis and treatment algorithms of chronic obstructive hydrocephalus based on CSF dynamics analysis, in addition to clinical and radiological criteria.

Development of normal pressure hydrocephalus following post-traumatic external hydrocephalus in an adult patient.

We report the case of 74-year-old patient suspected of post-traumatic external hydrocephalus (EH) following a mild traumatic brain injury with a progressive neurological decline and a concomitant enlargement of subarachnoid spaces without ventriculomegaly on CT scan. A lumbar puncture revealed raised ICP and a careful CSF withdrawal was performed, resulting in an immediate neurological improvement, confirming the diagnosis of EH. During the 20-month follow-up, the patient presented progressive signs of normal pressure hydrocephalus (NPH): gait and cognitive decline, ventriculomegaly and the lumbar infusion study confirmed disturbed CSF dynamics. The patient underwent a ventriculoperitoneal shunt surgery, resulting in a long-lasting improvement.

Surgical management of giant pituitary neuroendocrine tumors: Meta-analysis and consensus statement on behalf of the EANS skull base section.

Introduction: The optimal surgical treatment for giant pituitary neuroendocrine tumors(GPitNETs) is debated. Research question: The aim of this paper is to optimize the surgical management of these patients and to provide a consensus statement on behalf of the EANS Skull Base Section. Material and methods: We constituted a task force belonging to the EANS skull base committee to define some principles for the management of GPitNETs. A systematic review was performed according to PRISMA guidelines to perform a meta-analysis on surgical series of GPitNETs. Weighted summary rates were obtained for the pooled extent of resection and according to the surgical technique. These data were discussed to obtain recommendations after evaluation of the selected articles and discussion among the experts. Results: 20articles were included in our meta-analysis, for a total of 1263 patients. The endoscopic endonasal technique was used in 40.3% of cases, the microscopic endonasal approach in 34% of cases, transcranial approaches in 18.7% and combined approaches in 7% of cases. No difference in terms of gross total resection (GTR) rate was observed among the different techniques. Pooled GTR rate was 36.6%, while a near total resection (NTR) was possible in 45.2% of cases. Cavernous sinus invasion was associated with a lower GTR rate (OR: 0.061). After surgery, 35% of patients had endocrinological improvement and 75.6% had visual improvement. Recurrent tumors were reported in 10% of cases. Discussion and conclusion: After formal discussion in the working group, we recommend the treatment of G-PitNETs tumors with a more complex and multilobular structure in tertiary care centers. The endoscopic endonasal approach is the first option of treatment and extended approaches should be planned according to extension, morphology and consistency of the lesion. Transcranial approaches play a role in selected cases, with a multicompartmental morphology, subarachnoid invasion and extension lateral to the internal carotid artery and in the management of residual tumor apoplexy.

Ventriculoatrial Shunt Under Locoregional Anesthesia: A Technical Note.

BACKGROUND: Ventriculoatrial shunt is routinely performed under general anesthesia and is used to treat various kinds of hydrocephalus. Idiopathic normal pressure hydrocephalus patients are generally elderly and can have high comorbidities; in such patients, avoiding general anesthesia and limiting opioid administration could be beneficial. We started to perform ventriculoatrial shunt under locoregional anesthesia, in order to make this procedure more truly "minimally invasive". METHODS: Demographic data, American Society of Anesthesiologists (ASA) score and vital signs, Ramsay sedation scale, and procedural duration were collected. All procedures were performed combining sedation with cervical plexus and scalp block. After internal jugular vein cannulation, a catheter was inserted and connected with a programmable valve and then with the ventricular catheter. Outcome was assessed by the Idiopathic Normal Pressure Hydrocephalus Grading Scale and complications were recorded at 3-month follow-up. RESULTS: Ten consecutive patients were enrolled; the mean age was 74 years, 8 were male, ASA score median value was 3. Opioids were administered only in 4 patients, in 6 patients the value of Ramsay scale was 5. The average duration of surgery was 59.5 minutes. No procedure was converted to general anesthesia. CONCLUSIONS: Our preliminary experience with ventriculoatrial shunt under locoregional anesthesia demonstrates that this technique is feasible, is not associated with an increase in operating times or complications, can avoid general anesthesia, and helps to limit opioid administration in the elderly. It can therefore represent a valid option in order to improve treatment quality in these complex patients.

Neoadjuvant B-RAF and MEK Inhibitor Targeted Therapy for Adult Papillary Craniopharyngiomas: A New Treatment Paradigm.

Background: Surgical and clinical management of craniopharyngiomas is associated with high long-term morbidity especially in the case of hypothalamic involvement. Improvements in knowledge of craniopharyngioma molecular biology may offer the possibility of safe and effective medical neoadjuvant treatments in a subset of patients harboring papillary subtype tumors with a BRAFV600E mutation. Method: We report herein two cases of tubero-infundibular and ventricular Papillary Craniopharyngiomas in which BRAF/MEK inhibitor combined therapy was used as adjuvant (Case 1) or neoadjuvant (Case 2) treatment, with a 90% reduction in tumor volume observed after only 5 months. In Case 2 the only surgical procedure used was a minimal invasive biopsy by the trans-ventricular neuroendoscopic approach. As a consequence, targeted therapy was administered in purely neoadjuvant fashion. After shrinkage of the tumor, both patients underwent fractionated radiotherapy on the small tumor remnant to achieve long-term tumor control. A review of a previously reported case has also been performed. Result: This approach led to tumor control with minimal long-term morbidity in both cases. No side effects or complications were reported after medical treatment and adjuvant radiotherapy. Conclusion: Our experience and a review of the literature argue for a change in the current treatment paradigm for Craniopharyngiomas (CPs). In giant and invasive tumors, confirmation of BRAFV600E mutated PCPs by biopsy and BRAF/MEK inhibitor therapy before proposing other treatments may be useful to improve long term outcomes for patients.

Impact of Head-of-Bed Posture on Brain Oxygenation in Patients with Acute Brain Injury: A Prospective Cohort Study.

BACKGROUND: Therapeutic head positioning plays a role in the management of patients with acute brain injury. Although intracranial pressure (ICP) is typically lower in an upright posture than in a flat position, limited data exist concerning the effect of upright positioning on brain oxygenation and circulation. We sought to determine the impact of supine (0°) and semirecumbent (15° and 30°) postures on ICP, brain oxygenation, and brain circulation. METHODS: An observational cohort study was conducted between February 2012 and September 2015. Twenty-three patients with severe acute brain injury were successively observed at head elevations of 30°, 15°, and 0°. Postural-induced changes in ICP, cerebral perfusion pressure, brain tissue oxygenation pressure, and transcranial Doppler findings were simultaneously measured during three repeated experiments: 24 h after admission to the intensive care unit (exp1), 24 h later (exp2), and 96 h later (exp3). Cerebral perfusion pressure, arterial blood gases, hemoglobin content, and body temperature remained unchanged during the three experiments. RESULTS: Using linear random-slope mixed models, we found that during the early phase of acute brain injury (exp1), lowering the head posture from 30° to 15°, and then to 0°, was associated with a gradual mean ICP increase of 2.6 mm Hg (1.4-3.7 mm Hg; P < 0.001); and from 30° to 0°, an increase of 7.4 mm Hg (6.3-8.6 mm Hg; P < 0.001). Furthermore, brain tissue oxygenation pressure and mean blood flow velocity improved when the head posture was lowered from 30° to 0° by 1.2 mm Hg (0.2-2.3 mm Hg) and 4.1 cm/s (0.0-8.2 cm/s), respectively (both P < 0.05). CONCLUSIONS: Changing the positioning of stable patients with acute brain injury resulted in opposite changes of ICP versus brain oxygenation and circulation. This information supports the concept of an individualized approach to head positioning that is based on the multimodal monitoring of brain parameters.

External Hydrocephalus After Traumatic Brain Injury: Retrospective Study of 102 Patients.

INTRODUCTION: External hydrocephalus (EH) refers to impairment of extra-axial cerebrospinal fluid flow with enlargement of the subarachnoid space (SAS) and concomitant raised intracranial pressure (ICP). It is often confused with a subdural hygroma and overlooked, particularly when there is no ventricular enlargement. In this study, we aimed to describe the epidemiology of EH in a large population of adults with traumatic brain injury (TBI). METHODS: This observational, retrospective cohort study was conducted in adult patients who were admitted with TBI to the Department of Clinical Neuroscience at Addenbrooke's Hospital (Cambridge, UK) over a period of 3 years (2014-2017). Patients were included in the study if they had ICP monitoring and at least three CT scans within the first 21 days to assess SAS evolution. Patients who underwent a decompressive craniectomy were excluded. SAS was assessed individually on each CT scan by two independent investigators. ICP data were analysed with ICM+ software (Cambridge Enterprise Ltd., Cambridge, UK). Short-term and 6-month outcomes were examined. The groups of patients with and without EH were compared. RESULTS: Of the 102 patients included in the study, 30.4% developed EH after a delay of 2.98 ± 2.4 days. The initial Glasgow Coma Scale (GCS) scores did not differ between patients with and without EH. Subarachnoid haemorrhage was found to be the main risk factor for EH. Patients with EH required a significantly longer period of mechanical ventilation (+6.9 days), were more likely to have a tracheostomy (55% versus 33%), and had a longer stay in the intensive care unit (+8.5 days). ICP was higher during the 48 h after diagnosis of EH than during the previous 48 h. EH survivors had a lower mean Glasgow Outcome Scale Extended (GOS-E) score (4.6 versus 5.9, P = 0.031) and were more likely to receive a permanent shunt for secondary hydrocephalus (17.4% versus 1.8%, odds ratio 7.1). CONCLUSION: In adults with TBI, EH remains insufficiently understood and probably underdiagnosed. This study showed that it is a frequent complication of TBI, with significant clinical consequences.

Quick Assessment of the Lower Limit of Autoregulation by Use of Transcranial Doppler Ultrasound During Cardiac Surgery.

INTRODUCTION: Assessment of the individual safest minimal mean arterial pressure (MAP) during cardiac surgery remains empirical. The objective of this study was to evaluate the lower limit of autoregulation (LLA) within a short period (15 min). METHODS: After developing autoregulation software (OptiMAP) incorporated into transcranial Doppler ultrasound (Waki-Atys®, Lyon, France), we monitored the mean blood flow velocity (MV) and MAP. Thirty successive values of MV and MAP were automatically analysed to calculate the correlation (Mx) between the two parameters. We compared two methods of Mx sampling during a period of 15 min: Mx10s = long averaging windows (one MAP/MV pair recorded every 10 s), and Mx2s = short averaging windows (one MAP/MV pair recorded every 2 s). The LLA value calculated from the whole recording (Mx10s) was used as the reference. Autoregulation was considered impaired at an Mx value >0.35. RESULTS: Five patients were included in the study. The surgery lasted for 138 ± 32 min and cardiopulmonary bypass lasted for 72 ± 33 min. MAP and MV were recorded for 117 ± 24 min. MAP varied from 33 ± 10 to 92 ± 10 mmHg. LLA calculated from the whole recording (Mx10s) was similar to LLA calculated from the 15-min recording (Mx2s): 70 ± 2.5 versus 73 ± 3.5 mmHg. MAP remained below LLA during 48 ± 12% of the recording. During the 15-min recording, Mx10s was not able to calculate the LLA value. CONCLUSION: In cases of haemodynamic instability, decreasing the Mx sampling window seems to accurately detect LLA.

Should the Impact of Postural Change of Intracranial Pressure After Surgical Repair of Skull Base Cerebrospinal Fluid Leaks Be Considered? A Preliminary Survey.

INTRODUCTION: Managing skull base cerebrospinal fluid (CSF) leaks is often challenging. Postoperative care, especially regarding postural restrictions and bedrest recommendations, is variable and continues to be based on empirical habits. METHODS: An electronic survey was submitted to French experts in skull base surgery to evaluate current practice of postoperative postural recommendations in patients treated for skull base CSF leaks. RESULTS: Thirty-nine experts completed the survey. Postoperative recommendations were heterogenous. They depended on the size of defects: half of the surgeons did not recommend any constraints of posture for small defects; 84% recommended bed rest for large defects. The most preferred bed-rest modality was Fowler's position (20°-30° tilt). Standing/walking during short periods was allowed in up to 73%. From a physiological viewpoint, head elevation decreases ICP and thus limits the risk of recurrence of CSF leak. However, ICP can fall below 0 in the standing position, favouring pneumocephalus. DISCUSSION: These results confirmed that postural recommendations for patients surgically treated for skull base CSF leaks remain variable. Recommendations should take into consideration the postural change in ICP. Fowler's position may represent the best compromise between risk of recurrence of CSF leak and the risk of pneumocephalus in large CSF leaks.

Assessment of Pressure-Volume Index During Lumbar Infusion Study: What Is the Optimal Method?

INTRODUCTION: Assessment of the pressure-volume index (PVI) during lumbar infusion study (LIS) has been proposed to evaluate the overall compliance of the cranio-spinal system. It is calculated from the measurement of CSF pressure changes, ΔP from Pb to Pp, in response to repeated bolus injections of a volume (ΔV) within the lumbar subarachnoid space. MATERIAL AND METHODS: We retrospectively analyzed 18 patients who underwent LIS for suspicion of normal pressure hydrocephalus, including a series of three fast bolus injections of 3 mL of saline at different levels of CSF pressure. We compared two methods for PVI calculation: (a) PVIslope using the slope α of a linear fit ΔP = α(Pb - P 0), PVI = ΔV/log10(α + 1); (b) PVImean using the PVI calculated independently for each bolus injection assuming P 0 = 0, PVI = mean(ΔV/log10(Ppi/Pbi))i=1.3. RESULTS: We found a significant discrepancy between the two methods: the average difference (PVIslope - PVImean) was -3.93 mL (95% confidence interval [8.77; -16.64]). In the PVIslope, method, the mean P 0 was 2.12 mmHg (±3.41 mmHg). DISCUSSION: The clinical reliability of PVImean (assuming P 0 = 0) depends on the value of P 0. PVIslope provides results, independent of P 0. Future studies should focus on determining pathological PVI range rather than fixed cut-off values.

Postural Regulation of Intracranial Pressure: A Critical Review of the Literature.

INTRODUCTION: Mechanisms underlying postural regulation of ICP remain unclear. METHOD: Literature review in Medline 1900-2019 with search terms "Intracranial pressure," "Posture," "Jugular vein," "Collapse," "Regulation," "Physiology," resulting in 40 selected papers. RESULTS: Postural transition from supine to sitting position results in a biphasic decrease of ICP: a fast decrease during phase 1 (low tilt) followed by a stabilization during phase 2 (higher tilt/erect). Two main factors have been proposed to explain this decrease: (a) Fast CSF transfers from the non-distensible cranial compartment to the distensible spinal compartment during phase 1; the maximal spinal expansion corresponds to phase 2; (b) The gravitational effect within the venous system is transferred to the CSF system according to Davson's equation, modulated by jugular collapse that would be responsible for the stabilization of ICP decrease in phase 2. DISCUSSION: The impact of CSF transfers, from the cranial to spinal compartment, on postural regulation of ICP, has been well documented. Although they are sophisticated, models that support the major influence of jugular collapse likely underestimate the role of the vertebral venous plexus in cerebral venous outflow in the upright position. Moreover, Davson's equation supports slow CSF transfer from subarachnoid spaces to the venous system (a few mL/min) and thus cannot explain fast postural modulation of ICP (in a few seconds). Further data are thus needed to better understand postural regulation of ICP.