Differential Hemodynamic Response of Pial Arterioles Contributes to a Quadriphasic Cerebral Autoregulation Physiology.

Background Cerebrovascular autoregulation (CA) regulates cerebral vascular tone to maintain near-constant cerebral blood flow during fluctuations in cerebral perfusion pressure (CPP). Preclinical and clinical research has challenged the classic triphasic pressure-flow relationship, leaving the normal pressure-flow relationship unclear. Methods and Results We used in vivo imaging of the hemodynamic response in pial arterioles to study CA in a porcine closed cranial window model during nonpharmacological blood pressure manipulation. Red blood cell flux was determined in 52 pial arterioles during 10 hypotension and 10 hypertension experiments to describe the pressure-flow relationship. We found a quadriphasic pressure-flow relationship with 4 distinct physiological phases. Smaller arterioles demonstrated greater vasodilation during low CPP when compared with large arterioles (P<0.01), whereas vasoconstrictive capacity during high CPP was not significantly different between arterioles (P>0.9). The upper limit of CA was defined by 2 breakpoints. Increases in CPP lead to a point of maximal vasoconstriction of the smallest pial arterioles (upper limit of autoregulation [ULA] 1). Beyond ULA1, only larger arterioles maintain a limited additional vasoconstrictive capacity, extending the buffer for high CPP. Beyond ULA2, vasoconstrictive capacity is exhausted, and all pial arterioles passively dilate. There was substantial intersubject variability, with ranges of 29.2, 47.3, and 50.9 mm Hg for the lower limit, ULA1, and ULA2, respectively. Conclusions We provide new insights into the quadriphasic physiology of CA, differentiating between truly active CA and an extended capacity to buffer increased CPP with progressive failure of CA. In this experimental model, the limits of CA widely varied between subjects.

The Effects of Angiotensin II or Angiotensin 1-7 on Rat Pial Microcirculation during Hypoperfusion and Reperfusion Injury: Role of Redox Stress.

Renin-angiotensin systems produce angiotensin II (Ang II) and angiotensin 1-7 (Ang 1-7), which are able to induce opposite effects on circulation. This study in vivo assessed the effects induced by Ang II or Ang 1-7 on rat pial microcirculation during hypoperfusion-reperfusion, clarifying the mechanisms causing the imbalance between Ang II and Ang 1-7. The fluorescence microscopy was used to quantify the microvascular parameters. Hypoperfusion and reperfusion caused vasoconstriction, disruption of blood-brain barrier, reduction of capillary perfusion and an increase in reactive oxygen species production. Rats treated with Ang II showed exacerbated microvascular damage with stronger vasoconstriction compared to hypoperfused rats, a further increase in leakage, higher decrease in capillary perfusion and marker oxidative stress. Candesartan cilexetil (specific Ang II type 1 receptor (AT1R) antagonist) administration prior to Ang II prevented the effects induced by Ang II, blunting the hypoperfusion-reperfusion injury. Ang 1-7 or ACE2 activator administration, preserved the pial microcirculation from hypoperfusion-reperfusion damage. These effects of Ang 1-7 were blunted by a Mas (Mas oncogene-encoded protein) receptor antagonist, while Ang II type 2 receptor antagonists did not affect Ang 1-7-induced changes. In conclusion, Ang II and Ang 1-7 triggered different mechanisms through AT1R or MAS receptors able to affect cerebral microvascular injury.

De Novo Dural Arteriovenous Fistula on Draining Veins of Previously Treated Pial Arteriovenous Malformation: a Case Report.

A 71-year-old man, with a pial micro-arteriovenous malformation (pAVM) draining into the confluence of the vein of Trolard and the vein of Labbé was surgically removed, sparing these cortical veins. 4-months MR and angiographic controls showed a de novo dural arteriovenous fistula (dAVF) draining into the previously spared cortical veins. It was removed using intraoperative motor evoked potentials (MEP). This is the first case of iatrogenic dAVF developing on the same draining vein of a previously treated pAVM. De novo dAVFs are generally iatrogenic. This case suggests that the unresected venous drainage of an AVM might be the substratum for neo-angiogenetic processes; moreover inflammation related to surgery might be the trigger factor for the development of the dAVF.

Clinical, angiographic, and treatment characteristics of cranial dural arteriovenous fistulas with pial arterial supply.

BACKGROUND: The prevalence of pial arterial supply to cranial dural arteriovenous fistulas (dAVF) and its implication in the management of these fistulas is not well characterized. We performed a retrospective study to characterize pial arterial supply to dural arteriovenous fistulas and the implications for treatment. METHODS: Consecutive patients evaluated over a 12-year period were retrospectively reviewed. Angiograms were reviewed to characterize dAVF angioarchitecture and the presence of pial artery supply. Pial artery supply was categorized as dilated pre-existing dural branches and pure pial supply. We then studied the association between pial artery supply and clinical, angiographic, and treatment features. RESULTS: A total of 201 patients were included of which 27 (13.4%) had pial artery supply. Of these, 11 had supply from dilated pre-existing dural branches, nine had pure pial supply,and seven had both. There was a higher rate of dAVF rupture in the pial supply group (30.8% vs 9.8%, P=0.003) and these fistulas had a higher rate of Borden 2 and 3 (88.9% vs 38.4%, P<0.0001). Fistulas with pial artery supply had similar rates of endovascular and gamma knife treatment, but were more likely to undergo surgery than those without pial supply (25.9% vs 10.4%, P=0.03). Major complication rates were similar between groups (0% vs 1.1%, P=0.55). CONCLUSIONS: More than 10% of dAVFs also have pial supply but this is not a contraindication to embolization. In our study pure pial supply was associated with a more aggressive fistula and was most common in tentorial dAVFs.

Matas test revisited: carotid compression for embolization of high-flow pediatric pial arteriovenous fistulas.

OBJECTIVE: Cerebral pial arteriovenous fistula (AVF) is a rare vascular malformation and may cause hemorrhage and neurological deficit. The presence of high-flow shunts constitutes a challenge when performing the endovascular technique, due to risk of distal embolization. The authors report a simple maneuver, adapted from the Matas test, that was successfully applied to treat a child with two pial AVFs. METHODS: An 8-year-old boy presented with headache and vomiting due to two single-channel high-flow intracerebral pial AVFs. He was treated with an endovascular approach using brief, gentle compression of the ipsilateral cervical carotid artery. The temporary flow arrest ensured proper placement of the first coil, allowing definitive obliteration of the shunt. RESULTS: There were no complications with the procedure, and the patient recovered uneventfully. Throughout the 9-month follow-up, the patient experienced a stable neurological condition, with both fistulas occluded and improvement of local circulation. CONCLUSIONS: This easy-to-perform maneuver allows precise positioning of embolic material into high-flow shunts to facilitate treatment of pial AVF.

Pial arteriovenous fistula with appearance of hemorrhagic tumor: A case report.

INTRODUCTION: Pial arteriovenous fistula (PAVF) is a rare intracranial vascular disease, and its presentation with a huge tumor-resembling thrombus is rarer. PATIENT CONCERNS: A 38-year-old female patient presented with a sudden left-side motor disorder and loss of consciousness. The patient was otherwise in good health and had no history of hypertension or diabetes. During the physical examination, she appeared lethargic and manifested left limb paralysis with level zero muscle strength and a positive pathological reflex. DIAGNOSES: Because imaging failed to rule out a tumor stroke, an intracranial lesion resection was performed immediately. Because the lesion was considered to be a vascular structure, digital subtraction angiography was undertaken before the surgery, and PAVF was diagnosed. INTERVENTIONS: Endovascular embolization was conducted, followed by PAVF and hematoma resection. OUTCOMES: At the 3-month follow up, her left limb muscle strength was level 4, and she could live on her own (Modified Rankin Scale score = 2). CONCLUSIONS: It is noteworthy that PAVF with a large thrombus may appear as a tumor in the initial diagnosis, and therefore it is necessary to perform an intracranial vascular examination in patients with tumor stroke symptoms.

ACE (Angiotensin-Converting Enzyme) Inhibition Reverses Vasoconstriction and Impaired Dilation of Pial Collaterals in Chronic Hypertension.

Leptomeningeal anastomoses (LMAs) are pial collaterals that perfuse the penumbra and important for stroke outcome. We previously showed LMAs from SHRs (spontaneously hypertensive rats) were vasoconstricted compared with normotensive Wistar rats. Here, we investigated mechanisms by which hypertension causes LMA vasoconstriction. SHRs were treated with the ACE (angiotensin-converting enzyme) inhibitor captopril, an Ang II (angiotensin II)-independent antihypertensive agent hydralazine, or vehicle for 5 weeks in drinking water (n=8/group). A group of Wistar rats (n=8) had regular drinking water served as controls. Blood pressure was measured twice weekly by tail-cuff. LMAs were isolated and studied under pressurized conditions. Vasoreactivity of LMAs, including myogenic responses, reactivity to Rho-kinase inhibitor Y-27632, and nitric oxide were measured. Both captopril and hydralazine lowered blood pressure in SHRs similar to Wistar. However, only captopril normalized LMA increased tone compared with untreated SHRs (15±2% versus 50±3%; P<0.01) that was similar to Wistar (16±2%) but not hydralazine (38±6%; P>0.05). Vasodilatory response of LMAs to Y-27632 was impaired in SHRs compared with Wistar (28±3% versus 81±4%; P<0.01) that was restored by captopril (84±5%; P<0.01) and partially hydralazine (59±4%). LMAs from all groups constricted similarly to NOS (NO synthase) inhibition; however, the vasodilatory response of LMAs to the nitric oxide donor sodium nitroprusside was impaired in SHRs compared with Wistar rats (29±4% versus 80±2%; P<0.01) that was restored by captopril (84±4%; P<0.01), not hydralazine (38±8%; P>0.05). These results suggest that ACE inhibition during chronic hypertension reversed vascular dysfunction and hyperconstriction of LMAs that could improve stroke outcome by increasing collateral perfusion.

Multiple Cranial Dural and Pial Arteriovenous Fistulas with Occlusion of All After Embolization of Primary Superior Sagittal Sinus Dural Fistula.

BACKGROUND: We present a rare case of multiple intracranial arteriovenous fistulas (AVFs). A young female presented with headache and a left eyelid pulsatile swelling. CASE DESCRIPTION: Magnetic resonance imaging demonstrated numerous dilated cortical veins, along with a prominent left superior ophthalmic vein. A diagnostic cerebral angiogram revealed 5 distinct AVFs including 4 dural AVFs (dAVFs) and a pial AVF (pAVF). The largest dAVF was at the superior sagittal sinus. The others included bilateral ethmoidal, torcular, and a pAVF arising of the right pericallosal artery. She was treated by endovascular transarterial Onyx embolization. Only the superior sagittal sinus fistula was treated via middle meningeal artery feeders with complete occlusion. Immediate follow-up angiogram also showed complete spontaneous occlusion of the untreated dAVFs and pial AVF. CONCLUSIONS: This case is exceedingly unique considering the multiplicity of AVFs, concurrent presence of pial and dural AVF, and spontaneous occlusion of all untreated AVFs after embolizing the largest shunting fistula.

Surgical Disconnection of a Residual Pediatric Pial Arterio-Venous Fistula Following Partial Embolization: A Case Study.

BACKGROUND: Pial arteriovenous fistulas (AVFs) are rare intracranial vascular lesions consisting of 1 or more feeder arteries connecting directly to a venous system without a nidus, in the subpial space. Because of the high-flow system, they are commonly associated with a large varix. They are thought to represent between 1.6% and 7.3% of all pediatric arteriovenous malformations (AVMs). Morbidity and mortality is high in this condition and surgical or endovascular treatment options are usually considered. There have been limited reports on the clinical features, treatment options, and outcomes of pial AVMs due to its rarity. We present a case study of a pediatric patient in our institution and her clinical course, focusing on her presenting clinical features and management. CASE DESCRIPTION: A 1-year-old girl presents with progressively prominent and dilated facial veins and no other features suggestive of pial AVF. She was diagnosed with pial AVF with two feeder arteries and a large varix on imaging. Embolization was undertaken 3 times before successful surgical disconnection was done. Genetic testing for associated syndromes were all negative. CONCLUSIONS: Prominence of facial veins could be 1 of the more uncommon presenting features of pial AVFs. Genetic testing should always be considered in the pediatric population diagnosed with AVFs because of their association to various syndromes. Despite endovascular embolization being considered the less invasive choice, decision on mode of treatment should be a multifactorial decision.

Predictors for the extent of pial collateral recruitment in acute ischemic stroke.

BACKGROUND: Pial arterioles can provide a variable degree of collateral flow to ischemic vascular territories during acute ischemic stroke. This study sought to identify predictive factors of the degree of pial collateral recruitment in acute ischemic stroke. METHODS: Clinical information and arteriograms from 62 consecutive patients with stroke due to either middle cerebral artery (MCA) M1 segment or internal carotid artery (ICA) terminus occlusion within 6 h following symptom onset were retrospectively reviewed. Pial collaterals were defined based on the extent of reconstitution of the MCA territory. Patients with slow antegrade flow distal to the occlusion site were excluded and no anesthetics were used prior or during angiography. Results were analyzed using multivariate nominal logistic regression. RESULTS: Better pial collateral recruitment was associated with proximal MCA versus ICA terminus occlusion (p = 0.005; odds ratio (OR) = 9.3; 95% confidence interval (CI), 2.16-53.3), lower presenting National Institutes of Health Stroke Scale Score (NIHSSS) (p = 0.023; OR = 6.51; 95% CI, 1.49-41.7), and lower diastolic blood pressure (p = 0.0411; OR = 5.05; 95% CI, 1.20-29.2). Age, gender, symptom duration, diabetes, laterality, systolic blood pressure, glucose level, hematocrit, platelet level, and white blood cell count at presentation were not found to have a statistically significant association with pial collateral recruitment. CONCLUSIONS: Extent of pial collateral recruitment is strongly associated with the occlusion site (MCA M1 segment versus ICA terminus) and less strongly associated with presenting NIHSSS and diastolic blood pressure.

Hypertension and sympathetic nervous system overactivity rely on the vascular tone of pial vessels of the rostral ventrolateral medulla in spontaneously hypertensive rats.

NEW FINDINGS: What is the central question of this study? Is purinergic signalling in the pial vessels involved in the control of vascular tone in the ventral surface of the brainstem, affecting high blood pressure and sympathetic overactivity in spontaneously hypertensive rats? What is the main finding and its importance? The regulation of vascular tone in the ventral surface of the brainstem is tailored to support neuronal functions, arterial pressure and sympathetic activity. This adds one more piece in the complex puzzle to understand the central mechanisms underlying the genesis of hypertension. ABSTRACT: Evidence suggests the rostral ventrolateral medulla (RVLM) region is chronically hypoperfused and hypoxic in spontaneously hypertensive rats (SHR), which can facilitate ATP release throughout the brainstem. Thus, we hypothesized that purinergic signalling plays a key role in the increased vascular tone in the RVLM region, which in turn could be responsible for the high sympathetic tone and blood pressure in the SHR. The application of an antagonist of P2 receptors, pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (10 µm), or of P2Y1a receptors, MRS2179 (100 µm), on the surface of RVLM pial vessels of SHR produced an increase in the diameter of blood vessels (PPADS: 31 ± 1.4 µm or MRS2179: 32 ± 0.78 µm vs. saline: 27 ± 1.2 µm), an effect not observed in normotensive Wistar rats. In addition, the antagonism of P2 receptors was able to evoke a significant decrease in the arterial pressure, heart rate and splanchnic nerve activity in SHR, but not in Wistar rats. Our data show that SHR have higher vascular tone of pial vessels in the RVLM region when compared to the normotensive Wistar rats, a mechanism that relies on purinergic signalling through P2 receptors, suggesting a possible association with higher activity of sympathoexcitatory neurones, and sustained increases in blood pressure.

Hyperglycemia-induced transcriptional regulation of ROCK1 and TGM2 expression is involved in small artery remodeling in obese diabetic Göttingen Minipigs.

Obesity and diabetes in humans are associated with hypertrophic remodeling and increased media:lumen ratio of small resistance arteries, which is an independent predictor of cardiovascular events. In order to minimize increases in media:lumen ratio, hypertrophic remodeling should be accompanied by outward remodeling. We aimed to investigate the mechanisms of structural remodeling in small pial arteries (PAs) and terminal mesenteric arteries (TMAs) from obese Göttingen Minipigs with or without diabetes. Göttingen Minipigs received either control diet (lean control (LC)), high fat/high fructose/high cholesterol diet (FFC), or FFC diet with streptozotocin (STZ)-induced diabetes (FFC/STZ) for 13 months. At the end of the study (20 months), we assessed body weight, fasting plasma biochemistry, passive vessel dimensions, mRNA expression (matrix metallopeptidases 2/9 (MMP2, MMP9), tissue inhibitor of metallopeptidase 1 (TIMP1), transglutaminase 2 (TGM2), Rho-kinase 1 (ROCK1), TGFß-receptor 2 (TGFBR2), and IGF1-receptor (IGFR1) genes), and immunofluorescence in PAs and TMAs. We performed multiple linear correlation analyses using plasma values, structural data, and gene expression data. We detected outward hypertrophic remodeling in TMAs and hypertrophic remodeling in PAs from FFC/STZ animals. ROCK1 and TGM2 genes were up-regulated in PAs and TMAs from the FFC/STZ group. Passive lumen diameter (PLD) of TMAs was correlated with plasma values of glucose (GLU), fructosamine (FRA), total cholesterol (TC), and triglycerides (TGs). ROCK1 and TGM2 expressions in TMAs were correlated with PLD, plasma GLU, fructosamine, and TC. ROCK1 and TGM2 proteins were immunolocalized in the media of PAs and TMAs, and their fluorescence levels were increased in the FFC/STZ group. Hyperglycemia/hyperlipidemia is involved in regulation of ROCK1 and TGM2 expression leading to outward remodeling of small resistance arteries in obese diabetic Göttingen Minipigs.

Autoregulation assessment by direct visualisation of pial arterial blood flow in the piglet brain.

Impairment of cerebrovascular autoregulation (CAR) is common after brain injury, although the pathophysiology remains elusive. The mechanisms of vascular dysregulation, their impact on brain function, and potential therapeutic implications are still incompletely understood. Clinical assessment of CAR remains challenging. Observational studies suggest that CAR impairment is associated with worse outcomes, and that optimization of cerebral blood flow (CBF) by individual arterial blood pressure (ABP) targets could potentially improve outcome. We present a porcine closed cranial window model that measures the hemodynamic response of pial arterioles, the main site of CBF control, based on changes in their diameter and red blood cell velocity. This quantitative direct CAR assessment is compared to laser Doppler flow (LDF). CAR breakpoints are determined by segmented regression analysis and validated using LDF and brain tissue oxygen pressure. Using a standardized cortical impact, CAR impairment in traumatic brain injury can be studied using our method of combining pial arteriolar diameter and RBC velocity to quantify RBC flux in a large animal model. The model has numerous potential applications to investigate CAR physiology and pathophysiology of CAR impairment after brain injury, the impact of therapeutic interventions, drugs, and other confounders, or to develop personalized ABP management strategies.

The projection of anorectal afferents to cortex of the rat: Comparison of two methods of cortical mapping.

BACKGROUND: The rat has served usefully as a model for fecal incontinence and exploration of the mechanism of action of sacral neuromodulation. However, there is a gap in knowledge concerning representation(s) on the primary sensory cortex of this anatomical region. METHODS: Multi-electrode array (32 channels) and intrinsic optical signal (IOS) processing were used to map cortical activation sites following anorectal electrical stimulation in the rat. A simple method for expanding a 32-electrode array to a virtual 2700 array was refined. KEY RESULTS: The IOS method identified activation of parietal cortex following anorectal or first sacral nerve root (S1) stimulation; however, the signal was poorly localized and large spontaneous vasomotion was observed in pial vessels. In contrast, the resulting high-density maps showed two anatomically distinct cortical activation sites to anorectal stimulation. CONCLUSIONS & INFERENCES: There are two distinct sites of activation on the parietal cortex following anorectal stimulation in the rat. The implications for sacral neuromodulation as a therapy for fecal incontinence are discussed.

Formation and Resolution of Pial Microvascular Thrombosis in a Mouse Model of Thrombotic Thrombocytopenic Purpura.

OBJECTIVE: Microvascular thrombosis is the hallmark pathology of thrombotic thrombocytopenic purpura (TTP), a rare life-threatening disease. Neurological dysfunction is present in over 90% of patients with TTP, and TTP can cause long-lasting neurological damage or death. However, the pathophysiology of microvascular thrombosis in the brain is not well studied to date. Here, we investigate the formation and resolution of thrombosis in pial microvessels. Approach and Results: Using a cranial intravital microscopy in well-established mouse models of congenital TTP induced by infusion of recombinant VWF (von Willebrand factor), we found that soluble VWF, at high concentration, adheres to the endothelium of the vessel wall, self-associates, and initiates platelet adhesion resulting in the formation of pial microvascular thrombosis in ADAMTS13-/- (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) mice. Importantly, VWF-mediated pial microvascular thrombosis occurred without vascular injury to the brain, and thrombi consisted of resting platelets adhered onto ultra-large VWF without fibrin in the brain in rVWF (recombinant VWF) challenged ADAMTS13-/- mice. Prophylactic treatment with recombinant ADAMTS13 (BAX930) effectively prevented the onset of the VWF-mediated microvascular thrombosis and therapeutic treatment with BAX930 acutely resolved the preexisting or growing thrombi in the brain of ADAMTS13-/- mice after rVWF challenge. The absence of platelet activation and fibrin formation within VWF-mediated thrombi and efficacy of BAX930 was confirmed with an endothelial-driven VWF-mediated microvascular thrombosis model in mice. CONCLUSIONS: Our results provide important insight into the initiation and development of microvascular thrombi in mouse models that mimics TTP and indicate that rADAMTS13 could be an effective interventional therapy for microvascular thrombosis, the hallmark pathology in TTP.

Study on in Vivo Pial Vessels Alterations and Activity of Isolated Vascular Smooth Muscles in Abdominal Hypertension Rats.

BACKGROUND: Intra-abdominal hypertension is known as a factor affecting cerebral haemodynamics. Sustainably elevated abdominal pressure may disturb the balance of intracranial/blood pressure ratio, eventually developing perfusion pressure to drop. AIM: The aim of this study is to investigate the influence of artificially elevated intra-abdominal pressure upon brain pial vessels condition and contractile reactivity of isolated rat arteria carotis communis and vena jugularis to norepinephrine and serotonin. MATERIALS AND METHODS: The abdominal pressure of rats anaesthetized with xylazine 10 mg/kg and ketamine 100 mg/kg was increased up to 25 mm Hg by insufflation of air through venflon cannula and maintained for period of 1 to 3 hours. Craniotomy of left parietal area was carried out by micro drill. Open scull and cranial window techniques were applied. Outer diameters of superficial pial vessels were measured by USB digital microcamera (magnification up to 400x). Contractile reactivity of smooth muscle preparations from arteria carotis communis and vena jugularis of euthanized abdominal-hypertensive (AH) rats was registered isometrically. RESULTS: Increased smooth muscle reactivity of a. carotis communis from AH rats to serotonin (10-8-10-4 mol/l) but not to norepinephrine compared to controls was registered. The changes tended to be higher in long lasting (3 hours) exposure of AH rats. Increase in outer diameter of pial vessels during maintenance of abdominal hypertension in both open scull and cranial window techniques was found. CONCLUSIONS: The increased intra-abdominal pressure causes dilatation of small superficial cerebral blood vessels and increases the smooth muscle reactivity of isolated arteria carotis communis to 5-HT.

Cerebral amyloid-ß-related angiitis without cerebral microbleeds in a patient with subarachnoid hemorrhage.

Amyloid-ß-related angiitis (ABRA), a subtype of cerebral amyloid angiopathy (CAA), is vasculitis occurring in relation to amyloid-ß (Aß) deposition in the walls of intracranial blood vessels. ABRA is presumed to be caused by some immune response to the deposited Aß. An 81-year-old man on oral anticoagulant therapy complained of headache, nausea, and difficulty with standing after a head injury. Head computed tomography revealed subcortical bleeding in the right temporoparietal lobe, and 3 days after admission, magnetic resonance imaging (MRI) showed subarachnoid hemorrhage (SAH) around the hematoma. Cerebral microbleeds, a characteristic of CAA, were not detected on MRI. On worsening of his symptoms, intracranial brain biopsy and hematoma removal were performed. Intraoperative rapid diagnosis with a frozen section suspected vasculitis, which enabled the prompt initiation of steroid therapy. He was pathologically diagnosed with ABRA (granulomatous angiitis) using a formalin-fixed paraffin-embedded section. Vasculitis was prominent around blood vessels in the pia matter covering the cerebrum. In this case, the inflammatory cells seemed to appear via the subarachnoid space following cerebral hemorrhage and SAH. ABRA seemed to be developed by intracranial hemorrhage in this case.

Hydraulic resistance of periarterial spaces in the brain.

BACKGROUND: Periarterial spaces (PASs) are annular channels that surround arteries in the brain and contain cerebrospinal fluid (CSF): a flow of CSF in these channels is thought to be an important part of the brain's system for clearing metabolic wastes. In vivo observations reveal that they are not concentric, circular annuli, however: the outer boundaries are often oblate, and the arteries that form the inner boundaries are often offset from the central axis. METHODS: We model PAS cross-sections as circles surrounded by ellipses and vary the radii of the circles, major and minor axes of the ellipses, and two-dimensional eccentricities of the circles with respect to the ellipses. For each shape, we solve the governing Navier-Stokes equation to determine the velocity profile for steady laminar flow and then compute the corresponding hydraulic resistance. RESULTS: We find that the observed shapes of PASs have lower hydraulic resistance than concentric, circular annuli of the same size, and therefore allow faster, more efficient flow of cerebrospinal fluid. We find that the minimum hydraulic resistance (and therefore maximum flow rate) for a given PAS cross-sectional area occurs when the ellipse is elongated and intersects the circle, dividing the PAS into two lobes, as is common around pial arteries. We also find that if both the inner and outer boundaries are nearly circular, the minimum hydraulic resistance occurs when the eccentricity is large, as is common around penetrating arteries. CONCLUSIONS: The concentric circular annulus assumed in recent studies is not a good model of the shape of actual PASs observed in vivo, and it greatly overestimates the hydraulic resistance of the PAS. Our parameterization can be used to incorporate more realistic resistances into hydraulic network models of flow of cerebrospinal fluid in the brain. Our results demonstrate that actual shapes observed in vivo are nearly optimal, in the sense of offering the least hydraulic resistance. This optimization may well represent an evolutionary adaptation that maximizes clearance of metabolic waste from the brain.