Normal perfusion pressure breakthrough: the role of capillaries

Minor micro-rheological alterations in the presence of an artificial saphenous arteriovenous shunt, as an arteriovenous malformation model in the rat

BACKGROUND

Arteriovenous malformations (AVMs) are vascular anomalies characterized by abnormal shunting between arteries and veins. The progression of the AVMs and their hemodynamic and rheological relations are poorly studied, and there is a lack of a feasible experimental model.

OBJECTIVE

To establish a model that cause only minimal micro-rheological alterations, compared to other AV models.

METHODS

Sixteen female Sprague Dawley rats were randomly divided into control and AVM groups. End-to-end anastomoses were created between the saphenous veins and arteries to mimic AVM nidus. Hematological and hemorheological parameters were analyzed before surgery and on the 1st, 3rd, 5th, 7th, 9th, and 12th postoperative weeks.

RESULTS

Compared to sham-operated Control group the AVM group did not show important alterations in hematological parameters nor in erythrocyte aggregation and deformability. However, slightly increased aggregation and moderately decreased deformability values were found, without significant differences. The changes normalized by the 12th postoperative week.

CONCLUSIONS

The presented rat model of a small-caliber AVM created on saphenous vessels does not cause significant micro-rheological changes. The alterations found were most likely related to the acute phase reactions and not to the presence of a small-caliber shunt. The model seems to be suitable for further studies of AVM progression.

An Illustrative Review of the Pathomechanisms of Symptomatic Developmental Venous Anomalies

OBJECTIVE

Symptomatic developmental venous anomalies (DVAs) are rare. Here, we illustrate the varied clinicoradiologic profiles of symptomatic DVAs and contemplate the mechanisms that render these (allegedly) benign entities symptomatic supported by a review of literature.

METHODS

Institutional databases were searched to identify cases of symptomatic DVAs. Clinical and imaging (angiographic and cross-sectional) data of 9 cases with 11 neurovascular symptoms consequent to inflow/outflow perturbations and mechanical obstruction that manifested because of the strategic topography of underlying DVAs were analyzed. A review of the existing literature on DVAs in agreement with our case series was performed on publications retrieved from the PubMed database.

RESULTS

Symptoms secondary to venous hypertension arising from flow-related perturbations were broadly divided into those arising from restricted outflow and increased inflow. Restricted outflow occurred because of collector vein stenosis (n = 2) and collector vein/DVA thrombosis (n = 3), whereas the latter pathomechanism was initiated by arterialized/transitional DVAs (n = 2). A mechanical/obstructive pathomechanism culminating in moderate supratentorial ventriculomegaly was noted in 1 case. One patient was given a diagnosis of hemorrhage associated with a cavernoma.

CONCLUSIONS

Awareness and contextualization of potential flow-related perturbations and mechanical insults that render DVAs symptomatic aid in accurate diagnosis, management, and prognostication.

Spontaneous regression of a symptomatic developmental venous anomaly with capillary stain

BACKGROUND

Developmental venous anomalies are considered benign lesions; however, they can become symptomatic. A capillary stain, which is an atypical angiographical feature of developmental venous anomalies, is reported to be relevant to symptomatic developmental venous anomalies.

CASE DESCRIPTION

A 20-year-old man with no pertinent medical history had an epileptic seizure. Magnetic resonance imaging showed severe focal oedema and gadolinium contrast enhancement in the right precentral gyrus and inferior frontal gyrus adjacent to the Sylvian fissure, indicating venous congestion; these presentations had not been observed on magnetic resonance imaging 8 months before. Digital subtraction angiography revealed a developmental venous anomaly with capillary stain. After conservative treatment, the brain oedema resolved spontaneously and contrast enhancement of the lesion reduced significantly.

CONCLUSION

We report a rare case of a symptomatic developmental venous anomaly with unique radiological characteristics and its natural and clinical evolution. Despite the presence of a capillary stain, our patient exhibited temporary exacerbations and spontaneous regression, suggesting that the capillary stain was associated with a reversible condition. This is the first report to detail the spatiotemporal changes of a developmental venous anomaly with capillary stain through imaging, suggesting that regular follow-up imaging is warranted in the management of patients with developmental venous anomalies.

Neuroprotective effect of indomethacin in normal perfusion pressure breakthrough phenomenon

Loss of cerebral autoregulation in normal perfusion pressure breakthrough (NPPB) phenomenon has been reported in other Central Nervous System diseases such as neonatal intraventricular haemorrhage. Several studies have demonstrated that low-dose indomethacin prevents this latter condition. A previous rat model was used to resemble NPPB phenomenon. Study animals were distributed in 4 groups that received 3 doses of indomethacin at different concentrations prior to fistula occlusion 60 days after its creation. Control animals received saline solution. Intracranial pressure (ICP) increased in all groups following fistula creation, whereas mean arterial pressure (MAP) and cerebral perfusion pressure (CPP) decreased as a manifestation of cerebral hypoperfusion and intracranial hypertension. The administration of indomethacin was associated with raised MAP and CPP, as well as decreased ICP. Sodium fluorescein extravasation was slight in study animals when comparing with control ones. Histological analysis evidenced diffuse ischaemic changes with signs of neuronal apoptosis in all brain layers in control animals. These findings were only focal and slight in study animals. The results suggest the usefulness of indomethacin to revert, at least partially, the haemodynamic effects of NPPB phenomenon in this experimental model, as well as to reduce BBB disruption and histological ischemia observed in absence of indomethacin.

Postoperative hemodynamic management in patients undergoing resection of cerebral arteriovenous malformations: A retrospective study

Strict control of blood pressure (BP) has been recommended in patients after surgical resection of cerebral arteriovenous malformations (AVM) to prevent postoperative hyperemic complication. The aim of this study was to review the postoperative hemodynamic management in patients after surgical resection of cerebral AVM and the incidence of postoperative intracranial hemorrhage and/or cerebral edema. After the ethics approval, we retrospectively reviewed the medical records of 207 adult patients who underwent elective surgical resection of cerebral AVM from Jan 2005 to Oct 2016 in a single university hospital. We determined the incidence of postoperative symptomatic intracranial hemorrhage and/or cerebral edema, and reviewed the quality of postoperative BP control during the first 72 h postoperatively. Two hundred and seven patients who underwent cerebral AVM resection were included. The median (IQR) of postoperative maximal systolic BP target was 110 (100-120) mmHg but the range was 90-150 mmHg. Failed hemodynamic control was consistently found in half of the patients during the first 72 h postoperatively. The incidence of postoperative intracranial hemorrhage and/or cerebral edema was 4.4% (9/207 patients). All 9 of these patients experienced a hypertensive event prior to their postoperative hyperemic complication. Two patients required induced hypertension to treat postoperative symptomatic cerebral edema. We concluded that postoperative intracranial hemorrhage and/or cerebral edema is not an uncommon complication after surgical resection of cerebral AVM. Further studies are required to develop a more effective strategy to implement strict BP control in the postoperative period.

Spetzler-Martin grade IV and V arteriovenous malformations: Treatment outcomes and risk factors for negative outcomes after surgical resection

OBJECTIVE

Microsurgical resection may be recommended for high grade brain arteriovenous malformations (BAVMs) (HBAVMs) in individualized patients. Careful case selection is necessary to minimize postoperative complications. The aim of this study was to determine the surgical outcomes in patients with HBAVMs and to identify their risk factors associated with postoperative negative outcomes.

PATIENTS AND METHODS

We retrospectively studied 53 consecutive patients with HBAVMs. All patients had undergone preoperative diffusion tensor imaging (DTI), MRI, 3D time-of-flight MRA (3D TOF-MRA) and digital subtraction angiography (DSA) followed by resection. White matter (WM) eloquent fibre tracts, including the corticospinal tract (CST), optic radiation (OR) and arcuate fasciculus (AF), were tract. Both functional, angioarchitectural and operative factors were analyzed with respect to the surgical outcomes.

RESULTS

Nineteen (35.8%) patients suffered from negative surgical outcomes (MRS > 2) one week after surgery. At the last clinic visit, 10 patients (18.9%) suffered from negative surgical outcomes. Diffuse nidus (P = 0.018), Perforating arteries (PA) supplying (P = 0.009) and CST involving (P = 0.001) were independent risk factors for negative short-term outcomes. PA supplying (P = 0.039), CST involving (P = 0.026) and postoperative intracranial haemorrhage (ICH) (P = 0.014) were independent risk factors for negative long-term neurological outcomes. Larger nidus size (P = 0.024) was predictor of postoperative ICH. The cut-off point was 6.8 cm.

CONCLUSIONS

This study identified that diffuse nidus, PA supplying and CST involving are risk factors for negative short-term outcomes in patients with HBAVMs. PA supplying, CST involving and postoperative ICH are risk factors for negative long-term outcomes. Larger nidus size was risk factor for postoperative ICH.

Deliberate employment of postoperative hypotension for brain arteriovenous malformation surgery and the incidence of delayed postoperative hemorrhage: a prospective cohort study

OBJECTIVE

The aim of this study was to examine the impact of deliberate employment of postoperative hypotension on delayed postoperative hemorrhage (DPH) for all Spetzler-Ponce Class (SPC) C brain arteriovenous malformations (bAVMs) and SPC B bAVMs ≥ 3.5 cm in diameter (SPC B 3.5+).

METHODS

A protocol of deliberate employment of postoperative hypotension was introduced in June 1997 for all SPC C and SPC B 3.5+ bAVMs. The aim was to achieve a maximum mean arterial blood pressure (BP) ≤ 70 mm Hg (with cerebral perfusion pressure > 50 mm Hg) for a minimum of 7 days after resection of bAVMs (BP protocol). The authors compared patients who experienced DPH (defined as brain hemorrhage into the resection bed that resulted in a new neurological deficit or that resulted in reoperation during the hospitalization for microsurgical bAVM resection) between 2 periods (prior to adopting the BP protocol and after introduction of the BP protocol) and 4 bAVM categories (SPC A, SPC B 3.5− [that is, SPC B < 3.5 cm maximum diameter], SPC B 3.5+, and SPC C). Patients excluded from treatment by the BP protocol were managed in the intensive care unit to avoid moderate hypertensive episodes. The pooled cases of all bAVM treated by surgery were analyzed to identify characteristics associated with the risk of DPH. These identified characteristics were then examined by multiple logistic regression analysis in both SPC B 3.5+ and SPC C cases.

RESULTS

From a cohort of 641 bAVMs treated by microsurgery, 32 patients with DPH were identified. Of those, 66% (95% CI 48–80) had a permanent new neurological deficit with a modified Rankin Scale score of 2–6. This included a mortality rate of 13% (95% CI 4.4–29). The BP protocol was used to treat 162 patients with either SPC B 3.5+ or SPC C. For SPC B 3.5+, there was no significant reduction in DPH with the introduction of the BP protocol (p = 0.77). For SPC C, there was a significant (p = 0.035) reduction of DPH from 29% (95% CI 13%–53%) to 8.2% (95% CI 3.2%–18%) associated with the introduction of the BP protocol. Multiple logistic regression analysis found that the absence of the BP protocol (p = 0.011, odds ratio 7.5, 95% CI 1.6–36) remained significant for the development of DPH in patients with SPC C bAVMs.

CONCLUSIONS

Treating patients with SPC C bAVMs with a protocol that lowers BP immediately after resection seems to reduce the risk of DPH. For SPC A and SPC B 3.5− bAVMs, there is unlikely to be a need to do more than avoid postoperative hypertension. For SPC B 3.5+ bAVMs, a larger number of patients would be required to test the absence of benefit of the BP protocol.

Animal Models in Studying Cerebral Arteriovenous Malformation

Brain arteriovenous malformation (AVM) is an important cause of hemorrhagic stroke. The etiology is largely unknown and the therapeutics are controversial. A review of AVM-associated animal models may be helpful in order to understand the up-to-date knowledge and promote further research about the disease. We searched PubMed till December 31, 2014, with the term “arteriovenous malformation,” limiting results to animals and English language. Publications that described creations of AVM animal models or investigated AVM-related mechanisms and treatments using these models were reviewed. More than 100 articles fulfilling our inclusion criteria were identified, and from them eight different types of the original models were summarized. The backgrounds and procedures of these models, their applications, and research findings were demonstrated. Animal models are useful in studying the pathogenesis of AVM formation, growth, and rupture, as well as in developing and testing new treatments. Creations of preferable models are expected.

Experimental Animal Models of Arteriovenous Malformation: A Review

Arteriovenous malformations (AVMs) are congenital lesions that cause brain haemorrhage in children and young adults. Current treatment modalities include surgery, radiosurgery and embolization. These treatments are generally effective only for small AVMs. Over one third of AVMs cannot be treated safely and effectively with existing options. Several animal models have been developed with the aims of understanding AVM pathophysiology and improving treatment. No animal model perfectly mimics a human AVM. Each model has limitations and advantages. Models contribute to the understanding of AVMs and hopefully to the development of improved therapies. This paper reviews animal models of AVMs and their advantages and disadvantages.

Normal perfusion pressure breakthrough theory: a reappraisal after 35 years

The intrinsic ability of the brain to maintain constant cerebral blood flow (CBF) is known as cerebral pressure autoregulation. This ability protects the brain against cerebral ischemia and hyperemia within a certain range of blood pressures. The normal perfusion pressure breakthrough (NPPB) theory described by Spetzler in 1978 was adopted to explain the edema and hemorrhage that sometimes occur after resection of brain arteriovenous malformations (AVMs). The underlying pathophysiology of edema and hemorrhage after AVM resection still remains controversial. Over the last three decades, advances in neuroimaging, CBF, and cerebral perfusion pressure (CPP) measurement have both favored and contradicted the NBBP theory. At the same time, other theories have been proposed, including the occlusive hyperemia theory. We believe that both theories are related and complementary and that they both explain changes in hemodynamics after AVM resection. The purpose of this work is to review the current status of the NBBP theory 35 years after its original description.

Clinical aspects, management and outcome of brain arteriovenous malformations – results with microsurgery first policy

We performed a retrospective study, including patients operated for brain AVMs between 1999 and 2014, in the Clinic of Neurosurgery, Emergency Clinical Hospital Bagdasar-Arseni, Bucharest. 277 patients underwent surgery for brain AVMs. Mean age was 29.82 years. 195 patients (70.40%) presented with hemorrhage and 86 cases (31.05%) were admitted with seizures. We performed total resection of AVMs in 228 cases (82.31%) and subtotal resection in 49 cases (17.69%). Regarding patients with residual nidus, 16 of them underwent second surgery, 27 stereotactic radiosurgery Gamma Knife, 3 embolization and 3 refused further treatment. Modified Rankin Scale (mRS) improved following surgery (Z = -9.248, p = 0.000). Early complications (0-30 days) were encountered in 84 patients (30.32%). We found the following risk factors for postoperative complications occurrence: motor deficit (p = 0.006), co-morbidities (p = 0.023), higher mRS (p = 0.005), lower Karnofsky score (p = 0.003), lower GCS (p = 0.016), profound nidus (p = 0.001), eloquent aria (p = 0.000), large nidus (p = 0.000), multiple arterial territory (p = 0.000), deep feeding arteries (p = 0.000), higher number of feeding arteries (p = 0.000), deep venous drainage (p = 0.000), multiple draining veins (p = 0.000), higher Spetzler- Martin grade (p = 0.006), high flow (p = 0.000), vascular steel (p = 0.000), associated aneurysms (p = 0.010) and decompressive craniectomy (p = 0.019). Mortality was 6.1%. Microsurgery is the treatment of choice for brain AVMs. Surgical results are excellent, with low morbidity and mortality. Patients with poor surgical results belonged to the group admitted with severe altered general state, state of consciousness, massive hematomas and acute brainstem dysfunction. If part of the nidus cannot be safely surgical resected, stereotactic radiosurgery can provide definitive cure of the lesion.

Use of intracranial and ocular thermography before and after arteriovenous malformation excision

Excision of arteriovenous malformations (AVMs) is known to carry a risk of postoperative hemorrhage, postulated to be the result of normal perfusion pressure breakthrough. It is also possible that AVMs may cause a steal effect, reducing perfusion in nearby vessels. There is currently no simple method of visualizing the presence or absence of steal effect intraoperatively. We hypothesized that the infrared thermographic (heat sensitive) imaging of perilesional brain may be useful for detecting reduced perfusion due to steal. Moreover, we hypothesized that if steal effect was present, it could impact on ocular perfusion and thereby temperature. Our objective was, therefore, to investigate whether perilesional cortical and ocular temperature (OT) may be a marker of steal effect. We intraoperatively acquired conventional and thermal images of the surgical field and eyes bilaterally, pre- and post-excisions of a large left hemisphere AVM. We found OT asymmetry preoperatively, which was absent after the AVM was excised. Intraoperative thermal images showed an increase of perilesional temperature, although this could be confounded by generalized changes in cortical perfusion due to anesthetics or surgery.

Normal perfusion pressure breakthrough phenomenon: experimental models

One of the most life-threatening complications after the obliteration of intracranial arteriovenous malformations is the development of oedema and/or multifocal haemorrhage. Two main theories have been postulated so far in order to explain this situation. On one hand, "normal perfusion pressure breakthrough phenomenon" is based on the loss of cerebral vessel autoregulation due to the chronic vasodilation of perinidal microcirculation. On the other hand, the "occlusive hyperaemia" deals with thrombotic and venous obstruction phenomena that may also generate such manifestations. The aim of this study is to resume the main concepts of the "normal perfusion pressure breakthrough phenomenon" theory as well as the related animal models described up to date, their advantages and disadvantages, and the main conclusions obtained as a result of the experimental research.

Neurovascular abnormalities in humans and mice with Huntington's disease

Cerebral microvascular aberrations have recently become recognized as a source of pathologies in neurodegenerative disorders, but this concept has not been fully examined with respect to Huntington's disease (HD). A novel in vivo technique, three-dimensional microscopic magnetic resonance angiography (μMRA), allows visualization of the neurovascular system in exquisite detail and provides quantitative structural and functional information. This technique was applied in the present study, in parallel with immunohistological analysis and behavioral assessment, to a well-characterized mouse model of HD (R6/2). Dynamic contrast-enhanced magnetic resonance imaging was used to examine the integrity of the blood-brain barrier (BBB). The μMRA findings revealed an increase in vessel volume fraction and cerebral blood volume in the brains of R6/2 mice at the age of 7weeks when no apparent motor dysfunction was detected. Collagen IV immunostaining disclosed an enhancement in vessel density, but not in vessel size of the microvasculature in the mouse HD brain. This change in neurovasculature worsened with disease progression, with no apparent disruption in the BBB. Most importantly, immunohistological assays of human tissues revealed that the vessel densities in the cortex, caudate/putamen, and substantia nigra were higher in HD patients than in non-HD human subjects. The early onset of such vessel aberrations could be used as a biomarker for the early diagnosis of HD.

A study on blood–brain barrier ultrastructural changes induced by cerebral hypoperfusion of different stages

OBJECTIVES

To evaluate the ultrastructural changes in the blood-brain barrier (BBB) induced by cerebral hypoperfusion of different stages, which may predispose the brain to the formation of vasogenic edema and hemorrhage under cerebral luxury perfusion.

METHODS

Twenty cerebral steal models with left neck arteriovenous fistula (AVF) were surgically created in Wistar's rats, leading to a noninfarctional reduction in the cerebral blood flow (CBF) by between 25 and 50%, resulting in cerebral hypoperfusion in the AVF side for 3 days (acute stage), 3 weeks (subacute stage) and 3 months (chronic stage), respectively. Another six sham-operated models were made in age-matched rats as control. The BBB ultrastructural changes were assessed by transmission electron microscopy. Ridit analysis was conducted to compare the positive ratio of ultrastructural changes among multiple groups.

RESULTS

Electron microscopy demonstrated no ultrastructural change at the acute stage, however, at the subacute stage, slight vacuolar degeneration was found in the astrocytic foot process layer encircling the capillaries; furthermore, at the chronic stage, the astrocytic foot processes expressed marked vacuolization associated with the adjacent astrocytic degeneration. Meanwhile, in both capillary endothelium and basal lamina layers, no abnormal ultrastructures similar to those in the astrocytic foot processes layer were identified. After cerebral luxury perfusion took place, BBB was disrupted where astrocytic foot processes vacuolization was most distinguished.

CONCLUSION

Astrocytes generate ultrastructural abnormality as a result of chronic cerebral hypoperfusion. Astrocytic foot process vacuolization, which constitutes the major ultrastructural change in the BBB, is the extension of the degeneration of astrocyte body. It is inferred that BBB is prone to structure weakness and function instability, which forms the morphological basis of cerebral luxury perfusion.

Carotid Cavernous Fistulae Occurring After the Use of the Fogarty Catheter in Carotid Surgery

The Fogarty catheter represents a major advancement for the effective removal of distal thrombi during vascular surgery, including carotid endarterectomy (CEA). One complication related to its use is injury to the cavernous carotid artery with development of a carotid cavernous fistula (CCF). Including a recent case at our institution, 21 patients with a Fogarty-related CCF have been reported since 1967. We performed a detailed review of all Fogarty-related CCFs during the treatment of carotid occlusive disease. We suggest a management algorithm for post-CEA acute carotid occlusion.

Reducing Delay of Carotid Endarterectomy in Acute Ischemic Stroke Patients

Background and Purpose—

Guidelines recommend carotid endarterectomy (CEA) within 2 weeks from an ischemic event. However, previous studies have shown that only a minority of patients undergo CEA within this period. The aim of this study was to examine the effect of a multidisciplinary nationwide initiative aimed at reducing time to CEA after acute ischemic stroke.

Methods—

We examined a historic population-based observational cohort based on individual patient-level records from the Danish Stroke Registry and the Danish Vascular Registry. The implementation of early ultrasound examination of the carotids (within 4 days from admission) in medical departments coupled with fast CEA after referral to a department of vascular surgery were monitored and audited systematically from 2008 and onward.

Results—

A total of 813 acute ischemic stroke patients underwent CEA during 2007-2010. The percentage of patients undergoing CEA within 2 weeks increased from 13% in 2007 to 47% in 2010 (adjusted odds ratio, 5.8 [95% CI, 3.4–10.1]). The overall median time decreased from 31 days to 16 days. The percentage of relevant acute ischemic stroke patients receiving early ultrasound examination of the carotids increased from 41% in 2008 to 72% in 2010. The time from referral to operation at a vascular department was reduced by ≈40%.

Conclusions—

Establishing time limits of 4 days to ultrasound examination of the carotids and of 2 weeks to CEA from onset of stroke followed by a systematic multidisciplinary monitoring and auditing of processes was associated with a substantial increase in the proportion of acute ischemic stroke patients who undergo CEA within 2 weeks in Denmark.

Rapid brain shift, remote site hemorrhage, and a spinal hematoma after craniotomy for a large arachnoid cyst

Arachnoid cysts are prevalent among the general population. The management options of symptomatic arachnoid cysts each have their own merits and disadvantages. We report a case where a large arachnoid cyst was treated by open fenestration and marsupialization that was complicated by remote intraparenchymal and spinal subdural hemorrhage. The potential physiological changes underlying these complications as well as the related literature are reviewed.

Role of inhibition in chronic cerebral hypoperfusion

Chronic reductions in cerebral blood flow (CBF) of between 25 and 50% maintained for 26 weeks impair neuronal function, through a mechanism which is not known, but which is now explored. Increased GABAergic synaptic inhibition may play a role, as inhibitory interneurons are known to be relatively resistant to acute ischaemic insults. The phenomenon of tetanus-induced longterm potentiation (LTP) was previously found to be impaired in this setting, and was thus examined in the in vitro rat hippocampus in the presence of bicuculline, a specific GABA(A) antagonist, to evaluate the role of inhibition in the impairment of LTP in chronic cerebral hypoperfusion (CCH). Nine Sprague-Dawley rats aged 8-10 weeks had arteriovenous fistulae (AVF) surgically constructed to reduce CBF to between 25 and 50%. Ten animals were used as age-matched controls. After a further 26 weeks, 400 mum hippocampal slices were prepared. Tetanic stimulation was used in order to attempt to induce LTP. In vitro extracellular field potentials from control and AVF slices with 5 x 10(-)6 M bicuculline exposure and subsequent tetanic stimulation were compared. There was no statistical difference between the responses of the two groups in either scenario (P > 0.05), although LTP was in general more difficult to induce (only occurring in 60% of control animals). Possible causes of this are discussed. It is concluded that increased GABAergic synaptic inhibition does not play a role in impairment of neuronal function seen after 26 weeks of non-infarctional CCH.

Normal perfusion pressure breakthrough phenomenon: what still remains unknown

We report two cases of normal perfusion pressure breakthrough phenomenon after total brain arteriovenous malformation removal. Hereby, we demonstrate that not only autoregulation impairment in the ipsilateral hemisphere occurs but also contralateral remote vessels response does. Such findings may be observed at 2-4 weeks and may resolve after 1-3 months.

Dynamics of dystroglycan complex proteins and laminin changes due to angiogenesis in rat cerebral hypoperfusion

Permanent bilateral carotid occlusion is a well known cerebral hypoperfusion model in rats. The aim of our study was to investigate the different stages of vascular reaction by detecting changes in the extracellular martix proteins and to examine their relationship to angiogenesis after occlusion. Experiments were performed on adult male rats. Brain samples were investigated from day 1 to day 30 post-surgery. Immunohistochemical analysis was performed on the whole hippocampus and on the adjacent cortex in order to investigate extracellular martix proteins, such as the markers of dystroglycan complex (β-dystroglycan, α-dystrobrevin and utrophin) and a marker of basal lamina (laminin). The levels of the proteins were estimated by western blot analysis. Vascular density as well as blood-brain barrier permeability were studied on brain slices from the same regions. Our results showed altered laminin and β-dystroglycan immunoreactivity beginning 2 days after the onset of occlusion followed by an increased utrophin immunoreactivity without blood-brain barrier disruption 5 days later. By day 30 of hypoperfusion, when increased vascular density was detected, all changes returned to baseline levels. Western blot analysis showed significant differences in β-dystroglycan and utrophin expression. Our results indicate that the different stages of neovascularisation resulting from cerebral hypoperfusion can be well defined by the markers laminin, β-dystroglycan, and utrophin and that these markers are more likely to correlate with glio-vascular decoupling than does altered blood-brain barrier function.

RESUSCITATION AND CRITICAL CARE OF POOR-GRADE SUBARACHNOID HEMORRHAGE

AS OUTCOMES HAVE improved for patients with aneurysmal subarachnoid hemorrhage, most mortality and morbidity that occur today are the result of severe diffuse brain injury in poor-grade patients. The premise of this review is that aggressive emergency cardiopulmonary and neurological resuscitation, coupled with early aneurysm repair and advanced multimodality monitoring in a specialized neurocritical care unit, offers the best approach for achieving further improvements in subarachnoid hemorrhage outcomes. Emergency care should focus on control of elevated intracranial pressure, optimization of cerebral perfusion and oxygenation, and medical and surgical therapy to prevent rebleeding. In the postoperative period, advanced monitoring techniques such as continuous electroencephalography, brain tissue oxygen monitoring, and microdialysis can detect harmful secondary insults, and may eventually be used as end points for goal-directed therapy, with the aim of creating an optimal physiological environment for the comatose injured brain. As part of this paradigm shift, it is essential that aggressive surgical and medical support be linked to compassionate end-of-life care. As neurosurgeons become confident that comfort care can be implemented in a straightforward fashion after a failed trial of early maximal intervention, the usual justification for withholding treatment (survival with neurological devastation) becomes less relevant, and lives may be saved as more patients recover beyond expectations.

Ultrastructure of Perinidal Capillaries in Cerebral Arteriovenous Malformations

OBJECTIVE

The ultrastructure of perinidal capillaries in cerebral arteriovenous malformations (AVMs) was examined to clarify their pathomorphological features.

METHODS

Fifteen AVM specimens were dissected and divided into perinidal and intranidal groups and processed for ultrastructural study immediately after surgical removal. Eleven of the patients had presented with hemorrhage. Tissue from four normal controls was also studied. Electron microscopy was used to compare features of the blood-brain barrier and endothelial cells (ECs) of capillaries in perinidal, intranidal, and controls.

RESULTS

Perinidal capillaries demonstrated abnormal ultrastructure of the blood-brain barrier with no basement membranes and astrocytic foot processes. ECs had fenestrated luminal surfaces. Large gaps were observed at endothelial intercellular junctions. ECs contained numerous filopodia, large numbers of cytoplasmic processes, numerous micropinocytotic vesicles, and the cytoplasm contained more filaments than those observed in controls. Pericytes were rich in pinocytotic vesicles, vacuoles, and filaments. Their processes were in close contact with ECs. Weibel-Palade bodies were present in perinidal ECs.

CONCLUSION

The absence of blood-brain barrier components in perinidal capillaries may contribute to extravasation of red blood cells into the surrounding brain in the absence of major hemorrhage and explain the gliosis and hemosiderin occasionally seen around AVMs. Cellular differentiation and proliferation in perinidal capillaries should be included in a systematic study aimed at a better understanding of the mechanisms underlying the recurrence of surgically removed AVMs.

Experimental cerebral arteriovenous fistulas

OBJECTIVE

The aim of this paper is to analyse and summarize the main advances in experimental research on cerebral arteriovenous fistulas.

METHODS

A detailed analysis of the literature and my own research experience were employed to outline the methodology whereby experimental cerebral arteriovenous fistulas are created and further studied.

RESULTS

The analysis and quantification of the anatomical and functional variables in different experimental cerebral arteriovenous fistula models make it possible to develop more appropriate and individual ways of treatment in affected patients.

CONCLUSION

Experimental research on cerebral arteriovenous fistulas helps physicians to understand and predict more accurately the future evolution of arteriovenous malformations in humans.

Endovascular Treatment of Cerebral Arteriovenous Malformations

The modern management of cerebral arteriovenous malformations (AVMs) is based on three therapeutic modalities: microneurosurgery, endovascular embolization, and stereotactic radiosurgery. Embolization facilitates subsequent radiosurgery by reducing the volume of the nidus, prepares the resection of surgically accessible AVMs, and immediately addresses the risks related to associated intra/extranidal aneurysms and arteriovenous fistulas. We discuss in this article the current state of AVM endovascular therapy.

Postoperative hyperperfusion associated with steal phenomenon caused by a small arteriovenous malformation

A 41-year-old woman presented with a small occipital arteriovenous malformation (AVM) manifesting as headache. Cerebral angiography showed an AVM in the right occipital lobe fed by the right temporooccipital artery and draining into the superior sagittal sinus and right transverse sinus. Single photon emission computed tomography showed the steal phenomenon in the ipsilateral temporal cortex fed by the main feeding artery preoperatively, and hyperperfusion in the same cortex after removal of the AVM. Postoperative systolic blood pressure was maintained between 100 and 120 mmHg to avoid disastrous hemorrhagic complications. Cerebral blood flow evaluation before and after surgery is important to avoid postoperative disastrous complications even in patients with small AVM.

Angiogenesis in the brain during development: the effects of vascular endothelial growth factor and angiopoietin-2 in an animal model

OBJECT

The goal of this study was to examine the roles of vascular endothelial growth factor (VEGF) and angiopoietin-2 (Ang-2) in the formation of blood vessels in the brain in a developmental animal model not routinely used for such a study.

METHODS

Either VEGF, Ang-2, or a combination of the two factors were injected into the optic tectum of 4-day-old quail embryos. Immunohistochemical analysis and laser confocal microscopy were used to observe the effects on endothelial cells in the brain. Vascular endothelial growth factor and Ang-2 had very different effects on the development of blood vessels; the former caused expansion and the latter retraction of these vessels. Treatment with a combination of VEGF and Ang-2 caused retroorbital or intraventricular hemorrhage, and brain blood vessels appeared enlarged and dysmorphic, with dramatically extended filopodia.

CONCLUSIONS

Some of these observations may provide insight into how one may develop a better model of brain arteriovenous malformations.

Microsurgery for cerebral arteriovenous malformation management: a Siberian experience

Cerebral vascular malformations remain among the most difficult neurosurgical entities to treat. We report a retrospective study of the outcome in 95 consecutive patients with angiographically revealed arteriovenous malformations (AVMs). Fifty-four patients underwent microsurgical total AVM removal (group I). Forty-one patients who refused open surgery (group II) were managed either by endovascular embolisation (16 cases), radiosurgery (three) or followed up with medical treatment for their symptoms. In the first group pretreatment with the non-selective beta-blocker propranolol before surgery, the current neuronavigation techniques, intraoperative embolisation and AVM nidus colouring in high flow AVM were used for total microsurgical excision of the lesions. All AVM patients but one survived microsurgery. The mortality rate was 1.8% for group I. Six patients with grade IV-V AVM developed new temporal neurological symptoms following surgery. Four of them recovered completely in 3-6 weeks; two patients remained with mild persistent monoparesis and with homonymous hemianopsia postoperatively. In ten of 13 epileptic patients surgery produced a cure. No patient re-bled following surgery. No postoperative normal perfusion pressure breakthrough occurred. In the second group ten patients (24%) developed intracerebral haemorrhages, six of ten patients demonstrated progressive seizures. The mortality rate in group II totalled 17% over 6 years. Microsurgical management approaches must consider preoperative correction of impaired cerebral autoregulation, neuronavigation for preoperative planning and intraoperative orientation, intraoperative embolisation and dying of the nidus for large high-flow AVMs.

Postcarotid Endarterectomy Hyperperfusion or Reperfusion Syndrome

Background and Purpose— Hyperperfusion syndrome (HS) after carotid endarterectomy (CEA) has been related to impaired cerebrovascular autoregulation in a chronically hypoperfused hemisphere. Our aim was to provide new insight into the pathophysiology of the HS using magnetic resonance imaging (MRI) studies with diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI).

Methods— Five out of 388 consecutive patients presented 2 to 7 days after CEA, partial seizures (n=5), focal deficits (n=5), and intracerebral hemorrhage (n=3). In 4 patients, using sequential examinations, we identified vasogenic or cytotoxic edema by DWI; we assessed relative interhemispheric difference (RID) of cerebral blood flow (CBF) by PWI; and we measured middle cerebral artery mean flow velocities (MCA Vm) by transcranial Doppler (TCD).

Results— None of the patients presented pathological DWI hyperintensities, consistent with the absence of acute ischemia or cytotoxic edema. In 2 patients, we found an MRI pattern of reversible vasogenic edema similar to that observed in the posterior leukoencephalopathy syndrome. Middle cerebral artery (MCA) mean flow velocities (Vm) were not abnormally increased at any time. PWI documented a 20% to 44% RID of CBF in favor of the ipsilateral to CEA hemisphere.

Conclusions— HS can occur in the presence of moderate relative hyperperfusion of the ipsilateral hemisphere. MCA Vm values may not accurately reflect RID of CBF over the cortical convexity. We suggest that the hemodynamic pathogenetic mechanisms of the HS are more complicated than hitherto believed and that they may be more accurately described by the term “reperfusion syndrome.”

Chronic cerebral hypoperfusion and reperfusion injury of restoration of normal perfusion pressure contributes to the neuropathological changes in rat brain

Restoration of normal perfusion pressure after resection of cerebral arteriovenous malformations (AVMs) is sometimes complicated by unexplained postoperative brain swelling and/or intracranial hemorrhage, which has been termed normal perfusion pressure breakthrough (NPPB). The precise mechanism of NPPB is still unclear. In this study, we investigated the time courses of blood-brain barrier (BBB) disruption, water content, neuronal apoptosis, myeloperoxidase (MPO) activity and superoxide dismutase (SOD) activity in the brain during restoration of normal perfusion pressure in a new rat model of chronic cerebral hypoperfusion associated with AVMs. Male Sprague-Dawley rats were randomly divided into either a sham-operated group, a control group, or a model group with reperfusion assessed at 1, 12, 24 and 72 h after restoration of normal perfusion pressure. BBB disruption was judged by extravasation of Evans blue (EB) dye. We observed that EB and water content in rat brains of the model group with reperfusion were significantly increased compared with the other groups. The most predominant increase occurred at 1 h after reperfusion, and the next at 24 h after reperfusion, representing biphasic changes which are similar to the pathological processes of acute cerebral ischemia/reperfusion injury. There was no difference of the percentage of apoptotic cells in rat brains between the sham-operated group and the control group using flow cytometry. No prominent apoptotic cells were found in the model group with reperfusion at 1 h. However, the percentage of apoptotic cells increased significantly in rat brains of the model group with reperfusion at 12 h, peaked at 24 h, and decreased at 72 h after reperfusion. Apoptotic cells were confirmed with electron microscopy and terminal deoxynuleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL). A significant enhancement of MPO activity in combination with reduction of SOD activity was seen at 12, 24 and 72 h in rat brains of the model group with reperfusion. Our data indicates that reperfusion after restoration of normal perfusion pressure with chronic cerebral hypoperfusion lead to secondary neuronal damage which may associate with cerebral ischemia/reperfusion injury.

THE TRANSGENIC ARTERIOVENOUS FISTULA IN THE RAT: AN EXPERIMENTAL MODEL OF GENE THERAPY FOR BRAIN ARTERIOVENOUS MALFORMATIONS

OBJECTIVE

To introduce the transgenic arteriovenous fistula model in the rat, constructed by interposing mouse aorta in a fistula between the common carotid artery and external jugular vein in a nude rat, and to describe the model's technical feasibility, long-term patency, and expression of reporter genes.

METHODS

Carotid-jugular fistulae were surgically created in 112 rats. In 25 immunodeficient nude rats, wild-type mouse thoracic aorta (TAo) was interposed in the fistula; in 10 immunocompetent rats, TAo was interposed; in 19 nude rats, transgenic TAo with reporter genes for beta-galactosidase or green fluorescent protein was interposed; in 18 nude rats, wild-type mouse ascending aorta was interposed; and in 40 rats, a simple fistula was constructed without an interpositional graft. Host tolerance and graft viability were analyzed by histopathology and immunohistochemistry for CD31 (mouse endothelial cell marker), endothelial nitric oxide synthase, smooth muscle actin, fibronectin, beta-galactosidase, and green fluorescent protein.

RESULTS

The transgenic arteriovenous fistula was technically feasible and immunologically tolerated in nude rats but not in immunocompetent rats. The overall angiographic patency rate was 41% with TAo grafts and 56% with ascending aorta grafts, both lower than the 98% patency rate in fistulae with a single anastomosis and no interpositional graft. Mouse endothelium survived on the graft for 3 months according to CD31 staining, but longer survival by transgenic smooth muscle cells resulted in continued expression of beta-galactosidase for 6 months and green fluorescent protein for 4 months. Endothelium and smooth muscle in the fistula were functional, with normal expression of endothelial nitric oxide synthase as well as smooth muscle actin and fibronectin, respectively.

CONCLUSION

The transgenic arteriovenous fistula model enhances other carotid-jugular fistula models by integrating transgenic tissue, thereby creating an experimental system for investigating the molecular biology of and gene therapies for arteriovenous malformations.

Delayed hemorrhage following resection of an arteriovenous malformation in the brain

Object. Between 1989 and 2002 the authors treated 416 cases of angiographically confirmed arteriovenous malformations (AVMs) of the brain.

Methods. Three hundred fifty-five patients underwent resection of an AVM; 2% died and 12% experienced a permanent morbidity (1.7% experienced a deterioration of modified Rankin Scale [mRS] score of 3–5). Patient outcomes in this series were based on the Spetzler—Martin grade. For patients with Grade I and II AVMs the rate of permanent morbidity was 1% and the rate of mortality was 0.5%. For patients with Grade III AVMs the morbidity rate was 18.9% (2.7% experienced a deterioration of mRS score of 3–5) and the mortality rate was 2.7%. For patients with Grade IV and V AVMs the morbidity rate was 25.6% (5.1% experienced a deterioration of mRS score of 3–5) and the mortality rate was 7.7%. No patient with a Spetzler—Martin Grade I or II lesion had a worsened outcome due to delayed hemorrhage, whereas 3.6% of patients with a Grade III and 12.8% of patients with Grade IV and V AVMs experienced delayed hemorrhage that led to a permanent downgrade in function.

With the introduction of an aggressive postoperative blood pressure protocol (for AVMs with grades > II and sizes > 3.5 cm in diameter) the incidence of delayed postoperative hemorrhage leading to mortality or permanent morbidity decreased from 4.4 to 1%. This difference was significant. Neither case selection nor complications other than delayed hemorrhage changed between these two periods.

Conclusions. In selected cases an aggressive postoperative blood pressure protocol is likely to reduce delayed hemorrhage following AVM resection.

Vascular Endothelial Growth Factor Expression and Angiogenesis Induced by Chronic Cerebral Hypoperfusion in Rat Brain

OBJECTIVE

In a rat model, we studied the time courses of vascular endothelial growth factor (VEGF) expression and angiogenesis induced by chronic cerebral hypoperfusion in the brain, and we investigated the histological basis of normal-perfusion pressure breakthrough.

METHODS

Twenty-one Sprague-Dawley rats were randomly divided into a control group (n = 3) and a model group assessed at various time points after the creation of a carotid artery-jugular vein fistula (12 h, n = 3; 24 h, n = 3; 72 h, n = 3; 7 d, n = 3; 21 d, n = 3; 90 d, n = 3). The time courses of the expression of VEGF messenger ribonucleic acid (mRNA) and protein in rat brain were analyzed with semiquantitative reverse transcriptase-polymerase chain reaction and Western blot assays, respectively. Immunohistochemical techniques were used to evaluate VEGF protein localization with rabbit polyclonal anti-rat VEGF, VEGF receptor (VEGFR) expression with rabbit polyclonal antibodies to VEGFR-1 and -2, microvascular density with mouse monoclonal anti-rat CD31, and astrocytic reactivity with polyclonal anti-glial fibrillary acidic protein, in cerebral cortical tissue of the right middle cerebral artery territory.

RESULTS

Three alternative splicing forms, i.e., VEGF(188), VEGF(164), and VEGF(120), were observed in cerebral cortical tissue of the right middle cerebral artery territory in semiquantitative reverse transcriptase-polymerase chain reaction analyses. VEGF(164) mRNA was the predominant isoform expressed in rat brain. VEGF(188) mRNA and VEGF(120) mRNA were also detected but at very low levels (not statistically significant). Low levels of VEGF(164) mRNA were observed in the control brains. However, VEGF(164) mRNA levels were significantly increased in the model brains at 24 hours postoperatively, peaked by 7 days, decreased by 21 days, and returned to basal levels by 90 days after fistula formation. VEGF protein expression, as measured in Western blot assays, was also increased in rat brains in the model group from 24 hours to 21 days postoperatively but returned to control levels by 90 days after fistula formation. VEGF immunohistochemical analyses indicated that this increased expression was mostly associated with endothelial cells. Consistent with the VEGF protein expression findings, up-regulation of VEGFR-1 but not VEGFR-2 expression on endothelial cells in the model brains was observed. Microvascular density in the rat brains began to increase significantly 7 days after fistula formation in the model group, as assessed immunohistochemically, and the increase was maintained for 90 days. Although no prominent astrocytic reactivity was observed in the rat brains throughout the experiments, there was an absence of astrocytic foot processes surrounding some cerebral capillaries 90 days after fistula formation in the model group.

CONCLUSION

These results demonstrated that chronic cerebral hypoperfusion could induce sustained up-regulation of VEGF mRNA and protein expression in rat brain, which was correlated with angiogenesis. An absence of corresponding astrocytic reactivity during angiogenesis may be an important factor accounting for structural deficits of the blood-brain barrier and the occurrence of normal-perfusion pressure breakthrough.

Vision of the future: initial experience with intraoperative real-time high-resolution dynamic infrared imaging. Technical note

High-resolution dynamic infrared (DIR) imaging provides intraoperative real-time physiological, anatomical, and pathological information; however, DIR imaging has rarely been used in neurosurgical patients. The authors report on their initial experience with intraoperative DIR imaging in 30 such patients. A novel, long-wave (8-10 microm), narrow-band, focal-plane-array infrared photodetector was incorporated into a camera system with a temperature resolution of 0.006 degrees C, providing 65,000 pixels/frame at a data acquisition rate of 200 frames/second. Intraoperative imaging of patients was performed before and after surgery. Infrared data were subsequently analyzed by examining absolute differences in cortical temperatures, changes in temperature over time, and infrared intensities at varying physiological frequencies. Dynamic infrared imaging was applied in a variety of neurosurgical cases. After resection of an arteriovenous malformation, there was postoperative hyperperfusion of the surrounding brain parenchyma, which was consistent with a loss of autoregulation. Bypass patency and increased perfusion of adjacent brain were documented during two of three extracranial-intracranial bypasses. In seven of nine patients with epilepsy the results of DIR imaging corresponded to seizure foci that had been electrocorticographically mapped preoperatively. Dynamic infrared imaging demonstrated the functional cortex in four of nine patients undergoing awake resection and cortical stimulation. Finally, DIR imaging exhibited the distinct thermal footprints of 14 of 16 brain tumors. Dynamic infrared imaging may prove to be a powerful adjunctive intraoperative diagnostic tool in the neurosurgical imaging armamentarium. Real-time assessment of cerebral vessel patency and cerebral perfusion are the most direct applications of this technology. Uses of this imaging modality in the localization of epileptic foci, identification of functional cortex during awake craniotomy, and determination of tumor border and intraoperative brain shift are avenues of inquiry that require further investigation.

A new rat model of chronic cerebral hypoperfusion associated with arteriovenous malformations

OBJECT

A new experimental model of chronic cerebral hypoperfusion was developed to study the effects of systemic arterial shunting and obstruction of the primary vessel that drains intracranial venous blood on cerebral perfusion pressure (CPP), as well as cerebral pathological changes during restoration of normal perfusion pressure.

METHODS

Twenty-four Sprague-Dawley rats were randomly assigned to either a sham-operated group, an arteriovenous fistula (AVF) group, or a model group (eight rats each). The animal model was readied by creating a fistula through an end-to-side anastomosis between the right distal external jugular vein (EJV) and the ipsilateral common carotid artery (CCA), followed by ligation of the left vein draining the transverse sinus and bilateral external carotid arteries. Systemic mean arterial pressure (MAP), draining vein pressure (DVP), and CPP were monitored and compared among the three groups preoperatively, immediately postoperatively, and again 90 days later. Following occlusion of the fistula after a 90-day interval, blood-brain barrier (BBB) disruption and water content in the right cortical tissues of the middle cerebral artery territory were confirmed and also quantified with transmission electron microscopy. Formation of a fistula resulted in significant decreases in MAP and CPP, and a significant increase in DVP in the AVF and model groups. Ninety days later, there were still significant increases in DVP and decreases in CPP in the model group compared with the other groups (p < 0.05). Damage to the BBB and brain edema were noted in animals in the model group during restoration of normal perfusion pressure by occlusion of the fistula. Electron microscopy studies revealed cerebral vasogenic edema and/or hemorrhage in various amounts, which correlated with absent astrocytic foot processes surrounding some cerebral capillaries.

CONCLUSIONS

The results demonstrated that an end-to-side anastomosis between the distal EJV and CCA can induce a decrease in CPP, whereas a further chronic state of cerebral hypoperfusion may be caused by venous outflow restriction, which is associated with perfusion pressure breakthrough. This animal model conforms to the basic hemodynamic characteristics of human cerebral arteriovenous malformations.

The effect of n-3 polyunsaturated fatty acid-rich diets on cognitive and cerebrovascular parameters in chronic cerebral hypoperfusion

Western diets consist to a large part of n-6 polyunsaturated fatty acids (PUFAs). These n-6 PUFAs and their conversion products favor immune and inflammatory reactions and compromise vasoregulation, which can contribute to the development of dementia. Recent epidemiological studies associated dementia, particularly the type accompanied by a vascular component, with high, saturated dietary fat intake. Conversely, high fish consumption (a source of long chain n-3 PUFAs) was related to a reduced risk for cognitive decline. Therefore we studied the effects of long chain n-3 PUFAs in rats with bilateral occlusion of the common carotid arteries (2VO), which mimics cerebral hypoperfusion, a risk factor for dementia. Male Wistar rats received experimental diets with a decreased (n-6)/(n-3) ratio from weaning on. At the age of 3 months, the animals underwent 2VO surgery. The rats were tested in the elevated plus maze, an active avoidance paradigm and the Morris water maze (at different survival times). Following behavioral testing, the animals were sacrificed at the age of 7 months. The frontoparietal cortex was analyzed for capillary ultrastructure with electron microscopy. No effects of cerebral hypoperfusion or diet were found on elevated plus maze and active avoidance, while spatial memory in the Morris maze was compromised due to cerebral hypoperfusion under placebo dietary conditions. n-3 PUFA supplementation in combination with extra additives improved the performance of the 2VO animals. The number of endothelial mitochondria, as well as the ratio of microvessels with degenerative pericytes appeared to be lower due to long chain n-3 PUFAs. These results may indicate an improved condition of the blood-brain barrier.