Peripheral macrophages in the development and progression of structural cerebrovascular pathologies

The human cerebrovascular system is responsible for maintaining neural function through oxygenation, nutrient supply, filtration of toxins, and additional specialized tasks. While the cerebrovascular system has resilience imparted by elaborate redundant collateral circulation from supportive tertiary structures, it is not infallible, and is susceptible to developing structural vascular abnormalities. The causes of this class of structural cerebrovascular diseases can be broadly categorized as 1) intrinsic developmental diseases resulting from genetic or other underlying aberrations (arteriovenous malformations and cavernous malformations) or 2) extrinsic acquired diseases that cause compensatory mechanisms to drive vascular remodeling (aneurysms and arteriovenous fistulae). Cerebrovascular diseases of both types pose significant risks to patients, in some cases leading to death or disability. The drivers of such diseases are extensive, yet inflammation is intimately tied to all of their progressions. Central to this inflammatory hypothesis is the role of peripheral macrophages; targeting this critical cell type may lead to diagnostic and therapeutic advancement in this area. Here, we comprehensively review the role that peripheral macrophages play in cerebrovascular pathogenesis, provide a schema through which macrophage behavior can be understood in cerebrovascular pathologies, and describe emerging diagnostic and therapeutic avenues in this area.

Comparative cost analysis of endovascular and open approaches for elective treatment of middle cerebral artery aneurysms

BACKGROUND

Intracranial aneurysms of the middle cerebral artery can be treated using several open surgical and endovascular approaches. Given the growing evidence of clinical equipoise between these various treatment strategies, there is a need to assess the costs associated with each.

METHODS

Cost of aneurysm treatment was divided into two categories for comparison. "Initial cost" comprised the total in-hospital expenses for initial aneurysm treatment and "total cost" comprised initial aneurysm treatment and all expenses relating to readmission due to treatment-related complications, prescribed catheter angiograms for monitoring of treatment stability, and any retreatments needed for a given aneurysm. The open surgical group was subdivided into a pterional approach group and a lateral supraorbital (LSO) approach group for.

RESULTS

Median initial cost was $37,152 (IQR $31,318-$44,947) for aneurysms treated with the pterional approach, $29,452 (IQR $27,779-$32,826) for aneurysms treated with the LSO approach, and $19,587 (IQR $14,125-$30,521) for aneurysms treated with endovascular approaches. The median total cost was $39,737 (IQR $33,891-$62,259) for aneurysms treated with the pterional approach, $31,785 (IQR $29,513-$41,099) for aneurysms treated with the LSO approach, and $24,578 (IQR $18,977-$34,547) for aneurysms treated with endovascular approaches. Analysis of variance test demonstrated variance across groups for both initial and total cost (p = 0.004, p = 0.008, respectively). In our subsequent analysis, initial cost and total cost were higher in the pterional group than the endovascular group (p = 0.003 and p = 0.006, respectively).

CONCLUSIONS

Endovascular treatment of elective aneurysms has a significantly lower cost than open surgical treatment with the pterional approach, but not with the LSO approach. For aneurysms not amenable to endovascular treatment, a minimally invasive LSO approach carries a lower cost burden than a pterional approach.

A review of technological innovations leading to modern endovascular brain aneurysm treatment

Tools and techniques utilized in endovascular brain aneurysm treatment have undergone rapid evolution in recent decades. These technique and device-level innovations have allowed for treatment of highly complex intracranial aneurysms and improved patient outcomes. We review the major innovations within neurointervention that have led to the current state of brain aneurysm treatment.

Resection of an Intradural Extramedullary Capillary Hemangioma in the Lumbar Spine

BACKGROUND AND IMPORTANCE

Capillary hemangiomas are space-occupying lesions that rarely affect the central nervous system. When they present within the spinal canal, they can cause insidious symptoms and threaten neurological function. In this study, we present a case of an intradural extramedullary capillary hemangioma of the lumbar spine, discuss our management strategy, and review the current literature. For the first time for this diagnosis, we also provide an operative video.

CLINICAL PRESENTATION

The patient is a previously healthy 40-year-old man who presented with complaints of progressive low back and leg pain, numbness, and intermittent subjective urinary incontinence. MRI revealed a discrete, homogenously enhancing intradural extramedullary lesion at L4. This lesion was resected by performing an L4 laminoplasty, which entails en bloc removal of the L4 lamina and then securing it back into place once the intradural resection and dural closure are completed. Histological analysis revealed a diagnosis of capillary hemangioma. The patient had full resolution of his symptoms postoperatively.

DISCUSSION

Definitive management of spinal capillary hemangiomas involves gross total resection and can be accomplished with laminoplasty. Because these benign tumors can be adherent to adjacent structures, intraoperative neuromonitoring is helpful adjunct to preserve neurological function for a good outcome.

CONCLUSION

Capillary hemangiomas rarely affect the spine but should be considered on the list of differential diagnoses of intradural lesions.

Removal of a Penetrating Tree Branch in the Orbitofrontal Region-A Unique Application of an Orbitofrontal Craniotomy Through a Supraciliary Brow Approach

BACKGROUND AND IMPORTANCE

Orbitocranial penetrating injury (OPI) is associated with neurological, infectious, and vascular sequalae. This report describes unique application of an orbitofrontal craniotomy through a supraciliary approach to remove a wooden stick penetrating through the orbit and frontal lobe, postoperative management, and antimicrobial therapy.

CLINICAL PRESENTATION

A 51-yr-old male presented after a tree branch penetrated beneath his eye. He had no loss of consciousness and was neurologically intact with preserved vision and ocular motility. Computed tomography (CT) and CT angiogram revealed an isodense hollow cylindrical object penetrating though the left orbit and left frontal lobe. The object extended into the right lateral ventricle, abutting the left anterior cerebral artery. There was minimal intraventricular hemorrhage without arterial injury. The patient was treated with broad-spectrum antimicrobial coverage. The foreign body was removed and the dural defect repaired via an orbitofrontal craniotomy through a supraciliary eyebrow incision. He was treated with an extended course of antimicrobial therapy, and after 18 mo remained neurologically intact.

CONCLUSION

OPI are a subset of penetrating brain injuries with potential for immediate injury to neurovascular structures and delayed complications including cerebrospinal fluid leak and infection. Treatment includes attempted complete removal of the foreign body and antimicrobial therapy. An orbitofrontal craniotomy through a supraciliary eyebrow incision may be effective in selected patients.

Cortical spreading depolarizations induced by surgical field blood in a mouse model of neurosurgery

OBJECTIVE

Cortical spreading depolarization (CSD) has been linked to poor clinical outcomes in the setting of traumatic brain injury, malignant stroke, and subarachnoid hemorrhage. There is evidence that electrocautery during neurosurgical procedures can also evoke CSD waves in the brain. It is unknown whether blood contacting the cortical surface during surgical bleeding affects the frequency of spontaneous or surgery-induced CSDs. Using a mouse neurosurgical model, the authors tested the hypothesis that electrocautery can induce CSD waves and that surgical field blood (SFB) is associated with more CSDs. The authors also investigated whether CSD can be reliably observed by monitoring the fluorescence of GCaMP6f expressed in neurons.

METHODS

CSD waves were monitored by using confocal microscopy to detect fluorescence increases at the cortical surface in mice expressing GCaMP6f in CamKII-positive neurons. The cortical surface was electrocauterized through an adjacent burr hole. SFB was simulated by applying a drop of tail vein blood to the brain through the same burr hole.

RESULTS

CSD waves were readily detected in GCaMP6f-expressing mice. Monitoring GCaMP6f fluorescence provided far better sensitivity and spatial resolution than detecting CSD events by observing changes in the intrinsic optical signal (IOS). Forty-nine percent of the CSD waves identified by GCaMP6f had no corresponding IOS signal. Electrocautery evoked CSD waves. On average, 0.67 ± 0.08 CSD events were generated per electrocautery episode, and multiple CSD waves could be induced in the same mouse by repeated cauterization (average, 7.9 ± 1.3 events; maximum number in 1 animal, 13 events). In the presence of SFB, significantly more spontaneous CSDs were generated (1.35 ± 0.37 vs 0.13 ± 0.16 events per hour, p = 0.002). Ketamine effectively decreased the frequency of spontaneous CSD waves (1.35 ± 0.37 to 0.36 ± 0.15 CSD waves per hour, p = 0.016) and electrocautery-stimulated CSD waves (0.80 ± 0.05 to 0.18 ± 0.08 CSD waves per electrocautery, p = 0.00002).

CONCLUSIONS

CSD waves are detected with far greater sensitivity and fidelity by monitoring GCaMP6f signals in neurons than by monitoring IOSs. Electrocautery reliably evokes CSD waves, and the frequency of spontaneous CSD waves is increased when blood is applied to the cortical surface. These experimental conditions recapitulate common scenarios in the neurosurgical operating room. Ketamine, a clinically available pharmaceutical agent, can block stimulated and spontaneous CSDs. More research is required to understand the clinical importance of intraoperative CSD.

Ischemia-induced spreading depolarization in the retina

Cortical spreading depolarization is a metabolically costly phenomenon that affects the brain in both health and disease. Following severe stroke, subarachnoid hemorrhage, or traumatic brain injury, cortical spreading depolarization exacerbates tissue damage and enlarges infarct volumes. It is not known, however, whether spreading depolarization also occurs in the retina in vivo. We report now that spreading depolarization episodes are generated in the in vivo rat retina following retinal vessel occlusion produced by photothrombosis. The properties of retinal spreading depolarization are similar to those of cortical spreading depolarization. Retinal spreading depolarization waves propagate at a velocity of 3.0 ± 0.1 mm/min and are associated with a negative shift in direct current potential, a transient cessation of neuronal spiking, arteriole constriction, and a decrease in tissue O2 tension. The frequency of retinal spreading depolarization generation in vivo is reduced by administration of the NMDA antagonist MK-801 and the 5-HT(1D) agonist sumatriptan. Branch retinal vein occlusion is a leading cause of vision loss from vascular disease. Our results suggest that retinal spreading depolarization could contribute to retinal damage in acute retinal ischemia and demonstrate that pharmacological agents can reduce retinal spreading depolarization frequency after retinal vessel occlusion. Blocking retinal spreading depolarization generation may represent a therapeutic strategy for preserving vision in branch retinal vein occlusion patients.

Assessment of glial function in the in vivo retina

Glial cells, traditionally viewed as passive elements in the CNS, are now known to have many essential functions. Many of these functions have been revealed by work on retinal glial cells. This work has been conducted almost exclusively on ex vivo preparations and it is essential that retinal glial cell functions be characterized in vivo as well. To this end, we describe an in vivo rat preparation to assess the functions of retinal glial cells. The retina of anesthetized, paralyzed rats is viewed with confocal microscopy and laser speckle flowmetry to monitor glial cell responses and retinal blood flow. Retinal glial cells are labeled with the Ca(2+) indicator dye Oregon Green 488 BAPTA-1 and the caged Ca(2+) compound NP-EGTA by injection of the compounds into the vitreous humor. Glial cells are stimulated by photolysis of caged Ca(2+) and the activation state of the cells assessed by monitoring Ca(2+) indicator dye fluorescence. We find that, as in the ex vivo retina, retinal glial cells in vivo generate both spontaneous and evoked intercellular Ca(2+) waves. We also find that stimulation of glial cells leads to the dilation of neighboring retinal arterioles, supporting the hypothesis that glial cells regulate blood flow in the retina. This in vivo preparation holds great promise for assessing glial cell function in the healthy and pathological retina.

N-acetylated Proline-Glycine-Proline induced G-protein dependent chemotaxis of neutrophils is independent of CXCL8 release

Chronic inflammation in lung diseases contributes to lung tissue destruction leading to the formation of chemotactic collagen fragments such as N-acetylated Proline-Glycine-Proline (N-ac-PGP). In this study, we investigated in more detail the mechanism of action of N-ac-PGP in neutrophilic inflammation. N-ac-PGP was chemotactic for human neutrophils via pertussis toxin sensitive G protein-coupled receptors in vitro and directly activated this cell type, which led to cytosolic calcium mobilization and release of CXCL8. Furthermore, using a selective CXCR2 antagonist confirmed that N-ac-PGP-induced neutrophil chemotaxis is mediated through CXCR2 activation. To determine whether N-ac-PGP was solely responsible for the migration and activation of human neutrophils in vitro and not the released CXCL8 upon stimulation with N-ac-PGP, an antibody directed against CXCL8 was used. Performing chemotaxis and calcium influx assays in the presence of this antibody did not alter the effects of N-ac-PGP whereas effects of CXCL8 were attenuated. These experiments indicate that N-ac-PGP, in addition to the direct induction of chemotaxis, also directly activates neutrophils to release CXCL8. In vivo, this may lead in the long term to a self-maintaining situation enhanced by both N-ac-PGP and CXCL8, leading to a further increase in neutrophil infiltration and chronic inflammation.

Imaging retinal blood flow with laser speckle flowmetry

Laser speckle flowmetry (LSF) was initially developed to measure blood flow in the retina. More recently, its primary application has been to image baseline blood flow and activity-dependent changes in blood flow in the brain. We now describe experiments in the rat retina in which LSF was used in conjunction with confocal microscopy to monitor light-evoked changes in blood flow in retinal vessels. This dual imaging technique permitted us to stimulate retinal photoreceptors and measure vessel diameter with confocal microscopy while simultaneously monitoring blood flow with LSF. We found that a flickering light dilated retinal arterioles and evoked increases in retinal blood velocity with similar time courses. In addition, focal light stimulation evoked local increases in blood velocity. The spatial distribution of these increases depended on the location of the stimulus relative to retinal arterioles and venules. The results suggest that capillaries are largely unresponsive to local neuronal activity and that hemodynamic responses are mediated primarily by arterioles. The use of LSF to image retinal blood flow holds promise in elucidating the mechanisms mediating functional hyperemia in the retina and in characterizing changes in blood flow that occur during retinal pathology.