Identification of direct connections between the dura and the brain

The arachnoid barrier delineates the border between the central nervous system and dura mater. Although the arachnoid barrier creates a partition, communication between the central nervous system and the dura mater is crucial for waste clearance and immune surveillance1,2. How the arachnoid barrier balances separation and communication is poorly understood. Here, using transcriptomic data, we developed transgenic mice to examine specific anatomical structures that function as routes across the arachnoid barrier. Bridging veins create discontinuities where they cross the arachnoid barrier, forming structures that we termed arachnoid cuff exit (ACE) points. The openings that ACE points create allow the exchange of fluids and molecules between the subarachnoid space and the dura, enabling the drainage of cerebrospinal fluid and limited entry of molecules from the dura to the subarachnoid space. In healthy human volunteers, magnetic resonance imaging tracers transit along bridging veins in a similar manner to access the subarachnoid space. Notably, in neuroinflammatory conditions such as experimental autoimmune encephalomyelitis, ACE points also enable cellular trafficking, representing a route for immune cells to directly enter the subarachnoid space from the dura mater. Collectively, our results indicate that ACE points are a critical part of the anatomy of neuroimmune communication in both mice and humans that link the central nervous system with the dura and its immunological diversity and waste clearance systems.

Rapid lymphatic efflux limits cerebrospinal fluid flow to the brain

The relationships between cerebrospinal fluid (CSF) and brain interstitial fluid are still being elucidated. It has been proposed that CSF within the subarachnoid space will enter paravascular spaces along arteries to flush through the parenchyma of the brain. However, CSF also directly exits the subarachnoid space through the cribriform plate and other perineural routes to reach the lymphatic system. In this study, we aimed to elucidate the functional relationship between CSF efflux through lymphatics and the potential influx into the brain by assessment of the distribution of CSF-infused tracers in awake and anesthetized mice. Using near-infrared fluorescence imaging, we showed that tracers quickly exited the subarachnoid space by transport through the lymphatic system to the systemic circulation in awake mice, significantly limiting their spread to the paravascular spaces of the brain. Magnetic resonance imaging and fluorescence microscopy through the skull under anesthetized conditions indicated that tracers remained confined to paravascular spaces on the surface of the brain. Immediately after death, a substantial influx of tracers occurred along paravascular spaces extending into the brain parenchyma. We conclude that under normal conditions a rapid CSF turnover through lymphatics precludes significant bulk flow into the brain.

Impact of early surgery after aneurysmal subarachnoid haemorrhage

OBJECTIVES

To investigate the effect of early aneurysm surgery (<72 h) on outcome in patients with subarachnoid haemorrhage (SAH).

MATERIALS AND METHODS

We studied two consecutive series of patients with aneurysmal SAH [postponed surgery (PS) cohort, n = 118, 1989-1992: surgery was planned on day 12 and early surgery (ES) cohort, n = 85, 1996-1998: ES was performed only in patients with Glasgow Coma Scale (GCS) >13]. We used multivariable logistic regression analysis to assess outcome at 3 months.

RESULTS

Favourable outcome (Glasgow Outcome Scale 4 or 5) was similar in both cohorts. Cerebral ischemia occurred significantly more often in the ES cohort. The occurrence of rebleeds was similar in both cohorts. External cerebrospinal fluid (CSF) drainage was performed more often in the ES cohort (51% vs 19%). Patients with cisternal sum score (CSS) of subarachnoid blood <15 on admission [adjusted odds ratio (OR) for favourable outcome: 6.4, 95% confidence interval (CI) 1.0-39.8] and patients with both CSS <15 and GCS > 12 on admission benefited from the strategy including ES (OR 10.5, 95% CI 1.1-99.4).

CONCLUSIONS

Our results support the widely adopted practice of ES in good-grade SAH patients.

[Brain injuries in relation to morphological structure of dura mater spinalis in pregnant women]

Morphological and histochemical investigations on dura mater spinalis of the lumbar site in 5 women of reproductive age dead from accidents and 5 women dead during deliveries due to hemorrhage were carried out. It was found that one of the etiological factors of head-aches after subarachnoid anesthesia was functional reduction of mechanic and supporting function of dura mater spinalis along with elasticity loss of fibrous tissue, edema and friability. The stable non-healing postpuncture defect of dura mater spinalis resulted in liquorrhea with subsequent development of the "liquorrhea hypotension" syndrome.

Theoretical analysis of the pathophysiology of syringomyelia associated with adhesive arachnoiditis

OBJECTIVE

To apply a theoretical model to analyse the derangement of cerebrospinal fluid (CSF) dynamics in syringomyelia associated with adhesive arachnoiditis.

METHODS

An electrical circuit model of CSF dynamics in the spine was used. With this model, the derangement of CSF dynamics in adhesive arachnoiditis was simulated. The effects of various surgical procedures were then analysed, such as syringo-subarachnoid shunting, subarachnoid bypass, and foramen magnum decompression.

RESULTS

When CSF flow in the subarachnoid space was obstructed at a certain point, the pressure inside the spinal cord increased in the segment immediately distal to the blockage. This location of increased pressure corresponded to the preferred site of syrinx formation in adhesive arachnoiditis. Syringo-subarachnoid shunting, subarachnoid bypass, and foramen magnum decompression were all effective at reducing this pressure gradient.

CONCLUSIONS

Blockage of the spinal subarachnoid CSF pathway produces a relative increase in the pressure inside the spinal cord distal to the blockage point. Repetitive formation of this pressure gradient then induces CSF leakage into the spinal parenchyma, leading to the formation of syringomyelia. Using this model, alternative surgical procedures could be suggested that might be effective in treating this disease.

Evaluation of hyperintense vessels on FLAIR MRI for the diagnosis of multiple intracerebral arterial stenoses

BACKGROUND AND PURPOSE

Hyperintense vessel sign (HVS) on fluid-attenuated inversion recovery (FLAIR) has been described in hyperacute stroke patients with arterial occlusion. We sought to determine whether HVS was more frequent in patients with intracerebral arterial stenoses than in those without stenosis regardless of the presence of a brain infarct.

METHODS

In this case-control study (19 symptomatic patients with multiple intracerebral arterial stenoses compared with 19 age-matched asymptomatic patients without stenosis), we looked for HVS (ie, focal or tubular hyperintensities in the subarachnoid space) on FLAIR images. We compared the proportion of HVS-positive patients in the 2 groups and evaluated the concordance between the arterial distribution of stenoses on angiogram and that of HVS on FLAIR.

RESULTS

HVS was found in 13 of 19 patients (68%) in the study group and 1 of 19 control patients (5.2%) (P<0.0001). The concordance between the territorial distribution of stenoses on angiogram and HVS on FLAIR was higher for the right and left middle cerebral artery (kappa=0.6 and 0.63, respectively) compared with the right and left anterior cerebral artery (kappa=0.35 and 0.2, respectively). HVSs were observed in 1 of 7 patients with posterior cerebral artery stenoses on angiogram. HVSs were seen equally in patients with acute focal (7 of 10) or diffuse (6 of 9) cerebral involvement. In the 6 HVS-positive patients with acute stroke confirmed by MRI, additional HVSs were observed in a different arterial territory than that of the stroke lesion.

CONCLUSIONS

Although their significance remains unclear, multiple HVSs are more frequently observed in symptomatic patients with multiple intracerebral stenoses than in asymptomatic patients without stenosis.

[Vascular complications after acoustic neurinoma surgery]

OBJECTIVE

To report six cases of vascular complications occurring after acoustic neuroma surgery and to discuss the postoperative signs and symptoms that should alert the surgeon, in order to undertake the appropriate treatment as soon as possible.

METHODS

Four hundred thirty-two cases of acoustic tumors operated by the same surgeons between January 1991 and December 2000 were reviewed.

RESULTS

Six cases of vascular complications were identified: one case of cerebral vasospasm secondary to persistence of subarachnoid blood after injury to Dandy's vein; three cases of arterial infarction giving rise to a partial anterior inferior cerebellar artery (AICA) syndrome with an unusual nystagmus in two cases (ipsilateral in one patient and strong controlateral in one patient presenting preoperative vestibular areflexia); one case of hematoma of the cerebello-pontine angle (CPA) causing strong ipsilateral nystagmus; and one case of venous infarction of the cerebellar vermis secondary to accidental sinus thrombosis.

CONCLUSIONS

Vascular complications after acoustic neuroma surgery are potentially devastating and should be identified as early as possible. Rapid extubation is recommended for systematic neurologic assessment. Among abnormal signs and symptoms that should alert the surgeon, marked nystagmus ipsilateral to the operated side or contralateral in patient presenting preoperative vestibular areflexia appears to be of great value.

[Dilatation of Virchow-Robin spaces in patients with migraine]

The Virchow-Robin spaces (VRS) are subpial invaginations making a tubular revestment scabbard that contains a vase between the subarachnoid and subpial spaces. The magnetic resonance imaging (MRI) is the only imaging method able for evaluate this anatomic detail. We studied the possible association between dilated VRS and migraine. Seventy patients with ages ranging from 13 to 54 years (mean, 36.5 years), with clinical diagnosis of migraine were studied and compared with a control group, without past of headache, composed by the same number of patients with ages ranged from 14 to 64 years (mean, 42 years). We observed widening of VRS in 28 cases (40%) of the migraine patients. In the control group this feature was demonstrated in only 5 cases (7.1%). Alert for the importance of detecting and recognizing the VRS, as well as, the differentiation from lacunar infarctions and choroid fissure cysts.

Vascular trauma associated with routine spinal anaesthesia

Samples of cerebrospinal fluid obtained from 130 patients undergoing spinal anaesthesia were examined microscopically. Subarachnoid puncture was performed using either a 25G Whitacre or 25G Quincke spinal needle. Two samples were collected from each patient and the red blood cell count of the second sample collected was taken as a measure of the vascular trauma associated with the procedure. Red blood cells were seen in 50 (38%) of these samples, of which 18 (14%) contained > 100 red blood cells.mm-3. Paraesthesia was felt by 11 (8.5%) patients and the occurrence of paraesthesia was associated with significantly raised red blood cell counts (p < 0.0001). There was also a correlation between the number of needle passes made at lumbar puncture and the red blood cell count in the sample (p < 0. 0001). Neither spinal needle type nor antiplatelet drug therapy influenced red blood cell counts (p = 0.66 and 0.37, respectively). These findings suggest that routine spinal anaesthesia is often complicated by minor degrees of vascular trauma, especially when paraesthesiae or technical difficulty occur at subarachnoid puncture.

Microanatomy of the perforators of the anterior communicating artery complex

We describe the microanatomy of the perforating arteries arising from the anterior communicating artery complex (5 mm distal of the anterior cerebral artery, the anterior communicating artery, and 5 mm proximal of the distal anterior cerebral artery). Thirteen unfixed human brains were used in this study. The origin and number of perforators are described, as is the site of brain penetration, and results are correlated with previous studies. The hemodynamics of blood flow in relation to the formation of an anterior communicating artery aneurysm and different surgical approaches are mentioned. The neuropsychological outcome after aneurysm clipping with regards to the pattern of blood supply from the anterior cerebral artery complex is also discussed.

Microanatomical basis for the third ventriculostomy

In the last few years, there has been a resurgence of interest in endoscopic third ventriculostomy as a treatment for obstructive hydrocephalus. Although various techniques have been used to perform this procedure, not enough emphasis has been placed on the microanatomical details of the third ventricle and surrounding cisterns in relation to this procedure. Using a surgical microscope we examined the microsurgical anatomy of the floor of the third ventricle floor and related subarachnoid cisterns in 20 adult brains using the "immersion technique" in conjunction with microsurgical dissection. We believe that the optimal place to fenestrate is the midline of the floor of the third ventricle, behind the infundibular recess and in front of the mammillary bodies, communicating the third ventricle with the anterior interpeduncular cistern, minimizing the risk for vascular lesions. Stereotactic third ventriculostomy is a safe and effective way of re-establishing normal cerebrospinal fluid flow dynamics in selected cases of obstructive hydrocephalus. However, in an endoscopic exposure only a small portion of the anatomy can be seen at any one time, and important neurovascular structures may be located adjacent to the endoscope, but outside of the visual range of the lens. A thorough understanding of the microanatomy of the neural and vascular structures surrounding the third ventricle and related cisterns is essential in order to improve surgical results avoiding complications.

Meningitis after adenoidectomy: an anatomic explanation

Meningitis is a rare complication of adenoidectomy. During a 5-month period, two children at St Christopher's Hospital for Children developed meningitis within days following this surgical procedure. The potential causes of this complication that we investigated include coincidence, systemic hematogenous spread of bacteria to the central nervous system, and direct or indirect contamination of the cerebrospinal fluid by bacteria introduced by retropharyngeal injection of lidocaine hydrochloride and epinephrine. Based on statistical analysis of the available literature and anatomic studies of the pediatric nasopharyngeal region, we conclude that a retrograde flow of bacteria via a newly described anastomotic network of veins was the most likely cause of this sequela.

Surgical interruption of intradural draining vein as curative treatment of spinal dural arteriovenous fistulas

To establish if interruption of the intradural draining spinal vein or surgical excision are curative treatments for spinal dural arteriovenous fistulas (AVFs), the medical records and radiographic studies of 19 patients with spinal dural AVFs and progressive myelopathy were reviewed. Spinal arteriograms were obtained before and within 2 weeks after surgery in 19 patients, and after a delay of 4 months or more in 11 patients. The mean clinical and arteriographic follow up was at 37 and 35 months, respectively. In the 11 patients who underwent excision of the dural AVF there was no evidence of a residual lesion upon immediate or delayed postoperative arteriography. Surgery in eight patients consisted of simple interruption of the intradural draining vein as it entered the subarachnoid space. In six of these patients the vein draining the AVF intrathecally provided the only venous drainage of the AVF. In these six patients there was no immediate (six of six) or delayed (four of six) arteriographic evidence of residual or recurrent flow through the AVF. Two patients had an AVF with both intra- and extradural venous drainage; after intradural division of the draining vein there was residual flow through the AVF into the extradural venous system. In one of these two patients intrathecal venous drainage was reestablished, which required additional therapy. In the other patient the extradural AVF spontaneously thrombosed and was not evident on delayed follow-up arteriography. In patients with spinal dural AVFs with only intrathecal medullary venous drainage, which includes most patients with these lesions, surgical interruption of the intradural draining vein provides lasting and curative treatment. In patients with both intra- and extradural drainage of the AVF, complete excision of the fistula or interruption of the intra- and extradural venous drainage of the fistula is indicated. In patients in whom a common vessel supplies the spinal cord and the dural AVF, simple surgical interruption of the vein draining the AVF is the treatment of choice, as it provides lasting obliteration of the fistula and it is the only treatment that does not risk arterial occlusion and cord infarction. Simple interruption of the venous drainage of a spinal dural AVF provides lasting occlusion of the fistula, as it does for cranial dural AVFs, if all pathways of venous drainage are interrupted. This result provides further evidence that the venous approach to the treatment of dural AVFs can be used successfully.

Cranial base approaches to intracranial aneurysms in the subarachnoid space

The use of cranial base approaches to aneurysm surgery is illustrated by means of patient examples. Over a 9-year period, cranial base approaches were used to expose and treat 38 aneurysms involving the anterior communicating artery complex, proximal internal carotid artery, basilar artery, or vertebral artery. The approaches included orbital osteotomy, orbitozygomatic osteotomy, petrous apicectomy, presigmoid petrosectomy, and extreme lateral transcondylar methods. Complications related to the approaches included one partial ptosis and two cerebrospinal fluid leaks, which resolved with treatment. The technique of three-dimensional computed tomographic angiography was useful in delineating the vascular anatomy and its relation to the cranial base structures. This helped the surgeon plan the appropriate approach to the aneurysm. Cranial base approaches, used selectively, can provide improved exposure of deep-seated aneurysms and large or giant aneurysms, while minimizing brain retraction.

Bilirubin levels in subarachnoid clot and effects on canine arterial smooth muscle cells

BACKGROUND AND PURPOSE

Previous studies have suggested that bilirubin is a potential contributor to cerebral vasospasm. The purpose of this investigation was to determine whether bilirubin accrues in subarachnoid clot, whether its vasoconstrictive effect could involve a direct action on arterial smooth muscle cells, and, if so, whether bilirubin affects their Ca2+ uptake.

METHODS

Subarachnoid clots were analyzed for bilirubin using high-performance liquid chromatography. The length and 45Ca2+ uptake of vascular smooth muscle cells enzymatically dissociated from canine carotid arteries were measured before and after exposure to bilirubin solution. Additional experiments were conducted on cultured smooth muscle cells from canine basilar artery and on ATP-depleted cardiac myocytes.

RESULTS

Mean +/- SE bilirubin concentration in experimental clot was 263 +/- 35.7 mumol/L. Vascular smooth muscle cells exposed to bilirubin showed progressive shortening (P < .01) and an increased uptake of 45Ca2+ (P < .001). Contraction was prevented by Ca(2+)-free media but not by verapamil. Experiments with heart myocytes showed that bilirubin caused an increased uptake of 45Ca2+ but not of [14C]sucrose.

CONCLUSIONS

The results indicate that bilirubin accrues in subarachnoid clot, that it exerts a direct constrictive effect on arterial smooth muscle cells, and that this effect is associated with an increased uptake of Ca2+. Studies on heart myocytes suggest that the Ca2+ uptake induced by bilirubin could be due to a selective increase in membrane permeability to Ca2+.

Elevated cortical venous pressure in hydrocephalus

To gain a better understanding of cerebrospinal fluid (CSF) hydrodynamics and their relationship to the cerebrovascular system, normal and naturally hydrocephalic dogs were studied to determine transmantle [lateral ventricle (LV) to subarachnoid space] and transparenchymal [LV to cortical vein (CV)] pressures. Pressure was also measured in the sagittal sinus, cisterna magna, and femoral artery. CV pressure has not previously been measured in hydrocephalus. Ventricular volume was determined by computed tomography. Four groups of animals were studied. In Group 1 (n = 5) transmantle pressure was measured; in Group 2 (n = 5), transparenchymal pressure in normal animals was measured. In Group 3 (n = 5) was measured all the pressures in spontaneously normal animals, and in Group 4 (n = 6) was measured the pressures in hydrocephalic animals. The pressure-volume index and CSF outflow resistance were also measured. LV volume in the normal dogs was 1.3 +/- 0.7 ml and in the hydrocephalic dogs was 5.1 +/- 2.7 ml (P less than 0.005). Although LV, subarachnoid space, and sagittal sinus pressures were elevated in the hydrocephalic dogs (15.1 versus 10.2, 16.4 versus 10.5, and 8.4 versus 5.2 mm Hg, respectively), the transmantle pressure and subarachnoid space to sagittal sinus gradients were not significantly altered. CV pressure was markedly elevated in the hydrocephalic animals (21.5 versus 11.7 mm Hg, P less than 0.005). The pressure-volume index and outflow resistance were not significantly different. These results suggest that an elevated CV pressure plays a role in the development and/or maintenance of hydrocephalus, and that the pathway for CSF absorption includes transcapillary or transvenular absorption of CSF from the interstitial space.(ABSTRACT TRUNCATED AT 250 WORDS)

Three-dimensional reconstruction of the rat brain cortical microcirculation in vivo

We used confocal laser scanning microscopy (CLSM) to investigate the morphology and three-dimensional relationships of the microcirculation of the superficial layers of the rat brain cortex in vivo. In anesthetized rats equipped with a closed cranial window (dura mater removed), after i.v. injection of 3 mg/100 g of body weight of fluorescein in 0.5 ml of saline, serial optical sections of the brain cortex intraparenchymal microcirculation were taken. Excitation was at a wavelength of 488 nm (argon laser), and emission was collected above 515 nm. CLSM provided images of brain vessels with sufficient signal-to-noise ratio for three-dimensional reconstructions down to a depth of 250 microns beneath the surface of the brain. Compared to conventional fluorescence microscopy, CLSM has a much higher axial resolution and higher depth of penetration. Laser light-induced intravascular aggregates, irregularities of erythrocyte flow, or microvascular occlusions ("light and dye injury") were not apparent in the current experimental paradigm. CLSM is a promising new tool for in vivo visualization of the cerebral microcirculation. Future studies have to characterize the potential damage to the tissue dye mechanisms.

Initial CT findings in 753 patients with severe head injury. A report from the NIH Traumatic Coma Data Bank

In this prospective multicenter study, the authors have examined data derived from the initial computerized tomography (CT) scans of 753 patients with severe head injury. When the CT findings were related to abnormal intracranial pressure and to death, the most important characteristics of the scans were: midline shift: compression or obliteration of the mesencephalic cisterns: and the presence of subarachnoid blood. Diffuse hemispheric swelling was also found to be associated with an early episode of either hypoxia or hypotension.

Interrelationships of the pia mater and the perivascular (Virchow-Robin) spaces in the human cerebrum

Biopsies of histologically normal adult human cerebral cortex, underlying white matter and overlying leptomeninges were taken from frontal and temporal lobectomy specimens excised during the removal of cerebral tumours. Multiple blocks from 6 patients (aged 18-53 years) were examined by light and transmission electron microscopy. A thin sheath of pia mater cells was found to surround completely arterioles and arteries in the brain, in the subpial space and in the subarachnoid space. Pia mater cells, forming the perivascular sheath, were identified by the presence of desmosomes or small nexus junctions and by continuity with the pia mater itself. The presence of the pial sheath suggests that the perivascular spaces around intracerebral arteries are in direct continuity with the perivascular spaces around subarachnoid arteries. No similar pial sheath was observed around intracerebral or subpial venules. The role of the periarterial spaces, enclosed by the pial sheath, is discussed in relation to the results of physiological experiments suggesting drainage of interstitial fluid from brain tissue into the perivascular pathways along major cerebral arteries in the subarachnoid space. As arterioles in the brain become smaller and lose their smooth muscle coats, the pial sheath becomes incomplete. The anatomical relationships between the pia mater and blood vessels in the human cerebrum is summarised diagrammatically, and a possible role for pial cells as an enzymic barrier protecting the brain from exogenous catecholamines is discussed.

High levels of NPY in rabbit cerebrospinal fluid and immunohistochemical analysis of possible sources

We have analyzed rabbit cerebrospinal fluid for neuropeptide Y (NPY)-like immunoreactivity, using high performance liquid chromatography (HPLC) and radioimmunoassay (RIA) and examined the anatomical relationship of NPY-containing fibers to the cerebral vasculature and the third cerebral ventricle. Cerebrospinal fluid (CSF) obtained from the cisterna magna of rabbits was injected into a C18 column and subjected to HPLC. The fractions were collected, dried and reconstituted in buffer for NPY radioimmunoassay. A single peak of NPY immunoreactivity was obtained which corresponded in retention time to synthetic porcine NPY. Analysis of CSF samples produced displacement curves parallel to the standard curve. Immunohistochemistry revealed numerous NPY-labeled fibers which penetrated the ependymal lining of the third cerebral ventricle and directly bordered the ventricular lumen. Other fibers were observed in the pia which lines the ventral aspect of the hypothalamus. The basilar artery, its branches and other cerebral vessels were surrounded by NPY-labeled fibers. The results show that: (1) approximately 1 ng/ml of NPY immunoreactivity which corresponds chromatographically to synthetic porcine NPY is present in rabbit CSF; (2) NPY-containing fibers surround the basilar artery and other cerebral vessels; (3) NPY may be released into the CSF from axons in the pia and from axons which penetrate the ependymal lining of the third ventricle. These observations form the basis for our analysis of the vasoconstrictor effects of NPY and its role in cerebrovasospasm after experimental subarachnoid hemorrhage.

Activation of the coagulation system in the subarachnoid space after subarachnoid haemorrhage: serial measurement of fibrinopeptide A and bradykinin of cerebrospinal fluid and plasma in patients with subarachnoid haemorrhage

Fibrinopeptide A (FPA) levels as an indicator of thrombin activity in the cerebrospinal fluid (CSF) and plasma of 25 patients with subarachnoid haemorrhage (SAH) were measured serially by radioimmunoassay (RIA). FPA levels in CSF were extremely high on days 0-1 (1253 +/- 269 ng/ml, mean +/- standard error) but decreased rapidly (11.3 +/- 3.9 ng/ml on days 2-4, 10.7 +/- 5.9 ng/ml on days 5-7, and 6.3 +/- 1.5 ng/ml on days 8-14). In the controls the FPA concentration in CSF was 1.2 +/- 0.9 ng/ml (mean +/- standard deviation). Plasma FPA levels in patients with SAH showed no statistically significant changes with time. The bradykinin (BK) concentration in CSF and plasma in 27 patients with SAH was measured serially by RIA. The concentrations in CSF were 122.7 +/- 22.7 pg/ml (mean +/- standard error) on day 0, 38.6 +/- 6.1 pg/ml on day 1, 22.7 +/- 6.3 pg/ml on day 2, and 17.1 +/- 3.0 pg/ml or less thereafter. Plasma BK levels in patients with SAH were higher than those in the control group, but there was no statistically significant change over time. From the measurement of FPA it was apparent that the coagulation system in the subarachnoid space is strongly activated in the early stage of SAH. The formation of BK in CSF after SAH is thought to be due to the contact activation of Hageman factor (intrinsic factor) in the subarachnoid space. Trabeculae as collagen bundles in the subarachnoid space were considered to have a possible role in activating the Hageman factor of the coagulation system in SAH.

Leukodiapedesis and leukocyte migration in the leptomeninges and in the subarachnoid space

Pleocytosis in cerebrospinal fluid and infiltration of the leptomeningeal tissue have been studied after injection of ferritin into the subarachnoid space (SAS) of cats. The most important source of granulocytes in the leptomeninges are the relatively large veins of the pia mater, which have very thin walls. Passing between the lining cells of the pia mater the granulocytes leave the connective tissue space of the pia mater and reach the SAS. Leukodiapedesis has also been observed in veins crossing the SAS. During this process, gaps between the lining cells of the perivascular leptomeningeal sheath may develop. There are two possible ways for the granulocytes to pass from the vascular pia mater to the avascular arachnoidea: either they migrate actively on the surface of the leptomeningeal trabeculae or they reach the arachnoidea passively by the circulation of the cerebrospinal fluid. Leukodiapedesis in the vessels of the dura mater occurs relatively seldom and would not be able to cause the occasionally massive infiltration of the arachnoidea.

[Symptoms preceding rupture of subarachnoid aneurysms: an analysis]

In a group of 281 cases of subarachnoid haemorrhages including 105 cases of intracranial aneurysms confirmed on autopsy or by angiography the authors analyse the symptoms preceding subarachnoid haemorrhage and suggesting presence of aneurysm. The most frequent symptom suggesting presence of intracranial aneurysm were headaches, especially associated with other symptoms such as dizziness, nausea, paraesthesiae of extremities, visual disturbances. A careful analysis of these symptoms and early radiological examination may help in establishing the diagnosis of aneurysm before its rupture.

Time course of vasospasm in man

Measurements were made at eight predetermined positions on 627 sets of angiograms from 293 patients with aneurysms. A ratio between the sum of the vessel diameters in the subarachnoid space to the sum in the base of skull and neck was calculated and plotted against time. Vasospasm has its onset in man about Day 3 after subarachnoid hemorrhage, is maximal at Days 6 to 8, and is gone by Day 12. There is a tendency for patients in poor clinical grades to have more vasospasm. The patients with most vasospasm have a significantly higher mortality than those with the least.

Capillaries in the subarachnoid space

The fine structure of the small vessels of the subarachnoid spaces in the rat and mouse cerebral and cerebellar cortices was examined. Small vessels with lumen under 7 mu and whose walls consisted of a single layer of endothelial cells were found. These vessels are regarded as true capillaries.

Sequential changes of vascular ultrastructure in experimental cerebral vasospasm. Myonecrosis of subarachnoid arteries

✓ The authors describe the striking ultrastructural evolution of vacuolar degeneration of the media in subarachnoid arteries that have been in spasm following subarachnoid hemorrhage.

Raised intracranial pressure and cerebral blood flow. 2. Supratentorial and infratentorial mass lesions in primates

Changes in cerebral blood flow with increasing intracranial pressure were studied in anaesthetized baboons during expansion of a subdural balloon in one of two different sites. With an infratentorial balloon, cerebral blood flow bore no clear relation to intracranial pressure, but was linearly related to cerebral perfusion pressure. Apart from an initial change in some animals, cerebrovascular resistance remained constant with increasing intracranial pressure, and autoregulation appeared to be lost from the outset. With a supratentorial balloon, cerebral blood flow remained constant as intracranial pressure was increased to levels around 60 mm Hg, corresponding to a cerebral perfusion pressure range of approximately 100 to 40 mmHg. Cerebrovascular resistance fell progressively, and autoregulation appeared to be effective during this phase. At higher intracranial pressure levels (lower cerebral perfusion pressure levels), autoregulation was lost and cerebral blood flow became directly dependent on cerebral perfusion pressure. The importance of the cause of the increase in intracranial pressure on the response of the cerebral circulation and the relevance of these findings to the clinical situation are discussed.

Erythrocyte velocity and a velocity pulse in minute blood vessels on the surface of the mouse brain

High-speed microcinematography of vessels in the subarachnoid space of the anesthetized mouse was used to measure the velocity of erythrocytes in arterioles and venules less than 30µ in diameter. Within arterioles the velocity averaged 3.5 mm/sec, while in venules an average value of 1.9 mm/sec was obtained. A rhythmic alteration in velocity was often observed in the arterioles and was seen occasionally in venules. This cyclical change in velocity was termed the "velocity pulse." The frequency of the velocity pulse was virtually identical to that of the peripheral pulse and is believed to result from a propagation of that pulse into the microcirculation. The velocity pulse was not recognizable in vessels 5µ to 10µ wide. In vessels 10µ, to 30µ, in diameter, the velocity pulse was not accompanied by changes in the width of the vessels.