Patterns of peptide-containing perivascular nerves in the circle of Willis: their absence in intracranial arteriovenous malformations

Hemodynamic Perturbations in Cerebral Arteriovenous Malformations and Management Implications

Cerebral AVMs have high flow, low resistance shunts that induce regional hemodynamic disturbances and possibly neural derangements. A better understanding of these mechanisms may help treatment planning and the management of complications after endovascular or surgical treatment.

Although the precise mechanisms of hemodynamic perturbation are still relatively unclear, the presence of chronic cerebral hypoperfusion is central and widely believed to be associated with both neurological deficits at presentation (‘steal‘) and ‘hyperemic’ complications following shunt obliteration. The ‘normal perfusion pressure breakthrough‘ (NPPB) theory states that chronic hypoperfusion around AVMs induces the loss of autoregulatory capability; following AVM shunt obliteration, perfusion pressure elevation induces an increase in flow, due to ‘vasomotor paralysis’, which can cause hemorrhage. The ‘dissociative vasoparalysis' theory suggests that vasodilation is preserved but not vasoconstriction. However, pharmacologic exploration of cerebral autoregulation with induced vasoconstriction (phenylephrine) and vasodilatation (acetazolamide) helps identify 3 patterns of autoregulatory behavior. The vast majority of AVM patients appear to retain autoregulatory capability, despite low arterial feeding pressures, consistent with a “shift to the left” of the autoregulation curve. Pronounced hypotension may “exhaust” cerebrovascular reserve in some patients, predisposing to hemorrhagic complications in the post-operative period. Lastly, “vasoparalysis” may coexist with a combination of vascular insult and marked hypotension.

Clinical presentation, AVM angioarchitecture and peri-operative physiologic data (especially feeding artery and venous outflow pressures) may assist patient management. Patients can be identified in whom staged treatment is recommended initially. Following AVM obliteration, the patient's hemodynamic response, which may range from a minimal increase in A-V pressure gradient to significant CBF increase may be predicted, and blood pressure, fluid and ICP management adjusted accordingly, as the monitoring of post-operative cerebral hemodynamics remains difficult. Extreme attention to endovascular and operative technique must be exercised, as technical problems can be devastating.

Although incompletely understood, hemodynamic derangements associated with cerebral AVMs increasingly appear to be associated with intact cerebral autoregulation in most patients. As cerebral hemodynamics monitoring remains challenging, clinical, angiographic and physiologic data from interventional/operative monitoring must be used to guide patient management.

Cerebral vasospasm: a consideration of the various cellular mechanisms involved in the pathophysiology

The cellular mechanisms responsible for cerebral vasospasm (CVS) occurring after subarachnoid hemorrhage (SAH) have been of major interest over the past 50 years. The present review describes how each of the discrete anatomic components that comprise the cerebral artery may contribute to the pathology of CVS. The blood extravasated after SAH is hemolyzed and undergoes degradation with resultant production of free radicals, known to be powerful initiators of vascular damage. An inflammatory response is generated activating both leukocytes and platelets with subsequent release of inflammatory agents. The cerebral artery affected by CVS undergoes phenotypic change involving both the endothelial and smooth muscle cells. In the endothelium the production of nitric oxide and prostacyclin is affected. In the smooth muscle cells signal transduction pathways that enhance the function of the contractile proteins and induce the upregulation of contractile receptors are activated. In parallel, there is evidence that nervous reflex pathways involving the trigeminal ganglion and the hypothalamus are activated. However, the relative contributions of each of the systems are speculative. Therapy may be directed at disrupting the cascade leading from the SAH insult to CVS or at overcoming the dysfunction incurred by CVS; possible therapeutical interventions are considered.

Topography and associations of luteinizing hormone-releasing hormone and neuropeptide Y-immunoreactive neuronal systems in the human diencephalon

Neuropeptide Y (NPY) potentiates the effect of luteinizing hormone-releasing hormone (LHRH) on luteinizing hormone secretion in several species, including human. In addition to the pituitary sites, the interactions of the NPY and LHRH systems may involve diencephalic loci. However, the morphologic basis of this putative communication has not yet been elucidated in the human brain. To discover interaction sites, the distribution and connections of LHRH and NPY-immunoreactive (IR) neuronal elements in the human hypothalamus were investigated by means of light microscopic single- and double-label immunocytochemistry. NPY-IR perikarya and fibers were found to be widely distributed in the ventral diencephalon, with high densities in the preopticoseptal, periventricular, and tuberal regions. Small neuronal cell groups were infiltrated with a dense network of varicose NPY-IR fibers in the lateral preoptic area. The LHRH-IR perikarya were located mainly in the preopticoseptal region, diagonal band of Broca, lamina terminalis, and periventricular and infundibular nuclei. A few LHRH-IR neurons and fibers were scattered in the mamillary region. The overlap between the NPY and LHRH systems was apparent in the periventricular, paraventricular, and infundibular nuclei. Double-labeling immunohistochemistry showed NPY-IR axon varicosities in contact with LHRH-IR perikarya and main dendrites. The putative innervation of LHRH neurons by NPY-IR fibers was also seen in 1-microm-thick plastic sections and with confocal laser scanning microscope, thus further supporting the functional impact of NPY-IR terminals on LHRH-IR neurons. The present findings suggest that the hypophysiotropic LHRH-synthesizing neurons may be innervated by intrahypothalamic NPY-IR fibers. Confirmation by ultrastructural analysis would demonstrate that the LHRH system in the human hypothalamus is regulated by NPY, as has been demonstrated in nonhuman species.

Malignant intracerebral nerve sheath tumor with intratumoral calcification. Case report

The authors present the clinical, radiological, and pathological features of a malignant intracerebral nerve sheath tumor that occurred in the right parietooccipital lobe of a 4-year-old girl. Computerized tomography scanning and magnetic resonance imaging demonstrated a 5x5x4-cm multiloculated mass with considerable enhancement of the irregularly shaped septa and clearly calcified areas within the mass. Among five cases reported in the literature, this patient is the youngest and represents the first case in which there is radiological evidence of intratumoral calcification.

Transvenous retrograde nidus sclerotherapy under controlled hypotension (TRENSH): a newly proposed treatment for brain arteriovenous malformations--concepts and rationale

PURPOSE

An alternative endovascular treatment to conventional transarterial embolization of cerebral arteriovenous malformations (AVMs) is proposed.

CONCEPT

According to this proposed treatment, selected AVMs could undergo transvenous retrograde nidus sclerotherapy under controlled hypotensive anesthesia (TRENSH).

RATIONALE

It is hypothesized that TRENSH may provide the means of avoiding delivery of embolic agents via arterial feeders (thus preventing ischemic complications), in addition to a possible more complete permeation of an AVM nidus with a sclerosant than can otherwise be obtained with current agents via arterial feeders.

DISCUSSION

Instead of relying on access to an AVM nidus from the arterial side (with its usual complexity), TRENSH would require retrograde access to the lesion via much larger and anatomically simpler draining veins. Retrograde permeation of the AVM nidus may then be possible with a liquid sclerosant (to effect a "chemical embolization") provided that the arterial inflow is reduced sufficiently by temporary controlled systemic hypotension, with or without the aid of temporary balloon occlusion of the main arterial feeder(s). Retrograde spread of sclerosant within the nidus that falls short of filling arterial feeders and their branches to normal brain tissue may then be possible. Angioarchitectural and hemodynamic considerations are addressed, as are the potential role and limitations of TRENSH in the management of cerebral pial AVMs. Future implementation of this new technique in some specific selected cases in which the anatomic configuration of the AVM and its draining veins might be favorable could prove to be a potentially useful addition to the armamentarium of AVM therapies, which currently includes microsurgery, radiosurgery, and transarterial embolotherapy. Experimental studies directed at assessing the feasibility of TRENSH before potential future clinical application seem justified.

Innervation pattern of malformative cortical vessels in Sturge-Weber disease: an histochemical, immunohistochemical, and ultrastructural study

OBJECTIVE

This study was undertaken to elucidate the pattern of vascular innervation in areas of pial angiomatosis in Sturge-Weber disease (SWD) and eventually correlating it with the pathophysiology of the disease, namely its chronic ischemic changes.

METHODS

We processed part of a surgical specimen resected from a 3-year-old female patient who underwent functional hemispherectomy for SWD and characterized the pattern of innervation of the malformative cortical vessels using histochemical, immunohistochemical, and ultrastructural techniques.

RESULTS

Cortical vessels were observed to be supplied with numerous varicose nerve fibers containing immunoreactivity for neuropeptide tyrosine and the catecholamine-synthesizing enzyme, tyrosine, tyrosine hydroxylase. In contrast, no nerve fibers containing acetylcholinesterase activity and immunoreactivity for Substance P, a calcitonin gene-related peptide and vasoactive intestinal peptide, were detected. Ultrastructural studies revealed the presence of numerous axon varicosities at the adventitial-medial border. Neuropeptide tyrosine immunoreactivity was localized in large granular vesicles in nerve varicosities that also contained numerous small granular vesicles.

CONCLUSION

These results demonstrate that nerve supplying cortical vessels in SWD are arranged in a distribution pattern similar to the one observed in human normal cortical veins and suggest that these abnormal vessels are innervated only with noradrenergic sympathetic nerve fibers. This represents a clear difference from the pattern of innervation observed in both normal cortical arteries and veins, and is the consequence of the anatomic and functional dysangiogenic process characteristic of the affected cortical areas in SWD.

Prevention of cerebral vasospasm by calcitonin gene-related peptide slow-release tablet after subarachnoid hemorrhage in monkeys

OBJECTIVE

The goal of this work was to investigate the efficacy of a calcitonin gene-related peptide (CGRP) slow-release tablet (CGRP tablet) for the prevention of cerebral vasospasm after subarachnoid hemorrhage (SAH).

METHODS

Experimental SAH was produced in 10 cynomolgus monkeys by placing a clot around the internal carotid artery bifurcation (Day 0). In five animals, CGRP tablets (1200 micrograms of CGRP) were then placed in the cerebrospinal fluid space (CGRP group). In two animals, placebo tablets were similarly placed (placebo group). The remaining three animals were treated with no tablets after SAH (SAH group). A series of angiographic analyses were performed, before SAH and on Days 7 and 14, to examine changes in the diameters of the ipsilateral internal carotid artery, middle cerebral artery, and anterior cerebral artery. The CGRP concentration in the cerebrospinal fluid taken before each angiogram was also determined.

RESULTS

In the SAH and placebo groups, cerebral vasospasm developed on Day 7 (54.8% of the pre-SAH value at the internal carotid artery, 62.3% at the middle cerebral artery, 51.3% at the anterior cerebral artery, and 56.1% as an average of the three arteries). In the CGRP group, vasospasm was significantly ameliorated at the middle cerebral artery, at the anterior cerebral artery, and on average (81.7, 81.1, and 75.7%, P < 0.05, 0.03, and 0.02, respectively). The CGRP concentration was positive only on Day 7 for the CGRP group (6.5 nmol/L).

CONCLUSION

The CGRP tablet prevented cerebral vasospasm after SAH and may have significant potential for the treatment of patients with SAH.

Cerebral hyperemia after arteriovenous malformation resection is related to "breakthrough" complications but not to feeding artery pressure. The Columbia University Arteriovenous Malformation Study Project

To study the pathophysiology of idiopathic postoperative brain swelling or hemorrhage after arteriovenous malformation resection, termed normal perfusion pressure breakthrough (NPPB), we performed cerebral blood flow (CBF) studies during 152 operations in 143 patients, using the xenon-133 intravenous injection method. In the first part of the study, CBF was intraoperatively measured (isoflurane/N2O anesthesia) during relative hypocapnia in 95 patients before and after resection. The NPPB group had a greater increase (P < 0.0001) in mean +/- standard deviation global CBF (28 +/- 6 to 47 +/- 16 ml/100 g/min, n = 5) than did the non-NPPB group (25 +/- 7 to 29 +/- 10 ml/100 g/min, n = 90); both arteriovenous malformation groups showed greater increase (P < 0.05) than did controls undergoing craniotomy for tumor (23 +/- 6 to 23 +/- 6 ml/100 g/min, n = 22). Ipsilateral and contralateral CBF changes were similar. In a second cohort of patients with arteriovenous malformations, CBF was measured at relative normocapnia and it increased (P < 0.002) from pre- to postresection (40 +/- 13 to 49 +/- 15 ml/100 g/min, n = 57). There were no NPPB patients in this latter cohort. The feeding mean arterial pressure was measured intraoperatively before resection or at the last embolization before surgery (n = 64). The feeding mean arterial pressure (44 +/- 16 mm Hg) was 56% of the systemic arterial pressure (78 +/- 12 mm Hg, P < 0.0001) and was not related to changes in CBF from pre- to postresection. There was an association between increases in global CBF from pre- to postresection and NPPB-type complications, but there was no relationship of these CBF changes to preoperative regional arterial hypotension. These data do not support a uniquely hemodynamic mechanism that explains cerebral hyperemia as a consequence of repressurization in hypotensive vascular beds.