Arteriovenous malformation hemodynamics: a transcranial Doppler study

Brain reorganization after endovascular treatment in a patient with a large arteriovenous malformation: the role of diagnostic and functional neuroimaging techniques

We describe a case of brain cortical reorganization after embolization of a large right temporal arteriovenous malformation. A comprehensive imaging protocol, including functional magnetic resonance imaging (fMRI), cortical thickness analysis and 320-row computed tomography (CT) perfusion was used to provide information on brain plasticity and potential steal phenomenon. A 25-year-old man known for a right temporal grade V Spetzler-Martin classification arteriovenous malformation (AVM) presented with left progressive hemiparesis. He underwent functional 3T magnetic resonance imaging (fMRI), cortical thickness analysis, and CT perfusion (CT 320 row, Aquilion ONE, Toshiba, Tokyo, Japan) before and after endovascular treatment. The results were compared to look for modifications in brain perfusion and organization. An improvement in the left hemiparesis and a reorganization of motor function were observed after endovascular treatment. Modifications in the angioarchitecture and perfusion of an extensive AVM may be accompanied by a functional and structural reorganization of the brain. The location in the so-called eloquent regions may not be sufficient to explain the wide spectrum of symptoms that these patients can present. A more comprehensive approach considering a global involvement of the brain in patients with large AVMs is suggested to achieve the best treatment strategy and to stage treatment in incurable AVMs.

Suboccipital craniotomy in the surgical treatment of Chiari I malformation

OBJECT

The object of this study was to present craniotomy for Chiari type I patients.

MATERIALS AND METHODS

Six patients with Chiari type I underwent suboccipital craniotomy. All patients showed clinical improvement, and none had any complications. Two patients had syringomyelia; it disappeared in entirety. We describe the procedure for posterior fossa decompression.

RESULTS

Three-dimensional volumetric analysis using Vitrea workstation for postoperative posterior fossa volumes was calculated and was seen to have been increased on an average, from pre-operative (168 cc) to postoperative volume (192 cc).

CONCLUSION

We thus conclude that suboccipital craniotomy results in resolution of the Chiari symptoms yet achieves effective expansion of posterior fossa.

Pathophysiology and treatment of brain AVMs

Cerebral arteriovenous malformations (AVMs) are a major source of intracerebral hemorrhage in younger adults. First, some basic ideas about AVM anatomy, the influences of pressure, macrovascular flow, perfusion and the "steal effect", and some recent observations in the field of inflammatory markers and genetics are briefly discussed. Then, some clinical aspects in the presentation and the natural course of AVMs are highlighted, with special emphasis on the prediction of hemorrhage. Finally, some problems of the current treatment options are mentioned, and future directions in diagnostics and therapy considered.

The application of ultrasound in the management of cerebral arteriovenous malformation

Ultrasound is used in the diagnosis, treatment and follow-up of cerebral arteriovenous malformation (AVM). Several parameters including flow velocity, flow volume, resistance index, pulsatility index, vasomotor reactivity and their influencing factors are reviewed. The applications of ultrasound in the preoperative evaluation, intraoperative monitor and postoperative follow-up of AVM, are summarized. Although some limits exist, ultrasound can provide more reliable information about AVM, if lesions are classified according to their characteristics, compared in different conditions between preoperation and postoperation, feeding and non-feeding side, patients and healthy adults, and if ultrasound method is combined with other examinations and different developed ultrasound techniques. With the appearance and development of new ultrasound technique, its application will be wider in management of AVM.

Spontaneous pial single-channel arteriovenous fistulae with angiographically occult small feeding arteries: case report

BACKGROUND

Pial single-channel arteriovenous (AV) fistulae are usually cured by interrupting only the feeding arteries identified in cerebral angiography.

CASE DESCRIPTION

A 27-year-old woman presented after 3 complex partial seizures due to a pial single-channel AV fistula with the varix located in the right temporal lobe. When all feeding arteries identified by preoperative cerebral angiography were temporarily occluded, varix blood flow was confirmed with Doppler ultrasonography. Many small feeding arteries were identified, and the varix was dissected and removed. The postoperative course was uneventful and postoperative cerebral angiography revealed no abnormal vascular lesions.

CONCLUSION

Pial single-channel AV fistulae are not always cured by interrupting only the feeding arteries identified in cerebral angiography and might require varix removal.

Transcranial Doppler sonography in the early stage of critical enteroviral infection

OBJECTIVE

There is a high fatality rate in enteroviral infection with central nervous system involvement. Our aim was to investigate the change in intracranial blood flow to disclose the characteristic findings in the early stage of critical enteroviral infection.

METHODS

We examined 27 patients in critical condition with enteroviral infection in our pediatric intensive care unit. We performed transcranial Doppler sonography within 12 hours of admission to the unit. The data were compared with those of a group of 11 patients with nonenteroviral encephalitis.

RESULTS

The peak systolic, end-diastolic, and mean velocities of the critical enteroviral infection group were significantly higher than those of the control group (P < .05). Gosling pulsatility index and Pourcelot resistive index values for the right and left middle cerebral arteries (pulsatility index, [mean +/- SD], 0.68 +/- 0.22 and 0.77 +/- 0.19, respectively; resistive index, 0.48 +/- 0.01 and 0.52 +/- 0.01) in patients with critical enteroviral infection were significantly lower than those of patients with nonenteroviral encephalitis (pulsatility index, 1.10 +/- 0.30 and 0.98 +/- 0.22; resistive index, 0.62 +/- 0.01 and 0.60 +/- 0.01; P < .05).

CONCLUSIONS

Low pulsatility index and resistive index values for cerebral blood flow were observed in the early stage of critical enteroviral infection. This characteristic finding of cerebral blood flow might be associated with the increased sympathetic discharge induced by a brain stem-involved systemic inflammatory response and dysfunction of autoregulation caused by the infection or other disorders of autoregulation that might cause severe or fatal complications.

Steal affecting the central nervous system

Steal is a pathophysiological process in which increased blood flow through a low-resistance vascular bed is sufficient to divert flow away from a region of the central nervous system. Three disease states in which steal may cause neurological deficits due to central nervous system ischemia are reviewed. Subclavian steal occurs when stenosis of the subclavian artery proximal to the vertebral origin causes retrograde flow in the left vertebral artery. Patients with anatomic subclavian steal usually do not develop neurological symptoms but may rarely present with posterior circulation ischemia. Arteriovenous malformations alter cerebral blood flow patterns and regional perfusion pressure. It has been hypothesized that cerebral arteriovenous malformations may cause neurological deficits due to steal and that these deficits may be cured with arteriovenous malformation treatment. Intra-arterial pressure measurements and transcranial velocity studies show regional hemodynamic alterations. However, these changes have not been correlated with presenting symptoms. Evidence from single-photon emission computed tomography does suggest a relationship between regional hypoperfusion and neurological deficits. Coarctation of the aorta may divert flow from the spinal cord circulation through intercostal arteries distal to the stenosis. This is a possible but unproven mechanism of myelopathology. Steal syndromes may be amenable to treatment by open surgical or endovascular approaches. Experimental studies of the pathophysiology of steal are strengthened by precise definitions of the measured parameters and innovative applications of technology.

Cerebral arteriovenous malformation feeding artery aneurysms: a theoretical model of intravascular pressure changes after treatment

OBJECTIVE

A quantitative model may be used to estimate the magnitude of expected pressure changes along the vascular tree with shunt ablation and may provide information to assess the hemodynamic risk of arteriovenous malformation (AVM) treatment.

METHODS

A computer model of the cerebral circulation was applied to estimate the changes in intravascular pressure, velocity, biomechanical stress, and shear stress that might be expected from either endovascular or surgical ablation of AVMs. Two AVM sizes and two feeding artery constellations were simulated. The effect of different shunt flows on vascular pressure was modeled. In each simulation, AVMs were occluded in a stepwise fashion. The effects of systemic hypertension and hypotension in various vascular zones were also simulated.

RESULTS

As large (1000 ml/min) AVMs were occluded, the mean feeding arterial pressure increased from 18 to 68 mm Hg; the percent-occlusion at half-maximal pressure increase was 92%. For medium (500 ml/min) AVMs, feeding arterial pressure increased from 37 to 66 mm Hg; the percent-occlusion at half-maximal pressure increase was 71%. During manipulation of systemic pressure, hemodynamic changes in the circulation close to the nidus were proportionally less than changes in systemic pressure; the degree of proportionality depended on the magnitude of AVM shunt flow.

CONCLUSION

In this simulation, shunt obliteration increased pressure in the nidus and feeding arteries with little effect on the proximal circulation. The shunt provided a "buffering" effect, i.e., higher flow fistulas were exposed to smaller variations in intravascular pressure in feeding artery and nidal pressures during manipulation of systemic pressure.

A theoretical model of cerebral hemodynamics: application to the study of arteriovenous malformations

A comprehensive computer model of the cerebral circulation, based on both hydrodynamics and electrical network analysis, was used to investigate the influences of arteriovenous malformations (AVM) on regional cerebral hemodynamics. The basic model contained 114 normal compartments: 55 arteries, 37 veins, 20 microvessel groups (MVG), one compartment representing systemic and extracranial vascular resistance, and one representing the heart. Each microvessel group, which represented the arteriolar bed, consisted of 5000 microvessels. Cerebral blood flow autoregulation was simulated by a formula that determined the resistance and therefore the flow rate of the microvessel groups (arterioles) as a function of perfusion pressure. Elasticity was introduced to describe the compliance of each vessel. Flow rate was made a controlling factor for the positive regulation of the diameters of conductance vessels by calculation of shear stress on the vessel wall (vessel dilation). Models containing an AVM were constructed by adding an AVM compartment and its feeding arteries and draining veins. In addition to the basic model, AVM models were simulated with and without autoregulation and flow-induced conductance vessel dilation to evaluate the contributions of these factors on cerebral hemodynamics. Results for the model with vessel dilation were more similar to clinical observations than those without vessel dilation. Even in the presence of total vasoparalysis of the arteriolar bed equivalent, obliteration of a large (1000 mL/min) shunt flow AVM resulted in a near-field CBF increase from a baseline of 21 to a post-occlusion value of no more than 74 mL/100 g/min, casting doubt on a purely hemodynamic basis for severe hyperemia after treatment. The results of the simulations suggest that our model may be a useful tool to study hemodynamic problems of the cerebral circulation.

CO2 reactivity in arteriovenous malformations of the brain: a transcranial Doppler ultrasound study

Arteriovenous malformations (AVM's) are congenital tangles of vessels that have a high blood flow through a low-resistance nidus. The vessels in the nidus may lack normal vasoreactivity in response to changes in PaCO2 or perfusion pressure (autoregulation). Arteriovenous malformation hemodynamics have been assessed based on the response of AVM feeding arteries to hypocapnia. Twenty-five AVM patients, aged 34 +/- 11 years (mean +/- standard deviation), were admitted to the Massachusetts General Hospital for proton-beam radiation therapy. Fourteen healthy volunteers aged 30 +/- 7 years served as control subjects. Angiograms with calibrated markers permitting magnification correction were available for all patients. The limits of the middle cerebral artery, as determined by transcranial Doppler ultrasonography, were compared to measurements made on the angiograms. Hyperventilation was induced at a rate set by a metronome. Fixed bilateral Doppler probes allowed almost simultaneous sampling of two vessels. Volunteer control subjects were hyperventilated in two steps. The two PaCO2 step decreases were significant (mean resting PaCO2 40.6 +/- 3.5 mm Hg, Step 1 level 29.4 +/- 3.5 mm Hg and Step 2 level 23.8 +/- 3.5 mm Hg; p < 0.01). These decreases induced a significant decrease in mean flow velocity (Vm) and an increase in the pulsatility index (p < 0.001). Mean carbon dioxide reactivity (% delta Vm/delta PaCO2) was 2.74 +/- 1.0 for Step 1 and 1.44 +/- 1.8 for Step 2 (p < 0.003). The mean PaCO2 decrease in patients was from 39.5 +/- 4.0 mm Hg to 27.0 +/- 3.5 mm Hg. Carbon dioxide reactivity was 0.92 +/- 1.12 for feeding vessels and 2.59 +/- 1.78 for nonfeeding vessels (p < 0.001). Transcranial Doppler ultrasound and angiographic depth measurements correlated well. Hyperventilation induced significantly more hemodynamic changes in control and nonfeeding middle cerebral arteries than in feeding vessels. Impaired CO2 reactivity may help to identify AVM feeding vessels as well as the relative magnitude of the flow provided to the malformation.