Transcranial Doppler ultrasonographic changes after treatment for arteriovenous malformations

Digital intravascular pressure wave recording during endovascular treatment reveals abnormal shunting flow in vertebral venous fistula of the vertebral artery: illustrative case

BACKGROUND

An arteriovenous fistula is an abnormal arteriovenous shunt between an artery and a vein, which often leads to venous congestion in the central nervous system. The blood flow near the fistula is different from normal artery flow. A novel method to detect the abnormal shunting flow or pressure near the fistula is needed.

OBSERVATIONS

A 76-year-old woman presented to the authors’ institute with progressive right upper limb weakness. Right vertebral angiography showed a fistula between the right extracranial vertebral artery (VA) and the right vertebral venous plexus at the C7 level. The patient underwent endovascular treatment for shunt flow reduction. Before the procedure, blood pressures were measured at the proximal VA, distal VA near the fistula, and just at the fistula and drainer using a microcatheter. The blood pressure waveforms were characteristically different in terms of resistance index, half-decay time, and appearance of dicrotic notch. The fistula was embolized with coils and N-butyl cyanoacrylate solution.

LESSONS

During endovascular treatment, the authors were able to digitally record the vascular pressure waveform from the tip of the microcatheter and succeeded in calculating several parameters that characterize the shunting flow. Furthermore, these parameters could help recognize the abnormal blood flow, allowing a safer endovascular surgery.

Elevated end-diastolic ratio of the common carotid artery due to cerebral arteriovenous malformation: Two case reports

An elevated end-diastolic (ED) ratio of the common carotid artery (CCA) is an indicator of occlusive lesions of the distal portion of the internal carotid artery. We report 2 cases of cerebral arteriovenous malformation (AVM) showing an elevated ED ratio of the CCA, which decreased after surgery. Case 1 was a 28-year-old man with chronic recurrent headache with aura, and case 2 was a 29-year-old woman with sudden-onset headache and intracerebral hemorrhage without neurologic abnormality. In both cases, digital subtraction angiography revealed a Spetzler-Martin Grade IV AVM, which was mainly fed by branches of the left middle cerebral artery with venous drainage into superficial and deep cerebral veins. Preoperative carotid ultrasonography showed an elevated CCA ED ratio (1.38 in case 1 and 1.47 in case 2; left > right) without atherosclerotic lesions. Patients' AVMs were successfully resected. In both cases, the ED ratio was decreased after surgery (to 1.05 in case 1 and 1.20 in case 2). A decrease in vascular resistance on 1 side caused by cerebral AVM can result in an increase in the CCA ED ratio comparable to that of carotid axis occlusion.

Ascertaining the Value of Noninvasive Measures Obtained Using Color Duplex Ultrasound and Central Aortic Pressure Monitoring During the Management of Cerebral Arteriovenous Malformation Resection: Protocol for a Prospective, Case Control Pilot Study

BACKGROUND

Dramatic hemodynamic changes occur upon removal of an arteriovenous malformation of the brain (bAVM) with a number of potentially serious perioperative complications, such as intracranial hemorrhage and venous occlusive hypertensive syndrome. As these complications largely occur in the postoperative inpatient period, a rapid, repeatable noninvasive investigation to serially monitor relevant intracranial hemodynamics may be of benefit. Though, transcranial Doppler (TCD) and transcranial color duplex (TCCD) are techniques used and available to provide hemodynamic measurements postoperatively, the time course of hemodynamic sequences following bAVM resection remains uncertain.

OBJECTIVE

This is a prospective, case control pilot study conducted in participants having elective bAVM resection surgery.

METHODS

Each participant will undergo a preoperative color duplex ultrasound (CDU) of the bilateral extracranial carotid arteries, a CDU of the circle of Willis including the bAVM vessels, and a central aortic pressure measurement, repeated daily, postoperatively, for a 2-week period.

RESULTS

Patient accrual has commenced with anticipation of first results in 2018.

CONCLUSIONS

This protocol aims to strengthen the work of previous authors by providing documentation of the time course of hemodynamic changes following bAVM resection. The protocol is designed to determine whether noninvasive technology, including CDU imaging of the extracranial carotid and intracranial arteries in the form of TCCD along with central aortic pressure measurements, can determine whether there are any hemodynamically significant prognostic markers that may provide insight into the process of vessel remodeling, including insight into venous changes following bAVM resection.

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.

Quantification of blood flow in internal cerebral artery by optical flow method on digital subtraction angiography in comparison with time-of-flight magnetic resonance angiography

Objective

This study compared data on the blood flow velocity in the internal carotid artery, which was obtained using the optical flow method (OFM) with digital subtraction angiography (DSA) and the time-of-flight (TOF) technique using magnetic resonance angiography (MRA).

Materials and Methods

Images were obtained from 12 cerebrovascular patients who underwent both brain DSA and MRA imaging. The OFM was applied on the DSA images to determine the average blood flow velocity. The calculated results were compared with the values obtained from the TOF-MRA data. A linear fit was performed on the data and Bland-Altman plots were analyzed.

Results

The blood flow velocity was closely associated with vascular diseases. Color-coding of the OFM measurements were superimposed on to the DSA images, which quantitatively illustrated the relative flow in the vessels. The average blood flow velocity was calculated using OFM and DSA, which demonstrated a high correlation with the MRA measurements in the anterior-posterior (AP) view (R = 0.71). In contrast, the average blood flow velocity was low in the lateral view (R = 0.28). The consistency between the high and low blood velocity in the AP view was better compared to the lateral view. The blood flow velocity distribution in the AP view was statistically closer to the MRA measurement compared to the lateral view.

Conclusions

This study evaluated the correlation of blood flow measured using DSA and TOF-MRA in a small heterogeneous group of patients with cerebrovascular lesions. OFM with DSA imaging reveals hemodynamic information and TOF-MRA.

Transcranial Doppler study of cerebral arteriovenous malformations after gamma knife radiosurgery

The aim of this study was to evaluate the clinical value of the Transcranial Doppler (TCD) in follow-up examinations after gamma knife radiosurgery (GKS) for arteriovenous malformations (AVM). We performed TCD after GKS in 18 patients who had cerebral AVMs to evaluate the hemodynamic effects of the procedure. Ten patients underwent TCD within 12 months after GKS, and eight between 12 and 24 months. The mean blood velocity (Vm) and pulsatility index (PI) were primarily analyzed in the feeding arteries (FAs) and non-FAs. Fifteen healthy volunteers served as control patients. The Vm values in the FAs after GKS ranged from 31 cm/s to 90 cm/s, with PI values ranging from 0.48 to 1.03. The Vm values in the comparable normal arteries ranged from 28 cm/s to 87 cm/s, and the PI values in these arteries ranged from 0.62 to 1.02. The Vm and PI values in every FA in all patients were normal compared to the values in the non-FAs (p=0.67 and 0.38, respectively). Our results suggest that AVM vessels with high Vm and low PI values return to normal as the nidus of the AVM is obliterated after GKS. Although there was a trend toward a reduction of the Vm values after obliteration, this trend was not significant, except when the < 12 month subgroup was compared to the 12-24 month subgroup. In our limited study, TDC proved to be a reliable, safe and non-invasive method to monitor the outcome of GKS for cerebral AVMs.

Diagnosis of intracranial dural arteriovenous fistulas by carotid duplex sonography

OBJECTIVE

To validate carotid duplex sonography (CDS) in diagnosis of intracranial dural arteriovenous fistulas (AVFs) against the standard of cerebral catheter angiography.

METHODS

We investigated 35 patients with dural AVFs and 64 patients without dural AVFs confirmed by the catheter angiographic studies. Twenty CDS parameters in 4 categories, including resistive index (RI), flow volume, peak systolic velocity, and end-diastolic velocity, were evaluated. Abnormal CDS findings were defined as the data above 95th percentile or below 5th percentile values from 180 control subjects. We determined the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy in each CDS parameter.

RESULTS

The parameter of RI of the external carotid artery (ECA; cutoff points: right, 0.72; left, 0.71) yielded the highest sensitivity (74%), specificity (89%), positive predictive value (79%), negative predictive value (86%), and accuracy (84%) for predicting dural AVFs. All other ECA-related parameters yielded sensitivity lower than 70%, and those related to the internal carotid artery were lower than 30%. The sensitivity values for the parameter of RI of the ECA in different locations of dural AVFs were 54% (7 of 13 patients) in cavernous sinus dural AVFs and 86% (19 of 22 patients) in non-cavernous sinus dural AVFs (P = .05).

CONCLUSIONS

The RI of the ECA is the best CDS parameter for predicting intracranial dural AVFs. Carotid duplex sonography can be used as the initial screening tool for diagnosis in patients having symptoms related to dural AVFs.

Transcranial Doppler ultrasonography: year 2000 update

In this update, the main clinical applications of transcranial Doppler ultrasonography are reassessed. A specific format for technology assessment, personal experience, and an extensive review of the literature form the basis of the evaluation. The document is approved by the American Society of Neuroimaging and the Neurosonology Research Group of the World Federation of Neurology.

Hemodynamic changes in arterial feeders and draining veins during embolotherapy of arteriovenous malformations: an experimental study in a swine model

OBJECTIVE

Transcatheter assessment of changes in draining vein (DV) flow velocity has been proposed recently as a potentially useful procedure for hemodynamic monitoring of the progression of embolotherapy in cerebral arteriovenous malformations (AVMs). We compared and contrasted changes in hemodynamic parameters of arterial feeders (AFs) and DVs during experimental AVM embolotherapy.

METHODS

Carotid-jugular fistula-type AVM models were surgically created in eight swine. Pre- and postembolization transcatheter mean AF and DV pressures, DV-time average spectral peak velocity, and AF and DV pulsatility indices were assessed. An expression, the peak systolic velocity minus end-diastolic velocity (Vs - Ved), was also used in evaluating the transvenous Doppler spectra. Pre- and postembolization hemodynamic parameters were compared statistically.

RESULTS

Pre-embolization DV flow was pulsatile (Vs - Ved, 12 +/- 4.8 cm/s), with a mean DV velocity of 39.3 +/- 11.4 cm per second. Postembolization, this changed to a less/nonpulsatile pattern (Vs - Ved, 5.4 +/- 2.7 cm/s; P = 0.0035) with a lower mean DV-average spectral peak velocity of 7.0 +/- 3.1 cm per second (P = 0.0001). The mean DV pressure was also reduced from 52.0 +/- 8.2 to 45.5 +/- 8.7 mm Hg (P = 0.0023). The mean AF pressure increased from a mean of 79.5 +/- 15.5 to 96.8 +/- 16.2 mm Hg (P = 0.0004). The DV pulsatility index values also increased from a mean of 0.3 +/- 0.2 to 1.1 +/- 0.5 (P = 0.0003). Periembolization objective hemodynamic changes were detected in the DVs earlier than were the visually subjective angiographic changes observed within the nidus.

CONCLUSION

This preliminary study indicates that transvenous assessment of average spectral peak velocity and wave pattern (Vs - Ved) may be useful in the hemodynamic evaluation of AVM shunting. The convergence of these two parameters to a range less than 10 cm per second after nidus embolization may afford a theoretical advantage over AF pressure measurements when used for objective and quantitative monitoring of endovascular embolotherapy.

Normal perfusion pressure breakthrough: the role of capillaries

Excision of human cerebral arteriovenous malformations (AVMs) can be complicated by postoperative edema and hemorrhage in adjacent brain tissue, despite the complete excision of the malformation. Various theories have purported to explain the hemodynamic basis for this predisposition, including disordered autoregulation causing "normal perfusion pressure breakthrough" and obstruction of venous drainage leading to "occlusive hyperemia." This study did not evaluate the arterial or venous circulations in this scenario, but rather examined the capillaries in adjacent brain parenchyma for any structural deficiencies that would predispose the brain to the postoperative formation of edema and hemorrhage. Arteriovenous fistulas (AVFs) were created surgically in the necks of 10 male Sprague-Dawley rats, which caused chronic cerebral hypoperfusion with a reduction in cerebral blood flow of between 25% and 50%. Ten age-matched animals were used as controls. Twenty-six weeks after AVF formation the animals were killed and perfusion fixed. Their brain tissue was prepared for light microscopic studies by staining for glial fibrillary acidic protein or for transmission electron microscopy. In the CA1 pyramidal cell region of the hippocampus, it was found that in the animals with AVFs there was increased capillary density and absent astrocytic foot processes in some of these vessels. It was concluded that these vessels had developed as a result of neovascularization in response to chronic cerebral ischemia and that their anatomical configuration made them prone to mechanical weakness and instability following the increase in perfusion pressure that occurs in adjacent brain parenchyma after AVM excision. The authors believe that this study pinpoints a structural accompaniment to the hemodynamic changes that occur in brain tissue in the vicinity of cerebral AVMs that predispose these areas to the formation of edema and hemorrhage after AVM excision.

The influence of hemodynamic and anatomic factors on hemorrhage from cerebral arteriovenous malformations

The physiological and anatomical aberrations that result in hemorrhage from cerebral arteriovenous malformations (AVMs) remain unclear. In an attempt to clarify which conditions may predispose to hemorrhage, we examined clinical and physiological indices on presentation groups of either hemorrhage or nonhemorrhage in a large cohort of patients (n = 449). Variables examined included AVM size, type of venous drainage, transcranial Doppler (TCD) velocities, feeding mean arterial pressure (FMAP), and draining vein pressure. TCD and pressure data were obtained before any treatment. Age (mean +/- standard deviation) at the time of presentation was 33 +/- 13 years and did not differ between groups. Patients with small (< or = 2.5 cm) AVMs presented more frequently with hemorrhage (90%) than did patients with medium (> 2.5 and < or = 5.0 cm; 52%) or large (> 5.0 cm; 50%) AVMs (P = 0.0001). The 48 of 94 AVMs (51%) with deep venous drainage were more likely to have hemorrhage (P = 0.0219) than were those with superficial drainage (24 of 73 [33%]). Deep drainage was a predictor of hemorrhage even in the subgroup of medium and large supratentorial AVMs (P = 0.005). There was no difference in draining vein pressure (n = 18) between groups (21 +/- 10 and 19 +/- 11 mm Hg, respectively; P = 0.7812). FMAP (n = 52) was higher in the hemorrhage than in the nonhemorrhage group (44 +/- 13 versus 34 +/- 10 mm Hg; P = 0.0007) but was only weakly related to the size of the lesion (largest dimension) (y = -0.74x + 40; r = 0.09).(ABSTRACT TRUNCATED AT 250 WORDS)

Transcranial Doppler changes during staged surgical resection of cerebral arteriovenous malformations: a report of three cases

The removal of large arteriovenous malformations (AVMs) in stages has been advocated to reduce the risk of perioperative hyperemic complications. In three patients who had a two-stage surgical removal of their large (> 6 cm) frontal AVMs, transcranial Doppler (TCD) was performed 1 day before and 1 day after each surgery. Arteries still feeding the AVM after the first procedure had an increase in mean velocity (MV) and a decrease in the pulsatility index (PI) in the period between the two surgeries. MV reactivity to carbon dioxide before each stage was higher in feeding arteries at the second surgery, suggesting that the total magnitude of the shunt through the AVM was lower in spite of flow recruitment. TCD can be used to monitor the hemodynamic changes after embolization or partial surgery and may be of help in better defining the optimal time for final resection.

Pressure autoregulation is intact after arteriovenous malformation resection

The loss of autoregulatory control of cerebral perfusion to changes in perfusion pressure in tissue remote from an arteriovenous malformation (AVM) has been proposed as the mechanism underlying "normal perfusion pressure breakthrough." This study is the first direct test of this mechanism. Studies were performed during the resection of moderate to large AVMs in 25 patients undergoing 28 procedures under isoflurane anesthesia. Cerebral blood flow (CBF) was measured (xenon-133 method) in the hemisphere adjacent to the nidus before resection after dural exposure (pre), after AVM removal before dural closure at spontaneous systemic blood pressure (post), and, finally, with the mean arterial pressure increased by 20 mm Hg, using phenylephrine (post-BP). AVM resection resulted in a significant enhancement of perfusion in the adjacent hemisphere (30 +/- 2 vs. 25 +/- 1 ml/100g/min, P < 0.01), but no further increase of CBF occurred during increased perfusion pressure (30 +/- 2 ml/100g/min). One patient suffered a postoperative hemorrhage and another developed intraoperative brain swelling during the course of the resection that necessitated staging the procedure. These two patients had the highest increases in CBF, but intact pressure autoregulation. Preserved autoregulation to increased mean arterial pressure after resection does not support a hemodynamic mechanism for the observed increase in CBF from before the resection to after the resection. Pathological events, however, do appear to be related to increases in hemispheric perfusion.

Occlusive hyperemia: a theory for the hemodynamic complications following resection of intracerebral arteriovenous malformations

An alternative theory is proposed to explain the brain edema and hemorrhage that may occur after resection of high-flow intracerebral arteriovenous malformations (AVM's). This theory, termed "occlusive hyperemia," is based on a retrospective analysis of operative dictations along with postoperative imaging studies (191 angiograms and 273 computerized tomography scans) in 295 cases of intracerebral AVM's operated on at the Mayo Clinic between 1970 and 1990. In this series, 34 cases (12%) of postoperative deterioration were documented, of which 15 were due to incomplete resection of the AVM. Of the remaining 19 cases, six had brain edema alone and 13 had hemorrhage with edema, despite complete excision of the AVM. In these 19 cases, the AVM's were greater than 6 cm in diameter in 10 patients, between 3 and 6 cm in six, and less than 3 cm in three. Obstruction of the venous drainage system was observed in 14 (74%) of the 19 cases. Ten of these 14 were due to obstruction of the primary venous drainage of the brain parenchyma immediately surrounding the lesions, while four were due to obstruction of other venous structures. In no case was a rapid circulation identified on postoperative angiograms. The flow pattern was slow or stagnant in former AVM feeders and their parenchymal branches. It is proposed that postoperative intracranial hemorrhage and/or brain edema in AVM patients may be due to: 1) obstruction of the venous outflow system of brain adjacent to the AVM, with subsequent passive hyperemia and engorgement; and 2) stagnant arterial flow in former AVM feeders and their parenchymal branches, with subsequent worsening of the existing hypoperfusion, ischemia, and hemorrhage or edema into these areas. Supportive hemodynamic evidence for this theory was derived from the literature.

Transcranial Doppler in neurosurgery

This chapter describes the use of the transcranial Doppler apparatus in neurosurgery. The principles of Doppler insonation, the techniques of recording and the use of activation techniques is described. The relationship between blood flow and blood velocity is discussed, and the interaction of various pharmacological agents. The establishment of normal values for the laboratory and various vessels insonated is emphasised. The use of indices particularly the pulsatility index is described together with its variations. Cerebral vascular reactivity measurements and the interaction of Doppler recordings with raised intracranial pressure, useful in assessment of cerebral perfusion pressure as in head injury and in terminal cases, is documented. The use of transcranial Doppler in management of head injury and subarachnoid haemorrhage is described. The latter is probably the most useful routine place for Doppler measurement in neurosurgical practice and the documentation of the onset and progress of vasospasm is the final portion of the chapter.

Noninvasive assessment of intracranial fistulas and other small arteriovenous malformations

Twenty patients in whom the diagnosis of an intracranial arteriovenous malformation was suspected either by the history and clinical findings or by abnormal periorbital Doppler flow are discussed. Sixteen patients had only minor complaints or inconclusive signs or were clinically asymptomatic; 4 others presented with the syndrome of a carotid cavernous fistula. Patients were further examined by means of transcranial Doppler sonography, computed tomographic scanning, and cerebral angiography. In 17 patients, the diagnosis of an arteriovenous malformation could be established by transcranial Doppler sonography and could be confirmed by angiography. Transcranial Doppler sonography gave false negative results in 1 and false positive results in 2 patients. Our findings demonstrate the usefulness of modern ultrasound techniques in the assessment of small or even occult intracranial arteriovenous shunts before subjecting patients to more invasive procedures.

Transcranial Doppler ultrasonography: clinical applications in cerebrovascular disease

Transcranial Doppler ultrasonography was introduced in 1982 as a noninvasive procedure for assessment of the intracranial cerebral circulation. The lightweight and portable equipment used for transcranial Doppler examination facilitates its use in the bedside assessment of critically ill hospitalized patients and outpatients. Clinical applications include the diagnosis of vasospasm in patients with subarachnoid hemorrhage, assessment of intracranial collateral flow in patients with extracranial arterial occlusive disease, detection of intracranial arterial stenosis, identification of the feeding arteries of arteriovenous malformations and monitoring the hemodynamic effects of their treatment, confirmation of the clinical diagnosis of brain death, intensive-care unit monitoring of brain-injured patients, and intraoperative and postoperative monitoring of neurosurgical patients. Transcranial Doppler technology is also providing new insights into the pathophysiologic mechanisms of a variety of cerebrovascular conditions. Clinicians will find transcranial Doppler technology most helpful if they have a specific question about the status of the intracranial circulation. Further investigations may expand the clinical and research utility of this technology.