(Stroke. 1995;26:1215-1220.)
© 1995 American Heart Association, Inc.
Articles |
From the Departments of Neurology (H.M., J.P.M., R.S.M., R.M.L.), Anesthesiology (A.O., W.L.Y.), Neurological Surgery (J.P.-S., B.M.S., W.L.Y.), and Radiology (J.P.-S., W.L.Y.), ColumbiaPresbyterian Medical Center, New York, NY.
Correspondence to William L. Young, MD, Department of Anesthesiology, Box 46, Columbia University, 630 W 168th St, New York, NY 10032. E-mail wly1@columbia.edu.
| Abstract |
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Methods Using data from patient history and examination, CT or MRI, and transcranial Doppler sonography, we studied 152 consecutive, prospective AVM patients for evidence of FNDs unrelated to a hemorrhagic event. Feeding mean arterial pressure was measured during superselective angiography.
Results Two (1.3%) of 152 patients met the criteria for a progressive FND. Nonprogressive FNDs were seen in 11 (7.2%) patients (stable in 4.6%, reversible in 2.6%). The median observation time period was 17 months (range, 1 to 60 months). There were no differences in transcranial Doppler mean velocities in feeding arteries in FND versus non-FND groups (118±44 versus 112±37 cm/s, P>.05) or pulsatility indexes (0.53±0.20 versus 0.55±0.15, P>.05). Feeding artery pressure was similar in FND (n=10) and non-FND (n=96) groups (39±16 versus 39±16 mm Hg at a systemic pressure of 82±18 versus 75±14 mm Hg, NS).
Conclusions Nonhemorrhagic focal neurological syndromes in AVM patients are infrequent. Progressive deficits are especially rare. There was no relation between feeding artery pressure or flow velocities and FND. There does not appear to be sufficient evidence to assign steal as an operative pathophysiological mechanism in the vast majority of AVM patients.
Key Words: cerebral arteriovenous malformations diagnostic imaging hemodynamics perfusion
| Introduction |
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The reported clinical frequency of cerebral steal in
AVMs11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 (Table 1
) varies widely, but its
importance as a pathophysiological principle in
AVMs has been questioned.1 28 No large prospective study
has yet examined the clinically detectable frequency of neurological
deficits unrelated to hemorrhage. The AVM Data Bank of the
ColumbiaPresbyterian Medical Center offered the opportunity to
investigate this question in a prospectively collected data sample.
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| Subjects and Methods |
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An FND was assumed to be present under the following conditions: (1) the physical examination at the time of the first clinical presentation revealed an FND, (2) the patient's history suggested a focal deficit at one time (reversible event), or (3) the patient spontaneously developed an FND after inclusion in the study (treatment complications from embolization and surgical procedures were not included). Patients with imaging evidence of hemorrhage coinciding with the onset of a focal syndrome were excluded from the FND group.
Patients presenting with a deficit on examination and a history or follow-up evaluation of a continuous or stepwise deterioration were judged as having "progressive" FNDs. Neither seizure disorders nor reversible postictal focal deficits were rated as FNDs. Reversible FNDs with no additional elementary (involuntary rhythmic motor activity or positive sensory signs) or complex (vigilance/mental changes) partial-seizure features were accepted for the FND group. All cases included in the study were investigated by CT or MRI and cerebral angiography.
In addition to the results from the neurological examination, the Glasgow Outcome Score (score of 5, no or minimal impairment; 4, moderate impairment, independent in everyday activities; 3, severe impairment, dependent on help for everyday activities; 2, persistent vegetative state; 1, dead) was used to estimate the functional impairment of the FND group patients.
To further determine the impact of morphological and
hemodynamic factors on the development of focal
syndromes, we analyzed flow velocities and pressure in feeding
arteries, AVM size, drainage pattern, and AVM location. Data from FND
and non-FND patients were compared with
2
(frequencies) and t test (continuous variables)
statistical methods.
Intravascular pressures were measured using methodology previously described.8 Feeding mean arterial pressure (FMAP) was measured just proximal to the nidus using an intracranial microcatheter, 1.5F at its distal tip (Chimiotherapie, Balt), immediately before the initial endovascular embolization procedure (cyanoacrylate) in eight patients and immediately before the second embolization procedure in two. In one case, FMAP was measured intraoperatively by direct puncture of a main AVM feeding artery with a 26-gauge needle before resection. The systemic mean arterial pressure either in the extracranial internal carotid or vertebral artery (embolization patients) or in the radial artery (surgical patient) was simultaneously recorded. FMAP in the FND group was compared by unpaired t test to that of a group of non-FND patients who had FMAP measured immediately before either the initial or second endovascular embolization procedure.
A case report is included to illustrate that chronic hypotension does not necessarily result in a loss of neuronal function (assessed by neurobehavorial testing). The patient was trained in several language tasks at the bedside using a computer31 ; included were naming, reading aloud, repetition, and fluency.32 Naming consisted of the presentation of pictures derived from the Boston Naming Test33 ; the patient viewed each picture stimulus in the center of a notebook computer screen (Macintosh Duo 280c) and had 10 seconds to make a response. Single-word stimuli and sentences were presented on the computer screen for the reading-aloud test. Low- and high-frequency words and sentences were presented. Single-word stimuli were taken from the Wide Range Achievement Test.34 Repetition was tested with sentences taken from the repetition subtest of the Boston Diagnostic Aphasia Examination.35 Fluency was assessed by asking the patient to generate as many items in a single class as possible in 1 minute.
Superselective anesthetic injection consisted of sodium amobarbital (30 to 40 mg) followed by lidocaine (15 to 30 mg). The drugs were mixed with contrast and given through the superselective catheter, and an angiogram was obtained of the distribution of the drug/contrast mixture.36 37 Functional testing was carried out at baseline and after drug injection.
| Results |
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The functional impairment rated by the Glasgow Outcome Scale for the
two patients with progressive FNDs was moderate in one case and severe
in the other and mild to moderate for patients with stable syndromes
(Table 3
). AVM size in the 13 FND cases (Table 4
) was
similar to those in non-FND cases. There was no difference in the
presence of deep venous drainage. Transcranial Doppler
mean flow velocities in feeding arteries or pulsatility indexes also
were similar between FND and non-FND groups.
|
Table 4
shows FMAP and associated data for 10 of the 13 FND patients
who underwent intravascular pressure measurements. Compared with
patients presenting with symptoms and signs other than FND who also
underwent intravascular pressure measurements, FMAPs were similar in
the FND and non-FND groups.
Case Report
The patient was a 25-year-old right-handed female journalist with
a left temporal AVM who presented with seizures manifested by
speech arrest but who was otherwise intact. There was no measurable
aphasic disorder on comprehensive neuropsychological evaluation.
To determine the arterial supply to the language area, five
vessels were superselectively catheterized. Each vessel was injected
with anesthetic (amobarbital followed by lidocaine) with language
evaluation before and after each injection. Panels A and B of the
Figure
show a lateral view of a carotid injection with
the studied branches labeled in panel A and the corresponding
territories indicated in panel B.
|
When feeding arteries 1 and 2 to the AVM were injected, no
neurological deficits were noted. When the frontal opercular branch
(labeled "cand. op." in the Figure
) was injected, the patient
became mute and developed mild comprehension deficits. When the insular
branch was injected, she developed decreased repetition capabilities
and paraphasic errors (conduction aphasia); comprehension was intact.
When the angular branch was injected, the patient developed a dense
sensory (Wernicke's) aphasia. Fluency was intact, but naming and
comprehension were markedly impaired. The angular branch pressure was
25 mm Hg at a systemic mean of 55 mm Hg. Thus, we were able to
demonstrate that the angular artery territory subserved sensory
language function despite a markedly reduced arterial input
pressure in a patient who was not aphasic. The angular-branch
superselective injection is shown in panels C and D. Panel C shows the
arterial phase of the injection (the small arrow indicates
the tip of the catheter and the large arrow the main
arterial branch). Panel D shows the capillary stain of the
territory.
| Discussion |
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AVM size was not a strong determinant of FNDs. Flow velocities and intravascular pressure in feeding arteries also had little impact. The latter finding is of particular importance, since some authors13 38 have reported that AVMs with clinical features of steal show significantly higher flow velocities than AVMs with other modes of presentation, an observation that seemed to lend support for the concept of "misery perfusion." We were unable, however, to replicate these results with a larger data set. We also found no case histories in the reported samples13 38 that permitted an independent assessment of the basis for the diagnosis of progressive deficits.
The lack of clinical and hemodynamic evidence for steal is further supported by results from other reported pathophysiological studies. A positron emission tomography study of 14 AVM patients showed that, although cerebral blood flow in brain tissues surrounding AVMs was low, there was no corresponding increase in parenchymal blood volume. Furthermore, glucose and oxygen extraction fractions were normal.28 This constellation of physiological findings is not predicted on the basis of "misery perfusion," in which there should be an increase in blood volume as well as an increase in substrate extraction fraction.39
There are accumulating data that autoregulation is preserved in cerebral regions adjacent to AVMs.8 We have proposed that there is an adaptive leftward shift of the lower limits of the autoregulation flow-pressure curve in hypotensive regions adjacent to AVMs.8 Despite chronic hypotension well below a mean cerebral arterial pressure of 50 mm Hg, function remains intact and vasoparalysis in the arteriolar resistance bed does not necessarily occur. Cerebral perfusion pressure below 50 mm Hg has been suggested by several authors to exceed the lower limits of cerebral autoregulation.40 41 Reports describing maintained CO2 responsiveness in AVM patients lend further support to the hypothesis of an intact autoregulatory capacity.42
The question remains: why do some AVM patients present with focal deficits not due to hemorrhage? Mass effects of AVMs in "strategic regions" such as the posterior fossa may explain at least some of the syndromes.43
The inclusion of reversible FNDs in a steal group may be questionable, since a postictal etiology cannot be ruled out completely. However, exclusion of such patients from the analysis further reduces the number of cases with possible steal from 8.6% to 5.9% and has no effect on the results in the comparison of morphological and hemodynamic parameters. Another potential influence on our results could be patient referral bias. Because ColumbiaPresbyterian Medical Center is a tertiary referral center, there may be an overrepresentation of AVM cases that are more likely to pose difficult treatment problems, such as staged embolization before surgery. But if there is any bias resulting from this factor, we think it should also produce a higher rather than a lower frequency of cases with focal syndromes. It is also possible that patients initially may have had subclinical signs or symptoms of cerebral ischemia that were masked or overwhelmed by an intracerebral hemorrhage, but this is probably a rare occurrence.
Because most of our patients began a course of staged embolization procedures, the chances of finding progressive deficits during the time following study inclusion may have been reduced. Consequently, we cannot exclude the possibility that patients who presented with a stable or reversible deficit would later have developed a progressive course. However, the reported frequencies in the literature on FNDs largely reflect data from the initial clinical evaluation. Prospective long-term natural-course studies are not available (and may be regarded as ethically problematic, given the current treatment possibilities). The discrepancies between our findings and the high frequencies of FNDs in other samples11 13 therefore are not attributable to differences in study design. Small sample sizes and a retrospective design are principle sources of error in clinical studies. To our knowledge, this study addresses the question of focal deficits in the largest prospective sample of AVM patients.
In summary, the low frequency of FNDs not attributable to hemorrhage in AVM patients and the lack of associated hemodynamic derangements argue strongly against an uncritical acceptance of the steal concept.
| Acknowledgments |
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Received January 13, 1995; revision received April 6, 1995; accepted April 20, 1995.
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