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Magnetic Resonance Imaging in Basilar Artery Occlusion
Richard du Mesnil de Rochemont, MD;
Tobias Neumann-Haefelin, MD;
Joachim Berkefeld, MD;
Matthias Sitzer, MD;
Heinrich Lanfermann, MD
Arch Neurol. 2002;59:398-402.
ABSTRACT
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Context Acute basilar artery occlusion has particularly high mortality and morbidity.
Objective To determine the potential utility of advanced magnetic resonance imaging
(MRI) methods, including diffusion-weighted imaging, for the early management
of patients with basilar artery thrombosis.
Design Case series.
Setting Institute of Neuroradiology and Department of Neurology, Johann Wolfgang
Goethe University, Frankfurt, Germany.
Patients In 4 patients with occlusion of the basilar artery, MRI was performed,
including T2-weighted and diffusion-weighted imaging (DWI) sequences and magnetic
resonance angiography (MRA) in the short-term phase (<12 hours). Three
patients underwent intra-arterial thrombolysis. Clinical outcome was obtained
10 days after symptom onset.
Results The MRA was performed 3.5 to 11.5 hours after symptom onset and showed
basilar artery occlusion in all cases. The DWI revealed different patterns
of ischemic lesions. In 2 patients, no or only small lesions could be identified;
the remaining showed multiple and large lesions within the posterior circulation
territory. Initial clinical status was severely impaired in all cases (Rankin
scale score, 4-5). Thrombolysis was initiated in 3 patients, leading to successful
recanalization in 2. Clinical outcome was favorable in the 2 patients with
small DWI lesions and successful reperfusion (Rankin scale score, 2), whereas
it was worse in those with large DWI lesions and persisting occlusion (death,
persisting coma).
Conclusions In critically ill patients with acute basilar occlusion, the extent
of DWI lesion involvement can be highly variable. Small DWI lesions seem to
be associated with a favorable outcome if reperfusion is achieved with thrombolysis.
This could potentially be the case independent of time from symptom onset.
INTRODUCTION
OCCLUSION of the basilar artery is a neurologic emergency that requires
a rapid diagnostic evaluation and subsequent therapy. Intra-arterial thrombolysis
may improve overall outcome in patients with basilar artery occlusion,1-2 but predicting benefit from therapy
is still difficult in individual patients. This is probably partially owing
to the fact that tissue injury in critical brainstem structures may already
be irreversible in some patients before therapy is initiated. Angiographically,
short occlusions, good collateral flow, and fast recanalization correlate
with a favorable outcome.3-4 However,
angiography does not show the extent of ischemic tissue injury directly.
Modern magnetic resonance imaging (MRI) methods, on the other hand,
including diffusion-weighted imaging (DWI) and magnetic resonance angiography
(MRA), are highly sensitive for the detection of ischemic tissue injury and
may be suggestive of arterial occlusion, respectively.5-7
In the past, these methods have been applied mainly to anterior circulation
stroke,7-9 with
only a few case reports focusing on MRI (including DWI) in basilar artery
occlusion.10-11 Currently, there
are no established guidelines for selecting patients with suspected basilar
occlusion for intra-arterial thrombolysis based on clinical or MRI criteria.
Theoretically, the additional information provided by MRI methods could facilitate
patient management and be predictive of therapeutic benefit.
Herein, we report a series of 4 patients with basilar artery occlusion,
in whom MRI, including DWI and MRA, was performed in the short-term setting.
We show the feasibility of MRI in these patients and report their outcome
in relation to the initial MRI findings and subsequent treatment.
PATIENTS AND METHODS
Between January 8 and July 27, 2000, 4 patients (2 men and 2 women;
age range, 72-76 years) with acute basilar artery occlusion were included
in the study. The clinical diagnosis and the Rankin score on admission and
on follow-up 10 days later were established by a staff neurologist. In addition,
MRI was performed in all patients on a 1.5-T unit (Siemens Vision; Siemens
AG, Erlangen, Germany). Axial and coronal DWIs; axial T2-weighted, T2* (true
transverse relaxation time) -weighted, and fluid-attenuated inversion recovery
(FLAIR) images; and MRA were acquired using the following variables.
- T2-weighted turbo spin echo sequence: repetition
time (TR), 2400 milliseconds; echo time (TE), 98 milliseconds; flip angle,
180°; field of view (FOV), 173 x 230 mm; matrix, 130 x 256;
slices, 19; slice thickness, 6 mm; and acquisition time, 1 minute 8 seconds.
- FLAIR images: TR, 9000 milliseconds; TE, 110 milliseconds;
flip angle, 180°; FOV, 201 x 230 mm; matrix, 132 x 256; slices,
19; slice thickness, 5 mm; and acquisition time, 1 minute 57 seconds.
- T2*-weighted gradient echo sequence: TR, 950 milliseconds;
TE, 35 milliseconds; flip angle, 25°; FOV, 173 x 230 mm; matrix,
154 x 256; slices, 19; slice thickness, 6 mm; and acquisition time,
2 minutes 28 seconds.
- Echo planar imaging–DWI sequence: TR, 0.8
milli-seconds; TE, 123 milliseconds; flip angle, 90°; FOV, 230 x
230 mm; matrix, 128 x 128; slices, 19; slice thickness, 6 mm; acquisition
time, 5 seconds; and b = 1000 with the diffusion gradient in one direction.
- 3-Dimensional time-of-flight MRA: TR, 35 milliseconds;
TE, 6.6 milliseconds; flip angle, 20°; FOV, 142 x 190 mm; matrix,
200 x 512; slab thickness, 70 mm; number of partitions, 40; acquisition
time, 3 minutes 45 seconds; and maximum intensity projection reconstruction.
In 3 patients, intra-arterial cerebral angiography and subsequent intra-arterial
thrombolysis were performed using a microcatheter. The tip of the microcatheter
was placed near or within the thrombus and a bolus of 200 000 U of urokinase
was administered. For up to 2 hours, the basilar artery was perfused with
500 000 U/h of urokinase. In 1 patient, angioplasty of a basilar artery
stenosis was performed following thrombolysis. The result of thrombolysis
was documented by a selective control angiogram. In 1 patient, angiography
and thrombolysis were not performed because of medical contraindications.
The site of basilar artery occlusion was classified according to Archer and
Horenstein12 as caudal (from the confluence
of the vertebral arteries to the anterior inferior cerebellar artery), middle
(from the anterior inferior cerebellar artery to the superior cerebellar artery),
and distal (distal to the superior cerebellar artery). The length of occlusion
was termed short if only 1 part and long if 2 or more parts were involved. For follow-up imaging, either
MRI or computed tomography was used.
RESULTS
All patients presented with focal neurologic signs compatible with posterior
circulation ischemia and variable degrees of disturbed consciousness. The
clinical features on admission and at follow-up, as well as the corresponding
findings for MRI and MRA, are summarized in Table 1.
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Clinical and Neuroradiologic Data of Patients*
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Magnetic resonance imaging was performed between 2 and 11.5 hours after
symptom onset. Acquisition of the 6 MRI sequences required about 12 minutes.
In total, the MRI procedure required about 20 minutes, including transport,
positioning of the patient in the scanner, and MIP reconstruction. In all
patients, the MRI was diagnostic (despite reduced image quality in 2 patients
because of movement).
Patient 1 was a 72-year-old hypertensive man who presented with vertigo,
anarthria, mild left hemiparesis, and third nerve palsy. The MRI and DWI 2
hours after onset of symptoms revealed no structural lesion or diffusion deficit
in the posterior circulation. A short, partially occluded midbasilar segment
was visible on the MRA. Recanalization of the basilar artery was achieved
with 800 000 U of intra-arterial urokinase. The control MRI showed an
infarct in the posterior cerebellar artery territory on the right, probably
due to clot fragmentation in the basilar artery and subsequent distal embolization,
but no lesion in the brainstem or cerebellum was seen. The patient recovered
and had a Rankin score of 2 ten days later.
Patient 2 was a 75-year-old woman who presented with vertigo, anarthria,
severe right hemiparesis, third nerve palsy, and diminished level of consciousness.
The MRI 5.5 hours after onset showed patchy lesions in the brainstem and cerebellum
on DWI, which were partially also visible on T2-weighted images. A long occlusion
of the middle and distal basilar artery was detected, which could be recanalized
with intra-arterial thrombolysis (1 000 000 U of urokinase). A severe
atherosclerotic stenosis of the midsegment was dilated with a balloon. In
the control MRI, the DWI lesions diminished and only small infarcts were seen
on T2-weighted images, which were smaller than the initial lesions on DWI.
This patient also had a good recovery (Figure
1).
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Imaging in basilar artery thrombosis. Diffusion-weighted imaging
(DWI): bright lesions in the pons (A) (arrow) and in the cerebellar peduncle
(arrow) (B) indicating ischemia (arrow). Magnetic resonance angiography (MRA):
only minimal flow signal is detectable in the basilar artery (arrowheads)
(C) on MRA. Fluid-attenuated inversion recovery: control magnetic resonance
imaging on the day after thrombolysis shows the demarcated infarcts in the
pons (arrow) (D) and the cerebellar peduncle (arrow) (E). The infarct in the
peduncle (arrow) (E) appears smaller than the initial lesion on DWI (arrow)
(B). The left posterior cerebral artery originates from the internal carotid
artery (arrow) (F). Digital subtraction angiography: the angiogram before
thrombolysis shows occlusion of the middle and distal basilar artery (arrowheads)
(G). After thrombolysis, the basilar artery is open with severe arteriosclerotic
stenosis (H and I).
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Patient 3 was 76 years old and had dysarthria, palsy of cranial nerves
IX and XI, and diminished level of consciousness on admission that deteriorated
rapidly. The MRI 3 hours after onset of symptoms revealed a total occlusion
of the basilar artery with a large DWI lesion in the brainstem and both cerebellar
hemispheres. Intra-arterial thrombolysis was not successful, and the patient
died 10 days later.
Patient 4 was a 74-year-old woman who deteriorated rapidly 3 days after
coronary bypass surgery and was in deep coma when she underwent MRI 11.5 hours
after onset of symptoms. A distal occlusion of the basilar tip and large DWI
lesions in the right thalamus, the territory of the posterior cerebellar artery,
the brainstem, and the cerebellum were shown, which were partially already
visible on T2-weighted images. This patient remained comatose.
In all patients who received both MRA and intra-arterial angiography,
the site and length of occlusion were concordant on both imaging modalities.
COMMENT
Acute occlusion of the basilar artery is a neurologic emergency. The
extent of the DWI lesion involvement can be highly variable, and the lesion
volume does not significantly correlate with the National Institutes of Health
Stroke Scale score.13 Several studies1-2 have suggested that intra-arterial
thrombolytic therapy improves overall outcome in patients with basilar thrombosis.
However, currently no criteria are available to decide who will likely benefit
from thrombolysis and in which time window aggressive treatment should be
initiated. Our results indicate that advanced MRI methods, including DWI,
have the potential to become useful in this respect by revealing the extent
of severe ischemic tissue injury in critical brain regions such as the brainstem.
Based on our small case series, we can draw some conclusions. First,
patients with no or only relatively small DWI lesions have a potentially favorable
outcome if reperfusion is achieved rapidly with intra-arterial thrombolysis.
Most likely, the lack of a larger DWI lesion indicates tissue viability in
critical structures. Second, small DWI lesions, even if located in the brainstem,
do not exclude a favorable outcome. In one patient (patient 2) with successful
reperfusion, the small, acute DWI brainstem lesion did not increase in size
and the patient had a good recovery. In the same patient, another lesion located
in the cerebellar peduncle appeared to slightly decrease in size on follow-up.
Currently, we cannot make firm conclusions on the significance of larger
DWI lesions in acute basilar occlusion. Probably, larger DWI lesions, particularly
if located in the brainstem, are predictive of poor outcome, both with and
without treatment. However, the fact that DWI abnormalities may be potentially
reversible must be considered, as recently shown by Kidwell et al.14 Probably, acute DWI lesions contain not only irreversibly
injured tissue but also parts of the penumbra.5, 14
Taken together, there is currently not enough data available to exclude patients
with large brainstem lesions from thrombolysis.
Finally, from our experience, MRA seems to be highly accurate for predicting
or excluding basilar artery occlusion. Bhadelia et al15
have shown that MRA has a good correlation with digital subtraction angiography
in the detection and characterization of occlusive disease in the vertebrobasilar
system. Possibly, subtotal stenosis may be occasionally mistaken for complete
occlusion, but this does not have an impact on patient management, since both
conditions would require emergency angiography. However, to properly analyze
the accuracy of MRA, a substantially larger number of patients would have
to be examined.
In summary, advanced MRI methods have the potential to become useful
in the management of patients with possible basilar artery occlusion by (1)
revealing or excluding basilar artery occlusion noninvasively and (2) showing
the extent of severe ischemic tissue injury in critical brain structures.
AUTHOR INFORMATION
Accepted for publication October 31, 2001.
Author contributions: Study
concept and design (Drs du Mesnil de Rochemont, Neumann-Haefelin, Berkefeld,
and Lanfermann); acquisition of data (Drs du Mesnil
de Rochemont, Neumann-Haefelin, Berkefeld, Sitzer, and Lanfermann); analysis and interpretation of data (Drs du Mesnil de Rochemont,
Neumann-Haefelin, Sitzer, and Lanfermann); drafting of the
manuscript (Drs Neumann-Haefelin and Berkefeld); critical revision of the manuscript for important intellectual content
(Drs du Mesnil de Rochemont, Neumann-Haefelin, Berkefeld, Sitzer, and Lanfermann); study supervision (Drs du Mesnil de Rochemont and Lanfermann).
Corresponding author and reprints: Richard du Mesnil de Rochemont,
MD, Institute of Neuroradiology, University of Frankfurt, Schleusenweg 2-16,
60528 Frankfurt, Germany (e-mail: Mesnil{at}em.uni-frankfurt.de).
From the Institute of Neuroradiology (Drs du Mesnil de Rochemont, Berkefeld,
and Lanfermann) and Department of Neurology (Drs Neumann-Haefelin and Sitzer),
Johann Wolfgang Goethe University, Frankfurt, Germany.
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