(Stroke. 1999;30:606-612.)
© 1999 American Heart Association, Inc.
Original Contributions |
CT Angiography and Doppler Sonography for Emergency Assessment in Acute Basilar Artery Ischemia
From the Departments of Neurology (T.B., S.W., R.W., W.H.) and Neuroradiology (M.K., R. von K., K.S.), University of Heidelberg, Heidelberg, and the Technische Universität, Dresden (R. von K.), Germany.
Correspondence to Tobias Brandt, MD, Neurologische Universitätsklinik, Im Neuenheimer Feld 400, D 69120 Heidelberg, Germany. E-mail tobias_brandt{at}ukl.uni-heidelberg.de
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Abstract |
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Background and Purpose—Both Doppler sonography (DS) and spiral CT angiography (CTA) are noninvasive vascular assessment tools with a high potential for application in acute cerebral ischemia. The usefulness of CTA for vascular diagnosis in acute basilar artery (BA) ischemia has not yet been studied.
Methods—We prospectively studied 19 patients (mean±SD age, 58±11 years) with clinically suspected acute BA occlusion by DS and CTA. Prior extracranial and transcranial DS was performed in all but 1 patient, with DS 4 hours after CTA. In 6 of 19 patients, we performed digital subtraction angiography.
Results—CTA was diagnostic in all but 1 patient. CTA revealed complete BA occlusion in 9 patients and incomplete BA occlusion with some residual flow in 2 patients. A patent BA was shown in 7 patients. Because of severe BA calcification, CTA results were inconclusive in 1 patient. DS was diagnostic in only 7 of 19 patients, indicating certain BA occlusion in 3 patients and BA patency in 4 patients. In an additional 9 patients, the results of DS were inconclusive. DS was false-negative in 2 patients with distal BA occlusion shown by CTA and digital subtraction angiography. In 1 patient with DS performed after CTA, recanalization was demonstrated. In addition to the diagnosis or exclusion of BA occlusion, CTA provided information on the exact site and length of BA occlusion and collateral pathways. In our series, CTA results prompted indication for intra-arterial thrombolysis in 5 patients.
Conclusions—CTA was superior to DS in the assessment of BA patency in patients with the syndrome of acute BA ischemia in terms of feasibility and conclusiveness, particularly in cases with distal BA occlusion. Our study confirmed the usefulness of combined extracranial and transcranial DS in the diagnosis and exclusion of proximal BA occlusion.
Key Words: angiography, computed tomographic • basilar artery • brain stem • cerebral ischemia • ultrasonography, Doppler
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Introduction |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Acute basilar artery occlusion (BAO) is a frequent but often difficult differential diagnosis in patients with rapid onset of decreasing consciousness and progressive brain stem dysfunction. Intra-arterial thrombolytic therapy is a potentially lifesaving procedure in selected cases of acute BAO.1 2 Therefore, reliable and widely available tools for the assessment of basilar artery (BA) patency are needed. Traditionally, intra-arterial digital subtraction angiography (DSA) has been used for diagnosis of clinically suspected BAO.3 However, DSA is a time-consuming, expensive, and invasive method that requires good cooperation of the patient or general anesthesia. Extracranial and intracranial Doppler sonography (DS) has been used to confirm or exclude suspected acute BAO.4 5 6 Unfortunately, considerable technical limitations of DS, especially in the diagnosis of BAO, could not be overcome until now.4 5 6 7 In particular, ultrasound penetration of the distal parts of the BA or in cases of adipose necks is most often insufficient, and identification of the BA may remain uncertain.8 The value of MR angiography for diagnosis of BAO has not been studied thus far in large series of patients. Generally, MR angiography is neither well suitable nor accessible for emergency workup of unstable or intubated patients with acute cerebral ischemia. Moreover, examination of patients with impaired consciousness is frequently hampered by motion artifacts.9 10
Spiral CT angiography (CTA) is a new noninvasive vascular imaging tool with a high potential for application in acute cerebral ischemia.9 11 12 13 14 15 The usefulness of CTA for diagnosis or exclusion of BAO has been shown in only a few cases.16 To our knowledge, studies comparing CTA with DS for this purpose have not been published.
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Subjects and Methods |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Among 20 patients prospectively included for CTA examination of suspected BAO, 19 also underwent DS. All patients were admitted consecutively to the emergency ward of our department from December 1995 until February 1997. CTA findings of 5 patients have been published earlier by Knauth et al.16 This study refers to those 19 patients, aged 23 to 86 years (mean±SD age, 58±11 years), who underwent both CTA and DS. Clinical diagnosis was probable acute BAO in all cases. Inclusion criteria were variable clinical syndromes with sudden onset and progressive deterioration of consciousness, dizziness, double vision, dysarthria, oculomotor and other cranial nerve signs, or bilateral motor signs. Three patients were comatose. In 6 additional patients already ventilated on admission, clinical assessment was initially not possible.
Within a maximum of 30 minutes before CTA, we performed extracranial
Doppler sonography (ECD) and transcranial Doppler
sonography (TCD) in all but 1 patient according to standard procedures
(Medasonics CDS; extracranial 4-MHz probe with continuous wave
mode, transcranial 2-MHz probe with pulsed wave
mode).8 One patient with BAO shown by CTA was excluded
from the analysis because DS was not available at admission,
and he was transferred to a secondary care center because of poor
prognosis. In the remaining patient with BAO, DS was unavailable before
CTA. This patient was treated by local thrombolysis and
underwent DS 4 hours after CTA to assess
recanalization. We classified the findings on ECD
of both extracranial distal vertebral artery segments (V3 segments) and
on TCD of the intracranial distal vertebral artery segments (V4
segments), BA, and both posterior cerebral arteries (PCA) using the
suboccipital and temporal approaches into 3 categories: (1) no evidence
of BAO: normal BA flow signal with well-preserved diastolic
forward flow at a depth of 
95 mm detectable by
TCD8 ; (2) uncertain signs of BAO: absent flow or
high-resistance flow patterns in both vertebral artery V3 segments in
ECD4 5 6 ; no flow signal or flow signal without forward
diastolic flow component detectable in the BA by TCD;
diminished PCA flow without evidence of PCA
stenosis17 ; and (3) evidence of BAO:
high-resistance to-and-fro flow patterns at depths of 85 to 95 mm
in the BA (TCD), possibly combined with a sudden loss of flow signals
on increasing the examination depth, or demonstration of retrograde
flow in the distal BA.6 18
Immediately after conventional CT scanning (4-mm slice thickness for the posterior fossa), all patients had CTA of the vertebrobasilar circulation, after informed consent had been obtained from patients or their close relatives. Exclusion criteria for CTA were contrast medium allergy and renal failure.
For CTA of the main vertebrobasilar trunks from the foramen magnum to the top of the BA, including the circle of Willis, we used the method described by Knauth et al16 : 130 mL of a nonionic contrast medium (Omnipaque, Schering) was infused into an antecubital vein (>18-gauge cannula) with an injection rate of 4 to 5 mL/s using an injection pump. After a delay of 20 seconds, spiral scanning was done (Picker PQ 2000 CT, Picker International). The following parameters were used in all patients: slice thickness 2.0 mm, index 1.5 mm, spiral pitch 1.25 mm, total scanning time 21 seconds with 1 second per revolution, 130 kV, and 125 mA. For vascular diagnoses we used the CTA source images and 3-dimensional reconstructions of the data sets (surface-shaded display; voxel Q workstation; Picker International). Data sets were completed within 10 minutes after the start of scanning. Analysis of CTA data sets was performed by a neuroradiologist (M.K.) blinded to clinical data and prior DS results. The interrater reliability of the analysis of CTA data sets was assessed in a previous study and found to be high.13
For the description of the sites of segmental BAO, we used the
definitions suggested by Archer and Horenstein19 : (1)
proximal BAO included the lowest BA segment from the vertebral artery
junction up to the origin of the anterior inferior
cerebellar arteries; (2) mid BAO included the segment from the origin
of the anterior inferior cerebellar arteries to the origin
of the superior cerebellar arteries; and (3) distal BAO included the
top of the BA distally to the origin of the superior cerebellar
arteries. On the basis of CTA findings, collateral supply of the distal
BA via posterior communicating arteries and the circle of Willis was
graded as "good" if it was clearly visible or "poor" if it was
not detectable.20 Length of the occlusion was graded as
"short" if only 1 BA segment was occluded and as "long" if 2
segments were affected. The latter definition corresponds to the
category "extended" or "multilevel" occlusion given by Hacke
and coworkers.1
In 6 patients without contraindications for intra-arterial thrombolytic therapy, we additionally performed conventional intra-arterial angiography (DSA), including internal carotid artery injections for visualization of collateral flow to the distal BA in 2 patients.
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Results |
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In all 19 patients included in the study (Table
), technical feasibility of
CTA was good, with high-quality data sets. Site and length of BAO could
be assessed by CTA in all but 1 patient. In this case, with evidence of
BAO at DS, CTA was not diagnostic because of lack of
differentiation of the massive calcification and any possible contrast
enhancement in the BA (Figure 1).
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CTA indicated complete BAO in 9 patients (Figure 2). CTA revealed short segmental BAO in 6
patients and multisegmental BAO in 3 patients. The proximal BA segment
was occluded in 2 patients, the mid BA in 4, and the distal BA segment
in 3 patients. Good collateral supply with retrograde filling of the
distal BA from the anterior circulation via the posterior communicating
arteries was visualized in 3 patients with proximal or middle BA
segment occlusion, while collateral supply of the PCA was seen in
another 2 patients with distal BAO. In another patient with long mid to
distal BAO, CTA identified collateral SCA supply confirmed by DSA. In 1
patient with complete BAO, CTA additionally revealed left middle
cerebral artery occlusion. In an additional 2 patients, CTA revealed
extremely reduced BA contrast enhancement on 2 of the original
slices, indicating incomplete occlusion. In 7 patients, normal CTA
findings clearly excluded BAO (Figure 3).
Direct and indirect Doppler findings indicating BAO are shown in
Figure 4.
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In 6 patients with CTA-based diagnosis of BAO and possible indication for thrombolytic therapy, DSA was performed. It confirmed BAO without exception. Important additional DSA findings not visualized by CTA, however, were extracranial vertebral artery dissection and anterograde cerebellar collaterals in 2 patients.
DS was diagnostic in 7 of 19 patients. Clear evidence of BAO, however, was demonstrated only in 3 patients with proximal or mid BAO according to CTA. DS correctly excluded BAO in 4 patients. In the remaining patients, signs of BAO were uncertain, with BA flow completely undetectable in 3 patients or absent in diastole, corresponding to a high-resistance flow pattern in 2 patients. Additional PCA hypoperfusion confirmed the assumption of BAO in 1 of these patients. DS was false-negative in 2 patients, 1 with complete and 1 with subtotal distal BAO on CTA and DSA. In 1 of these patients, follow-up DS revealed findings typical of BAO. DS findings indicated vertebral artery occlusion not confirmed by CTA in another patient. Results of DS were inconclusive in an additional 4 patients, 2 of whom were intubated and hyperventilated. In 1 of these patients, DS was technically insufficient, with no flow signal detectable in the vertebral arteries and the BA. One patient with BAO had no DS before CTA and DSA because of unavailability of DS but showed normal DS results 4 hours later, indicating recanalization after thrombolysis.
New infarcts in the posterior circulation on follow-up CT consistent with transient BAO were shown in 3 of 7 patients without BAO on CTA. Other final single diagnoses were transient brain stem ischemia of unknown origin, intoxication, large middle cerebral artery territory infarction, and postictal coma.
Intra-arterial thrombolytic therapy was performed in 5 patients with BAO. Three of 4 patients with successful recanalization survived. One patient without recanalization died.
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Discussion |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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In patients with acute brain stem symptoms and negative cranial CT, vascular evaluation may provide important information concerning a possible occlusive ischemic etiology. Successful thrombolytic therapy with recanalization of BAO is associated with improved survival of progressive brain stem ischemia in selected cases.1 2 Therefore, rapid and reliable assessment of BA patency is mandatory in cases of clinically suspected BAO without contraindications for thrombolysis. While the validity of DSA for the diagnosis and exclusion of BAO is beyond question, attempts are made to confine it to patients undergoing intra-arterial thrombolytic therapy. The main reasons are its hazards, limited availability, high costs, and time consumption. To select patients for thrombolytic therapy as well as to assess patients who are not suitable for this invasive therapy, other methods of BA patency assessment are needed. In patients with contraindications for thrombolysis, DSA is not necessary in the acute stage because of lack of therapeutic consequences. Confirmation of the clinical diagnosis of BA thrombosis in these patients, however, is important for the assessment of further prognosis and for clinical decision making.
DS has become a standard vascular assessment tool. Unfortunately, technical problems limit the validity of DS, especially for the diagnosis and exclusion of BAO.5 7 8 18 Several studies confirmed the diagnostic value of some signs clearly indicating BAO, especially bilateral high-resistance flow patterns in the distal vertebral arteries and the proximal BA.5 6 7 18 In our series, these signs were identified by DS in only 3 of 9 patients with proximal complete BAO. DS correctly excluded BAO in 4 patients. In 2 patients with distal BA occlusions, however, DS findings were clearly false-negative. Therefore, the decision not to perform DSA is not to be based reliably on negative DS findings alone if BAO is clinically suspected. More recent technical developments, such as transcranial duplex sonography with application of contrast agents, have not been tested in large series of patients with BAO. Some case reports, however, indicate an improvement of visualization of the proximal and middle segments of the BA, whereas visualization of the distal parts still remained technically insufficient.21 22 The ability of DS to provide information on flow dynamics, however, and its usefulness for repeated flow monitoring are advantages that may be used for therapy and follow-up. Once the exact diagnosis has been defined, even uncertain DS signs of BAO may be useful for this purpose.
CTA has been introduced as a new tool for emergency vascular assessment.9 11 15 It has been reported to more reliably depict the normal anatomy of the circle of Willis than MR angiography.9 In this series, CTA proved to be a feasible and rapid technique for evaluation of the posterior circulation, even in severely ill patients. Definite diagnosis or exclusion of BAO was possible in all but 1 patient. In all patients in whom DSA was performed, CTA-based diagnosis of BAO was confirmed without exception. CTA showed collateral supply of the distal BA in 6 patients with proximal BAO. The site and length of BAO and the collateral status have been shown to have an important impact on prognosis.2 This information was provided by CTA in all but 1 patient. With DSA, additional carotid artery injections are necessary to assess the length of BAO and the retrograde collateral flow.
The important drawbacks of CTA are its narrow scanning range, showing only selected parts of the vascular tree, its limited repeatability, and the low yield of dynamic flow information.9 14 23 The latter may be an explanation for the discrepancy between CTA and DS in one case with no forward vertebral artery flow detected by DS and the normal display of the V4 segment of the same vertebral artery by CTA. DSA was superior to CTA in depicting relevant vascular details such as collateral flow through cerebellar arteries. Whether high-grade BA stenoses may appear completely occluded on CTA has not been determined thus far.11
All 3 modes of vascular examination may be hampered by motion artifacts. In our series, the only CTA without diagnostic value was obscured by BA atherosclerosis with massive calcification. Flow-related examinations such as DSA and DS are probably influenced to a lesser extent by vessel wall calcification.
We conclude that CTA is a useful tool for the emergency evaluation of patients with suspected acute BAO. In our series it provided reliable information on BA patency, on the exact site and extent of BAO, and to some extent on collateral pathways. It appears reasonable to rely on CTA results in decisions concerning thrombolytic therapy in clinically suspected BAO. Although DSA was superior to CTA in depicting vascular details, CTA may provide a clear-cut indication for DSA or even replace it in some cases. The small number of patients studied in our series precludes definite conclusions on the accuracy of CTA in BAO. Further evaluation of CTA, especially in high-grade BA stenosis, is necessary.
Our study confirmed the ability of DS to detect or exclude proximal BAO. Because of its limited feasibility in distal BAO and the low sensitivity of DS findings clearly indicating BAO, DS cannot replace DSA or exclude the need for thrombolytic therapy. It may be used, however, as a rapid vascular screening method before CTA and/or DSA to exclude extracranial carotid or vertebral artery occlusion.
Received May 26, 1998; revision received December 2, 1998; accepted December 2, 1998.
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