(Stroke. 1999;30:70-75.)
© 1999 American Heart Association, Inc.
Original Contributions |
From the Department of Neurology, Justus-Liebig-University, Giessen, Germany (E.S., W.D.), and the Department of Neurology, Medical University at Luebeck, Germany (M.K.).
Correspondence to Dr Erwin Stolz, Department of Neurology, Justus-Liebig-University, Am Steg 14, D-35385 Giessen, Germany. E-mail erwin.stolz{at}neuro.med.uni-giessen.de
| Abstract |
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MethodsIn 75 healthy volunteers (aged 45.8±17.4 years), normal values for the deep cerebral veins (DCVs) and the posterior fossa sinuses were established by transtemporal insonation. Eight patients with cerebral venous thrombosis were assessed by TCCS, through which the hemodynamics of the DCVs were measured, and the patients were followed-up over a period of between 33 and 387 days after examination. MR angiography served as the "gold standard" technique for confirming the venous status in all 8 patients.
ResultsNo side differences in flow velocities were detected in the paired venous structures in normal volunteers. As indirect signs of (and diagnostic criteria for) cerebral venous thrombosis, pathologically increased flow velocities or significant side differences in the DCVs were registered in 5 of the 8 patients; the other patients showed nonsignificant increases in flow velocity which decreased over time. During follow-up, the status of the posterior fossa sinuses could be diagnosed correctly in seven patients after contrast enhancement when these results were compared with those of venous MR angiography. In 1 patient, a partial recanalization was mistakenly diagnosed as an occlusion.
ConclusionsTCCS allows a reliable evaluation of the major DCVs and posterior fossa sinuses. The anterior and mid portions of the superior sagittal sinus and cortical veins cannot be assessed. Increased venous blood flow velocity can be used as an indirect criterion for indicating a cerebral venous thrombosis. Clinical recovery coincided with decreases in blood flow velocity in the series of patients investigated in this study.
Key Words: ultrasonography, Doppler TCCS cerebral veins cerebral sinus dural sinus thrombosis
| Introduction |
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The main disadvantage of conventional transcranial Doppler sonography is the need for arterial landmarks to locate the venous structures and the inability to reliably insonate the dural sinuses. Encouragement for a new approach is now provided through the use of transcranial color-coded sonography (TCCS) combined with contrast enhancing agents. Such agents can elevate low-intensity Doppler signals from intracranial venous vessels above the detection threshold and allow an unambiguous anatomic allocation of the backscattered signals. Only a limited number of patients have been studied to date; these studies have indicated either disturbed venous hemodynamics2 3 4 5 6 or the absence of venous segments,7 both of which suggest the presence of thrombosis. Furthermore, studies of venous hemodynamics are also intriguing, because our knowledge about the pathophysiology of congestive cerebral bleeding is still rather preliminary.
For these reasons we monitored venous flow velocities in the deep cerebral veins (DCVs) of 8 consecutive patients with cerebral venous thrombosis.
| Subjects and Methods |
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The color program was optimized to achieve the highest sensitivity for low blood flow velocities: after the arteries of the circle of Willis were identified, pulse repetition frequency was reduced to the lowest possible setting and color gain was adjusted to the optimal signal-to-noise ratio.
The deep middle cerebral vein (dMCV) was located slightly posterior to
the middle cerebral artery (MCA) at an insonation depth of 40 to
60 mm, with a flow direction away from the transducer. The basal
vein of Rosenthal (BV) follows the course of the posterior cerebral
artery (PCA) and was insonated posteriorly and cranially to the P2
segment. Flow was directed away from the probe. The depth of the
examination window was then adjusted so that the contralateral skull
became visible. After an upward tilt of the probe to the level of the
third ventricle, the vein of Galen (VG) could be examined in the
midline just posterior to the pineal region. The anterior tip of the
transducer was then rotated upward to align the apex of the cerebellar
tentorium and the internal occipital protuberance in the insonation
plane. In this position, the straight sinus was located by
following the flow direction of the VG away from the transducer. The
straight sinus was insonated in its middle portion to distinguish it
from the VG and the confluens sinuum. The superior sagittal sinus was
located above the internal occipital protuberance, where the direction
of flow was toward the probe. For visualizing the confluens sinuum and
transverse sinus, the anterior tip of the transducer was then rotated
downward to the nose saddle again and the probe as a whole was tilted
downward to the cranial base (Figure 1A
).
The contralateral transverse sinus displayed a flow direction away from
and the ipsilateral transverse sinus one toward the transducer.
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Venous peak-systolic blood flow velocity (PSV) and end-diastolic velocity (EDV) as well as identification rates were recorded. Because of difficulties with the reliable construction of an envelope curve around the venous Doppler spectra, the measurement of mean flow velocities was not performed.
Reference Values
To establish normal values for the DCVs and posterior
fossa sinuses, 75 healthy volunteers (aged 45.8±17.4 years;
median, 44 years; range, 14 to 76 years; 32 females and 43 males) were
examined according to the above protocol. For further evaluation, the
following age groups were defined:
40 years (n=30; mean, 28.2±6.9
years), 41 to 60 years (n=26; mean, 49.3±6.1 years),
60 years (n=19;
mean, 68.9±5.2 years). All volunteers were examined without ultrasound
contrast enhancement. Venous flow velocities and identification rates
were recorded. To prevent inaccurate measurements, angle correction
was performed only if the insonation angle did not exceed 60°.
Patients
Blood flow velocities in the DCVs were assessed in 8 patients
with acute cerebral venous thrombosis: (3 with complete superior
sagittal sinus thrombosis, 1 with partial superior sagittal sinus
(anterior and middle portion) and transverse sinus thrombosis, 1 with
cortical vein thrombosis, 1 with transverse and sigmoid sinus
thrombosis, 1 with superior sagittal sinus and bilateral transverse
sinus thrombosis, and 1 with partial confluens sinuum thrombosis
(mean±SD age, 41±15 years; range, 23 to 66 years) by TCCS, digital
subtraction angiography, and MRA. Detailed patient characteristics are
given in Table 1
. The follow-up interval
ranged from 33 to 387 days. TCCS examinations were performed every
1±1.4 days (n=17) during the first week after admission; further
examinations followed between days 9 and 92 after admission (mean,
34±32 days; n=11) and during the later course of clinical follow-up
(mean, 215±54.3 days; n=7). Seven patients were treated with
dose-adjusted intravenous heparin so that the initial PTT
was at least doubled. One patient received low-dose heparin
treatment.
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All patients were followed-up by contrast-enhanced TCCS (ce-TCCS) in order to optimize the signal-to-noise ratio for identifying recanalization or persistent thrombosis of the venous vessels. Levovist (Schering AG) was used for contrast enhancement in all patients; intravenous injections of 10 mL of the agent were given at concentrations of 300 to 400 mg/mL. Venous MRA served as a noninvasive morphological reference technique. During the first 6 weeks of follow-up, ce-TCCS data could be compared with 14 venous MRAs. In the time interval 6 weeks to 6 months after admission, 6 venous MRAs and ce-TCCS examinations could be correlated. Two reference examinations were obtained >6 months after admission.
At follow-up the examiner was blind to the venous MRA findings obtained between 0 and 2 days after the contrast-enhanced TCCS examination. The study was carried out in accordance with institutional ethical guidelines.
Statistical Analysis
For data analysis, the software package Turbo Statistik
3.0 was used. The normal range of PSV and EDV was defined as the
mean±2 SDs. Side differences in peak-systolic,
end-diastolic, or mean flow velocities of the paired venous
structures of the deep cerebral venous system of
50% were considered
pathological. For comparison of flow velocities between different age
and sex groups, nonparametric ANOVA (Mann-Whitney U test)
was used; for evaluation of side differences, a Wilcoxon
matched-pairs test was used. To compare identification rates of venous
vessels, we used Fisher's exact test. For correlation of venous and
arterial blood flow velocities, we used a linear regression
model. As quality control of the follow-up examinations, the PSVs in
the MCA were used to assess the intraobserver repeatability over the
observation period.
| Results |
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40 years (dMCV, 87%; BV, 90%; VG, 90%;
straight sinus, 77%; transverse sinus, 82%; and superior sagittal
sinus, 63%) but tended to drop with increasing age. This finding
reached the level of significance for the cerebral veins when comparing
the age group
40 years versus >60 years (Fisher's exact test,
P<0.05) and was more pronounced for the dural sinuses (age
40 years versus 41 to 60 years, P<0.05; age group 41 to
60 years versus >60 years, P<0.05). In the age group >40
years, the number of identified vessels was higher in men than in
women, without statistical significance. Venous flow velocities
decreased with age. This finding was significant (P<0.05)
for the age group >60 years compared with those
40 years for the BV,
transverse sinus, and superior sagittal sinus. Women tended to have
higher flow velocities than men, which reached the level of
significance for the dMCV and BV (for the dMCV, a mean PSV of 11.5
versus 9.4 cm/s; for the BV, a mean PSV of 14.7 versus 13.3 cm/s,
respectively; P<0.05).
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In the same collective, the rate of identification of the
different segments of the basal cerebral arteries was highest for the
M1 segment of the MCA at 87%, declined for the P1 segment of the PCA
at 85% and the P2 segment of the PCA at 79%, and was lowest for the
A1 segment of the anterior cerebral artery (ACA) at 78%. The
arterial identification rate tended to drop with increasing
age. This finding was significant in comparison of the age groups
40
years and 41 to 60 years (P<0.05). This decline of
identification rate was more pronounced for the cerebral veins than for
the arteries (P<0.05). The overall identification rate of
the M1 segment of the MCA was significantly higher than that of the
dMCV (P<0.05); however, the BV was identified more
frequently than the P2 segment of the PCA (P<0.05),
comparing those arterial and venous vessels that lie in
close proximity. Arterial identification rates were higher
in men than in women (P<0.05).
PSV and EDV for the different arterial segments of the circle of Willis were as follows: M1 MCA, 110.6±33.1 and 47.2±14.8 cm/s; A1 ACA, 85.6±22.1 and 38.0±10.8 cm/s; P1 PCA, 67.3±20.5 and 29.0±9.1 cm/s; and P2 PCA, 63.9±14.5 and 28.8±8.6 cm/s, respectively. Arterial flow velocities decreased with age. This finding was significant (P<0.05) for the MCA and the PCA. Women tended to have higher flow velocities than men, which reached the level of significance for the MCA and PCA (P<0.05).
A paired comparison of venous and arterial flow velocities showed only weak correlations. Overall correlation was better for the EDVs than for the PSVs. A linear regression analysis of flow velocities in the MCA related to flow velocities in the dMCV showed no correlation (PSV, r=0.06, P=0.53; EDV, r=0.12, P=0.22). However, EDVs in the PCA and the BV correlated significantly (P1 PCA, r=0.22, P<0.05; P2 PCA, r=0.22, P<0.05). Best correlation was reached for the flow velocities in the PCA and transverse sinus (for the P2 PCA: PSV, r=0.27, P<0.01; EDV, r=0.36, P<0.001; for the transverse sinus PCA: PSV, r=0.26, P<0.05; EDV, r=0.51, P<0.001).
Venous Thrombosis
Four patients (1 with superior sagittal sinus and unilateral
transverse sinus thrombosis, 1 with transverse and sigmoid sinus
thrombosis, 1 with superior sagittal and bilateral transverse sinus
thrombosis, and 1 with cortical vein thrombosis) displayed
pathologically increased flow velocities in the DCVs ipsilateral to the
side of a hemorrhagic infarct (Figure 2
)
that normalized within 3, 8, 13, and 252 days, respectively, resulting
in a reduction of flow velocities of 46% (left dMCV in patient 5),
52% (left BV in patient 7), 57% (left dMCV in patient 8), and 82%
(left dMCV in patient 4) (the numbering of patients follows that in
Table 1
). In these patients, despite the fact that absolute flow
velocity values were normal on follow-up, pathological side differences
in flow velocities within the dMCV or BV persisted that resolved in 2
of the patients within 195 and 266 days, respectively. In 1 patient
with superior sagittal sinus thrombosis, a significant and persistent
side difference in flow velocities within the dMCVs could be
demonstrated in the acute stage of illness, despite normal absolute
flow velocities. All other patients displayed no significantly
increased flow velocities in the DCVs or significant side differences,
although there was a tendency for the flow velocities in the dMCV and
BV to decrease with time: a reduction of flow velocities of 22.6% (BV
in patient 6), 24% (dMCV in patient 1), 35% (dMCV in patient 3), and
59% (dMCV in patient 2) was found. In all patients we found a
gradual decrease of flow velocities over time in the great VG, although
even in the acute stage of illness PSVs and EDVs lay within the normal
range, as defined by the mean±2 SDs rule (PSVs of 24.0, 20.1,
19.8, 18.4, 16.8, 13.2, 12.0, and 10.8 cm/s, without angle
correction).
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In patients with transverse sinus thrombosis and partial confluens sinuum thrombosis, angle-corrected PSVs in the straight sinus gradually decreased during the observation period. In the acute stage of illness in 3 of these patients, flow velocities still lay within the normal range on admission; in 1 case they were pathologically increased (48 cm/s, insonation angle <50°). In this case, flow velocities normalized within 3 days after admission, concurrent with the reappearance of flow signals in the initially occluded transverse sinus. One of the patients with unilateral transverse sinus thrombosis displayed pathologically increased PSVs (51 cm/s on admission) and a strong color signal in the contralateral sinus as sign of compensatory blood flow, which normalized within 3 days after admission. At this time, a flow in the initially occluded vessel was detectable. One day after admission the patient with bilateral transverse sinus thrombosis showed a stringlike color signal in 1 transverse sinus with PSVs of 68 cm/s, interpreted as venous stenosis in a partially recanalized transverse sinus. Flow velocities normalized within 6 days, concurrent with a partial recanalization confirmed by venous MRA. For all patients, flow velocities within the arteries of the circle of Willis remained normal. During the follow-up period, flow velocities in the MCA showed a fluctuation of 0.09±12.2 cm/s.
On follow-up with contrast-enhanced TCCS (ce-TCCS),
recanalization of the affected posterior fossa
sinus could be diagnosed correctly in 4 of the 8 patients (Figure 1B
). At least partial recanalization could
be confirmed by venous MRA within the first 6 weeks after admission in
these patients. The patient with cortical vein thrombosis displayed
normal posterior fossa sinuses. The cortical venous system was not
accessible by contrast-enhanced TCCD. In the patient with transverse
and sigmoid sinus thrombosis, persistent occlusion was diagnosed that
could be confirmed by MRA. In the patient with partial superior
sagittal sinus thrombosis, the posterior part of the sinus was
diagnosed correctly as nonoccluded on admission; however, the occlusion
of the middle portion of the sinus was not recognized. One high-grade
residual stenosis of the superior sagittal sinus thrombosis
recognized by MRA up to 10 months after admission was mistaken for
persistent occlusion on contrast-enhanced TCCS examinations.
| Discussion |
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In our series the dorsal part of the superior sagittal sinus was detected at high success rates, but reliable angle-corrected measurements could not be made because of the perpendicular insonation angles, similar to those encountered in the study by Baumgartner et al.6 Our results from healthy volunteers agree well with values reported in the literature5 6 9 and demonstrate that the DCVs and posterior fossa sinuses are detectable by transtemporal TCCS with success rates ranging between 50% and 90%. Angle-corrected flow velocity measurements of the VG, the straight sinus, and the superior sagittal sinus are not likely to improve the accuracy of measurement, owing to the unfavorable insonation angles. Differences in detection rate may be partly explained on the one hand by the age dependence of the identification rate and on the other by the slightly different examination protocol. The decrease of the identification rate of cerebral veins and, more pronounced, of the dural sinuses imposes no major drawback for the clinical application of the method, because patients with cerebral venous thrombosis are usually of younger age. The reliable accessibility of the deep middle cerebral and basal veins predisposes them for follow-up studies in pathological states.
Paired venous and arterial correlations have not been reported thus far. The arterial blood flow velocities in the circle of Willis of our normal collective are in good accordance with the values reported in the literature.10 11 We noted a decline in the identification rate of the intracranial vessels that was, overall, more pronounced for the cerebral veins than the arteries. When we compared the identification rates of those arterial and venous vessels in close anatomical proximity, the rates were higher for the MCA than the dMCV because of the frequent problem of separating the venous from the arterial Doppler spectrum. However, identification rates were higher for the BV than for the P2 segment of the PCA. The reason for this may be the slightly curved and superiorly concave12 course of the P2 segment, which makes it difficult to align the insonation plane with the course of the artery. Parallel to the venous side we found a reduction of flow velocities with increasing age and found higher flow velocities in men than in women. Linear regression analysis of paired venous and arterial flow velocities showed overall a poor correlation. The level of significance was reached with comparison of the EDVs in the P2 segment of the PCA and the BV, and PSVs and EDVs in the P1 and P2 segments of the PCA and the transverse sinus. Correlation was better for the EDVs than the PSVs, since the former are more closely related to the arterial inflow resistance13 that influences venous outflow. Regression coefficients, however, were low. This finding is explained by the poor overlap of the territories of arterial supply and venous outflow.
Venous Thrombosis
Conventional TCD has been used for diagnosis in small
patient collectives with cerebral venous thrombosis, revealing
pathologically increased venous blood flow velocities in the dMCV or
the basal cerebral vein in some but not all patients as indirect signs
of thrombosis.2 3 4 The main disadvantage of conventional
TCD in the evaluation of intracranial veins is the need for
arterial reference points to identify the venous
structures. In 3 patients with superior sagittal sinus thrombosis, TCCS
was able to demonstrate increased venous flow velocities in the dMCV,
the straight sinus, and the confluens sinuum.5 6 A flow
reversal in the basal cerebral veins was shown by TCCS in 2 patients
with a thrombosis of the straight sinus.6
Taking into consideration both our findings and the reports from the literature, the following indirect ultrasonographic signs of cerebral venous thrombosis can be summarized: (1) pathologically increased flow velocities in the DCVs; (2) a pathological side difference of flow velocities in the paired DCVs; and (3) flow reversal in the BVs.
Normalization of elevated flow velocities in the DCVs during follow-up is frequently reported.2 3 6 In our patients, significant side differences (>50%) in the DCVs persisted during follow-up if they were present at the initial examination; however, absolute flow velocities returned to the normal range within days to several months. In all but 1 patient (with transverse and sigmoid sinus thrombosis), a recanalization of the affected venous structures could be confirmed by MRA; in 1 case, a high-grade residual stenosis of the dorsal part of the superior sagittal sinus persisted. Monitoring flow velocities in the straight and transverse sinuses can give additional information on the complex venous hemodynamics in cerebral venous thrombosis and changes caused by recanalization.
It cannot be clearly stated whether there is a causal relationship between clinical status and venous flow velocities, because to date only a few patients have been closely followed-up. The increase of venous flow velocities did not correlate with the severity of our patients' symptoms on admission. Normalization or decrease of flow velocities on follow-up coincided with an improvement of the initial neurological deficits. This, of course, does not prove any causal relationship, but it may indicate either recanalization of the affected venous structures or collateralization.
The occurrence of pathological flow velocities in the DCVs is determined by the venous structure occluded and the anatomy of the venous collaterals, whereas changes in flow velocities in the sinuses accessible by TCCS seem to be more closely related to the thrombotic process itself. We found pathologically increased venous flow velocities only in patients who presented with extensive hemorrhagic infarcts, suggesting significant cortical venous obstruction as the underlying defect that forces venous blood toward the deep cerebral venous system.15 The latency (which usually cannot be determined exactly) between onset of thrombosis, the neurological symptoms, and the first ultrasound investigation influences the extent of observable flow pathology in the DCVs. Recanalization may occur within the first days after heparinization. Therefore, the timing of the first ultrasound examination in relation to treatment onset is also of importance for the detection of raised venous blood flow velocities. No registrations have been reported that were obtained during propagation of thrombosis or during the phase of clinical deterioration. More information is also needed concerning the temporal relationship between venous hemodynamics and the development of venous hemorrhage.
The repeatability of our follow-up examinations was good, considering the variations in PSVs in the MCA. The observed variations were only slightly higher than in a controlled TCCS validation study.14
Application of Echo Contrast Agents
As shown in previous studies, using transtemporal
TCCS,5 7 16 the application of echo
contrastenhancing agents improves the identification of intracranial
venous vessels and facilitates the measurement of venous flow
velocities. Ries and coworkers7 systematically used
contrast-enhanced TCCS (ce-TCCS) in 14 patients for the diagnosis of
suspected transverse sinus thrombosis. After application of the echo
contrast enhancer, an absence of blood flow was found in 1 transverse
sinus in 4 cases, in which complete transverse sinus occlusion was
confirmed by MRI and MRA in 3 cases and transverse sinus aplasia in 1
case. One thrombotic occlusion was missed on ce-TCCS. Side-to-side
asymmetry of blood flow in the transverse sinus was correctly diagnosed
in 10 of the 14 patients, 6 of whom displayed only residual color flow
signals after contrast enhancement. In these patients, MRI and MRA
showed a partial transverse sinus thrombosis in 4 patients due to the
demonstration of an intraluminal clot signal, and in 1 case a
transverse sinus hypoplasia was revealed.
In our study, contrast enhancement was used for follow-up. The status of the posterior fossa sinuses could be assessed in 7 of the 8 patients regarding recanalization or persistent occlusion, which confirmed the results of venous MRA. However, despite contrast enhancement, neither cortical veins nor the middle and anterior portion of the superior sagittal sinus could be identified. In 1 patient, a high-grade partial residual stenosis of the dorsal part of the superior sagittal sinus was mistakenly identified as occlusion (when taking into consideration the results of MRA). Considering the difficult accessibility of the superior sagittal sinus, contrast enhancement may improve the signal-to-noise ratio but will not improve the unfavorable anatomic localization. In agreement with the results reported by Ries and coworkers,7 we found direct ce-TCCS criteria for the diagnosis of cerebral sinus thrombosis in the form of absent color signals. Using these direct ultrasonographic criteria alone, echo contrast enhancement was decisive for the sonographic diagnosis in 7 of our 8 patients.
However, sinus thrombosis cannot be ruled out by either TCCS or ce-TCCS. TCCS is not suitable as a screening method for cerebral venous thrombosis; however, it proved useful as a noninvasive bedside technique for the follow-up of such patients.
Received July 21, 1998; revision received September 18, 1998; accepted September 29, 1998.
| References |
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