Transoccipital Power-Based Color-Coded Duplex Sonography of Cerebral Sinuses and Veins
Background and Purpose Power-based transcranial color-coded duplex sonography is a new development for cerebrovascular imaging that is suited for detection of slow velocities. The purpose of this study was to evaluate the ability of this technique to detect cerebral sinuses and veins by means of the occipital window and to provide reference data.
Methods The straight and inferior sagittal sinuses, great and internal cerebral veins, and basal veins were insonated in 120 normal subjects. The number of identified vessels, peak systolic (PSV) and end-diastolic (PDV) velocities, and resistance indices were determined.
Results In subjects aged 20 to 59 years, straight sinuses were identified in 81% and great and internal cerebral veins in 34%. In subjects aged 60 to 79 years, straight sinuses were detected in 50%, great cerebral veins in 20%, and internal cerebral veins in 13%. All insonated inferior sagittal sinuses and basal veins were missed. Velocities were highest in straight sinuses (PSV, 35 [7 to 64] cm/s; PDV, 23 [2 to 43] cm/s), slower in great cerebral veins (PSV, 23 [12 to 34] cm/s; PDV, 16 [7 to 26] cm/s), and slowest in internal cerebral veins (PSV, 14 [10 to 18] cm/s; PDV, 10 [5 to 15] cm/s) (mean with 95% confidence intervals [CIs]). Straight sinus velocities decreased with age for PSV (20 to 39 years, 40 [7 to 73] cm/s; 60 to 79 years, 28 [9 to 46] cm/s; P<.01) and PDV values (20 to 39 years, 28 [4 to 52] cm/s; 60 to 79 years, 16 [5 to 26] cm/s; P<.001) (mean with 95% CIs) and were higher in women than men in the group aged 20 to 39 years. (P<.05). Resistance indices increased with age in the straight sinus (20 to 39 years, 0.30 [0.18 to 0.42]; 60 to 79 years, 0.42 [0.31 to 0.53]; P<.001) (mean with 95% CIs).
Conclusions Transoccipital power-based color-coded duplex sonography enabled imaging and velocity measurements in the straight sinus of subjects aged 20 to 59 years. In elder subjects detection rate of the straight sinus decreased, and it was low for deep cerebral veins in all age groups.
Frequency-based TCCD has been shown to be useful for the evaluation of the basal cerebral arteries.1 2 3 Recent advances in ultrasonics have enabled the introduction of power Doppler sonography for transcranial imaging.4 Differences in signal-to-noise ratio allow greater gain increases in power-based than in frequency-based color Doppler imaging, rendering power Doppler sonography more suited for visualization of slow velocities, which occur in cerebral veins and sinuses.5 The occipital window has been used to insonate the straight sinus by means of conventional transcranial Doppler sonography in healthy volunteers.6 The present study was performed to assess the ability of transoccipital power-based TCCD to image and measure velocities in cerebral sinuses and veins and to provide age- and sex-matched reference data.
Subjects and Methods
Subjects were 120 healthy volunteers (mean±SD age, 50±17 years; range, 20 to 79 years; 60 women, 60 men) of Caucasian descent with no cerebrovascular risk factors and no history of cerebrovascular and cardiopulmonary disease. Forty were aged 20 to 39 years (median, 31 years; 20 women, 20 men), 40 were aged 40 to 59 years (median, 49 years; 20 women, 20 men), and 40 were aged 60 to 79 years (median, 70 years; 20 women, 20 men).
Intracranial cerebral veins and sinuses were studied with an Acuson 128 XP/10 device equipped with a 2.0- to 2.5-MHz 90° sector scan providing the same Doppler energy output as reported previously.4
Transoccipital insonation (Fig 1⇓) was performed with the patient in a sitting position and the head bent slightly forward. The transducer was positioned approximately 1 cm above the external occipital protuberance. Sagittal scanning planes were used. The straight and inferior sagittal sinuses and great cerebral, internal cerebral, and basal veins were insonated. They were identified according to their anatomic location and the direction of flow as described by Huang and Wolf7 and Ono et al8 and according to the velocity changes occurring during Valsalva’s maneuver. The clivus and the frontal skull were used as anatomic landmarks.
The straight sinus (Fig 2⇓) was insonated in its proximal part, providing the lowest insonation angles possible. The flow was directed toward the transducer. Attention was paid to detect a venous signal without superposition of Doppler spectra resulting from neighboring branches of the posterior cerebral artery. The inferior sagittal sinus was insonated in its distal part before entering the straight sinus, and its flow was expected to be directed toward the transducer. For diagnosis of the inferior sagittal sinus, the depiction of a trifurcation consisting of the great cerebral vein and the inferior sagittal and straight sinuses was required. The flow of the great cerebral vein (Fig 3⇓) was expected to be directed toward or away from the transducer. Velocity measurements for the internal cerebral vein (Fig 4⇓) were performed where the vessel lies between the two layers of the tela choroidea of the third ventricle and describes a flattened sine wave in the sagittal plane. The flow was expected to be directed toward the transducer. The basal vein was insonated in its third (posterior, posterior mesencephalic) segment. The flow was expected to be directed toward the transducer. For diagnosis of the basal vein, the visualization of a trifurcation consisting of the basal, internal cerebral, and great cerebral veins was required.
The number of identified cerebral sinuses and veins was registered. The angle of insonation was maximally 60°. PSV and PDV were determined with the corresponding insonation angles and depths. For evaluation of the pulsatility in sinovenous structures and because reliable delineation of peak mean velocity is difficult for cerebral veins and sinuses, the resistance index was calculated for each vessel as PSV−PDV/PSV.9
Statistical analysis was performed with the Systat software package. Comparison of the data between age groups was performed with nonparametric ANOVA (Mann-Whitney U test). Two-sided values of P<.05 were considered significant. Correlation of blood velocities and resistance indices with age was performed with Pearson’s correlation coefficient.
The number of identified straight sinuses and great and internal cerebral veins according to sex and age is given in Table 1⇓. All inferior sagittal sinuses and basal veins were missed. Transoccipital insonation identified more vessels in women than in men (P<.01). The straight sinus and internal cerebral vein were less frequently detected with age when the group aged 20 to 39 years was compared with the group aged 60 to 79 years (straight sinus, P<.05; internal cerebral vein, P<.01) and the group aged 40 to 59 years was compared with the group aged 60 to 79 years (straight sinus, P<.01).
Velocity data according to sex and age are given in Table 2⇓. The velocities were highest in straight sinuses, slower in great cerebral veins, and slowest in internal cerebral veins. In particular, PDV values showed a trend to decline with age. This trend was significant when the group aged 20 to 39 years was compared with the group aged 60 to 79 years (straight sinus: PSV, P<.01; PDV, P<.001; internal cerebral vein: PDV, P<.05) and the group aged 40 to 59 years was compared with the group aged 60 to 79 years (straight sinus: PDV, P<.01; internal cerebral vein: PDV, P<.05). Velocities in the straight sinus declined with age as analyzed with Pearson’s correlation coefficient (PSV: r=.38, P<.001; PDV: r=.50, P<.001). Women showed higher straight sinus velocities than men in the group aged 20 to 39 years (P<.05).
As shown in Table 3⇓, the resistance indices were higher for the straight sinus (0.35 [0.18 to 0.52]) than for the great (0.30 [0.17 to 0.43]) and internal (0.29 [0.11 to 0.47]) cerebral veins (P<.001) (mean with 95% CIs) but did not differ between sexes. The resistance indices increased with age only in the straight sinus (20 to 39 years, 0.30 [0.18 to 0.42]; 40 to 59 years, 0.36 [0.12 to 0.53]; 60 to 79 years, 0.42 [0.31 to 0.53]) (mean with 95% CIs), since they were higher in the oldest than in the youngest age group (P<.001). There was an increase in straight sinus resistance indices with age as analyzed with Pearson’s correlation coefficient (r=.54, P<.001).
The mean angles and depths of insonation did not differ with age and between sexes in all detected vessels. Mean (95% CI) insonation angles were for the straight sinus 3° (0° to 22°), for the great cerebral vein 43° (0° to 57°), and for the internal cerebral vein 0° (0° to 0°). Mean (95% CI) insonation depths were for the straight sinus 56 (44 to 67) mm, for the great cerebral vein 65 (55 to 75) mm, and for the internal cerebral vein 73 (63 to 84) mm.
In recent years frequency-based TCCD has become a well-established technique for the assessment of the major basal cerebral arteries.1 2 3 In contrast, the intracranial sinovenous system of adults was considered inaccessible to transcranial ultrasound. Meanwhile, Aaslid et al6 reported successful insonation of the straight sinus using conventional transcranial Doppler sonography through the occipital bone. Recently, the transtemporal window has been used by means of conventional Doppler sonography and frequency-based TCCD to investigate the straight sinus and deep middle cerebral and basal veins in adults with normal and thrombosed cerebral veins and sinuses.10 11 12 13 Power Doppler sonography is a new method of color imaging that overcomes some shortcomings of frequency-based TCCD, since it is essentially independent of the angle of insonation, not subject to aliasing, and has a better signal-to-noise ratio.5 The latter property allows the gain to be increased in power-based sonography over the level at which noise begins to obscure frequency-based color Doppler images. Therefore, power-based TCCD should be the most accurate technique for ultrasonic assessment of the slow cerebral sinovenous flow.
In the present study power-based transoccipital insonation of subjects aged 20 to 59 years identified the straight sinus in 81%. In contrast, detection of the great and internal cerebral veins was poor, and the inferior sagittal sinus and basal vein were missed in all subjects. This difference in detection probably results from both the larger caliber and the smaller depths used for insonation of the straight sinus compared with the other cerebral veins and sinuses.14 15 As expected from transcranial insonation of cerebral arteries, in subjects older than 60 years detection was lower for the straight sinus and poor for the great and internal cerebral veins. Using the same transoccipital approach and conventional transcranial Doppler sonography, Aaslid et al6 detected the straight sinus in nine of 12 healthy adults with a mean age of 33 years. With the use of the transtemporal approach, frequency-based TCCD was reported to detect the straight sinus in 73% of 30 normal subjects with an average age of 49 years.10
As expected, transoccipital insonation of the medially and paramedially located great and internal cerebral veins furnished lower insonation angles than the transtemporal approach.16 Thus, it is assumed that insonation of the internal cerebral vein where it describes a flat curve in the roof of the third ventricle7 will lead to adequate velocity measurements. However, the low resolution of the color Doppler signal and the short length of the great cerebral vein provide some limitations to angle-corrected velocimetry in this vessel.
Transtemporal conventional transcranial Doppler sonography was reported to detect the basal vein in 93% of normal subjects with a mean age of 42 years.12 These findings suggest that the combination of transoccipital with transtemporal TCCD will improve the ultrasonic assessment of the deep sinovenous system. Using contrast-enhanced, frequency-based transtemporal TCCD, Bogdahn et al16 were able to delineate the inferior sagittal sinus, the internal and great cerebral veins, and the straight sinus in 70% of patients with a mean age of 51 years. Using the same ultrasound technique and MR venography as standard of reference, Ries et al17 evaluated 20 of 22 examined transverse sinuses correctly in 11 patients with sinovenous thrombosis and a mean age of 53 years. Therefore, the use of ultrasound contrast agents may further increase the frequency of TCCD detection of cerebral sinuses and veins.
Surprisingly, and in contrast to transtemporal insonation of cerebral arteries, the transoccipital approach detected more sinuses and veins in women than men. The low number of examined subjects, however, precludes a generalization of this finding, and further studies are needed.
Velocities were highest in the straight sinus, slower in the great cerebral vein, and slowest in the internal cerebral vein. These findings suggest that velocities correlate positively with increasing vessel diameter and demand of blood flow. Straight sinus velocities and resistance indices found in the present study were similar to the results obtained by conventional transoccipital insonation.6 Conversely, Becker et al10 detected slower velocities with a less pulsatile character using the transtemporal approach. Transtemporal insonation, however, resulted in less favorable insonation angles and greater insonation depths.10 This increased the attenuation of the ultrasound beam, which may have impaired the quality of the Doppler spectra. Moreover, the straight sinus has an oblique course in the sagittal plane with a mean angle of 41°, with the “Deutsche Horizontale” reflecting a line that joins the deepest part of the orbit with the upper edge of the external acoustic meatus. Therefore, transtemporal TCCD may have underestimated straight sinus velocities due to inadequate rotation of the transducer in the sagittal plane.
Velocities decreased with age in the straight sinus and the internal cerebral vein. This finding is in accordance with the results of several studies using different techniques showing that cerebral blood flow and velocities in arteries and sinuses of the brain decrease with age.3 18 19 20 21 22 Straight sinus velocities were faster in women than men in the youngest age group. These results agree with those of several studies showing that premenopausal women have higher cerebral artery velocities and blood flow than men.3 23 24
The resistance indices were small in this series, indicating lower pulsatility of sinovenous compared with arterial flow. Moreover, the resistance indices increased with age in both sexes, probably reflecting the age-dependent increase of arterial pulsatility. As expected, the resistance indices were lower in deep cerebral veins than in the rigid-walled straight sinus.25
In summary, we have demonstrated that transoccipital power-based TCCD enabled imaging and velocity measurement in the straight sinus of normal adults younger than 60 years of age, whereas detection of deep cerebral veins was insufficient. A combination of the transtemporal approach and the use of ultrasound contrast agents may increase the number of detected sinuses and veins. Patients with sinovenous thrombosis are rarely older than 60 years of age.26 Therefore, TCCD may supply hemodynamic information and prove useful in noninvasive follow-up of the treatment of such patients, but it should not be the first-line diagnostic test. Because the walls of cerebral sinuses are rigid,25 insonation of the straight sinus may prove useful for monitoring6 the effects of various disease processes and factors such as pharmaceutical agents on cerebral blood flow.
Selected Abbreviations and Acronyms
|PSV||=||peak systolic velocity|
|PVD||=||peak end-diastolic velocity|
|TCCD||=||transcranial color-coded duplex sonography|
- Received November 14, 1996.
- Revision received March 24, 1997.
- Accepted April 14, 1997.
- Copyright © 1997 by American Heart Association
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