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59Special Arterial Anatomy and Ultrasound Anatomy

Valdueza et al., Neurosonology and Neuroimaging of Stroke: A Comprehensive Reference, Second Edition (ISBN 978-3-13-141872-2), copyright © 2017 Thieme Medical Publishers All rights reserved. Usage subject to terms and conditions of license.

Fig. A2.119 TCCS , tr anste mpor al i nsonati on, midb rain plan e. Midbrain traced in white. Right: Color-mode imaging of the proximal PCA. (A) Proximal P2-PCA. (B) Anterior temporal artery. (C) Distal P2-PCA. (D) Occipitotemporal artery. Left: Doppler spectrum analysis of vessel segments in A–D: (A) 60/31 cm/s, (B) 36/16 cm/s, (C) 57/29 cm/s, (D) 49/20 cm/s.

Fig. A2.121 TCCS , t rans tempo ral insona tion , t hala mic p lane. T h a l a m u s t r a c e d i n w h i t e , p i n e a l g l a n d t r a c e d i n y e l l o w . Right: Color-mode imaging of the distal PCA. (A) P3-PCA. (B) Calcarine artery. (C) Parietooccipital artery. (D) Basal vein of Rosenthal. Left: Doppler spectrum analysis of vessel segments in A–D: (A) 47/24 cm/s, (B) 30/14 cm/s, (C) 35/23 cm/s, (D) 12/9 cm/s.

Fig. A2.120 TCCS , tr anste mpor al i nsonati on, midb rain plan e. Midbrain traced in white. Color-mode imaging of the proximal (arrow) and distal OTA (arrows).

Posterior Communicating Artery (PCoA)

Anatomic details: The PCoA connects the anterior and the posterior circulation. Posteriorly it inserts between the P1 and the P2 segment. The vessel has a mean length of 14 mm (range 12–17 mm). The diameter is, however, highly variable with a mean caliber of 1.2 mm (range 0.5–

3.3 mm). In ~40% of cases, a diameter larger than 2 mm can be found, which should be wide enough to provide collateral ﬂ ow if necessary. About 20% have a diameter of less than 1 mm. Interestingly, vessel diameters in children seem to be larger than in adults (Padget 1944).

Fig. A2.122 TCCS, tra nstempora l insonat ion, midbrain p lane. I mages of a stroke patient with chronic M1-MCA occlusion after osteoclastic trepanation. (A) Color-mode imaging of the PCA. Calcarine artery encircled in yellow. (B) Calcarine artery, blood ﬂ ow velocity at rest 32/12 cm/s. (C) Calcarine artery, blood ﬂ ow velocity during a visual task 42/22. Note a systolic and diastolic ﬂ ow increase of 31% and 83%, respectively.

60 2 Vascular Anatomy and Structure of Ultrasound Examination

0–20 years

Normal 100% 93% 35%

0% 7% 65%Tor tu ou s

Fig. A2.123 Anatomic variants of the PCoA in relation to age. (Adapted from Huber 1982.)

21–50

years

51–74

years

The vessel may run a straight or a tortuous course (Fig. A2.123), the latter being more frequent in the older population.

An important variant is the fetal-type PCA (FT-PCA) in which the PCA directly originates from the ICA without connection to the BA. Such a “complete” FT-PCA however, is rare, as postmortem analysis mostly reveals the existence of a small vessel bridge, i.e., a hypoplastic P1 segment (Saeki and Rhoton 1977). This variant, which can today often be depicted by neuroimaging techniques, should then be called a partial FT-PCA. However, the criteria for diﬀ erentiating between a par- tial FT-PCA and a strong PCoA are inconsistent. For instance, from a morphologic point of view a FT-PCA can be assumed to be present if the PCoA diameter equals the diameter of the other basal cerebral arteries. If a PCoA diameter of greater than 2 mm is used as a cutoﬀ value, FT-PCA can be found in 12% of hemispheres (Lang 2001). A more pragmatic approach is to deﬁ ne an FT-PCA whenever the PCoA diameter exceeds the P1 diameter, which has been found in 22% of hemispheres (Lang 2001). Saeki and Rhoton (1977) reported similar ﬁ ndings of 20% unilateral and 2% bilateral FT-PCA. Other published anatomic data vary between 15% and 36% (see overview in van Raamt et al 2006).

Position and vessel identiﬁ cation: The PCoA is insonat- ed via the axial transtemporal approach and is usually detected between the upper pontine and midbrain plane (Fig. A2.48 and Fig. A2.50). In normal-type PCA the PCoA usually arises where anterior and posterior circulation vessels are located closest together (Fig. A2.124). It is noteworthy that in marked vessel elongations the posterior and anterior vessels may lie closely together and PCoA identiﬁ cation might be i m p o s s i b l e ( Fig. A2.125). In real fetal-type PCA the P2 arises directly from the ICA, showing an almost straight course from the distal ICA (Fig. A2.126). If ﬂ ow measurement is possible, velocities and ﬂ ow pattern correspond to the signal of the P2 segment. In these cases, an obvious P1 signal should be absent. If it is assumed to be present, confusion with the SCA signal

Fig. A2.124 Left: MRI 3D TOF-MRA, axial MIP, 90° counterclockwise rotated to correspond with ultrasound image. Right: TCCS, transtemporal approach, axial midbrain plane. Midbrain encircled in white (right). Top left: Ipsilateral normal type PCA and small PCoA on the contralateral side. Top rig ht: Cerebral arterial circle (circle of Willis) with normal anterior and posterior circulation anatomy with P1 and P2 PCA arising from the BA head. Bottom left: Fetal-type PCA of the ipsilateral PCA and small PCoA on the contralateral side. Bottom right: Distal ICA (arrow) with branch-oﬀ of the fetal-type PCA (arrows). Note the straight course of the proximal PCA characteristic of this variant.

has to be assumed. Between both extremes—normal and complete fetal-type PCA—the PCoA appearance may vary greatly. Depending on the PCoA caliber the PCA blood supply may be mainly via P1-PCA or PCoA itself. In a dominant PCoA, the P1-PCA ﬂ ow signal is correspondingly reduced; in a dominant P1-PCA the same occurs in the PCoA. In some cases a physiologic biphasic ﬂ ow pattern may even be observed in the PCoA and a steal-like signal in a hypoplastic P1-PCA (Fig. A2.127; Video

A2.35).

In a group of young healthy subjects (mean age 38 years) a PCoA ﬂ ow was observed unilaterally in 70% and bilaterally in 30%. The ﬂ ow direction was toward the ICA in ~75% of cases (Klötzsch et al 1996b). In an older population (mean age 61 years) only 13% of vessels were detected in all cases with a ﬂ ow from the ICA to the PCA (Hoksbergen et al 2000b). Vessel identiﬁ cation might, however, be impaired due to a low net ﬂ ow or an elon- gated vessel course. The latter can lead to a bidirectional PCoA ﬂ ow, which may partly explain the discrepant published ﬁ ndings on the direction of its ﬂ ow, which

61General Venous Anatomy

Fig. A2.125 TCCS , trans temp oral appr oach , axial m idbrain pla ne. Left: Color-mode image showing an attached course of ICA, PCA,

and SCA. This “kissing artery” constellation may be problematic if using the TCD technique. Right: Corresponding Doppler spectrum analysis: top—ICA (36/16 cm/s), middle—PCA (41/19 cm/s), bottom—SCA (47/21 cm/s). The low ICA ﬂ ow velocities are caused by the unfavorable insonation angle in the axial plane.

in our experience is almost always directed toward the posterior circulation. In the FT-PCA variant the PCoA becomes a strong vessel frequently visible on color-mode TCCS. Applying the CCA compression test, Hoksbergen and coworkers (2000b) found an FT-PCA—deﬁ ned as re- duction or cessation of ﬂ ow in the PCoA—in 6.5% of hem- ispheres and 13% of cases. However, this test cannot be recommended as a routine procedure, both because of the inconvenience for the patient caused by the applied supraclavicular pressure and because of the 0.4% risk of triggering transient ischemia (Jatuzis et al 2000). Individual cases have even been reported to suﬀ er a manifest ischemic stroke (Khaﬀ af et al 1994). Instead, we suggest the use of a tap test for analysis of PCA blood supply. Similar to the superﬁ cial temporal artery tap maneuver for ECA/ICA diﬀ erentiation, the eﬀ ects of ipsilateral subman- dibular extracranial digital ICA tapping and extracranial digital V3-VA tapping of the dominant VA onto the P2or P3-PCA waveforms can be analyzed. A stronger eﬀ ect caused by ICA tapping favors the diagnosis of an FT-PCA and a stronger eﬀ ect caused by VA tapping favors a regu- lar-type PCA (Fig. A2.128; see also Video

A2.36). Using

this technique, a 17% FT-PCA prevalence has been found, which is in good agreement with the results of the published CCA compression test data (Siemieniec et al 2006) (for fur ther infor mation , see Chapter 5, “Fetal-t ype Posterior Cerebral Artery” under “Collateral Pathways”).

Normal values: For ﬂ ow velocities see Table A2.3.

General Venous Anatomy

For many years, ultrasound studies of the cerebral arteries have almost exclusively been the focus of scientiﬁ c research and clinical application. Reasons for the

Fig. A2.126 Left: MRI 3D TOF-MRA, axial MIP, 90° counterclockwise rotated to correspond with ultrasound image. Fetal-type PCA of the ipsilateral PCA and normal-type PCA on the contralateral side. Right: TCCS, transtemporal approach, axial midbrain plane, midbrain encircled in white. Good color-mode signal of the anterior circulation (arrow) and the fetal-type PCA origin (arrows) with an undisturbed Doppler spectra signal with a ﬂ ow away from the probe (58/28 cm/s).

Fig. A2.127 Left: MRI 3D TOF-MRA, axial MIP, 90° counterclockwise rotated to correspond with ultrasound image. Partial fetal-type PCA (arrows) of the contralateral PCA with a short P1 segment (arrow) and a normal PCA on the ipsilateral side. Right: TCCS, transtemporal approach, axial midbrain plane: Color-mode signal demonstrating corresponding anatomy. Note that the P1-PCA Doppler spectrum shows a biphasic ﬂ ow pattern, indicating P1 hypoplasia.

relative lack of understanding of the venous part of the cerebral circulation have been the lower absolute numbers of purely venous diseases, the assumed greater anatomic variability of veins and sinuses, and technical limitations of analysis of “low ﬂ ow” vessels. However, the intracranial venous circulation, assumed to be 60– 70% of the global cerebral blood volume, has an important role in the equilibrium of cerebral perfusion and is involved in a variety of arteriovenous pathologies, e.g., AVM s a nd dur al ﬁ stulas, and in primary venous diseas- es such as cerebral sinus and venous thrombosis.

62 2 Vascular Anatomy and Structure of Ultrasound Examination

P2-R while tapping ICA-R

P2-R while tapping ICA-L

Fig. A2.128 Ultrasound determination of right fetal-type PCA. Left column: Top: Digital tapping of the right submandibular ICA;

middle: Marked transient signal changes in the right P2-PCA in- duced by tapping of the right ICA; bottom: No signal changes in the right P2-PCA during tapping of the left ICA. Middle column:

Top : Digital tapping of the right V3-VA at the atlas loop; middle, bottom: Slight transient signal changes in the right P2-PCA during

tapping of the left and right V3-VA. Right column: Top: TOF-MRA, 3D-reconstruction: Note the fetal-type PCA (arrow) and absence of the right P1-PCA; bottom: TCCS , tran stemp oral appro ach, a xial u pper pontine insonation plane: Corresponding color-mode image. Note the strong right PCA signal originating directly from the ICA (arrow). Note the site of insonation of the right P2-PCA (marked in yellow).

P2-R while tapping V3-R

P2-R while tapping V3-L

The potential pathophysiologic role of the cervical and cerebral venous system in several other diseases, including transient global amnesia (Akkawi et al 2001, Sander and Sander 2005, Sander et al 2000, Schreiber et al 2005a), idiopathic intracranial hypertension (Nedelmann et al 2009a), primary exertional headache (Doepp et al 2008b), age- related white matter lesions (Chung et al 2011), amaurosis fugax (Hsu et al 2008), or even in acute arterial stroke (Pranevicius et al 2011, Yu et al 2009) is currently debated. The most controversial theory during the last years, however, has been the so-called “chronic cerebrospinal venous insuﬃ ciency” and its pathophysiologic role in multiple sclerosis (Zamboni 2006; Zamboni et al 2009). After numerous studies a causative relationship between venous drainage abnormalities and multiple sclerosis can be refuted (Baracchini et al 2012b, Comi et al 2013, Doepp et al 2010, Siddiqui et al 2014, Valdueza et al 2013).

In contrast to the arteries with their Windkessel function, the intracranial veins and sinuses are mainly blood ﬂ ow conductors. Two more important diﬀ erenc- es from the general venous system should be mentioned here. First, intracranial venous vessels do not collapse, even if the transmural pressure is zero—e.g., in an upright body position. Second, there is complete absence of any venous valves up to the level of the IJVs, permitting free blood ﬂ ow in any direction depending on need.

Intracranial Venous Anatomy

The intracranial veins can be divided into a larger superﬁ cial venous system draining the blood from the

hemispheres and a smaller deep venous system collecting blood from the thalamus, white matter, and basal ganglia. The superﬁ cial veins over both hemispheres connect to a vascular network which can be classiﬁ ed, according to the common ﬂ ow direction, into ascend- ing and descending veins. The ascending veins take the blood via 10–12 bridging veins into the superior sagittal sinus (SSS). The most prominent of these veins is the superior anastomotic vein (vein of Trolard), located in the postcentral region. The most prominent descending superﬁ cial veins are the inferior anastomotic vein (vein of Labbé), draining into the transverse sinus (TS), and the sylvian vein, also called superﬁ cial middle cerebral vein, predominantly draining into the sphenoparietal sinus (SpPS) (Fig. A2.129, left).

The main deep cerebral veins are the paired basal veins of Rosenthal (BVR) collecting blood from both anterior cerebral veins (ACVs) and both deep middle cerebral veins (DMCVs), the internal cerebral veins (ICVs) with their tributaries, the thalamostriatal veins and septal veins of the cavum septum pellucidi. The BVR and ICV ﬂ ow into the unpaired great cerebral vein (vein of Galen, VG) which along with the inferior sagittal sinus (ISS) merge to form the straight sinus (StS) (Fig. A2.129, right and Fig. A2.130).

The venous sinuses are the ﬁ nal recipients of the blood. In contrast with the other intracranial veins they have an almost ﬁ xed diameter as they are surrounded by an inﬂ exible dural sheath. The StS and SSS merge oc- cipitally at the conﬂ uence of sinuses (CoS) and split into the paired TSs which then take the blood via the sigmoid sinus (SiS) into the IJVs. Besides the CoS the paired cavernous sinus (CS) is another major blood-collecting and distributing venous segment, especially in younger subjects. It collects blood from the orbit and from the sylvian veins mainly via the SpPS. From there the blood can be distributed via the inferior petrosal sinus (IPS) or superior petrosal sinus (SPS) into the IJVs or alternatively via the emissaries of the skull base into the pterygoid plexus (Fig. A2.130).

Extracranial Venous Anatomy

For a long time the paired IJVs were thought to be the main cerebral drainage pathways, collecting the blood via the superior jugular bulb from the SiS and the IPS (Fig. A2.131). However, several studies have shown that the jugular drainage strongly depends on body position. In the supine position the main drainage in most individuals indeed follows the IJVs. However, changing to an upright position leads to a dramatic reduction and frequently even complete cessation of jugular blood ﬂ ow (Valdueza et al 2000). At the same time an increase in blood ﬂ ow can be detected in the vertebral venous system (VVS) which is frequently omitted in anatomic textbooks (Fig. A2.132). It consists of a complex vessel conﬁ guration with several longitudinal valveless chan- nels, connected via multiple segmental anastomoses. The total cross-sectional area of the VVS surpasses that of the IJVs (Batson 1944). The VVS can be divided into the anterior and posterior intraspinal segments and the anterior and posterior extraspinal segments. The

63General Venous Anatomy

Fig. A1.129 Schematic of the cerebral venous system. 1 = sylvian vein (superﬁ cial middle cer- ebral vein); 2 = superior anastomotic vein (vein

of Trolard, postcentral vein); 3 = inferior anastomotic vein (vein of Labbé); 4 = Rolandic vein

(central vein) 5 = anterior cerebral vein; 6 = deep

middle cerebral vein; 7 = basal vein of Rosenthal; 8 = internal cerebral vein; 9 = great cerebral vein

(vein of Galen). Venous vessel segments accessi-

ble with duplex sonography are shown in blue. (Adapted from Feneis 1970.)

15 14 13 12 11 10 9 8

6 7

anterior intraspinal segment probably has the greatest drainage capacity. It lies within the epidural fatty tissue and its veins have a diameter up to several millimeters (Eckenhoﬀ 1971). It receives blood at the craniocervical junction in a complex manner via the anterior, lateral, and posterior condylar veins which themselves receive blood via the condylar conﬂ uence from the IPS, superi- or jugular bulb, and basilar plexus (San Millán Ruíz et al 2002). The posterior intraspinal segment is usually small and not well developed; it receives blood from the CoS via the occipital sinus. The anterior extraspinal segment is probably of little signiﬁ cance. It is connect- ed to the CS via the pterygoid plexus and the pharyngeal plexus. More important is the posterior extraspinal segment which consists of the vertebral veins (VVs) and the deep cervical vein(s). The former develop from the suboccipital venous plexus with anastomoses to the anterior, lateral, and posterior condylar veins, in great part surrounding the VAs, and run parallel as single or doubled vessels to the VAs through the transverse processes of the cervical vertebra C1–C6. There are multiple radicular veins, like a rope-ladder connecting with the anterior intraspinal segment via the neural foramina. The deep cervical vein receives blood from the SiS via the mastoid emissary and runs as a singular vessel

Fig. A1.130 Schematic of the cerebral venous system. 1 = superior sagittal sinus; 2 = inferior sagittal sinus; 3 = internal cerebral vein; 4 = great cerebral vein (vein of Galen); 5 = straight sinus;

6 = conﬂ uence of sinuses; 7 = transverse sinus; 8 = basal vein of Rosenthal; 9 = sigmoid sinus; 10 = internal jugular vein, 11 = basilar plexus; 12 = inferior petrosal sinus; 13 = cavernous si-

nus; 14 = pterygoid plexus; 15 = sphenoparietal

sinus; 16 = superior petrosal sinus. Venous vessel

segments accessible with duplex sonography are

shown in blue. (Adapted from Feneis 1970 and Huber 1982.)

9 6

7 6

Fig. A2.131 Schematic of the jugular drainage system (right: adapted from Schünke et al 2006; drawing: Karl Wesker). 1 = superior sagittal sinus; 2 = conﬂ uence of sinuses; 3 = sigmoid sinus; 4 = superior bulb of the internal jugular vein; 5 = pterygoid plexus; 6 = suboccipital plexus; 7 = internal jugular vein (IJV); 7-1 = IJV segment 1; 7-2 = IJV segment 2; 7-3 = IJV segment 3 with valves; 8 vertebral vein (VV); 8-1= VV segment 1 with valves;

8-2 = VV segment 2; 8-3 = VV segment 3; 9 = deep cervical vein; 10 = anterior intraspinal segment of the vertebral venous system; 11 = subclavian vein. Black dotted lines indicate the clavicle.

64 2 Vascular Anatomy and Structure of Ultrasound Examination

Fig. A2.132 Schematic of the vertebral venous system. Left: The ramiﬁ ed intraspinal segment of the vertebral venous system is demonstrated in this historical picture (adapted from Bock 1823). The vertebral veins are indicated by arrows. Right: Schematic drawing of the cervical spine (brown), cervical spinal cord and roots (yellow), transverse plane: Vertebral venous system. 1 = anterior intraspinal segment; 2 = posterior intraspinal segment; 3 = vertebral vein as part of the posterior extraspinal segment; 4 = anterior extraspinal segment; 5 = transverse radicular veins vein communicating between the extraspinal and intraspinal venous vessels. Note also the small segmental communicating veins between the anterior and posterior intraspinal longitudinal orientated veins.

or in form of multiple vessels in between the posterior muscles of the neck. It may also connect via segmental anastomoses to the VVs. The VVs and deep cervical vein frequently drain into the brachiocephalic or subclavian vein. However, they may also merge into the IJV before draining into the brachiocephalic and superior vena cava. Fig. A2.133 summarizes the extracranial venous anatomy.

General Structure of Venous Ultrasound Examination

For insonation of the cerebral veins, as for the insonation of the arteries supplying the brain, the patient should lie in a comfortable supine position. In general, the access paths and transducers used are also identical. However, the system settings, including ﬁ lters and the PRF, have to be adjusted for the analysis of low-velocity signals, i.e., ﬁ lters have to be switched oﬀ and the PRF must be re- duced. For extracranial examination the patient’s head needs to be in a straight position to avoid ﬂ ow altera- tions caused by unilateral or bilateral venous outﬂ ow obstruction. Also, care must be taken not to compress vessels, e.g., the IJV when the transducer is applied to the skin of the neck, if reliable velocity measurements are to be taken. Because of the strong dependency of venous outﬂ ow on body position, the patient should preferably be studied in a completely supine position and if possible without elevating the head. As in arterial insonation, we generally recommend angle-corrected extracranial measurements and noncorrected intracranial measurements.

Fig. A2.133 Anatomy of the extracranial venous drainage pathways. (A) DSA, right IJV injection. (Reproduced from Théron and Djinjdjian 1973.) (B) 3D time-resolved MRA. 1 = internal jugular vein; 2 = vertebral vein; 3 = intraspinal segment of the vertebral venous system. Note the craniocervical junction with condylar conﬂ uence and anterior, lateral, and posterior condylar veins, with outﬂ ow to the superior jugular bulb and the vertebral venous system (arrowheads).

Special Venous Anatomy and Ultrasound Anatomy

The following section is ordered according to the ﬂ ow of blood from the brain toward the heart, i.e., from the distal intracranial to the proximal cervical vessels. Instructions for insonation focus on duplex ultrasound only. However, the reported normal values for ﬂ ow velocities might also have been derived from TCD studies. TCD also allows analysis of the intracranial venous vessels but, even more than in the arterial system, has clear limitations because of the lack of spatial orientation (Aaslid et al 1989, Doepp et al 1999, Valdueza et al 1996, 1998). Fusion imaging with MRI facilitates venous vessel assignment, especially if no well-deﬁ ned relationship to an artery is present (for fusion imaging see also Video of reported normal values for ﬂ ow velocities are sum- marized in Table A2.4. For all relevant veins and sinuses, further video examples are available online in the Thieme MediaCenter.

Intracranial Veins and Sinuses

As in the examination of intracranial arteries a sector transducer with transmission frequencies of 1–3 MHz is required for vessel analysis. A low PRF facilitates the detection of venous vessels. The intraobserver and interobserver variability is low if non-angle-corrected velocities are used (Stolz et al 2001). Venous ﬂ ow velocities can vary greatly in the inﬂ ow and outﬂ ow regions of vessels. Flow velocity analysis should only be done if the vessel is clearly visible. Measurements at junctions with other vessels should be avoided.

A2.37). Reference data

65Special Venous Anatomy and Ultrasound Anatomy

Deep Middle Cerebral Vein (DMCV)

Anatomic details: The DMCV is found in up to 80% of

cases and receives blood from the insular region and the caudal parts of the striatum. It runs directly adjacent to the MCA. At the level of the optic chiasm it unites with the ACV to form the BVR. Sometimes it may directly drain via a sylvian vein into the CS.

Position and vessel identiﬁ cation: The vessel is visualized via the transtemporal bone window using the axial midbrain plane (Fig. A2.134; see also Video ommend starting insonation by identifying the color signal of the distal M1-MCA segment in its transition to the M2 segment where the DMCV is best insonated. In most cases a visual diﬀ erentiation between the opposite-color- ed signals of the MCA and DMCV will not be possible because the aliasing phenomenon using a low PRF will cover the weak venous signal. In M1-MCA occlusion the DMCV becomes clearly visible. If the distance between the artery and vein is large enough the DMCV may be detected over a short distance posterior to the MCA. Doppler analysis reveals a venous spectrum in 64–91% of cases if the Doppler sample volume is positioned within the posterior border of the MCA color signal. The ﬂ ow direction is away from the probe (Fig. A2.135). Only rarely can the transition into the BVR be visualized (Fig. A2.136).

A2.38). We rec-

Fig. A2.134 MRI, T2-weighted image, axial plane (A) and coro- nal plane (B). MR contrast-enhanced T1-weighted image, sagittal plane (C). Insonation ﬁ eld and transducer position for examina- tion of the DMCV, BVR, ICV, and VG.

Normal values: For ﬂ ow velocities see Table A2.4.

Basal Vein of Rosenthal (BVR)

Anatomic details: The BVR is a very constant vein draining parts of the frontobasal brain, the hippocampal and parahippocampal region, the uncus, the limbic system, the hypothalamus, the mesencephalon, the basal ganglia, the internal capsule, and the insular region. The vessel can be divided into three segments. In its classic variant, the anterior segment evolves from the conﬂ uence of the DMCV, inferior thalamostriatal vein, and ACV. In its middle segment it runs parallel and superior to the P2-PCA and proximal P3-PCA segments in the ambient cistern circumscribing the midbrain. The third, posterior segment starts at the back end of the mesencephalon where it either merges into the ICV or the VG and in only 8% of cases directly into the StS. However, in its middle segment it may also turn caudally to merge via the petrosal vein and into the SPS.

Position and vessel identiﬁ cation: The BVR is best in- sonated in its distal segment via the transtemporal bone window using the axial thalamic plane. More proximal parts can be visualized in the midbrain plane (Fig. A2.134). We recommend starting insonation by identifying the color signal of the distal P2-PCA segment. In several cases the suspected PCA turns out to be the BVR as both vessels have identical ﬂ ow directions. The BVR may have a larger diameter than the PCA, which may then lead to a stronger color signal. The proximal BVR is found lateral to the proximal P2-PCA segment, and similar to the PCA with a ﬂ ow toward the transducer.

Fig. A2.135 (A) Schematic, axial plane. Note the blue DMCV (arrows). (B) TCCS, transtemporal approach, midbrain axial plane. Color-mode imaging of the DMCV visible as a small blue-coded segment (arrows). Note the presence of a blue-coded M2-MCA branch with a ﬂ ow direction away from the probe (arrowhead). (C) CTA, axial MIP. DMCV (arrows) in close spatial relation, posterior of the MCA. Note again the prominent M2 MCA branch (arrowhead). (D) Doppler spectrum analysis of the DMCV (ﬂ ow velocity 12/9 cm/s) with a ﬂ ow away from the probe.

The distal BVR, which is easier to detect, runs medial and superior to the distal P2-PCA and P3-PCA segments with a ﬂ ow direction away from the transducer (Figs. A2.137 and A2.138). Sometimes the BVR and the distal P2 and P3-PCA segment can be identiﬁ ed as two parallel blue-coded vessel segments, the vein medial, the artery lateral (Fig. A2.139; see also Video

A2.39).

Normal values: For ﬂ ow velocities see Table A2.4.

Internal Cerebral Vein (ICV)

Anatomic details: The ICV originates from the conﬂ uence

of the thalamostriatal vein and septal vein of the cavum

66 2 Vascular Anatomy and Structure of Ultrasound Examination

Fig. A2.136 (A) CTA, axial MIP, 90° counterclockwise rotated to correspond with the ultrasound image. Image illustrating the DMCV vessel course merging into the BVR (arrow). (B) TCCS, transtemporal approach, midbrain axial plane. Color-mode image of a prominent blue-coded DMCV segment (arrow) located between the proximal M1-MCA and the proximal P2-PCA. (C) Doppler spectrum analysis of the DMCV (ﬂ ow velocity 11/9 cm/s) with a ﬂ ow direction away from the probe.

Fig. A2.138 Top: Doppler spectrum analysis (left) and colormode imaging (right) of the BVR (ﬂ ow velocity 12/10 cm/s) with a ﬂ ow toward the probe. Note the simultaneous registration of the BVR and the proximal P2-PCA spectrum while color mode suggests presence of a single vessel. Bottom: Doppler spectru m analysis (left) and color-mode imaging (right) of the BVR (ﬂ ow velocity 14/11 cm/s) with a ﬂ ow away from the probe. Note the simultane- ous registration of the BVR and the distal P2-PCA spectrum while color-mode suggests presence of a single vessel.

septum pellucidi at the level of the interventricular foramen (foramen of Monro). It develops in 100% of cases and follows a constant course along the thalamus within the tela choroidea of the third ventricle. It mainly drains the upper and medial aspects of the thalamus. The paired veins unite with each other and together with the BVR to form the VG.

Fig. A2.137 (A) Schematic, axial plane: Note the blue-colored BVR. (B) TCCS, transtemporal approach, axial midbrain plane (midbrain encircled): Color-mode imaging of the BVR as a blue-coded segment. (C) MRI T2-weighted image, axial plane: Note the DMCV merging into the BVR which encircles the midbrain (arrows). Here the PCA runs medial to the BVR. (D) Doppler spectrum analysis of the BVR (ﬂ ow velocity 15/12 cm/s) with a ﬂ ow away from the probe. Note the simultaneous imaging of the PCA and BVR spectrum despite the color image demonstrating only one vessel signal.

Position and vessel identiﬁ cation: The ICV can only rare- ly be insonated through the transtemporal bone window using an approach between the thalamic and cella media planes. The ipsilateral and contralateral ICVs can be detected with a ﬂ ow away from and toward the transducer respectively. Compared with the transtemporal access (23%) (Stolz et al 1999c). higher rates (52%) have been reported using the unusual transfrontal bone window (Stolz et al 1999b) (Fig. A2.140).

Normal values: For ﬂ ow velocities see Table A2.4.

Great Cerebral Vein or Vein of Galen (VG)

Anatomic details: The VG is located in the quadrigemi-

nal cistern. It is a short unpaired vessel draining into the StS. The angle between the VG and the StS varies between over 90° (10% of cases), 30–90° (60% of cases), and less than 30° (30% of cases).

Position and vessel identiﬁ cation: The VG can be easily in- sonated through the transtemporal bone window using an axial thalamic insonation plane in the midline posterior to the hyperechoic pineal gland. It can also be found by following the signal of the BVR until its junction with the VG (Fig. A2.141; see also Video turns into the StS can usually not be distinguished. Reported success rates for VG insonation vary from 30% to 90%.

Normal values: For ﬂ ow velocities, see Table A2.4.

A2.40). The point where the VG

67Special Venous Anatomy and Ultrasound Anatomy

Fig. A2.139 Left: Color-mode imaging of vessels in the ambient cistern, midbrain encircled in white dotted lines. Note that in this case two vessels can be distinguished in color mode with the BVR located more medially (arrow) and the distal P2-PCA located more laterally (arrows). Right: Color-mode image and Doppler spectrum analysis of the BVR (top) and the distal P2-PCA (bottom).

Straight Sinus (StS)

Anatomic details: The StS is a mainly unpaired, triangu-

lar vessel with a median length of 50 mm. It arises from the merging VGs and the ISS and descends toward the CoS where it frequently drains into the CoS at the internal occipital protuberance or into preferably the left TS. A double lumen is found in ~15% of cases. Aplasias are exceptionally rare.

Position and vessel identiﬁ cation: The proximal StS, like the VG, is insonated through the transtemporal bone window in an axial thalamic plane. The transition between the VG and proximal StS is often not clearly deﬁ ned. To visualize a long longitudinal segment the transducer position has to be adapted by turning it in a line between the pineal gland and the internal occipital protuberance to achieve an oblique axial insonation plane. Therefore, the dorsal part of the transducer has to be tilted downward (Fig. A2.142). Flow velocities should be recorded from the middle segment of the vessel to avoid confusion with the VG or the CoS (Fig. A2.143). Flow turbulences and raised velocities may be seen in its proximal part, presumably caused by a lumen narrowing within the StS inﬂ ow region or because of large arachnoid (Pacchionian) granulations (Fig. A2.144;

Video

also be seen because of the vessel’s triangular shape and varying lumen diameters (Fig. A2.145). Reported rates of detection vary between 50% and 80%. Because of the straight course of the vessel blood ﬂ ow velocities may be measured using angle correction.

Normal values: For ﬂ ow velocities see Table A2.4.

A2.41). Variations of blood ﬂ ow velocities may

Fig. A2.140 (A) Schematic, sagittal plane: Note the blue-coded

ICV in its distal part. (B) TCCS, transtemporal approach, thalamic to cella media axial plane. Color-mode imaging of the contralateral ICV as a red-coded segment over the thalamic roof (arrowhead). Note the ipsilateral thalamus (semicircular line) and the straight sinus (arrows). (C) CTA, axial MIP. Note the ICV merging into the VG (arrows). (D) Doppler spectrum analysis of the opposite ICV (ﬂ ow velocity 13/11 cm/s) with a ﬂ ow toward the probe.

Fig. A2.141 (A) Schematic, sagittal plane. Note the blue-colored VG. (B) TCCS, transtemporal approach, thalamic to cella media axial plane. Color-mode imaging of the VG as a small blue-coded segment posterior to the hyperechoic pineal gland (arrow). (C) CTA, axial MIP. Note both ICV and BVR merging into the VG (arrows). (D) Doppler spectrum analysis of the VG (ﬂ ow velocity 11/8 cm/s) with a ﬂ ow away from the probe.

Conﬂ uence of Sinuses (CoS), Transverse Sinus (TS), and Superior Sagittal Sinus (SSS)

Anatomic details: The CoS is one of the main venous

blood distributors, located directly in front of the internal occipital protuberance. It collects blood from the superﬁ cial venous system via the SSS as well as from the deep venous drainage system via the StS, and connects them with each other. From there it transfers the blood via the paired TS and SiS into both IJVs. However, a “perfect” CoS exists in only ~20% of cases

68 2 Vascular Anatomy and Structure of Ultrasound Examination

Fig. A2.142 MR T2-weighted image, axial plane (A) and coronal plane (B). MR ce T1-weighted image, sagittal plane (C): Insonation ﬁ eld and transducer position for examination of the StS, TS, and SSS.

Fig. A2.143 (A) Schematic, sagittal plane. Note the blue-colored StS. (B) TCCS, transtemporal approach, thalamic to lower pontine oblique axial plane. Color-mode imaging of the StS visible as a blue-coded segment pointing toward the hyperechoic internal occipital protuberance (arrowhead). (C) CTA, lateral midsagittal MIP. Note the StS (arrows). (D) Doppler spectrum analysis of the StS (ﬂ ow velocity without angle correction 18/14 cm/s; with angle correction 42/34 cm/s), with a ﬂ ow away from the probe.

Fig. A2.144 (A) CTA, lateral midsagittal MIP. Note the lack of contrast in the transitional region between VG and StS which indicates a large Pacchionian granulation (arrow). (B) Color-mode imaging of the transition between the BVR, VG, and the StS. Note the aliasing phenomenon in the proximal StS (arrow). (C,D) TCCS, transtemporal approach, thalamic plane. Color-mode imaging Doppler spectrum analysis of the StS revealing a nonpathologic elevated venous ﬂ ow velocity (71/42 cm/s) which is probably caused by a large arachnoid (Pacchionian) granulation.

(Fig. A2.146). Divergent results have been published in regard to variants and their prevalence, but it seems clear that the drainage is usually asymmetric with the SSS more frequently passing the blood into the right TS and the StS draining into the left TS. A complete separation of superﬁ cial and deep venous drainage, which means that no CoS is present, can be assumed in ~10% of cases but has also been reported in more than 20% (Bisaria 1985, Hempel and Elmohamed 1971). Occasionally the CoS may be a venous plexus rather than a singular vessel junction. The adjacent TS runs horizontally

Fig. A2.145 Doppler spectra and color-mode imaging of the StS in diﬀ erent depths revealing a high variation of blood ﬂ ow ve- locities despite similar insonation angles. (A) In 90 mm of depth (19/14 cm/s). (B) In 95 mm of depth (62/49 cm/s). (C) In 100 mm of depth (22/19 cm/s). Blood ﬂ ow velocity measurements without angle correction. (D) Anatomic scheme of the triangular cross-sectional area of the StS, which is probably one of the major reason for the highly divergent ﬂ ow velocities of the StS at diﬀ erent depths.

from the internal occipital protuberance to the edge of the petrous bone pyramid where it turns downward to become the SiS. Diﬀ erences between the right and left sides are frequent. Aplasias have been reported in conventional angiography from 0.5% to 3% on the right side and from 2% to 14% on the left. Higher values have been published based on MRA, ranging from 4% on the right side to 20% on the left, which reﬂ ects the lower sensitivity of MRA (Alper et al 2004, Durgun et al 1993, Hacker 1974). With regard to the diameter, a right-sided dominance is found in ~50% of cases and a left-sided

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