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39Special 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. A2.58 (A) Schematic of the relationship between the C6-ICA,
the petrosal bone (arrow), and the MMA in the temporal fossa
(arrowhead). (Adapted from Kretschmann and Weinrich 2003.)
(B) Corresponding 3D TOF-MRA, axial source image, rotated 90°
counterclockwise, indicating C6-ICA (arrow) and MMA (arrowhead). (C,D) TCCS, color-mode image and Doppler spectrum analysis, lower pontine plane, revealing the MMA spectrum analysis (fl ow
velocity 20/8 cm/s, PI = 1.5).
Excursion: Middle Meningeal Artery (MMA)
Anatomic details: The MMA is one important branch
of the maxillary artery which itself is the last branch
of the ECA. After originating from the maxillary artery
in the infratemporal fossa, it runs through the foramen
spinosum to supply the dura mater and the calvaria.
The MMA is the largest artery that supplies the meninges. In 1.2% of cases the MMA alone ensures the blood
fl ow of the OA (see Case 42) (Hayreh and Dass 1962).
Recently a major focus has been given to the MMA in
patients with migraine studied by MRA (Nagata et al
2009, Schoonman et al 2008) and also by duplex ultrasound (Alijagic-Schultze et al 2010). The MMA may
also serve as an important feeder or collateral in dural
arteriovenous fi stula (see Case 34), meningioma, and
moyamoya disease (see Case 9) (Deng et al 2014, Hori
et al 2015, Shah et al 2015).
Position and vessel identifi cation: The MMA is iden-
tifi ed by its anatomic relationship to the C6-ICA. In a
series of 27 subjects with excellent temporal acoustic
bone window and a detectable C6-ICA and MCA, the
MMA was visualized in 63% of cases (Alijagic-Schultze et
al 2009). When the C6-ICA is visualized the probe has to
be tilted slightly downward. The MMA can be insonated medially of the mid or distal third of the C6-ICA and
usually just below it with a red-colored signal and low
fl ow velocities as well as high pulsatility. The PRF, color
window size, and color gain therefore have to be adapted (Fig. A2.58; Video
A2.17).
Normal values: For fl ow velocities, see Table A2.3.
C5 Segment
Anatomic details: This segment is the ascending part up
to the beginning of the carotid siphon (Fig. A2.59).
Fig. A2.59 Top: MR contrast-enhanced T1-weighted image, coronal plane, image rotated 90° counterclockwise to correspond
with the ultrasound image. Arrows: C5 segment. Bottom: TCCS,
transtemporal approach, coronal plane. Right: Color-mode image
demonstrates the C5 segment. Left: Doppler spectrum analysis
(fl ow velocity 31/13 cm/s).
Position and vessel identifi cation: The C5 segment can
best be visualized in one of the coronal planes (Jurgita et al 2002) (Fig. A2.54 and Fig. A2.55). Because of an
u n f a v o r a b l e i n s o n a t i o n a n g l e , b l o o d fl ow velocity meas-
urements are usually not recommended (Fig. A2.59).
Normal values: For fl ow velocities, see Table A2.3.
C3/C4 Segment
Anatomic details: The C3/C4 segment and the C2 segment form the carotid siphon, which can have a variable
appearance. Its shape can vary from an almost straight
course in young subjects to a C-shaped or a tortuous
S-shaped vessel course, the latter more often seen in the
elderly population (Fig. A2.60). Anatomic length including C5 is 30–50 mm.
Position and vessel identifi cation: The C3/C4 segment
can best be visualized in the axial upper pontine plane
(Fig. A2.50; Video
A2.18). It is visible in subjects with
good insonation quality without exception (Eggers et al
2009). Exact measurements of fl ow velocities are diffi -
cult as angle correction is impaired by the vessel course
(Fig. A2.61). A straight course with a fl ow away from
the probe is observed in young subjects. Elderly subjects present variable elongations and often a bidirectional fl ow (Fig. A2.62). The highest measured velocity
should be recorded. In cases of a missing transtemporal
bone window, visualization of the carotid siphon via the
transorbital approach can be attempted. Because of the
restrictions on insonation power, a low detection rate
can be expected. The OA, the PCoA, and the AChA arise
from C2 and C3. Due to their diameter the OA and PCoA
may be insonated (see below).
Normal values: For fl ow velocities see Table A2.3.
40 2 Vascular Anatomy and Structure of Ultrasound Examination
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.
0–20
years
Normal 100% 74% 41%
0%
Tor tu ou s
Fig. A2.60 Anatomic variants of the carotid siphon in relation to
age. (Adapted from Huber 1982.)
0%
21–50
years
24%
2% 8%
51–74
years
51%Omega
C1/C2 Segment
Anatomic details: Both segments form the rising
cisternal, most distal part of the vessel—also called the
terminal ICA (TICA)—before it bifurcates to form the
carotid-T, which also refers to its anatomic shape. The
anatomic length is 13–18 mm.
Fig. A2.61 Top: MRI, 3D TOF-MRA, axial source image, upper pontine
plane, image rotated 90° counterclockwise to correspond with the
ultrasound image revealing the C3/C4 segment (arrows). Bottom:
TCCS , tra nste mpor al ap pro ach, axi al up per pon tine p lane : Right:
Color-mode image demonstrates the C-shaped part of the carotid
siphon. Left: Doppler spectrum analysis (fl ow velocity 50/25 cm/s).
Position and vessel identifi cation: The C1/C2 segment
usually follows a mediolateral course, which allows good
color imaging in the coronal plane. Color-mode visualization might be impaired if the vessel runs perpendicular to
the ultrasound beam (Fig. A2.54, Fig. A2.55, Fig. A2.63).
It is visible over a length of 11 ± 2 mm in 100% of cases with a patent bone window (Eggers et al 2009). Often
the C1/C2 segment follows a long, straight course and in
these cases angle-corrected fl ow velocity measurement
may be obtained (Fig. A2.64). If the vessel anatomy is
unclear the distal ICA can also be studied in successive
transverse slices by using the conventional transtemporal
axial approach starting at the midbrain plane and tilting the probe caudally toward the carotid siphon in the
upper pontine plane. Such an approach impedes correct
fl ow velocity measurements but allows the assessment of
vessel integrity and evaluation of high-grade stenosis.
Normal values: For fl ow velocities see Table A2.3.
By using an intermediate plane between the axial and
the coronal plane (called the oblique coronal plane) the
intra cranial ICA may become almost completely visible.
Tog et he r w it h t he p ro xi mal M1 -M CA i t t he n fo rm s a
U-shaped color signal (Fig. A2.65; Video
A2.16).
Ophthalmic Artery (OA)
Anatomic details: After arising from the C2 or C3 segment
of the ICA, the OA runs through the optic canal into the
Fig. A2.62 TCC S, tr anst empo ral a ppro ach, u pper p onti ne pl ane,
color-mode images. Top: Carotid siphon anatomy in younger people with a straight or only mild elongated course. Bottom: Elderly or
hypertensive subjects—the carotid siphon may reveal severe elongations, coils, and loops. Note that a prominent temporal M2 branch of
the MCA may be observed in the upper pontine plane (arrow).
orbital socket, where it branches into the orbital arteries
(lacrimal artery, supraorbital artery, anterior and posterior ethmoidal artery, medial palpebral artery, dorsal nasal artery, supratrochlear artery) and the ocular arteries
(central retinal artery [see below], ciliary arteries, muscular branches). The main stem has a mean diameter of
0.8–1.2 mm. A dual origin with a dominant contribution
via the MMA has been observed in 2.4% of cases. In 1.2%
of cases the OA arose solely from the MMA (Hayreh and
Dass 1962). Its origin is usually intradural; an extradural
41Special 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.
origin has been observed in 7.5% of cases (Yasargil 1984).
The OA can be partially insonated during its intracranial
course via the transtemporal bone window and during its
course through the orbital socket via the transorbital insonation approach.
Intracranial Ophthalmic Artery
Position and vessel identifi cation: For intracranial inson-
ation the transtemporal upper pontine imaging plane is
chosen and the carotid siphon is visualized (Fig. A2.50).
The color-mode signal of the OA can then be identifi ed at
least as a small color dot in ~90% of cases with a patent
transtemporal bone window ~5–10 mm anterior of the
carotid siphon and ~5 mm medially of the lesser wing of
the sphenoid bone (Schreiber et al 2006). To maximize
color gain the PRF has to be reduced, i.e., optimized for
detection of low fl ow velocities. The color box should be
small. The insonation depth may vary between 55 mm and
70 mm. The OA shows a Doppler spectrum with fl ow di-
rection toward the transducer. Vessel identifi cation can be
confi rmed by slight tapping of the ocular bulb (two fi ngers
applied fl at on the closed eye). This results in a positive os-
cillation phenomenon within the OA Doppler profi le (Fig.
A2.66; Video
A2.18).
Normal values: For fl ow velocities, see Table A2.3.
Fig. A2.63 CTA, coronal MIP. Examples of variations in carotid-T
anatomy. Top left: A marke d obl ique cou rse f acil itating TCC S ins on-
ation in the anterior coronal plane. Bottom right: A more vertical
course which may impede duplex color imaging.
Fig. A2.65 (A) Probe position in an oblique coronal plane. (B) 3D
TOF-MRA, coronal MIP, 90° counterclockwise rotated to correspond
with ultrasound image. (C,D) TCCS, transtemporal approach,
oblique plane showing two examples of a large part of the ICA and
MCA in one insonation fi eld.
Fig. A2.64 Top: MRI, T2-weighted image, coronal plane, image
rotated 90° to correspond with the ultrasound image. Note the
fl ow void in the C1/2 segment (arrows). Bottom: TCCS, transtem-
poral approach, anterior coronal plane. Right: Color-mode image
demonstrates a fl ow signal in C1/C2 toward the probe. Left: Dop-
pler spectrum analysis (angle-corrected fl ow velocity 113/36 cm/s).
Fig. A2.66 (A) Tapping maneuver. (B) Schematic of the origin of
the OA from the carotid siphon (arrows). (Adapted from Schünke
et al 2006; drawing: Karl Wesker.) (C,D) TCCS, transtemporal approach, upper pontine plane. (C) Doppler spectrum demonstrates
low fl ow velocities (top) and a positive oscillation phenomenon on
digital tapping of the ipsilateral optic bulb (bottom). (D) Color-
mode image demonstrates a red-coded OA signal toward the
probe, anterior and slightly laterally to the carotid siphon (arrows).
42 2 Vascular Anatomy and Structure of Ultrasound Examination
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.
CBA
ED
Fig. A2.67 (A) Transducer position for transorbital OA insonation.
Warning: Reduce insonation energy (MI <0.26). (B) 3D TOF-MRA,
axial source image, post contrast. Note the OA in the tip of the orbital socket (arrows). (C) Corresponding B-mode image of the orbital socket. (D) Doppler spectrum analysis shows a pulsatile fl ow
(fl ow velocity 28/7 cm/s). (E) Color-mode image with a typical OA
signal toward the transducer.
Extracranial Ophthalmic Artery
Position and vessel identifi cation: For extracranial in-
sonation of the OA within the orbital socket using the
transorbital approach the same 2-MHz transducer
may be used but with a maximally reduced insonation
p o w e r ( F D A r e c o m m e n d a t i o n s f o r i n s o n a t i o n o f t h e
eye: MI <0.26). The insonating hand holds the weight
of the axially oriented probe, to avoid pressure on the
ocular bulb. The OA can be identifi ed at a depth be-
tween 35 mm and 50 mm as a color and Doppler signal
toward the probe within the tip of the orbital socket
(Fig. A2.67; Video
A2.19). However, with an elongated
vessel course, fl ow directions away from the transducer
might occasionally be seen. In this case the OA has to
be followed over a longer course to be sure which fl ow
direction is present. If in doubt, the fl ow pattern can
be compared with the contralateral OA. If both signals
are identical in the case of unilateral ICA vessel disease
an antegrade fl ow can be assumed. The OA may also be
examined with the linear transducer with the frequencies used for ECA examination. The approach allows a
good visualization of the distal OA segments. Its major
advantage, however, is the examination of the central
retinal artery (see below) and other orbital arteries and
veins (Ertl et al 2014).
Normal values: For fl ow velocities see Table A2.3.
Central Retinal Artery (CRA)
Anatomic details: The CRA is one of the ocular OA
branches providing the blood supply to the retina. Together with the central retinal vein, the CRA penetrates
through the optic nerve sheath into the optic nerve
~1 cm before the optic bulb. From there it runs within
the optic nerve to the macula where it sends branches
toward the retina.
Fig. A2.68 (A) Transducer position for transorbital CRA insonation.
Warning: Reduce insonation energy (MI <0.26) (B) Ultrasound im-
age of the ocular bulb and optic nerve (B-mode), color-mode signal
of the CRA and central retinal vein within the sample volume as
well as retinal and ciliary arterial branches lateral to the optic nerve.
(C) Doppler spectrum analysis concomitantly showing the CRA fl ow
toward and the central retinal vein signal away from the probe (fl ow
velocity 15/2 and 12/8 cm/s, respectively).
M4
Pars corticalis
M3
Pars opercularis
M2
Pars insularis
M1
Pars horizontalis
Fig. A2.69 Schematic of the MCA segments, coronal view.
(Adapted from Huber 1982.) M1 segment, pars horizontalis; M2
segments, pars insularis; M3 segments, pars opercularis; M4 segments, pars corticalis.
Position and vessel identifi cation: Insonation is performed
with a linear probe positioned on the closed eye bulb
(Fig. A2.68) with a reduced insonation power (FDA recommendations for insonation of the eye: MI <0.26). The insonating hand holds the weight of the probe, avoiding any pressure on the ocular bulb. Through the easily visible ocular
bulb the optic nerve is identifi ed as a hypoechoic structure
ending in the bulb. A color box, size adapted to the target
region, yields the CRA and central retinal vein and Doppler
spectrum analysis usually shows both spectral signals at the
same time (see also Video
A2.20). Depending on the ul-
trasound system, other vascular structures, e.g., the ciliary
arteries may also become visible and may be analyzed.
Normal values: For fl ow velocities see Table A2.3.
43Special 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.
0–20
years
Rising 71% 15% 2%
28%
Descending
Fig. A2.70 Anatomic variants of the M1-MCA segment in relation
to age. (Adapted from Huber 1982.)
1%
21–50
years
47%
38% 96%
51–74
years
2%Horizontal
Middle Cerebral Artery (MCA)
Anatomic details: The MCA is the terminal continuation
of the ICA. It is the clinically most important intracranial vessel with the largest perfusion area including the
f r o n t a l , p a r i e t a l , a n d t o l e s s e r e x t e n t t h e t e m p o r a l a n d
occipital lobes. Classifi cation of the MCA segments is
still controversial, although four segments can be distinguished (Fig. A2.69). Small lenticulostriate perforators,
usually 5–15 in number, arise from the dorsal aspect of
the M1 segment or—in ~20% of cases—from one of the
proximal M2 segments, in an almost perpendicular fashion. Provided that a suffi cient bone window is present,
the entire horizontal M1 segment and the proximal horizontal and insular M2 segments as well as M3 branches
can be insonated by TCCS in combined axial and coronal
planes. In its M1 segment the MCA shows a constant
and symmetrical and often horizontal course. In advanced age the main stem of the MCA frequently follows
a descending course (Fig. A2.70). Anatomic variants such
as hypoplasia (Huber 1982, Lang 2001) or duplication
(Gómez-Choco and Valdueza 2013a, 2013b) range from
0.5 to 3%. The M1 segment has a mean caliber of 2.7 mm
(range 1.5–3.5 mm) and a mean length of 16 mm (range
5–24 mm). It commonly separates into its M2 branches
within a depth of 35–45 mm. According to an angiographic study by Huber (1982), the main pattern was bifurcation into an anterior and posterior branch and the second
most common pattern was a branch trifurcation. In the
same study, a division starting less than 10 mm distal to
the MCA off spring (medial bifurcation) was observed in
3% and a prominent early temporal M1 branch was seen
in 6% of subjects.
Position and vessel identifi cation: For insonation of the
M1 and M2 the transtemporal approach can be used
Fig. A2.71 (A) Schematic indicating the CSF-fi lled cisterns and
vessels. 1 = lateral (sylvian) cistern; 2 = Interpeduncular cistern;
3 = ambient cistern; 4 = quadrigeminal cistern. (B) B-mode image.
Note the sylvian (lateral) cistern indicating the vessel course of
the M1-MCA (arrowheads). Even the division of the M1 into two
M2 branches is seen in the B-mode (arrows) (C,D) Corresponding
color-mode signal of the M1-MCA segment. (E) Doppler spectrum
analysis of the M1 segment (fl ow velocity 77/28 cm/s without angle
correction (C) and 129/47 cm/s with an angle correction of 53° (D).
either in the axial midbrain plane or in the anterior coronal plane. Routinely, the axial plane is favored, at least
for the M1 segment (see also Video
A2.21). It is advisable to recognize the lateral (or sylvian) fi ssure in the
B-mode image to be sure of following the course of the
M1 segment before starting with the color mode. Vessel pulsations may also be seen in the B-mode image
(Fig. A2.71). The M1 most frequently divides into its M2
branches after 1.5–2 cm. In a TCCS study of 50 subjects
using both insonation planes, the MCA division pattern
prevalence was found to be similar to the catheter angiography data: a bifurcation was seen in 65% of cases and
a trifurcation in 33% of cases (Fig. A2.72 and Fig. A2.73).
In anatomic studies higher rates of M1 bifurcation ranging from 66% to 88% have been reported (Gibo et al 1981,
Tanriover et al 2003, Umansky et al 1988). A possible
explanation for the diff erences might be that TCCS and
catheter angiography tend to misinterpret a prominent
early M2 branch as presence of a trifurcation. The abovedescribed medial M1 bifurcation was seen in 2% of cases
in the TCCS study (Fig. A2.74). Independently of the MCA
division pattern, 26% of the examined subjects presented an early temporal M1 branch, detected only in the
coronal insonation plane (Rogge et al 2015) (Fig. A2.75).
Both variants—a medial M1 bifurcation and an early
temporal M1 branch—but also an MCA duplication (Fig.
A2.76) can be crucial in acute stroke and may be a pitfall in detecting proximal MCA occlusion (see also Case
22). Fig. A2.77 summarizes the observed TCCS variations.
For axial evaluation of the M2 origin and assessment of
distal M2 and M3 segments within the lateral fi ssure,
the probe has to be turned slightly upward toward the
t h a l a m i c a n d c e l l a m e d i a p l a n e . I n g o o d i n s o n a t i o n c o n ditions the insular and opercular branches in the sylvian fi ssure may become evident. Due to their course and
loops the observed fl ow direction might vary (Fig. A2.78).
44 2 Vascular Anatomy and Structure of Ultrasound Examination
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. A2.72 MCA bifurcation (circled in red). Left: MRI, 3D TOF-
MRA, axial MIP, midbrain plane, image rotated 90° counterclockwise to correspond with the ultrasound image. Demonstration of
the M1-MCA and two M2 branches. Right: Corresponding TCCS
images (transtemporal approach, axial midbrain plane).
Fig. A2.74 Left: DSA, left ICA injection, posteroanterior view.
M1 revealing a medial bifurcation in almost two equal M2
branches (arrow). Middle: TCCS , trans temporal app roac h, ax ial
midbrain plane. Note that the M1 anatomy seems “normal” in this
plane. Right: TC CS , t ran st em por al ap pro ac h, ant er io r co ro na l pl an e.
The coronal plane of the same individual reveals the presence of a
medial MCA bifurcation into two prominent M2 branches.
Fig. A2.73 MCA trifurcation (circled in red). Left: MRI, 3D TOFMRA, axial MIP, midbrain plane, image rotated 90° counterclockwise to correspond with the ultrasound image. Demonstration of
the M1-MCA and three M2 branches. Right: Corresponding TCCS
images (transtemporal approach, axial midbrain plane).
Fig. A2.75 Left: MRI, 3D TOF-MRA, coronal MIP, image rotated 90°
counterclockwise to correspond with the ultrasound image: Note
the early temporal M1 branch (arrowhead), originating opposite
the (not visible) lenticulostriate arteries. Diff erentiation from a
medial bifurcation is by its rectangular off spring and smaller vessel
size, compared with a usual M2 branch. Right: TCCS, transtemporal
approach, anterior coronal plane. To detect the usually slow fl ow
signal of the early temporal M1 branch (arrowhead), the PRF and
the size of the color box have to be reduced.
Sometimes a long horizontal MCA segment evolves from
the posterior M2 branch which can be followed in the
sylvian fi ssure (thalamic and cella media plane) with a
fl ow away from the probe. Considering the known major cortical MCA branches, this vessel can be defi ned
with vertical orientation, i.e., the insular and opercular M2/3 branches, to distinguish the distal ICA from
the proximal M1 segment, and to visualize a medial bifurcation or the early temporal M1 branch if present
(Fig. A2.81; see also Videos
A2.24 and A2.25).
as the angular artery or its corresponding infl ow vessel
(Fig. A2.79 and Fig. A2.80; see also Videos
A2.23). In a small TCCS study of 40 hemispheres in young
healthy subjects, this vessel segment was found in 45%
A2.22 and
Normal values: For fl ow velocities for M1, M2, and M3
(infl ow of the angular artery) see Table A2.3.
of cases showing a mean length of 17.7 ± 6.8 mm (range
9–36 mm) (Rogge et al 2008b).
The coronal insonation plane makes it possible to
complete and to refi ne the above discussed branching
patterns. In addition, it is helpful to detect MCA branches
Anterior Cerebral Artery (ACA)
Anatomic details: Like the MCA, the ACA can be divid-
ed into four segments (Fig. A2.82). The perfusion area
ABCD
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.
65% 33% 2% 26%
45Special Arterial Anatomy and Ultrasound Anatomy
Fig. A2.76 3D TOF-MRA, axial (A) and coronal (B) orientation
showing duplication of the left MCA. Corresponding color-mode
images in the axial (C) and coronal (D) plane demonstrating MCA
duplication especially in the coronal plane, which would have been
overlooked in routine axial examination. (Reproduced with permission of the American Institute of Ultrasound in Medicine, from
Gómez-Choco and Valdueza 2013a; permission conveyed through
Copyright Clearance Center, Inc.)
Fig. A2.78 Top left: Schematic (sagittal view) of the insular and
opercular M3 branches of the MCA (adapted from Schünke et al
2006; drawing: Markus Voll). Remaining images: TCCS examples
of the corresponding region (transtemporal approach, axial thalamic to cella media plane).
Fig. A2.77 Anatomic variants of M2 branches as observed by TCCS
examination. (Images adapted from Huber 1982.) (A) Bifurcation:
65%. (B) Trifurcation: 33%. (C) Medial bifurcation: 2%. (D) Early tem-
poral M1 branch: 26% (independent of the division pattern).
Fig. A2.79 Top: MRI, 3D TOF-MRA, axial MIP, image rotated 90°
counterclockwise to correspond with the ultrasound image demonstrating a prominent M3 MCA branch (arrows) fed by the posterior
M2 trunk (arrow). Bottom: Corresponding TCCS images, transtemporal approach, axial planes. Left: Midbrain plane with M1 and normal bifurcation into two branches. Right: The dorsal, more prominent M2 trunk develops into a large horizontal vessel within the
sylvian fi ssure, corresponding to the angular artery infl ow vessel.
Proximal part with fl ow toward the probe, distal part: fl ow away
from the probe—similar, but in a diff erent location (more lateral and
dorsal) to the perimesencephalic course of the PCA.
is usually smaller than that of the MCA and comprises mainly the frontal lobe and to a lesser extent the
p a r i e t a l l o b e . T h e A 1 s e g m e n t m a y s h o w c o n s i d e r a b l e
variations in its course (Fig. A2.83). If asymmetry is
present, the left side is usually larger. In DSA, unilateral hypoplasia (usually defi ned as a diameter <1 mm)
is seen in ~4%. The A1 segment has a mean caliber
of 2.1 mm (range 0.8–3.8 mm) and a mean length of
14 mm (range 8–19 mm). In 25% its diameter is equal
to the M1-MCA segment, in 5% even larger, the latter
indicating the anatomic variant of one A1 providing
blood fl ow into both ACA territories. This explains
the fi nding that if microembolic signals were detect-
ed with ultrasound 70.4% were seen in the MCA and
the remaining 29.6% in the ACA (Wijman et al 2000).
The A2 segments begin after the ACoA is emitted
(Fig. A2.84). Both A2 segments usually lie close
together. If one A2 segment is hypoplastic, the other
46 2 Vascular Anatomy and Structure of Ultrasound Examination
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. A2.80 Left: MRI, 3D TOF-MRA, axial MIP, image rotated 90°
counterclockwise to correspond with the ultrasound image demonstrating the circle of Willis. Right: TCCS, color-mode image, midbrain plane. PCA “loop” (in white circles), MCA “loop” (in yellow
circles). One-plane visualization of the PCA “loop” surrounding the
midbrain and of the MCA in the sylvian fi ssure is rarely possible, and
only in excellent insonation conditions.
A4
Pars supracallosa
A3
Pars precallosa
A2
Pars infracallosa
A1
Pars precommunicalis
Fig. A2.81 Left: MRI, T2-weighted image, coronal plane, rotated
90° counterclockwise. Flow void in the C5-ICA segment, C1/C2-ICA
segment, and ipsilateral M1-MCA segment. Note an early temporal
branch (arrow). Right: TCCS, transtemporal approach, anterior coronal plane. Corresponding color-mode image demonstrating blood
fl ow in the distal C1/C2-ICA segment, partly in the carotid siphon,
in the A1-ACA segment, and the proximal M1-MCA segment (ipsilateral and contralateral). Note the red and blue color coding indicating fl ow directions toward and away from the transducer. Note
also an early temporal branch (arrow).
Horizontal/
mild rise
Sharp
rise
Descending
loops/coils
0–20
years
72% 69% 60%
23%
5%
21–50
years
3%
28% 40%
51–74
years
0%
Fig. A2.82 Schematic drawing of the ACA segments, sagittal view.
(Adapted from Huber 1982.) A1 segment—Pars precommunicalis,
A2 segment—Pars infracallosa, A3 segment—Pars precallosa, A4
segment—Pars supracallosa.
often provides blood supply to both hemispheres,
which might explain bilateral ACA infarction in unilateral ICA stenosis. This anomaly occurs in ~2% of cases. At the A1–A2 junction a prominent medial striate
artery (recurrent artery of Heubner) starts to supply
the anterior parts of the striatum and the anterior limb
of the internal capsule (Perlmutter and Rhoton 1976).
Beyond the proximal segments connections allow communicating fl ow between both hemispheres.
Fig. A2.83 Anatomic variants of A1-ACA segment courses in relation to age. (Adapted from Huber 1982.)
preferably in the axial plane (Fig. A2.84 and Fig. A2.85;
Video
A2.26). For axial evaluation of the complete
A1 segment the probe might need to be turned upward or downward depending on the anatomic variant
(Fig. A2.83). If one A1 segment shows agenesis or hypo-
plasia, the contralateral A1 segment takes over the blood
supply to both A2 segments. In this case the fl ow veloc-
ity of the dominant A1 will be similar to or higher than
that of the ipsilateral M1 as their perfusion territories
are then similar (Fig. A2.86). In case of A1-ACA hypo-
plasia an aplasia may wrongly be diagnosed if the duplex
Position and vessel identifi cation: Provided that a suf-
fi cient bone window is present, the entire A1 segment
and the proximal A2 segments can be insonated by TCCS,
system parameters are not adjusted for low fl ow settings
(Fig. A2.87). As both A2 segments usually run close
together within the interhemispheric fi ssure, most
47Special 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. A2.84 Top: Schematic, TOF-MRA, and TCCS color-mode image (transtemporal approach, axial midbrain plane) of a symmetric
A1-ACA variant. Note that both proximal A2 segments as well as the
contralateral A1 and proximal M1 segments are visible. Bottom:
Respec tive image series with right-sided A1-ACA hypo-/aplasia
(arrows). Note the color visualization of both A2-ACA segments.
Fig. A2.86 Left: DSA, posteroanterior view. Large image: right
ICA injection. Both A2 segments are fed by the right A1 ACA.
Small image: left ICA injection confi rms left A1-ACA aplasia.
Right: TCCS, transtemporal approach, axial midbrain plane,
right-sided color and Doppler mode images. Top: Right ipsilateral
M1: 135/51 cm/s. Bottom: Right A1: 166/69 cm/s. Note: The ACA
fl ow velocity is higher than the ipsilateral M1 velocity corresponding with the double supply of both A2 segments.
Fig. A2.85 TCCS, tr anstempor al a pproach , ax ial m idbr ain pla ne:
Color-mode image and Doppler spectrum analysis of the A1 segment of a normal-type ACA variant (fl ow velocity 66/27 cm/s). Note
the ideal angle of insonation of the A1-ACA.
Fig. A2.87 (A) 3D TOF-MRA, axial view, rotated 90° counterclockwise to correspond with ultrasound images suggestive of left A1ACA aplasia (arrow). (B) Same subject—DSA, posteroanterior view,
left ICA injection, rotated 90° counterclockwise to correspond with
ultrasound images showing A1-ACA hypoplasia (arrow). (C,D) TCCS
color-mode image (transtemporal approach, axial midbrain plane).
(C) Missing A1-ACA signal (arrow) with normal TCCS parameter settings. (D) Faint A1-ACA color signal after PRF reduction and color
gain increase (arrow). (E) Doppler spectrum signal with low antegrade A1-ACA fl ow (21/7 cm/s) confi rming A1-ACA hypoplasia.
u l t r a s o u n d s y s t e m s w i l l s h o w o n l y a s i n g l e c o l o r - m o d e
A2-ACA signal. Provided that the transtemporal insonation conditions are good, both A2 segments can be visualized in up to 40% of cases. A single A2 signal can be
detected in at least 90% of subjects (Rogge et al 2008a).
In good insonation conditions, often the contralateral A1
and proximal parts of the contralateral M1 are visible
(Fig. A2.84).
To f ol low th e i nf rac al lo sa l A2 s eg me nt the pr ob e h as
to be tilted further upward. In excellent insonation conditions (low PRF, reduced color box size) the ACA may
be visualized encircling the knee of the callosum (A3
la media plane level—the fl ow direction changes into
a low fl ow signal toward the probe which then cor-
responds to the A4 segment, the pericallosal artery
(Fig. A2.88). A more superior insonation plane might lead
to the detection of a prominent callosomarginal artery
instead. In a small TCCS study of subjects with excellent
transtemporal insonation conditions the pericallosal artery was detected in half of the examined subjects with a
mean length of 12.0 ± 4.4 mm (Rogge et al 2008a).
For coronal insonation, the anterior coronal plane is
used (see M1-MCA and C1/2-ICA).
48 2 Vascular Anatomy and Structure of Ultrasound Examination
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. A2.88 (A) Schematic (sagittal view) of the ACA and its
branches. The red-circled vessel segment corresponds to the
pericallosal artery. (B) MRI, gadolinium-enhanced T1-weighted
axial image at the cella media shows part of the elongated pericallosal artery (red circle). (C) DSA, right ICA injection, lateral view
of the same patients revealing the elongated course of the pericallosal artery (red circle). (D) TCCS image, transtemporal approach,
cella media plane. Visible part of the pericallosal artery (red circle)
with a fl ow toward the probe (31/15 cm/s). Note the enlarged lat-
eral ventricle (arrow).
Normal values: For fl ow velocities see Tabl e A2 .3. No sys-
tematic values have been reported for A2-ACA segments.
Anterior Communicating Artery (ACoA)
Anatomic details: The ACoA—the shortest cerebral ar-
tery—connects both ACAs to form the anterior part of the
CW. Furthermore, it divides the ACA into its A1 and A2
segments. In up to 75% of cases, the ACoA is a singular
arterial vessel; in more than 20% it is doubled, and occasionally it may even have a reticular structure. Frequently
it has a large caliber, ranging from 0.1 mm to 3 mm. Its
length ranges from 1 mm to 3 mm. Variations of the ACoA
are rare (<2%) and include aplasia, an azygous A2 arising
from two A1 segments, and three A2 arising from two A1
segments, also called median callosal artery (Fig. A2.89).
Position and vessel identifi cation: In healthy individuals
the ACoA can rarely be detected. This changes as soon as
the vessel becomes a collateral vessel in case of high-grade
extracranial carotid artery stenosis or occlusion; for further details, see also Chapter 5, “Primary Collaterals (ACoA
and PCoA)” under “Intracranial Collateral Pathways in
ICA Occlusive Processes.” It can then be identifi ed by its
strongly disturbed and often bidirectional fl ow profi le and
position between both distal A1 segments. Under physiologic conditions and in the case of a long- segmented vessel, occasionally a low fl ow signal may be found.
Vertebral Artery (VA)
V4 and Distal V3 Segment
Anatomic details: After entering the foramen magnum
the VA may show considerable variations in its
Fig. A2.89 Schematics of ACoA variants. (Adapted from Yasargil
1984.) (A) Frequent variants: Note that the ACoA has more than
one channel in 25% of cases. (B) Rare variants of aplasia, azygous
artery, and a third A2 segment.
intracranial V4 segment with regard to vessel length and
vessel course. A strictly symmetric appearance of the VAs
is the exception (Fig. A2.90). Extracranial evaluation of
the VAs facilitates intracranial fl ow pattern interpretation
as the intracranial caliber of the VA mostly corresponds
to the extracranial caliber, i.e., a hypoplastic VA in its extracranial course will continue to be so into its intracranial segments. Sometimes the nondominant VA does not
merge into the BAs but ends as the PICA (Fig. A2.91). A
small vessel bridge between the distal V4 segment and
the BA is usually present, however (Fig. A2.92). A complete PICA termination without any connection to the BA
has been reported in only 0.2% of cases (Yasargil 1984). In
our own experience the prevalence of at least an incomplete PICA-ending VA seems to be higher. For clinical purposes it is therefore advisable to distinguish a pre-PICA
from a post-PICA V4 segment of the VA. In VA hypoplasia
the dominant VA more or less directly becomes the BA,
so diff erentiating between VA ending and BA beginning
might then be diffi cult.
Position and vessel identifi cation: VA a nd BA a re s tu d-
ied via the transforaminal approach with the transducer
placed in or near the midline in a skin impression between
the occipital bone and the atlas. In most cases it will be
suffi cient to keep the patient in the supine body position
with the head in an anteverted position, rotated by 30–45°
to the left or the right. A small pillow may helpful for positioning the probe comfortably in the skin impression of
the neck. In the rare cases in which this does not yield adequate insonation conditions, having the patient lying on
one side or in a sitting position may be of help. If both VAs
merge to form the BA, V4 segment identifi cation is easy.
However in cases with hypoplasia or elongated vessel
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