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7 Transcranial Doppler (TCD) and Trancranial Color-Coded Duplex Sonography…
131
• Average length: 12.7–20mm.
• Insonation: Through transtemporal bone window.
• TCD >> Depth: 60–75mm.
• TCCS: Blue color (ipsilateral)/red color (contralateral).
• Note: Chosen routinely by TCD/TCCS.
(b) Postcommunicating segment.
A2 Segment
• Insonation: Through frontal bone window.
• TCCS: Duplex: red color (ow forward to the transducer).
(c) Postcommunicating segments.
A3 to A5 segments
• Insonation: Difcult.
Anterior Communicating Antery
The anterior communicating artery arises from the anterior cerebral artery and
serves as an anastomotic bridge between the left and right anterior circulation [19].
• Length: 3–4mm.
• Diameter: 2mm.
• Note: Great physiological utility in the occlusion of the internal carotid artery.
Middle Cerebral Artery (Fig.7.13)
It is the largest terminal branch of the ICA and is the initial artery to insonate at the
beginning of any TCD/TCCS study.
Fig. 7.13 Scheme:
anatomy of middle cerebral
artery segmentation;
MCA-M1 (horizontal),
MCA-M2 (insular), and
MCA-M3 (cortical–distal).
(Author: Camilo
N.Rodríguez)
132
C. N. Rodríguez and R. Splittgerber
On its journey from the internal carotid artery, the MCA is fragmented into four
segments from its origin to the convexity, where three of those segments (M1, M2,
and M3 segments) become more accessible [18, 23, 24, 26]:
A. Origin of MCA: Terminal branch of the internal carotid artery (ICA).
B. Vessel route: Sylvian ssure to convexity.
1. Horizontal Segment (M1) (Figs.7.3 and 7.13).
Note: The most proximal segment chosen routinely for the TCD/
TCCS study.
Length: 19±3.8mm.
Insonation: Transtemporal window (mesencephalic plane).
TCCS: Red color (ipsilateral) / blue color (contralateral).
TCD (depth): 35–60mm
2. Insular Segment (M2) (Figs.7.3 and 7.13).
Note: In general, there are two M2 segments.
Bifurcation: (63%) Upper branch and lower branch.
Sometimes three segments can be found (trifurcation (32%)).
Insonation: Transtemporal window (mesencephalic plane).
TCCS: Red color (ipsilateral: ow forward to the transducer)
3. Opercular or distal segment (cortical) (M3).
Note: Difcult to access by TCD/TCCS.
TCCS: Through transtemporal window in cella media plane (ventricu-
lar plane).
7.3.1.3 Posterior Circulation
Vertebrobasilar System
Vertebral Arteries (Fig.7.14)
The VA originate from the subclavian artery, ascend toward the foramen magnum
by passing through the transverse foramen of the cervical vertebrae of C6 to C2. At
the pontine-medullary junction, the vertebral artery joins with its contralateral to
form the basilar artery [15, 23].
• Diameter: 2.5–3mm.
• Length: 250mm.
A. The VA are subdivided into four segments.
(a) Segment (V1).
From its origin to transverse process foramen of C5 or C6
(b) Segment (V2).
From transverse foramen of C6 to transverse process foramen of C2
(c) Segment (V3).
7 Transcranial Doppler (TCD) and Trancranial Color-Coded Duplex Sonography…
Fig. 7.14 Scheme:
anatomy of vertebral artery
(VA); (1) subclavian artery,
(2) internal carotid artery,
(3) vertebral arteries, (4)
basilar artery, (5) posterior
cerebral arteries, and (6)
posterior communicating
artery and (I-VI) cervical
vertebrae. (Transverse
processes). (Author:
Camilo N.Rodríguez)
133
From its exit from the transverse foramen of C2 to the foramen magnum
(occipital foramen)
(d) Segment (V4).
From its entry into the skull, through the foramen magnum, to its anastomosis with the contralateral homonymous vessel and formation of the
basilar artery
• TCCS: Blue color (ow away from transducer).
• TCD: Suboccipital window (transforaminal).
Depth: 45–75mm.
Basilar Artery (Fig.7.15)
BA is formed by the anastomosis of the two vertebral arteries at the medulla-pontine
junction and ascends adjacent to the abducens nerve and oculomotor nerve through
the basilar sulcus on the ventral aspect of the pons. It terminally forms the right and
left posterior cerebral arteries (PCA) [23].
• Length: 20–40mm.
134
ab
c
C. N. Rodríguez and R. Splittgerber
d
Fig. 7.15 (a) Scheme: anatomy of vertebrobasilar system; (1) and (2) vertebral arteries, (3) basilar
artery, (4) posterior cerebral artery– P1 segment, (5) posterior cerebral artery– P2 segment, (6)
posterior communicating artery, (7) superior cerebellar artery, (8) anteroinferior cerebellar artery
(AICA), and (9) posterior inferior cerebellar artery (PICA). (b) Scheme of occipital bone: (1)
occipital bone, (2) occipital condyle, and (3) foramen magnum. (c) Scheme of the anatomy of the
vertebrobasilar system by TCCS through transforaminal acoustic window: (1) basilar artery; (2)
right vertebral artery– V4 segment; (3) left vertebral artery– V4 segment; (4) foramen magnum,
(arrow) It highlights that the ow moves away from the transducer (blue color). (d) Vertebrobasilar
system insonation by TCCS through transforaminal acoustic window: (1) V4 segment of vertebral
artery (blue), (2) basilar artery (blue). Arterial ow moves away from the transducer. (Author:
Camilo N.Rodríguez)
• Diameter: 2.5–3.5mm.
• TCD.
– Bone window: Transforaminal.
– Depth: 70–120mm.
• TCCS.
– Window: Transforaminal/submandibular.
– Duplex: Blue color.
7 Transcranial Doppler (TCD) and Trancranial Color-Coded Duplex Sonography…
135
Posterior Communicating Artery
After its origin in the internal carotid artery (C1–C2 segments), it extends posteriorly (above the common ocular nerve) to anastomose with the posterior cerebral
artery (terminal branch of the basilar artery) [15, 20, 23].
• Length: 12,5±3,2mm.
• Diameter: 1,5±0,6mm.
• TCD.
– Insonation: Transtemporal window.
– Depth: 55–65mm.
Flow: The ow velocity is difcult to measure as it is located perpendicu-
larly to the probe
• TCCS (difcult).
– Window: Transtemporal window.
– Plane: Mesencephalic.
– Duplex: Blue Color.
Posterior Cerebral Arteries
The PCA are the terminal branches of the basilar artery, receiving the posterior
communicating artery from the internal carotid artery. It surrounds the cerebral
peduncle dening two clinically relevant segments: a precommunicating segment
(P1) and another postcommunicating segment (P2) [15].
The PCA branches are divided into four anatomical segments [17, 21–24]:
A. Precommunicating Segment (P1 segment) (Fig.7.15).
• Origin: From the basilar artery to the anastomosis with the posterior communicating artery, found within the interpeduncular cistern.
• Length: 3–20mm.
• Diameter: 1.9–2.1mm.
• TCD.
1. Window: Transtemporal.
Depth: 65–80mm
2. Window: Transforaminal.
Depth: 95–100mm.
Flow: Forward to the Transducer
• TCCS.
– Window: Transtemporal window.
– Duplex: Red color (ow forward to the transducer).
B. Anterior Postcommunicating Segment (P2A) (Fig.7.15).
• Origin: From the posterior communicating artery (lateral to the cerebral
peduncle) to the origin of the P2P subsegment in the ambiens cistern.
136
C. N. Rodríguez and R. Splittgerber
• Length: 18–30mm.
• Diameter: 1–3mm.
• TCD.
– Window: Transtemporal.
– Depth: 65–80mm.
– Window: Transforaminal.
– Depth: 95–100mm.
– Flow: Away from transducer.
• TCCS:
– Window: Transtemporal window.
– Duplex: Blue color (ow away from transducer).
C. Posterior Postcommunicating Segment (P2P).
• Origin: From the P2A subsegment (lateral to the brainstem) to the origin of
P3 segment, it runs through the ambiens cistern.
• Length: 9–25mm.
• Diameter: 0.8–2mm.
• TCD.
– Window: Transtemporal.
– Depth: 65–80mm.
– Window: Transforaminal.
– Depth: 95–100mm.
– Flow: Away from transducer.
• TCCS.
– Transtemporal window.
– Duplex: Blue color (ow away from transducer).
D. Quadrigeminal Segment (P3 Segment).
• Origin: From the ambiens cistern through the quadrigeminal cistern; it runs
through the quadrigeminal cistern.
• Length: 19,8mm.
• Diameter: 1,1mm.
• TCD: Difcult insonation.
• TCCS [25].
– Window: Transtemporal (mesencephalic-diencephalic planes).
– Duplex: Blue color.
E. P4 Segment.
• Origin: Runs from the parieto-occipital ssure to the distal calcarine ssure.
7 Transcranial Doppler (TCD) and Trancranial Color-Coded Duplex Sonography…
Posterior-Inferior Cerebral Artery (PICA) (Fig.7.15)
The PICA is the most variable and tortuous cerebral artery. Its origin can be variable
both extracranially and intracranially as a branch of the vertebral artery (VA). It may
even be absent. In 84% of the population, PICA has a single trunk; in the 83%, it
arises superior to the foramen magnum.
PICA supplies the cerebellar vermis, cerebellar hemispheres, and structures of
the medulla oblongata, and has a close relationship with cranial nerves: III, V, VI,
VIII, IX, and XII [17, 23].
• Diameter: 1.7–1.8mm.
• TCCS.
– Window: Transforaminal.
– Duplex: Red color (ow forward to the transducer).
• TCD.
– Depth: 50–70mm.
– Window: Transforaminal.
137
7.4 Cerebral Circulation: Anatomical Distribution
ofCerebral Blood Flow (CBF)
By studying the anatomy of the circle of Willis with magnetic resonance imaging
(MRI), it is possible to demonstrate the anatomical distribution (%) of the CBF in
the population where the circle was complete [26].
1. Internal carotid system (Right).
1.1 ICA >> (36%±4).
1.2 MCA >> (21%±3).
1.3 ACA >> (12%±4).
2. Internal carotid system (Left).
1.1 ICA >> (36%±4).
1.2 MCA >> (21%±3).
1.3 ACA >> (11±%4).
3. Vertebrobasilar system (right and left).
1.1 VA >> (15%±5).
1.2 PCA >> (8%±1).
1.3 BA >> (20%±4).
138
The CBF in the anterior and posterior communicating vessels is especially evident during situations of CBF obstruction in one of the two feeding systems of the
arterial circle (circle of Willis) [37, 38].
C. N. Rodríguez and R. Splittgerber
7.5 Cerebral Circulation: Anatomical Variations
The circle of Willis probably has two theoretical functions in human brain. Despite
the communicating arteries being too small or hypoplastic in a majority of the population, these branches probably serve two particular functions: (1) as a passive pressure dissipating system, where they transfer pressure, without considerable blood
ow, from the high pressure end to the low pressure end, and (2) circulation compensatory function, especially on impairment function (stenosis/occlusion) of ICA.
The circle of Willis was discovered with its complete anatomy with autopsy studies, CT studies, and MRI, where it is visible 14–55% of its entire part [27–29].
7.5.1 Anatomical Variations intheCircle ofWillis
7.5.1.1 Anterior Circulation
Most Common Variations [28]
Anterior Communicating Artery
(a) Hypoplastic or absent (7–13%).
(b) Doubled (9–30%).
(c) Unique artery (56%).
Anterior Cerebral Artery
(a) (A1) Segment: hypoplastic or absent (2–12%)
Posterior Communicating Artery
The most variable artery within the circle of Willis [11, 28–30].
(a) Bilaterally hypoplastic (7%).
(b) Unilateral absent or hypoplastic (27%).
(c) Bilateral present (54%).
(d) Hypoplastic or unilateral absence of posterior communicating artery (PComA),
absence of P1 segment, or hypoplastic PCA (1%).
15
72
7 Transcranial Doppler (TCD) and Trancranial Color-Coded Duplex Sonography…
7.5.1.2 Posterior Circulation
Most Common Variants [28]
Posterior Cerebral Artery
(a) Blood supply comes from the BA (82%).
(b) Blood supply comes from the ICA (11%).
(c) Hypoplastic or unilateral absence of P1 segment (1%).
(d) Hypoplastic or unilateral absence of P1 segment and PComA (1%).
Vertebral Artery
(a) Dominant left vertebral artery (45%).
(b) Dominant right vertebral artery (21%).
(c) Shared dominance (34%).
7.6 Veins andVenous Sinuses oftheBrain: Anatomy
andUltrasound
Three venous systems that drain blood from the brain:
1. Deep cerebral veins.
2. Dural venous sinuses.
139
We will focus on the identication of the deep cerebral veins and the dural
venous sinuses by TCD/TCCS.
Ultrasound of deep intracranial venous does not belong, even, to the routine
examination techniques applied in daily practice in the ICU.However, the deeper
and more serious the pathological effects on the intracerebral venous circulation,
the easier it is to detect them by TCCS/TCD [11, 31].
The relevant anatomy of intracerebral are the venous structures with a high probability of access by ultrasound (Table7.1).
Table 7.1 Normal venous blood ow values
Vein / Sinus Flow Velociti es (cm/s)
Basal vein (of Rosenthal)
Deep middle cerebral vein
Great vein (of Galen)
Straight sinus
Transverse sinus
Sphenoparietal sinus
Superior petrosal sinus
a
Systolic/Diastolic velocities. Adapted from manual of Neurosonology; Csiba L, Baracchini
7–20/5–15 80–100%
4–15/3–1
6–32/4–25 80–95%
6–39/4–2
6–56/5–38 20–84%
27±17
27±17
C. 2016. Cambridge. [11, 32–39]
a
Detection Rate (%)
0–95%
3–82%
84%
84%
140
C. N. Rodríguez and R. Splittgerber
Ultrasound of the deep intracerebral venous system and sinuses of the dura is a
complementary tool (diagnostic modality for a rapid screening at the bedside of the
critical patient) in which there is no consensus in the sequence of examination
approach [36].
7.6.1 Deep Cerebral Veins (Fig.7.16)
• Normal Flow: Low ow velocity (Table7.1).
• Identication: B-mode+Doppler.
7.6.1.1 Deep Middle Cerebral Vein (DMCV)
Identication: The deep middle cerebral vein is adjacent to the middle cerebral
artery (MCA) with drainage in the basal vein.
TCCS
Acoustic bone window: Transtemporal.
Insonation plane: Mesencephalon.
Duplex: Flow away from transducer into the dural venous sinuses (blue color).
TCD
Acoustic bone window: Transtemporal.
Flow: Increase in the ow velocity (thrombosis?) [35, 37].
Fig. 7.16 Scheme:
cerebral veins detectable
by TCCS and arterial
relationship; (1) vein of
Galen, (2) basal vein
(Rosenthal), (3) deep
middle cerebral vein, (4)
basilar artery, (5) posterior
cerebral artery, (6) internal
carotid artery, (7) middle
cerebral artery, (8) anterior
cerebral artery, and (9)
mesencephalon (midbrain).
(Author: Camilo
N.Rodríguez)