Добавил:

Sekretar kiopkiopkiop18@yandex.ru t.me/Prokururor I Вовсе не секретарь, но почту проверяю Опубликованный материал нарушает ваши авторские права? Сообщите нам.

Вуз:

Ростовский Государственный Медицинский Университет

Предмет:

Медицина общая

Файл:

Книга_5776_Библиотеки_им_академика_М_И_Перельмана

.pdf

Скачиваний:

Добавлен:

30.08.2026

Размер:

53 Мб

Скачать

☆

<<< < Предыдущая 1 2 3 4 5 6 78 / 508 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 > Следующая >>>

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.

PICA

AICA

BA SCA PCA

49Special Arterial Anatomy and Ultrasound Anatomy

Fig. A2.90 Schematic of the posterior intracranial circulation

showing the regular, symmetric anatomy of the posterior circulation. (Adapted from Schünke et al 2006; drawing: Markus Voll.) Image rotated 180° to correspond with the ultrasound anatomy presentation. Note the origin of the PICA from the V4-VA segment, the origin of the AICA from the proximal BA, and the SCA from the distal BA. VA = vertebral artery; PICA = posterior inferior cerebellar artery; AICA = anterior inferior cerebellar artery; BA = basilar artery; SCA = superior cerebellar artery; PCA = posterior cerebral artery.

courses interpretation can be diﬃ cult, especially as the VA might be mistaken for the PICA and vice versa.

Using the transforaminal approach, two axial insonation planes can be distinguished with a transversely held transcranial probe (Fig. A2.93). The lower transforaminal insonation plane (transducer pointing toward the root of the nose) allows visualization of the VA from the distal extracranial V3 loop to the V4 segment and the proximal BA. The upper transforaminal insonation plane (transducer pointing toward the frontal eminence) facilitates insonation of the distal V4 and the proximal and mid segments of the BA. For conﬁ dent and fast vessel identiﬁ cation, we recommend starting with B-mode imaging (similar to the transtemporal insonation approach). Using an insonation depth of 10–12 cm allows depicting the hypoechoic foramen magnum and the hyperechoic clivus. Both structures should be positioned in the middle of the monitor to get reproducible images as in MR or CT (Fig. A2.94). A small oval hypoechoic structure with a hyperechoic dorsal structure and a posteroanterior diameter of at most

2.5 cm deﬁ nes the rostral cervical spinal canal with the atlas. From there an upward probe tilt and subsequent insonation with a steeper angle will then visualize the foramen magnum and clivus (Fig. A2.95 and Fig. A2.96). We recommend starting the routine insonation with the lower transforaminal insonation plane. This conﬁ dently allows visualizing the distal V3 with its typical vertebral artery grove, the distal V3 loop, and proximal V4. The distal V3 segment appears with a bidirectional color signal due to the loop in its course caused by surrounding the posterior atlas arch (Fig. A2.97 and Fig. A2.98; see also Videos

A2.27–A2.29). The border between the V3

and V4 segments—i.e., the transition to the intracranial part of the VA—is not visible using TCCS although sometimes a small color-mode narrowing can be observed which might result from VA penetration through the

Fig. A2.91 Top: DSA, vertebral artery injection, posteroanterior view. Left: PICA-ending right-sided VA with only PICA territory i r r i g a t i o n . Right: Dominant left-sided VA feeding the bilateral PCA, SCA, and AICA territory and the ipsilateral PICA territory. Bottom: Extracranial duplex, longitudinal insonation plane. Color-mode image and Doppler spectrum analysis of the right V2-VA (diameter

3.2 mm, ﬂ ow 38/12 cm/s), and the left V2-VA (diameter 4.9 mm, ﬂ ow 62/21 cm/s). Note: in comparison, the right VA reveals a higher pulsatility and a reduced blood ﬂ ow velocity.

Fig. A2.92 Anatomic variations of the distal VA. (A–C) MRI 3D TOF- MRA, coronal MIP. (A) Bilateral signal reduction in distal vertebral artery (arrows). (B) MRA-deﬁ ned complete right PICA-ending VA with prominent PICA (arrow) but no VA connection to the basilar artery (arrows). (C) Incomplete right PICA-ending VA with hypoplastic post-PICA VA ( arr ow) . (D) DSA, right VA injection, posteroanterior view. Image similar to C. Note the identical caliber of the contralateral dominant VA and the BA. The hypoplastic post-PICA VA (arrow) appears and functions like a communicating artery, e.g. the brainstem may be perfused via this small distal V4 segment in case of contralateral VA occlusion.

50 2 Vascular Anatomy and Structure of Ultrasound Examination

Fig. A2.93 Left: Tra ns du cer p os it ion f or t ra nsf or ami na l VA an d BA insonation. Patient in supine body position, head turned to one side. Top: Tr an sdu ce r po si ti on f or l owe r t ran sf or ami na l in so nat io n plane. Bottom: Transducer position for upper transforaminal insonation plane. Right: MR T2-weighted image, midsagittal plane: Yellow lines indicate direction of the upper transforaminal insonation plane aiming for the frontal bone at the level of the frontal eminence. Orange lines indicate direction of the lower transforaminal insonation plane aiming for the nasion.

Fig. A2.95 Ultrasound-MRI matched fusion imaging technique (Esaote MyLab Twice). Corresponding MR T2-weighted image (left) and transforaminal B-mode ultrasound image (right). The foramen magnum is delineated by a red circle. Note the medulla oblongata signal in the center of the foramen magnum on both imaging modalities (arrow).

Fig. A2.94 Left: Skull base with foramen magnum and clivus. Foramen: mean length 35 mm, range 30–41 mm; mean width 30 mm, range 21–38 mm. Clivus: mean anteroposterior length 45 mm, range 37–52 mm (Lang 2001). Right: Corresponding B-mode ultrasound image delineating the hypoechoic foramen magnum and the hyperechoic clivus. Note B-mode medulla oblongata signal within the foramen magnum (arrows). The foramen magnum should not be confused with the C1-atlanto-cervical joint level (see Fig. A2.96).

Fig. A2.96 (A,B) Ultrasound-MRI matched fusion imaging technique (Esaote MyLab Twice). (A) MRI plane automatically adjusted to the ultrasound image (B). Note the oval-shaped cervical spinal canal at the atlanto-occipital joint (green dotted line) and the dens axis (arrow). (C) Image plane adjusted to the atlanto-occipital joint (ﬁ rst vertebra) which should not be mistaken for the foramen mag- num plane (see Fig. 2.93). In comparison, the measured diameter is smaller—~2.4 × 1.4 cm (own data).

atlanto-occipital ligament and the dura mater. Using the fusion imaging technique (for details see Chapter 1, “Ultrasound Fusion Imaging” under “Imaging Modalities, Parameters, and Settings”), it becomes apparent that the proximal V4 starts early after revealing a ﬂ ow away from the probe (Fig. A2.99). In good insonation conditions both V3–V4 junctions are often detectable in one insonation ﬁ eld. If necessary, the head is rotated to the other side to study the contralateral distal V3 and V4.

In the lower insonation plane the PICA can be visual-

ized (Fig. A2.100). Although usually starting lateral from

the mid-V4 it often appears medially on transforaminal insonation because of its tortuous course. The anterior spinal artery merging medially from the distal V4 may also be detected on rare occasions with a ﬂ ow toward the probe. If from there the probe is tilted upward, both distal VAs, the vertebrobasilar conﬂ uence, and the proxi- mal parts of the BA are visualized. The depth of the vertebrobasilar conﬂ uence should be noted. The V4 segment and the BA commonly show a ﬂ ow away from the probe (Fig. A2.101). If two diﬀ erent ﬂ ow patterns are detected in the intra cranial VA an anatomic variant, e.g., a hypoplastic

51Special Arterial Anatomy and Ultrasound Anatomy

Fig. A2.97 (A) CTA, 3D reconstruction (occipital skull removed), image rotated 180° to correspond with the ultrasound image. The course of the right and left VAs is symmetric from the extracranial V3 segments (arrows) to the intracranial V4 segments, which join to form the BA. Note the PCA originating from the top of the BA (arrow). The junction between V3 and V4 (black double-lines) is not directly visible. Note that the cerebellar artery was erased by the postprocessing of the otherwise highly informative CTA. (B) TCCS, lower transforaminal insonation plane. Corresponding color-mode image of the right V3 (arrows), right V4, left distal VA, and proximal BA. (C) TCCS, upper transforaminal insonation plane. Corresponding distal V4-VA, BA and one PCA or SCA (arrow).

Fig. A2.98 (A–C) Transforaminal insonation with foramen magnum, clivus, and the vertebral artery groove surrounding the posterior arch of the atlas (white circle in B). (C) Color signal of the left distal V3 and V4 VA. (D) TOF-MRA, image rotated 180° to correspond with the ultrasound images. Note the double white line in (C) and (D) indicating the assumed transition from V3 to V4.

Fig. A2.99 Ultrasound-MRI matched fusion imaging technique: MR image automatically adjusted to the ultrasound image. (A) Transforaminal insonation, lower insonation plane, color-mode imaging revealing the transition from V3 to V4 (arrow). (B) Corresponding ce-MRI fusion image. (C) Slight upward tilt of the probe reveals the proximal V4 segment within the foramen magnum (arrow). (D) Corresponding ce-MRI fusion image.

VA a nd /o r a VA w it h in c om pl et e P I CA ending, can be assumed. In these cases, a low but almost normal pre-PICA

ﬂ ow is seen while the post-PICA VA may show a marked ﬂ ow reduction or an incomplete steal phenomenon—

Grade 1 or even Grade 2 with a bidirectional ﬂ ow pattern (Fig. A2.102 and Fig. A2.103; see also Video

A2.30).

Fig. A2.100 Left: CTA, 3D reconstruction (occipital skull removed), image rotated 180° to correspond with the ultrasound image. Symmetric course of both V4-VA segments. Left-sided PICA originating from the mid-V4 VA with a straight course at its origin (arrows). Note the tortuous course of the right-sided PICA (arrow). Right: TCC S, upp er tran sforami nal approac h: Corresponding color-mode image of the PICA arising laterally from the left VA (arrows).

I n s o n a t i o n d e p t h o f t h e i n ﬂ ow of the VAs into the BA varies remarkably and signiﬁ cantly correlates with the neck circumference (Schier-Laita et al 2003). Variable ﬂ ow directions might be found in cases with marked elongations in which vessel identiﬁ cation and interpre- tation might be diﬃ cult.

This phenomenon must not be confused with proximal steno-occlusive disorder of the SA, and unnecessary CTA or even DSA must be avoided (Johnsen et al 2012).

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

52 2 Vascular Anatomy and Structure of Ultrasound Examination

Fig. A2.101 TCC S, l ower transf oraminal inso nati on p lane: C o l o r - m o d e i m a g i n g a n d D o p p l e r s p e c t r u m a n a l y s i s o f b o t h V A s with a mild left-sided dominance of ﬂ ow. Top: 57/25 cm/s. Bottom: 46/16 cm/s.

Posterior Inferior Cerebellar Artery (PICA)

Anatomic details: The PICA is the largest VA outﬂ ow vessel (Lister et al 1982). In 80–90% of cases the PICA originates in the mid-V4 segment, ~10–20 mm proximal to the vertebrobasilar conﬂ uence. Its origin is usually lateral, but sometimes medial. The PICA has considerable variations of length, caliber, and vessel course. There is unilateral aplasia in up to 10% of cases and hypoplasia in 5%. In these conditions a prominent AICA or large perforators originating from the distal VA are present. Rarely one PICA provides blood to both PICA territories (Cullen et al 2005). The PICA has a mean diameter of 1.2 mm, ranging from 0.3 mm to 1.9 mm.

Fig. A2.102 Left: 3D TOF-MRA, coronal view, 180° rotated to c o r r e l a t e w i t h u l t r a s o u n d i m a g e . N o t e t h e r e l a t i v e h y p o p l a s t i c right pre-PICA V4 (arrow) changing to marked hypoplasia in the post-PICA V4-segment (arrows). Note the strong right-sided PICA (arrowhead). Right: TCCS, lower transforaminal insonation plane, c o l o r - m o d e i m a g i n g a n d D o p p l e r s p e c t r u m . Top: Normal antegrade ﬂ ow (49/23 cm/s) in the right pre-PICA VA at 45 mm. Middle: Reduced ﬂ ow (21/7 cm/s) in the post-PICA VA at 62 mm. Bottom: Normalized ﬂ ow (52/16 cm/s) in the right post-PICA VA during head rotation to the left suggesting a rotation-induced transient ﬂ ow obstruction in the left VA; i.e., the normalized right post-PICA VA ﬂ ow is caused by a compensatory ﬂ ow increase.

Position and vessel identiﬁ cation: As vessel loops are common, PICA ﬂ ow may be detected with a sig- nal toward and/or away from the transducer. Mostly it is found lateral, occasionally in a position medial to the V4-VA (Fig. A2.100 and Fig. A2.104). In severe e l o n g a t i o n s a n d l o o p s , e s p e c i a l l y i n e l d e r l y p a t i e n t s , conﬁ dent identiﬁ cation may be diﬃ cult and cautious interpretation of ﬁ ndings is recommended. Insonation rates of 40–50% have been reported in a small series (Kaps et al 1992a, Postert et al 1997b).

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

Fig. A2.103 Left: 3D TOF-MRA, coronal view, 180° rotated to cor-

relate with ultrasound image. Note the hypoplastic right pre-PICA V4 (arrow) and the additionally reduced signal intensity indicating low ﬂ ow in the post-PICA V4 (arrows). Note the strong PICA on both sides (arrowheads). Right: TCCS, lower transforaminal insonation plane, color-mode imaging, and Doppler spectrum analysis. Top: Right pre-PICA VA, depth 60 mm shows a reduced but antegrade ﬂ ow (38/20 cm/s) with incisures of systolic ﬂ ow resembling systol- ic slowing. Middle: Right post-PICA VA, depth 68 mm shows biphasic ﬂ ow (retrograde systolic, antegrade diastolic) (−5/12 cm/s). Bottom: Normal ﬁ ndings in the proximal (not shown) and distal left V4 VA segment, depth 70 mm (53/22 cm/s). Extracranial ultrasound revealed right-sided VA hypoplasia but normal ﬂ ow signal in both extracranial VAs, SA and brachial arteries (not shown).

53Special Arterial Anatomy and Ultrasound Anatomy

Fig. A2.104 TCCS, tra nsforam inal ins onation pla ne: Co lor-mode imaging and Doppler spectrum analysis of the PICA starting from the lateral surface of the VA with a ﬂ ow direction toward the trans- ducer (ﬂ ow velocity 57/31 cm/s).

Basilar Artery (BA)

Anatomic details: The BA is a constant vessel with a high-

ly variable length ranging from 20 mm to 50 mm (mean 30 mm). Its mean caliber is 3 mm (range 2.5–3.5 mm). With increasing age, elongated vessel courses can be observed (see Fig. A2.14). The vessel starts at the pontomed- ullary junction and ends at its terminal bifurcation in the interpeduncular cistern. In its proximal course it gives oﬀ the paired AICAs. Its largest branches are the paired SCAs originating from the BA’s distal segment and the two P1-PCA segments at its end (Fig. A2.97). Numerous short paramedian and larger circumferential perforators also emerge from the vessel and embrace the pontine p a r e n c h y m a . R a r e a n a t o m i c B A v a r i a n t s a r e a h y p o p l a s t i c proximal BA in cases with a persistent trigeminal artery, deﬁ ned as a fetal connection between the C5-ICA segment and the upper third of the BA, and a hypoplastic basilar top in cases with a bilateral fetal-type PCA (for further details see also “Posterior Communicating Artery” below).

Proximal Basilar Artery

Position and vessel identiﬁ cation: The proximal BA is insonated via the lower and/or upper axial transforaminal plane demonstrating a ﬂ ow direction away from the transducer (for patient and transducer position see “V4 and Distal V3 Segment” under “Vertebral Artery” above). The beginning of the BA is found at a variable depth ranging from 58 to 82 mm and a mean of 70.6 ± 5.7 mm in a study including 60 volunteers (Pade et al 2011). A larger study including 248 healthy subjects reported a mean depth of 75 ± 8 mm and a range from 55 mm to 100 mm (72 ± 7 mm for women versus 78 ± 8 mm for men). Also, the neck circumference correlated positively with the depth of the vertebrobasilar conﬂ uence (Schier-Laita et al 2003). It is easy to assess as long as both VAs merge to form the BA in a typical manner (Fig. A2.105). In cases

Fig. A2.105 (A) MR T2-weighted image, coronal plane, image rotation 180° to correspond with the ultrasound image. The red box indicates the vessel segments which can be visualized by transforaminal TCCS. (B,C) TCCS, upper transforaminal insonation plane. Color-mode imaging and Doppler spectrum analysis of the midbasilar region (ﬂ ow velocity 73/31 cm/s). In this example the v e r t e b r o b a s i l a r c o n ﬂ uence is at a depth of 72 mm and the BA can be followed 18 mm up to a depth of 90 mm.

of elongated vessel courses or a unilateral hypoplastic VA terminating as the PICA the evaluation might be diﬃ cult. For maximal signal yield from the distal BA segments the probe can be pressed ﬁ rmly onto the skin using the upper transforaminal approach. The steeper the angle using the keyhole technique the lower the position of the probe at the neck should be (see Fig. A2.93). Anteversion of the head facilitates distal insonation. With the transforaminal approach, the proximal and middle segments of the BA can routinely be evaluated within the prepontine cistern over a mean length of 10–20 mm. The location of its distal ending varies. In 61% of cases the distal segment of the BA rises posteriorly by following the course of the pons into the interpeduncular cistern and therefore leaves the focus of the ultrasound beam (Fig. A2.106). In these cases the distance between the dorsum sellae and the tip of the BA is more than 0.5 cm. Successful insonation may be possible if a large transforaminal window is present, or an excellent transoccipital window which allows insonation through the bone. Both these features are usually absent in the typical elderly stroke patient population. In the remaining 39% of subjects the distal BA follows a straighter course, with the distance between the dorsum sellae and superior BA bifurcation less than 0.5 cm (Huber

1982). However, even in these patients, distal transforaminal BA insonation is often diﬃ cult. In an elaborate com- parative study of duplex ultrasound and anatomic data by Schulte-Altedorneburg and colleagues, the BA was analyzed via the transforaminal approach. The BA was visible with a mean length of 22 mm (range 11–37 mm) while the mean anatomic length, assessed by postmortem examination, was 33 mm (range 25–57 mm). The calculated missing length was ~12 mm, corresponding to the distal third of the vessel. The distal BA segment with its parting into the PCA was visible in only 11% of cases (Schulte-Altedorneburg et al 2000). The missing distal BA segment may, however, be assessed via the transtemporal

54 2 Vascular Anatomy and Structure of Ultrasound Examination

Fig. A2.106 MR T2-weighted images, sagittal plane. (A) BA with a concave course into the interpeduncular cistern (common type). (B) Straight BA course toward the suprasellar cistern (rare type). The red dotted lines indicate the insonation plane, illustrating the problem of basilar top detection with ultrasound.

approach, provided that a patent bone window is present (see also “Distal Basilar Artery” below) (Fig. A2.107). In routine clinical practice we recommend describing the depth of the vertebrobasilar conﬂ uence and the de- tectable length of the BA. A report such as “the BA was followed up to a depth of 80 mm” is not useful, as the beginning of the vessel varies greatly. A BA signal at a depth of 80 mm in a patient with a slim neck might be derived from the distal BA, while in a patient with a large neck circumference the vertebrobasilar conﬂ uence might not even be reached.

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

Anterior Inferior Cerebellar Artery (AICA)

Anatomic details: The vessel originates from the proximal in 75% and from the middle segment of the BA in 15%. It is usually much smaller than the PICA, comparable to a prominent perforator vessel. However, in cases of PICA aplasia or hypoplasia it may be a strong and prominent vessel. Duplication and triplication has been reported in 20% of each variant. AICA aplasia is found in up to 10% of cases. In general, the AICA presents a constant diameter of 1.0 ± 0.1 mm (Shrontz et al 1986). Unlike the other cerebellar arteries the AICA branches oﬀ at a sharp angle.

Position and vessel identiﬁ cation: If detectable, the ves- sel can be identiﬁ ed via the transforaminal approach as an arterial signal originating from the proximal BA with a ﬂ ow direction toward the transducer in its proximal part. Flow direction may change more distally (Fig. A2.108 and Fig. A2.109). An identiﬁ cation rate of 8% has been reported in one publication (Postert et al 1997b).

Fig. A2.107 Left: MR T2-weighted image, coronal plane rotated 90° counterclockwise: BA segments which can be visualized by TCCS . Yello w box: V isible B A seg ment via th e tra nsfor amin al ap proach. Red box: Visible BA segment via the transtemporal coronal approach. Note the ipsilateral PCA (arrow) and SCA (arrowhead). Right: TCCS, color-mode images. Top: Transforaminal insonation. The proximal BA is visible over a length of 18 mm. Bottom: Same subject, transtemporal insonation, posterior coronal plane: The distal BA is visible over a length of 19 mm. Note the ipsilateral presence of the PCA (arrow) and SCA (arrowhead).

Normal values: No systematic values have been r e p o r t e d .

Distal Basilar Artery

Position and vessel identiﬁ cation: Insonation of the distal BA via the transforaminal approach is rarely possible. If there is no continuing color signal along the BA, distal color signals observed near the BA might be originating from the PCoA, ICA, or ACA rather than the distal BA. If the color signal is followed continuously, the most distal detectable TCCS signals are observed within in a range of 78–116 mm (mean 96 ± 8 mm) (Pade et al 2011). Transtemporal TCCS detection rates of the BA vary between 60% and 80% depending on the quality of the acoustic bone window. The rate can be increased up to 100% after administration of echo-contrast agents (Iglseder et al 2000, Postert et al 1998, Stolz et al 2002b). The distal BA can be conﬁ dently identiﬁ ed using the transtemporal approach and the posterior coronal insonation plane. We recommend starting the insonation by identiﬁ cation of the “carotid-T-junction” (C1-ICA, A1-ACA, and M1-MCA) in the anterior coronal plane. From there the transducer is pointed more posteriorly to identify the “basilar T-junction” (distal BA, both P1-PCA) in a midline position (distal BA, both P1PCA) (Fig. A2.110; see also Videos

A2.16 and A.2.31). The hyperechoic prepontine cistern and clivus and/or the sometimes observed hypoechoic vascular sheath of the BA can be of help for orientation. In a nonelongated BA the vessel should be in a strictly midline position. Changing from the anterior to the posterior coronal plane the BA should then be detected between both carotid-Ts. Because of the unfavorable insonation angle (often near 90°), exact ﬂ ow velocity measurements or even vessel detection may be impaired. In this

55Special Arterial Anatomy and Ultrasound Anatomy

Fig. A2.108 Left: anatomic preparation of the BA and its tributaries (adapted from Gänshirt 1972). Note the bilateral origin of the AICA (red arrows). Right: TCCS, uppe r transfo rami nal a ppro ach: Corresponding color-mode image of the VAs merging to form the BA. Note the two bilateral vessel signals with a ﬂ ow direction to- ward the probe representing both AICAs (white arrows).

i n s o n a t i o n a p p r o a c h , m i l d e l o n g a t i o n s , w h i c h a r e present in most of the elderly population, are actually helpful and will result in good color-mode images (Fig. A2.111). Alternatively, the distal BA can also be examined in the axial plane, following its dot-like signal from the BA head downwards by tilting the probe slowly from the midbrain to the pontine planes. Again, no representative ﬂ ow velocity can be measured by this approach but information about to BA patency and integrity can be obtained (Fig. A2.112). Using a combined transforaminal and transtemporal approach duplex ultrasound is therefore able to analyze the complete BA. In a recent published study with young volunteers and excellent insonation conditions the BA was visualized in all subjects via both approaches. The maximal detectable BA length was 26 ± 8 mm (range 6–45 mm) via the transforaminal approach and 18 ± 5 mm (range 8–27 mm) via the transtemporal approaches. Assuming the reported average total BA length of 33 ± 6 mm, complete vessel visualization was achieved in 73% of cases. Furthermore, a transforaminal BA tip and PCA origin visualization was possible in only 13% of cases, similar to the results of Schulte-Altedorneburg and coworkers (2000). All of the latter revealed shorter BA lengths than the remaining subjects (Pade et al 2011). Only rarely may all vessels of the vertebrobasilar system be detected in a single plane through the transforaminal approach (Fig. A2.113).

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

Superior Cerebellar Artery (SCA)

Anatomic details: The SCA is the most consistent cerebellar artery in terms of origin and location. It arises from the BA head, below but directly adjacent to the origin of the PCA. It has a mean diameter of 1.3 mm (range 0.8–

2.3 mm). At the beginning, it takes a course parallel to the

Fig. A2.109 Left: MRI, 2D TOF-MRA, coronal MIP, rotated 180° to correspond with the ultrasound image. Right: TCCS, upper transforaminal insonation plane: Color-mode imaging (top) and Doppler spectrum analysis (bottom) of a prominent AICA (arrows) originating from the mid-BA and ﬂ ow direction toward the probe (51/22 cm/s). Note the change in color coding from proximal red to distal blue, caused by an elongated vessel course.

Fig. A2.110 (A) MR T2-weighted image, coronal plane, rotated 90° counterclockwise to correspond with the ultrasound image: Yellow box indicating the vessel segments which can be visualized by transtemporal TCCS. (B,C) TCCS, transtemporal insonation, coronal insonation plane: Color-mode imaging and Doppler spectrum analysis of the distal BA. Note also both proximal PCA segments.

PCA in the ambient cistern, but closer to the brainstem than the PCA. Unilateral duplication of the main trunk occurs in 28% of cases and bilateral duplication in 10% (Icardo et al 1982). About 2 cm from its origin within the ambient cistern, the SCA bifurcates into a rostral and a caudal branch. Two percent of individuals have a triplicate SCA. If there is duplication, the upper branch of the SCA may arise from the PCA. In 5% of cases it does not rise from the distal BA but from the P1-PCA segment (Mani et al 1968, Hardy et al 1980).

Position and vessel identiﬁ cation: When transtempo- ral TCCS is performed in the axial imaging plane, the proximal SCA segments may be confused with the P1

56 2 Vascular Anatomy and Structure of Ultrasound Examination

Fig. A2.111 CTA, coronal MIP. Examples of variations in distal BA (basilar T) anatomy. Top left: Straight and vertical BA course which may impede adequate duplex color imaging in the coronal imaging plane. Bottom right: A marked oblique course facilitating TCCS i n s o n a t i o n .

Fig. A2.112 Top: MRI T2-weighted images, axial orientation, rotated 90° counterclockwise to correspond with ultrasound image. Note the BA ﬂ ow void in the prepontine cistern (arrow). Bottom: TCCS , color -mod e im age, tran stemp oral ins onation , up per pont ine plane. Note the color signal of the BA (arrow) in the prepontine cistern. Color coding should not be used to determine ﬂ ow direction as elongations may simulate retrograde ﬂ ow. For this, the coronal planes are required.

and/or the proximal P2 segment of the PCA because of their close spatial relation. As a consequence, PCA occlusion may possibly be overlooked while a prominent SCA is being insonated. Also in P1-PCA hypoplasia, the SCA might falsely be identiﬁ ed as the proximal PCA segment. Best transtemporal SCA identiﬁ cation can be obtained by using the posterior coronal plane where it can be found parallel to the PCA in up to 84%, provided that a good temporal acoustic bone window is present (Fig. A2.114). A further aid for diﬀ erentiation is the visual stimulus paradigm. Opening of the eyes leads to a 24% increase of ﬂ ow velocity in the PCA but only 6% increase in ﬂ ow in the SCA (Pade et al 2010) (see also Video

A2.32). In patients with marked

vessel elongation the SCA and PCA may both be visible on the axial insonation plane. Apart from the diﬀ erence in the visual stimulation test the SCA runs closer to the midbrain and (in normal PCA anatomy) has lower ﬂ ow velocities than the PCA, which facilitates the correct identiﬁ cation of both vessels. In incomplete fetal-type PCA the SCA usually presents higher ﬂ ow velocities than the P1-PCA segment (Fig. A2.115 and Fig. A2.116).

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

Posterior Cerebral Artery (PCA)

Anatomic details: The PCAs represent the terminal bifurcation of the BA. Like the MCA and ACA the PCA is divided into four segments (Yasargil 1984; Fig. A2.117 and Fig. A2.118). In a normal-type PCA its ﬁ rst, short P1

Fig. A2.113 TCCS , t rans foram inal in sonat ion, col or image and Doppler spectra of the vertebrobasilar and cerebellar arteries in one single plane. 1 = left VA (59/27 cm/s); 2 = vertebrobasilar conﬂ uence determined by merging of both VA ﬂ ow signals; 3 = BA (64/31 cm/s); 4 = Right V4 (34/14 cm/s); 5 = left PICA (57/21 cm/s); 6 = right AICA (35/16 cm/s), 7 right SCA (35/15 cm/s); 8 = right PCA (43/19 cm/s). Note the prominent and elongated left PICA corresponding to the prominent right AICA. Note that the insonation angle for SCA and PCA insonation will cause underestimation of ﬂ ow velocities.

segment extends from the vessel’s origin at the basilar tip to the origin of the PCoA within the interpeduncular cistern. The normal variant P1 segment has a mean caliber of 2.1 mm (range 0.7–3 mm) and mean length of 6 mm (range 3–9 mm). In the fetal-type PCA variant,

57Special Arterial Anatomy and Ultrasound Anatomy

Fig. A2.114 Left: MRI, 3D TOF-MRA, axial MIP, 90° counterclockwise rotated to correspond to ultrasound images demonstrating a normal anatomic pattern with symmetrical PCAs (arrows) and SCAs (arrow) merged by the BA (arrowhead). Right: TCCS, color-mode image, posterior coronal plane. Two examples of normal anatomy with bilateral PCAs (arrows) and SCAs (arrow) as well as distal BA imaging (arrowhead). The insonation angle is often favorable for the PCA, less optimal for the SCA, and worse for the BA. For best imaging results the PRF has to be decreased and the size of the color box to be minimized.

the ICA provides the blood supply to the PCA via a normally conﬁ gured vessel segment present instead of a PCoA (see Fig. A2.16). Depending on the method of investigation (anatomic, MRA, or ultrasound) a fetal-type PCA is present in 10–15% of subjects. In its P2 segment, the PCA runs further distally within the ambient cistern backward and initially slightly downward but then upward, paralleling the midbrain and ending at its posterior margin. The mean diameter of the P2 segment is 2.3 mm (range 1.2–3 mm) and its mean length considering anatomic data is 28 mm (range 15–46 mm). It may also be further divided into an anterior (proximal) and posterior (distal) part, each ~15–20 mm in length. In contrast to the often asymmetric P1 segment; the P2 segments are usually symmetrically developed. Numerous perforators, e.g., the thalamogeniculate arteries, arise from the P1 and the proximal P2 segments. In addition, the P2 segment gives oﬀ two main branches: the anterior temporal ar- tery (ATA), located at the border between proximal and distal P2, and the well-developed occipitotemporal artery (OTA) usually arising from the distal P2 segment—the latter feeding large areas of the temporal and occipital lobes. The P3 segment is short. It runs slightly upward and medially within the quadrigeminal cistern. It reaches the medial surface of the occipital lobe and often ends at the anterior limit of the calcarine ﬁ ssure. At this point the P3 usually divides into two major terminal branches deﬁ ning the P4 segment. These are the calcarine artery (CA) and the parietooccipital artery (POA). Often, the POA begins medially, crossing the CA in its course to rise upward and laterally into the parietooccipital ﬁ ssure, located between the thalamic and the cella media planes. The CA turns medially within the midbrain plane into the interhemispheric space of the calcarine ﬁ ssure (Fig. A2.117). The perfusion area of the CA includes, but

Fig. A2.115 Left: MRI, 3D TOF-MRA, axial MIP, 90° counterclockwise rotated to correspond to ultrasound images demonstrating a normal anatomic pattern with normal symmetrical PCAs (arrows). The SCAs show lower signal intensities, corresponding to size and lower ﬂ ow velocities. Right: TCCS, color-mode images, transtem- poral plane between the upper pontine and midbrain plane. Both examples show SCA elongations resulting in simultaneous visualization of PCA (arrows) and SCA (arrow) in the same axial imaging plane. Note, similar to the TOF-MRA, the SCA signal appears less prominent and the SCA runs closer to the midbrain.

Fig. A2.116 Color-mode and Doppler spectra images, transtemporal approach, axial plane between the upper pontine and midbrain plane. Top: PCA ﬂ ow velocity 59/29 cm/s. Bottom: SCA ﬂ ow velocity 39/24 cm/s. Note that both ﬂ ow velocities are within a sim- ilar range although on direct comparison the PCA ﬂ ow is higher. The reverse is true, however, in cases with P1 PCA hypoplasia.

58 2 Vascular Anatomy and Structure of Ultrasound Examination

Fig. A2.117 Schematic drawing of the PCA segments and the major cortical branches (adapted from Huber 1982), axial view.

1 = anterior temporal artery; 2 = occipitotemporal artery; 3 = parietooccipital artery; 4 = calcarine artery.

is not limited to, the visual cortex. Variations of branch anatomy are frequent: e.g., the POA and the CA may arise from the distal P2 segment (Zeal and Rhoton 1978).

Position and vessel identiﬁ cation: Early transcranial Doppler (TCD) studies divided the PCA into a P1 segment with its ﬂ ow direction toward the transducer and a P2 segment with a ﬂ ow direction away from the transducer. Real anatomy, however, is diﬀ erent and TCCS permits an anatomically correct description. Recognition of the basal cisterns surrounding the midbrain is helpful. In the mesencephalic plane within the interpeduncular cistern, the P1 and—in the proximal part of the ambient cistern— the proximal P2 are visualized with a ﬂ ow toward the transducer. The junction between P1 and P2 is deﬁ ned by the presence of a PCoA. If the PCoA is not detectable because of its unfavorable angle of insonation despite downward tilting of the probe to the upper pontine plane and optimized low PRF settings, it is assumed to be at the place of the shortest distance between the ICA–MCA arch and the PCA arch, usually 5–10 mm distal of the PCA origin. The P2 segment can be divided into a proximal and distal part within the ambient cistern which follows the lateral midbrain surface. The proximal part has a red-coded signal and the distal P2 part a blue one. The ATA is deﬁ ned as a signal toward the probe which is often found at the junction between the proximal and distal P2. To follow the upward course of the P2-PCA the insonation plane has then to be adapted to the thalamus plane. Here the distal P2 is visible with a ﬂ ow away from the probe. The OTA usually originates from the midpart of the distal P2 with a ﬂ ow toward the probe (Fig. A2.119 and Fig. A2.120; see also Video

A2.33). Its signal is usually stronger compared with the ATA. P3 is the vessel segment which runs within the quadrigeminal cistern. A vessel bifurcation in the quadrigeminal cistern or more distal deﬁ nes the origin of the POA and CA (P4 segments). The vessel running upward and lateral within the thalamic and cella media plane is the POA, and the vessel

Fig. A2.118 Top: Schematic of the PCA segments (adapted from Huber 1982), sagittal view. 1 = anterior temporal artery; 2 = occipitotemporal artery; 3 = parietooccipital artery (POA); 4 = calcarine artery (CA). Bottom: MRI, T1-weighted image, sagittal plane. White line indicating the course of the BA and PCA with the most prominent cortical branches and the POA in the parietooccipital ﬁ s- sure (3) and the CA within the calcarine ﬁ ssure (4).

running medially in the midbrain–thalamic plane near the interhemispheric space is the CA. If in doubt, a short visual stimulation test makes it possible to diﬀ erentiate between them—the vessel with the stronger response is the CA (Fig. A2.121 and Fig. A2.122; Video

A2.34).

Recently, we studied the distal course of the PCA with its branches in a group of 60 subjects with an excellent temporal bone window. The P2 was insonated in all subjects (120/120). The P1 was found in 97.5% (117/120). By using the above-mentioned criteria the four main cortical PCA branches were identiﬁ ed to varying degrees: ATA in 88%, OTA in 96%, the POA in 69% and the CA in 62%. The highest blood ﬂ ow velocities were measured in the POA, followed by the CA and OTA with similar values. The ATA showed the lowest blood ﬂ ow velocities (Frid et al 2015). According to their signiﬁ cance in the perfusion of visual relevant brain areas, the highest ﬂ ow response to a visual stimulation test regarding the diastolic ﬂ ow velocity was seen in the CA (42%), followed by the POA (27%), the OTA (16%), and the ATA (9%). The P2 segment itself showed an increase of 30%, corresponding well with previously published data from the literature.

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

<<< < Предыдущая 1 2 3 4 5 6 78 / 508 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 > Следующая >>>

Соседние файлы в папке Библиотека им академика М.И. Перельмана

#
30.08.202663 Мб0Книга_5771_Библиотеки_им_академика_М_И_Перельмана.pdf
#
30.08.202658 Мб0Книга_5772_Библиотеки_им_академика_М_И_Перельмана.pdf
#
30.08.202658 Мб0Книга_5773_Библиотеки_им_академика_М_И_Перельмана.pdf
#
30.08.202657 Мб0Книга_5774_Библиотеки_им_академика_М_И_Перельмана.pdf
#
30.08.202656 Мб0Книга_5775_Библиотеки_им_академика_М_И_Перельмана.pdf
#
30.08.202653 Мб0Книга_5776_Библиотеки_им_академика_М_И_Перельмана.pdf
#
30.08.202651 Мб0Книга_5777_Библиотеки_им_академика_М_И_Перельмана.pdf
#
30.08.202648 Мб0Книга_5778_Библиотеки_им_академика_М_И_Перельмана.pdf
#
30.08.202642 Мб0Книга_5779_Библиотеки_им_академика_М_И_Перельмана.pdf
#
30.08.202678 Мб0Книга_578_Библиотеки_им_академика_М_И_Перельмана.pdf
#
30.08.202642 Мб0Книга_5780_Библиотеки_им_академика_М_И_Перельмана.pdf