Demonstration of brain perforating arteries by ultra-highresolution CT angiography

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1 Demonstration of brain perforating arteries by ultra-highresolution CT angiography Award: Cum Laude Poster No.: C-1135 Congress: ECR 2018 Type: Educational Exhibit Authors: M. Gomyo, K. Tsuchiya, H. Machida, S. Katase, A. Ohara, H. Tateishi, H. Shiga, M. Koyanagi, K. Yokoyama ; Tokyo/JP, 2 Kawagoe City, Saitama/JP Keywords: Education and training, Education, CT-High Resolution, CTAngiography, CNS DOI: /ecr2018/C-1135 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 39

2 Learning objectives To understand basic facts and technological advancements of the latest ultra-high-resolution CT (UHRCT). To learn improved demonstration of cortical branches and critical perforating arteries by brain CT angiography (CTA) using UHRCT. To know basic anatomy and clinical significance of the perforating arteries as demonstrated using UHRCT. Page 2 of 39

3 Background Although precise depiction of the perforating arteries is required in making strategies for direct surgery and stroke management, capability of conventional CT has been limited due to limited spatial resolution. The latest ultra-high-resolution CT (UHRCT) scanner (Aquilion Precision ; Toshiba Medical Systems, Tokyo, Japan) provides slice collimation of 0.25 mm x 160 and matrix size of 1024 x 1024 or 2048 x Major features of this CT scanner include an improved detector system (the minimal slice thickness, 0.25 mm; the maximal channel number, 1792) and a small x-ray focus (the smallest size, 0.4 x 0.5 mm) compared to a conventional multi-detector CT (MDCT) scanner (the minimal slice thickness, 0.5 mm; the maximal channel number, 896; the smallest x-ray focus size, 0.8 x 0.9 mm) (Fig. 1). UHRCT has recently become available for clinical testing in order to improve spatial resolution enabling robust depiction of cortical branches of the main arteries and critical perforating arteries by brain CTA, compared to conventional MDCT (Figs. 2, 3). In this exhibit, we show the anatomical and clinical significance of intracranial cortical branches and perforating arteries which were difficult to visualize with conventional MDCT but are now visualized by using the UHRCT. Page 3 of 39

4 Images for this section: Fig. 1: The latest ultra-high-resolution CT (UHRCT) has been newly introduced with improved in- and through-plane spatial resolution. The smallest focus spot size (0.4 x 0.5 mm) for 0.15-mm spatial resolution is realized by Focal Spot size Control (FSC) technology. The vendor (Toshiba Medical Systems) manufactured UHR X-ray tube anode spins at a remarkable 10,000 rpm (almost twice as fast as conventional tubes today) which combined with a liquid metal bearing provides the rapid heat dissipation necessary to guarantee fine focus size. Page 4 of 39

5 Fig. 2: This figure shows comparative results between conventional MDCT and UHRCT using a vessel phantom. Use of a small focus spot decreased geometrical blurring and improved spatial resolution. Note that UHRCT demonstrates a vessel phantom more sharply and clearly than MDCT. Page 5 of 39

6 Fig. 3: This figure shows maximum intensity projection (MIP) CTA images from the same patient using the conventional MDCT and UHRCT. Both MIP CTA images were performed by the same administration method and scan timing. UHRCT was able to depict cortical branches of the main arteries by brain CTA, compared to conventional MDCT. Page 6 of 39

7 Findings and procedure details We will illustrate anatomical and clinical significances of cortical branches and critical perforating arteries including the internal carotid artery (ICA), ophthalmic artery (OA), vertebral artery (VA), basilar artery (BA), anterior cerebral artery (ACA), middle cerebral artery (MCA), and posterior cerebral artery as listed in Fig. 4 depicted by UHRCT. Imaging Acquisition CT scanner; Aquilion Precision ; Toshiba Medical Systems, Tokyo, Japan Scan parameters and image reconstruction; We present scan and image reconstruction parameters in Table 1. Injection method; We place a 20-G needle in the right antecubital vein of the patient. At the beginning, we inject 10 ml each of high concentration (350 mgi/ml) contrast medium and saline as a test injection using a power injector, and measure the peak time of M1 segment of the MCA. Subsequently, the administration is performed using a high concentration contrast medium at the fractional dose of 30 mgi/kg/sec for 15 seconds, then saline flash of 40 ml was injected at the same rate. Scan is started at the M1 peak time. Findings The cerebrum is mainly perfused by three pairs of main cerebral arteries; the ACA, MCA and PCA. As UHRCT has enabled depiction of cortical branches of these main arteries, it is possible to identify the watershed area that is the boundary of perfusion area of each main cerebral artery (Figs. 5, 6). Furthermore, UHRCT has made it possible to depict critical perforating arteries. We will explain the anatomical significance and clinical significance of the intracranial cortical branches and perforating arteries below. #Internal carotid artery# 1) Ophthalmic artery Page 7 of 39

8 The OA is the first branch of the intracranial ICA and often originates from inside the anterior wall at the distal dural ring of the ICA and run inward of the optic nerve and passes anteriorly through the optic canal and the orbit (Fig. 7). The origin and route of the OA affect the site of occurrence and protrusion direction of the ICA-OA bifurcation aneurysm. By them the extent to which the aneurysm compress and shift the OA is different. So, identification of origin and route of the OA is important in considering the posture and approach in order to ensure a sufficient field of view for direct surgery. The central retinal artery is the first branch of the OA and supplies the inner retinal layers and related to visual function. It is important that the OA is usually one end-artery with poor vascular anastomosis, but it is difficult to visualize on CTA because the diameter is extremely small. 2) Posterior communicating artery The posterior communicating artery (PCoA) passes between the ICA and the PCA, and becomes a collateral between the anterior and the posterior circulations (Fig. 8). Depending on the relationship between the diameter of the PCoA and the P1 segment of the PCA, it is classified into the following three types. Normal type: the diameter of the PCoA is 1 mm or more and narrow than the P1 segment. Hypoplastic type: the diameter of the PCoA is 1 mm or less. Fetal type: the diameter of the PCoA is 1 mm or more and larger than the P1 segment. About seven perforating arteries arise from the upper wall of the PCoA and supply the optic tract, the optic chiasm, the mammillary body, the gray tuber, the posterior part of the hypothalamus, the anterior part of the thalamus, the genu of internal capsule and anterior third of the posterior limb of internal capsule. If the PCoA gets occluded, it causes hemiplegia, hemisensory disturbance, alalia, memory disturbance, affective disorder, and visual field disturbance. The role of collateral is irrelevant to the diameter of the PCoA, and the damage by surgery tends to occur in cases where the diameter of the PCoA is narrow [1]. Page 8 of 39

9 As many perforating arteries arise from the anterior part of the PCoA, if you have to sacrifice the PcoA by surgery, the PCA side is safer. Usually, the oculomotor nerve exists lateral inferior of the PCoA, but there are many variations in the positional relationship between the oculomotor nerve and the PCoA, so attention is required during surgery. 3) Anterior choroidal artery The anterior choroidal artery (AchoA) originates from the posterior wall of the ICA slightly distal from the origin of the PCoA. The AchoA runs to the posterior medial side and passes through the inferior of the optic tract, and goes upward drawing a S-shaped curve passing outside the cerebral peduncle. Then it forms a convex vertex upwards and enters the choroidal fissure. The top of AChoA is called the uncal point (Fig. 9). Branches of AchoA supply medial temporal lobe, optic tract, middle third of cerebral peduncle, posterior two-thirds of posterior limb of internal capsule, lateral geniculate body and choroid plexus. Therefore, if the ACoA get occluded, it causes hemiplegia, hemisensory disturbance and hemianopia. It is known as Abbie or Monakow syndrome. Especially, as the collateral of posterior limb of internal capsule is poor, hemiplegia appears with high probability when the AChoA is occluded. Since all these branches of AchoA originate proximal to the uncal point, identification of the uncal point is important during transcatheter embolization. <Posterior cerebral artery> The PCA originates from the distal end of the BA, and it is divided into four segments (Fig. 10). Cortical branches of the PCA (Fig. 11) 1) Temporal arteries Temporal arteries are classified into the hippocampal artery, anterior temporal artery, middle temporal artery, posterior temporal artery and Page 9 of 39

10 common temporal artery depending on the region of the temporal lobe which is supplied. They supply the ventral surface of the temporal lobe and anastomose with branches of the MCA. 2) Parieto-occipital artery The parieto-occipital artery arises from the P3 segment, and runs inside of the parieto-occipital fissure and supply the parietal lobe, the posterior medial part of occipital lobe, the cuneus and the pre-cuneus. The posterior pericallosal artery branching from parieto-occipital artery runs on the superior surface of corpus callosum and anastomoses with the pericallosal artery which branches from the ACA. As in moyamoya disease, this branch often develops working as collateral pathways. 3) Calcarine artery The calcarine artery arises from the P3 segment, and runs through the calcarine fissure. It supplies the major part of the visual cortex, and it is important to identify this artery before surgery for preservation of visual function. 4) Splenial artery (posterior pericallosal artery) The splenial artery runs on the superior surface of the corpus callosum. It supplies the splenium of the corpus callosum. Perforating arteries of the PCA 5) Posterior thalamoperforating artery The posterior thalamoperforating artery originates from the top of BA or P1 segment, and its diameter on average is 0.7 mm (Fig. 12) Page 10 of 39

11 It supplies the internal thalamus and the midbrain. Its branch originating from the P1 segment that supplies both sides of the thalamus and midbrain is called the artery of Percheron. If it is occluded, bilateral paramedian thalamic infarction syndrome is caused even by one side of the P1 occlusion, resulting in disturbance of consciousness and ocular movement disorder such as vertical gaze paresis and convergence palsy. 6) Thalamogeniculate arteries Thalamogeniculate arteries arise from P2 segment, and diameter of this arteries are mm (Fig. 13). They supply the geniculate nucleus, pulvinar, posterior part of the thalamus, posterior limb of internal capsule, superior colliculus and optic tract. So, obstruction of this arteries causes disturbance of contralateral superficial and deep sensibility, severe thalamic pain, light hemiplegia and involuntary action known as Dejerine-Roussy syndrome. <Anterior cerebral artery> The ACA is smaller and more medial terminal branch of supraclinoid ICA, and it can be classified into five segments (Fig. 14). Cortical branches of the ACA (Fig. 15) 1) Orbitofrontal artery The orbitofrontal artery is usually the first cortical branch of the A2 segment, and ramifies over inferior surface of frontal lobe. 2) Frontopolar artery The frontopolar artery is the next cortical branch arising from the mid-a2 segment over the corpus callosum, and extends anteriorly to the frontal lobe. Page 11 of 39

12 Both the orbitofrontal and the frontopolar arteries are orbital branches and supply over the orbital surface of the frontal lobe: olfactory cortex; gyrus rectus; medial orbital gyrus. 3) Pericallosal artery The pericallosal artery arises from the A2 segment near the corpus callosum genu, and runs posterosuperiorly above the corpus callosum. It gives off many small branches to the corpus callosum. 4) Callosomarginal artery The callosomarginal artery arises from the A3 segment and runs posterosuperiory in the cingulate sulcus. The pericallosal-callosomarginal arterial junction is the site of predilection for distal anterior cerebral artery aneurysm (DACAAN). In the case of DACAAN, the operative field is narrow. Particularly when the aneurysm exists below the corpus callosum genu, it is difficult to reach the parent artery, so it is important to understand the location of the aneurysm and the direction of protrusion before surgery. Perforating arteries of the ACA 5) Recurrent artery of Heubner The recurrent artery of Heubner arises typically from the nearby A1-A2 junction, and curves back parallel to the A1 segment. The diameter of this artery is mm (Figs. 16, 17). It supplies the anterior part of the caudate nucleus and putamen, anterior limb of internal capsule and fasciculus uncinatus. Obstruction of this artery causes facial paralysis, upper-limb hemiparesis and aphasia on dominant side. 6) Medial lenticulostriate arteries Page 12 of 39

13 The medial striate arteries (MSAs) are generally arising from the A1 segment. The MSAs supply the globus pallidus and medial part of the putamen. Although, some investigators divide the lenticulostriate arteries that arise from the M1 segment into medial (those arising proximally) and lateral (those arising more distally) groups. In fact, the frequency of occurrence of the MSAs is low, and clinically the infarction of this perfusion area is rare. #Middle cerebral artery# The MCA arises from the ICA and continues to the lateral sulcus where it then branches and projects to many parts of the lateral cerebral cortex. The MCA supplies the majority of the lateral surface of the hemisphere, except the superior portion of the parietal lobe and the inferior portion of the temporal and occipital lobes. In addition, it supplies part of the internal capsule and basal ganglia. In its territory lie the motor and sensory areas excluding leg and perineum and auditory and speech areas. The MCA are classified into four segments (Fig. 18). M4 segment coursing over surface on the cortex are cortical branches and those names are based on their perfusion area (Fig. 19). Cortical branches of the MCA Supply the anterior lobe 1) Orbitofrontal artery 2) Prefrontal artery 3) Precentral artery 4) Central artery Supply the parietal and occipital lobe Page 13 of 39

14 5) Postcentral artery 6) Posterior parietal artery 7) Angular artery Supply the temporal and occipital lobe 8) Temporo-occipital artery 9) Posterior temporal artery 10) Middle temporal artery 11) Anterior temporal artery 12) Temporopolar artery Perforating arteries of the MCA 13) Lateral lenticulostriate artery The lateral lenticulostriate artery (LSA) usually arises from the mid- and distal M1 segment (Fig. 20). Variations of origin are as follow: M1, 40%; both M1 and M2, 20%; M2, 25%; M1-2 bifurcation, 12% and accessory MCA, 3%. Branching patterns are also variable as follows: branching from one trunk, 40%; branching from two trunks, 30%; direct branching from M1 segment, 30% [2]. LSAs are small perforating arteries with a diameter of 0.5 mm or less, but they supply very important areas such as the caudate nucleus, the globus pallidus, the putamen and the part of the posterior limb of internal capsule. These small arteries are particularly susceptible to damage from hypertension. They may rupture, resulting in an intracerebral hemorrhage that is initially centered in the region they supply. Especially, outermost branch of LSAs is known as Charcot-Bouchard artery that commonly causes external putamen hemorrhage with hypertension. Moreover, LSAs are "end arteries", meaning that the regions they supply do not have significant collateral blood supply. When occluded, it produces a Page 14 of 39

15 lacunar infarct in the tissue they supply. The origin of LSA is also a common site of MCA aneurysm. So, in the case of M1/M2 stenosis or before surgery of aneurysm or brain tumor, it is important to understand the origin and branching of LSAs. #Basilar artery# The BA courses superiorly in the prepontine cistern. Branches of the BA 1) Anterior inferior cerebellar artery The anterior inferior cerebellar artery (AICA) usually arises from the proximal BA. The AICA supplies anterolateral part of the cerebellum. 2) Superior cerebellar artery The superior cerebellar artery (SCA) arises from the distal BA, and course posterolaterally around the midbrain. The SCA supplies the superior vermis, superior cerebellar peduncle, dentate nucleus, brachium pontine, superomedial surface of cerebellum and upper vermis. 3) Posterior cerebral artery Refer to the PCA. Perforating arteries of the BA 4) Pontine arteries Page 15 of 39

16 Usually 3-5 pair branches arising from the BA between the AICA and SCA (Fig. 21). Pontine arteries supply the pons and anatomies adjacent to the pons. The pontine arteries arising from the lower third of the BA supply the foramen cecum and medulla oblongata, and thus are especially important because their obstruction can lead to severe motor paralysis. #Vertebral artery# After the VA enters skull through foramen magnum is V4 segment, and unites with the contralateral VA at pontomedually junction to the BA. Branches of the VA 1) Posterior inferior cerebellar artery The posterior inferior cerebellar artery (PICA) arises from distal VA. It curves around tonsil, and gives off perforating medually, choroid, tonsillar and cerebellar branches. The PICA supplies lateral medulla, choroid plexus of fourth ventricle, tonsil and inferior vermis and cerebellum. Perforating artery of the VA 2) Anterior spinal artery The anterior spinal artery (ASA) arises from the VA at the level of the medulla oblongata and descends along the anterior median fissure located on the anterior surface of the spinal cord (Fig. 22). The ASA supplies the anterior portion of the spinal cord. Occlusion of it causes anterior spinal artery syndrome. Page 16 of 39

17 Images for this section: Fig. 4: We illustrate anatomical characteristics and clinical significances of cortical branches and critical perforating arteries listed in Fig.4 using brain CTA by UHRCT. Page 17 of 39

18 Fig. 5: A top-down view of the fusion image of CTA by UHRCT and 3D-FLAIR is shown on the left, and the map of vascular territories of three major cerebral arteries is shown on the right. On both fusion image and map of vascular territories, anterior cerebral artery (ACA) is shown in red, middle cerebral artery (MCA) is shown in blue, and posterior cerebral artery (PCA) is shown in yellow. The ACA supplies most of the medial hemispheric surface except for the occipital lobe. The MCA supplies most of the lateral and superior surface of the hemisphere except for a small strip over the vertex, occipital pole and inferolateral temporal lobe. The PCA supplies the occipital pole and most of the temporal lobe. The junction of these territories forms the cortical watershed area. The posterior confluence where all three vascular distributions meet together is especially vulnerable to cerebral hypoperfusion. Page 18 of 39

19 Fig. 6: A submentovertex view of the fusion image of CTA by UHRCT and 3D-FLAIR is shown on the left, and the map of vascular territories of three major cerebral arteries is shown on the right. Note that the temporal tip is supplied from the middle cerebral artery. Page 19 of 39

20 Fig. 7: A top-down view of volume-rendered CTA images by UHRCT are shown. The ophthalmic artery (OA) is the first branch of the intracranial internal carotid artery (ICA) and often originates from inside the anterior wall at the distal dural ring of the ICA and runs inward of the optic nerve and passes anteriorly through the optic canal and the orbit. The diameter of the OA just after origination from the ICA is 1 or 2 mm. The origin and route of the OA affect the site of occurrence and protrusion direction of the ICA-OA bifurcation aneurysm. Page 20 of 39

21 Fig. 8: A lateral view of volume-rendered CTA image by UHRCT is shown. The posterior communicating artery (PCoA) passes between the internal carotid artery (ICA) and the posterior cerebral artery (PCA), and becomes a collateral between the anterior and the posterior circulation. Usually the PCoA origins from the posterior wall of the ICA and is slightly larger on the ICA side than on the PCA side so that blood flows from the ICA to the PCA. Many perforating arteries arise from the anterior part of the PCoA, and their role of collateral is irrelevant to the diameter of the PCoA. As CTA by UHRCT well depicts the entire part of the PCoA, it is important before surgery of an IC-PC aneurysm. Page 21 of 39

22 Fig. 9: Volume-rendered (VR) CTA images by UHRCT are shown. A left is top-down view, and both middle and right are lateral views. A VR CTA image by UHRCT clearly demonstrates throughout the length of anterior choroidal artery (AchoA). The AchoA originates from the posterior wall of the ICA slightly distal from the origin of the posterior communicating artery (PCoA), and runs to the posterior medial side and goes upward drawing a S-shaped curve passing outside the cerebral peduncle (left). Then it forms a convex vertex upwards and enters the choroidal fissure (middle). The top of AChoA is called the uncal point (middle and right). The AchoA is the main artery of posterior limb of the internal capsule, having unnamed perforating branches. Since all these branches of the AchoA originate proximal to the uncal point, identification of the uncal point is important during transcatheter embolization. Page 22 of 39

23 Fig. 10: A top-down view of volume-rendered CTA images by UHRCT are shown. The PCA can be classified into four segments as follows: P1 (precommunicating or crural) segment, extends from the basilar artery bifurcation to the junction with PCoA; P2 (ambient) segment, extends from the P1/PCoA junction, curves around the cerebral peduncle within the ambient cistern; P3 (quadrigeminal) segment, extends behind the midbrain to the calcarine fissure (occipital lobe); P4 (calcarine) segment, terminates after the P3 segment. Page 23 of 39

24 Fig. 11: Lateral view of the volume-rendered (VR) CTA image by UHRCT is shown on the left, and medial view of the VR 3D-T1WI image is shown on the right. The calcarine artery runs through the calcarine fissure. The calcarine fissure is where the primary visual cortex is concentrated. The central visual field is located in the posterior portion of the calcarine fissure and the peripheral visual field in the anterior portion. Therefore, depiction of calcarine artery is important before surgery. Parieto-occipital artery runs through the parieto-occipital fissure. In cases where parieto-occipital fissure cannot be identified by brain tumor, this artery marks the boundary between the parietal and occipital lobes. Page 24 of 39

25 Fig. 12: Coronal MPR image from CTA by UHRCT is shown. The posterior thalamoperforating artery originates from the top of basilar artery or P1 segment. It supplies the internal thalamus and the midbrain. Obstruction of this artery causes the severe disturbance of consciousness. Its branch originating from the P1 segment that supplies both sides of the thalamus and midbrain is called the artery of Percheron. Page 25 of 39

26 Fig. 13: Left is the sagittal MPR image, and right is the coronal MPR image from CTA by UHRCT. Thalamogeniculate arteries arise from P2 (circle). They supply the geniculate nucleus, pulvinar, posterior part of the thalamus, posterior limb of internal capsule, superior colliculus and optic tract. So, obstruction of this arteries causes disturbance of contralateral superficial and deep sensibility, severe thalamic pain, light hemiplegia and involuntary action known as Dejerine-Roussy syndrome. Page 26 of 39

27 Fig. 14: Lateral view of the volume-rendered CTA image by UHRCT. The ACA supplies the corpus callosum, the medial of frontal and parietal lobe. The ACA can be classified into five segments as follows: A1 segment, extends from ICA bifurcation to junction with anterior communicating artery (ACoA); A2 segment, runs superiorly in interhemispheric fissure, extends from A1/ACoA junction to anterior to rostrum and genu of the corpus callosum; A3 segment, curves around the corpus callosum genu; A4 segment, anterior part of the corpus callosum body; A5 segment, posterior part of the corpus callosum body Page 27 of 39

28 Fig. 15: Lateral view of the volume-rendered CTA image by UHRCT. Cortical branches of the ACA supply the corpus callosum, the medial side of frontal and parietal lobes. There are two types of branching patterns of cortical branches of the ACA as follows: as cortical branches of each ACA shown in this patient, some of them are branched from the callosomarginal artery and others, directly from the pericallosal artery. The pericallosal artery anastomoses with the posterior pericallosal artery branching from parieto-occipital artery. As in moyamoya disease, this branch often develops as collateral vessels. The pericallosal-callosomarginal arterial junction is important that it is the site of predilection for distal anterior cerebral artery aneurysm (DACAAN). Page 28 of 39

29 Fig. 16: A top-down view of the volume-rendered CTA image by UHRCT. There are numerous variations of origin and numbers of the recurrent artery of Heubner. Variations of origin are as follows: A2 78%; A1 14%; A1-A2 junction 24%, and numbers of this artery are as follows: single 28%; double 48%; triple or quadruple 24%. Page 29 of 39

30 Fig. 17: An AP view of the volume-rendered CTA image by UHRCT. In this case, the number of the left recurrent artery of Heubner is two and one of them arises from distal A1, another from A1-A2 junction. This artery supplies the anterior part of caudate nucleus and putamen, anterior limb of internal capsule and fasciculus uncinatus. Obstruction of this artery causes facial paralysis, upper-limb hemiparesis and aphasia on dominant side. Page 30 of 39

31 Fig. 18: Coronal fusion of CTA by UHRCT and 3D-FLAIR image. The MCA can be classified into four segments as follows: M1 (sphenoidal segment), extends from the terminal ICA bifurcation to the sylvian fissure; M2 (insular segments), course superiorly within the sylvian fissure and ramify over surface of the insula; M3 (opercular segments), begin at top of the sylvian fissure and course inferolaterally through the sylvian fissure towards the cortex; M4 (cortical segments), begin at the external of the sylvian fissure and extend over the lateral surface on the cortex of hemisphere. Page 31 of 39

32 Fig. 19: Lateral view of volume-rendered CTA image by UHRCT is shown. Cortical branches of MCA coursing over surface on the cortex are those names are based on their perfusion area. Some parts of cortical branches are used as a recipient artery in operation of superficial temporal artery to middle cerebral artery (STA-MCA) bypass. Page 32 of 39

33 Fig. 20: Left is a MIP CTA image and right is a coronal MPR CTA image. Both CTA images by UHRCT clearly demonstrate lateral lenticulostriate arteries (LSAs) arising from the mid- and distal M1 segment (circle, open arrow). LSAs are clinically critical as the frequent source of cerebral hemorrhage and infarction of the basal ganglia. Coronal MPR image shows severe stenosis at the distal left M1 segment (arrowhead), though LSAs arising slight distal stenosis (open arrow) are clearly demonstrated by UHRCT. LSAs are "end arteries", meaning that the regions they supply do not have significant collateral blood supply. When occluded, it produces a lacunar infarct in the tissue they supply. Page 33 of 39

34 Fig. 21: MIP CTA image by UHRCT demonstrates the pontine arteries, perforating branches of the basilar artery (arrows). In this case with asymptomatic basilar artery stenosis (arrowhead), the pontine arteries originate distal to the stenosis as well as the anterior inferior cerebellar artery (open arrow) originated proximal to the stenosis are intact. Page 34 of 39

35 Fig. 22: Coronal MPR image from CTA by UHRCT demonstrates the anterior spinal artery (ASA). The ASA arises from the vertebral artery at the level of the medulla oblongata. The two vertebral arteries (one of which is usually bigger than the other) anastomose in the midline to form a single anterior spinal artery at the level of the foramen magnum. The ASA descends along the anterior median fissure located on the anterior surface of the spinal cord. Therefore, depiction of the ASA is important marker of the anterior median fissure before surgery. Page 35 of 39

36 Table 1 Page 36 of 39

37 Conclusion It has become possible to readily demonstrate not only cortical branches but also perforating branches of the major cerebral arteries by CTA using UHRCT as shown in this exhibit. However, this demonstration is generally difficult even with UHRCT, because these perforating branches are very small and their delineation is often obscured by surrounding image noise and spatial overlap by adjacent vessels. Thus, it is critical for radiologists and radiology technicians to fully understand the anatomy and clinical significance of the perforating branches for providing clinically useful CTA images by removing unnecessary vessels. Page 37 of 39

38 Personal information 1) 2) 1) 1) Miho Gomyo, Kazuhiro Tsuchiya, Haruhiko Machida, Shichiro Katase, Masamichi 1) 1) 1) Koyanagi, Arisa Ohara, Hisae Shiga, Kenichi Yokoyama 1) 1) Department of Radiology, Kyorin University Faculty of Medicine, Mitaka city, Tokyo, Japan. 2) Department of Radiology, Saitama Medical Center, Saitama Medical University, Kawagoe city, Saitama, Japan Page 38 of 39

39 References 1) Yuzo M, Chie S, Koji T, et al. Difficulties in neck clipping of internal carotid posterior communicating aneurysms. Surgery for cerebral stroke. 19; 1: ) Yasargil MG. Middle cerebral artery, inferior medial group or "lenticulostriate or striate vessels". IN: Yasargil MG, editor. Microneurosurgery #. New Yrok: Georg Thieme Verlag Stuttgart; P Page 39 of 39