How to recognize the variations of the cerebral vasculature? CT angiography snapshot

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1 How to recognize the variations of the cerebral vasculature? CT angiography snapshot Award: Cum Laude Poster No.: C-0412 Congress: ECR 2014 Type: Educational Exhibit Authors: Y. Pekcevik; Karabaglar/Izmir/TR Keywords: Computer Applications-3D, CT-Angiography, Vascular, CNS, Anatomy, Education and training DOI: /ecr2014/C-0412 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 65

2 Learning objectives To define the variations and anomalies of cerebral and cerebellar circulation. To show variations and anomalies of each cerebral and cerebellar artery at CT angiography and emphasize the clinical importance of these variations. To tell the tips and tricks of how to recognize and differentiate the vascular variations. Images for this section: Page 2 of 65

3 Fig. 1: Simple schematic diagrams of the fenestration(f)and duplication(d). Page 3 of 65

4 Background Computed tomography (CT) angiography has proven to be a very valuable tool for evaluation of the cerebral circulation (1). Owing to recent advances in CT technology it allows for better visualization of small vessels and has partially replaced digital subtraction angiography (2). Variations and anomalies of cerebral and cerebellar arteries are common and identification of them at CT angiography is clinically relevant. Anatomy and vascular variations are important for neurosurgeons and interventional neuroradiologists. Some variations such as persistent trigeminal artery may change surgical planning (3). Knowing the presence of variations such as fetal origin of the posterior cerebral artery may help management of a stroke patient. They may increase the incidence of aneurysm formation and sometimes may compress the cranial nerve and cause neurologic symptom (4,5). For interpreting the cerebral CT angiography correctly, radiologists should be familiar with the appearances of these variations. Images for this section: Page 4 of 65

5 Fig. 2: Schematic diagram of the double origin of the posterior inferior cerebellar artery (PICA). VA: vertebral artery. Page 5 of 65

6 Findings and procedure details The terms anomalous or abnormal are used to define any variant form observed in less than 1% of the general population. Some of the variability in the reported incidence likely reflects referral bias and even variability in definitions of "anomalous" and "normal" variant. We prefer to use the term 'vascular variation'for make it simple. Fenestration and duplication are two terms that can be confusing. Actually they describe different pathologies (Fig. 1). Page 6 of 65

7 Fig. 1: Simple schematic diagrams of the fenestration(f)and duplication(d). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Page 7 of 65

8 Fenestration is used for an arterial lumen that divides into distinctly separate lumens with distal convergence (they may or may not share an adventitial layer) (1, 6). There may be increased risk of aneurysm formation but definite association has not been found. Duplication is used for two distinct arteries with separate origins and no distal arterial convergence (1, 6). Double origin is a term that describes a vessel that forms from two separate vessels (7) (Fig. 2) Page 8 of 65

9 Fig. 2: Schematic diagram of the double origin of the posterior inferior cerebellar artery (PICA). VA: vertebral artery. References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Middle cerebral artery (MCA) Page 9 of 65

10 Early branching of the MCA: Early division of the MCA before insula (within 10 mm of its origin from the ICA) Clinical significance: No or little *Tips and Tricks: Do not call the anterior temporal branch (frontopolar branch) as an early bifurcation. It is the first branch of the MCA M1 (Fig. 3). Look at the big parting of the ways!!! Fig. 3: CT angiography 3D image shows anterior temporal branch (frontopolar branch), the first branch of the MCA M1 (arrows). Do not call these early braching of the MCA. Look for the big bifurcation (arrowheads). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Trifurcation: More than two divisions (Fig. 4) Clinical significance: No or little Page 10 of 65

11 *Tips and Tricks: It is a frequent finding and easy to recognize. Do not call the anterior temporal branch (frontopolar branch) as a trifurcation. It is the first branch of the MCA M1 (Fig. 3). Look at the big parting of the ways!!! Fig. 4: CT angiography 3D image shows bilateral trifurcation of the MCA (arrowheads). There is also trifurcation of anterior cerebral artery (three A2 segments) (arrow). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Duplication: A vessel originates from ICA, courses parallel to the main MCA and supplies the anterior temporal lobe (Fig. 5). Clinical significance: Rarely may be associated with aneurysm formation at its origin (8) *Tips and Tricks: Duplication originates from ICA and accessory MCA originates from anterior cerebral artery (ACA)!!! Compare anatomy with other side to recognize the variation!!! Page 11 of 65

12 Fig. 5: CT angiography 3D image shows duplication of the MCA, a small branch that originates from ICA (long arrow).there is also ipsilateral A1 hypoplasia (short arrow). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Accessory MCA: A vessel originates from ACA, courses parallel to the main MCA and supplies the anteriorinferior of the frontal lobe (Fig. 6, Fig. 7). Clinical significance: Aneurysm formation(9). Provide collateral supply to the distal MCA territory (1). *Tips and Tricks: Difficult to differentiate from the recurrent artery of Heubner (RAH). Accessory MCA courses parallel to the main MCA and has cortical territory but RAH do not course parallel to the main MCA and do not have cortical territory!!! (Fig. 8) Page 12 of 65

13 Fig. 6: CT angiography 3D image shows accessory MCA, a small branch that originates from ACA (arrow).there is also anterior communicating artery fenestration (arrowhead) and MCA trifurcation (double arrows). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Fig. 7: CT angiography 3D image shows accessory MCA, originates from ACA at the A1-A2 level (arrow). The vessel courses parallel to the main MCA. This feature helps differentiate it from the recurrent artery of Heubner. Page 13 of 65

14 References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Fig. 8: CT angiography 3D image shows recurrent artery of Heubner (arrowhead). The course of the artery is not parallel to the main MCA. It is medial lenticulostriate artery and does not have cortical territory. There is also early braching of the left MCA (arrow). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Fenestration: Very rare. Usually located in the proximal portion of the M1 segment. Clinical significance: Unknown. Aneurysm formation? *Tips and Tricks: May be difficult to catch. Look at 3D images! (Fig. 9) Page 14 of 65

15 Fig. 9: CT angiography 3D image shows fenestration of the distal portion of the middle cerebral artery M1 segment (arrow). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Anterior cerebral artery (ACA) Hypoplasia and aplasia of the ACA A1 segment: Hypoplasia is frequent, aplasia is rare (Fig. 5, Fig. 10) Clinical significance: Most or all of the territory may be supplied by contralateral normalsized ACA. In the thromboembolic disease, this may cause increased risk of infarction (10). *Tips and Tricks: To differentiate aplasia and hypoplasia, look for thin-slice maximum intensity projection (MIP) images! In the event of subarachnoid hemorrhage small vessel size may be due to vasospasm!!! Page 15 of 65

16 Fig. 10: CT angiography 3D image shows absence of the left ACA A1 segment (arrow). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Trifurcation: Presence of three A2 segments. Third artery represents persistence of the median callosal artery (1, 11). (Fig. 4) Clinical significance: unknown *Tips and Tricks: An additional third A2 segment arising from anterior communicating artery and coursing parallel to the other segments!!! Page 16 of 65

17 Fig. 4: CT angiography 3D image shows bilateral trifurcation of the MCA (arrowheads). There is also trifurcation of anterior cerebral artery (three A2 segments) (arrow). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Bihemispheric ACA: Hypoplasia of one A2 segment. Bilateral major arterial supply is from the other, dominant A2 segment. (Fig. 11) Clinical significance: Thromboembolism of the dominant A2 segment results in ischemia of both hemispheres (1) *Tips and Tricks: Precence of a thin A2 segment help differentiate bihemispheric ACA from azygos ACA!!! Page 17 of 65

18 Fig. 11: CT angiography 3D image demonstrates bihemispheric ACA. Dominant A2 segment that supplies both ACA territories has operated aneurysm at the level of furcation (short arrow). The smaller, nondominant A2 segment (arrowhead) courses parallel to the dominant segment. There is small aneurysm at MCA bifurcation (double arrows). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Azygos ACA: Single midline A2 represents persistence of the median callosal artery (Fig. 12). Clinical significance: May be associated with holoprosencephaly and various congenital anomalies. May be associated with aneurysm formation. Occlusion of the single A2 results in ischemia of both hemispheres (12) *Tips and Tricks: Make sure that there is no other A2 segment to differentiate azygos ACA from bihemispheric ACA!!! Page 18 of 65

19 Fig. 12: CT angiography 3D image demonstrate azygos ACA, a single midline A2 trunk (arrow). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Fenestration: Very rare (Fig. 13) Clinical significance: unknown, aneurysm formation? *Tips and Tricks: May be difficult to catch. Look at both MIP and 3D images!!! Page 19 of 65

20 Fig. 13: CT angiography 3D image demonstrates fenestration of the distal portion of the right ACA A1 segment (arrow). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Anterior communicating artery (ACoA) Fenestration and duplication: Common (Fig. 14) Clinical significance: Aneurysm formation? *Tips and Tricks: Sometimes they may be mistaken for an aneurysm. Look at both MIP and 3D images to differentiate!!! Page 20 of 65

21 Fig. 14: CT angiography 3D image shows aneurysm formation associated with fenestration of the AcoA (arrow). Arrowheads indicate posterior communicating artery infundibulum. References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Absence: Absence of the AcoA (Fig. 15) Clinical significance: It is one of the main collateral supplies at the circle of Willis. *Tips and Tricks: Look at a thin slice MIP images to make sure that it is absent!!! Page 21 of 65

22 Fig. 15: CT angiography 3D image shows absence of the AcoA (arrow). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Anterior choroidal artery (AChA) and posterior communicating artery (PcoA) Hyperplastic AChA: Prominent AChA, larger than usual (Fig. 16). Clinical significance: The temporo-occipital branches of the PCA may arise from the AChA. *Tips and Tricks: Be aware AChA-PcoA confusion! AChA originates supraclinoid ICA above the PcoA!!! Fig. 16: CT angiography 3D image shows prominent, hyperplastic AChA (arrow). Arrowhead indicates prominent PcoA (fetal origin of the PCA, partial). Do not mistake Page 22 of 65

23 fetal origin of the PCA with hyperplastic AChA because it also originates from ICA, but little bit lower level, but continues with PCA P2 segment (double arrowheads) References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Infundibulum: Cone-shaped dilatation at the origin of the artery, smaller 2 mm, usually symmetric (Fig. 14) Clinical significance: Should be distinguished from aneurysm. *Tips and Tricks: PcoA arises from the apex of a cone-shaped infundibulum and the base of the infundibulum is located at the ICA (Fig. 17). Fig. 17: CT angiography sagittal thin slice MIP image demonstrates the PcoA arising from the apex of a cone-shaped infundibulum (arrow). The AChA is originating from the supraclinoid ICA above the PcoA (double arrows). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Absence of the PcoA: Page 23 of 65

24 Absence of the one or both PcoA Clinical significance: It is one of the main collateral supplies at the circle of Willis. *Tips and Tricks: Look at a thin-slice MIP images to make sure that it is absent!!! Fenestration: Very rare (Fig. 18) Clinical significance: unknown, aneurysm formation? *Tips and Tricks: May be difficult to catch. Look at 3D images!!! Page 24 of 65

25 Fig. 18: CT angiography 3D image demonstrates fenestration of distal portion of the PcoA (arrow). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Posterior cerebral artery (PCA) Fetal origin of the PCA: The embryonic posterior cerebral artery fails to regress (PcoA is prominent). There is ipsilateral the same size or hypoplastic PCA P1 segment (partial type). Rarely P1 is absent (full type fetal PCA) (14) (Fig. 16, Fig. 19) Clinical significance: Dominant blood supply to the occipital lobes comes from ICA. ICA atheromatous disease may cause PCA territory stroke *Tips and Tricks: Look at a thin slice MIP images to make sure that ipsilateral PCA P1 is absent!!! Fig. 19: CT angiography 3D image shows prominent PcoA (double arrowheads) with ipsilateral hypoplasia of the PCA P1 segment (arrowhead) (fetal origin of the PCA, partial). There is also basilar artery fenestration (double arrows). Page 25 of 65

26 References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Fenestration: Extremely rare (Fig. 20) Clinical significance: unknown, aneurysm formation? *Tips and Tricks: May be difficult to catch. Look at 3D images!!! Fig. 20: CT angiography 3D image demonstrates fenestration of the PCA P1 segment (arrow). Page 26 of 65

27 References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Basilar artery (BA) and vertebral artery (VA) BA fenestration: Common (Fig. 19). Can be seen in various forms! (Fig. 21 a-d) Clinical significance: Aneurysm formation *Tips and Tricks: Look like broken zipper!!! Sometimes they may be mistaken for an aneurysm. Look at both MIP and 3D images to differentiate!!! Page 27 of 65

28 Fig. 21: (a-d). CT angiography 3D images show various types of basilar artery or vertebrobasilar fenestration (arrows). There is also an aneurysm associated with BA fenestration in d (arrows) References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR VA Fenestration: Very rare (Fig. 22) Page 28 of 65

29 Clinical significance: unknown, aneurysm formation? *Tips and Tricks: May be missed!!! 3D images are very helpful! Fig. 22: CT angiography 3D image demonstrates fenestration of the VA extradural and extraforaminal (V3) segment (arrow). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Page 29 of 65

30 VA hypoplasia: VA is less than 2.0 mm in diameter. Clinical significance: May be predisposing factor for posterior circulation cerebral ischemic events (15). *Tips and Tricks: Look at all other images and trace vertebral artery to make sure that it is not an occlusion or a dissection!!! VA continuation as PICA: Equal-sized VA and PICA with hypoplasia of the ipsilateral VA (Fig. 23). Clinical significance: May change vascular stroke areas at cerebellum. *Tips and Tricks: Look at all other images and trace vertebral artery to make sure that it is not a VA occlusion or stenosis distal to its PICA branch!!! Page 30 of 65

31 Page 31 of 65

32 Fig. 23: CT angiography 3D image shows equal-sized vertebral artery (short arrow) and PICA (double arrows). Vertebral artery has hypoplasia just after its PICA branch (arrowhead). There is also a basilar artery fenestration and associated aneurysm (long arrow). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Superior cerebellar artery (SCA) Duplication: Two SCA with separate origins and no distal convergence (Fig. 24a). Clinical significance: Unknown *Tips and Tricks: Look at MIP images to identify! Early bifurcation: Bifurcation of the SCA before expected distal portion (Fig. 24b). Clinical significance: Unknown *Tips and Tricks: Look at MIP images to identify! Common trunk of the PCA and SCA: SCA and PCA P1 segment have common origin (Fig. 24c). Clinical significance: May be associated with cranial nerve compression (16) *Tips and Tricks: Sometimes it can resemble aneurysm at 3D images. Look at MIP images to differentiate!!! SCA originating from PCA: SCA take its origin from PCA rather than BA (Fig. 24d). Clinical significance: Unknown *Tips and Tricks: BA looks like open zipper in the upper segment! Page 32 of 65

33 Fig. 24: CT angiography 3D images show variations of the SCA (arrows). (a) Duplication, (b) early bifurcation, (c) SCA and PCA originating as a common trunk, (d) bilateral SCA originating from PCA. References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Fenestration: Extremely rare Clinical significance: Unknown, aneurysm formation?. May predispose vessel occlusion (thinner vessels)? *Tips and Tricks: May be difficult to catch. Look at thin-slice MIP images!!! Anterior inferior cerebellar artery (AICA) and posterior inferior cerebellar artery (PICA) Duplication of AICA, PICA: Page 33 of 65

34 Two vessels with separate origins, without distal arterial convergence Clinical significance: May predispose vessel occlusion (thinner vessels)? May change vascular stroke areas at cerebellum *Tips and Tricks: May be difficult to catch. Look at thin-slice MIP images!!! Double origin of the PICA: Two PICA with separate origins and distal arterial convergence (Fig.1, Fig. 25) Clinical significance: May predispose vessel occlusion (thinner vessels)? *Tips and Tricks: May be difficult to catch. Look at thin-slice MIP images!!! Page 34 of 65

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36 Fig. 25: CT angiography 3D image shows double origin of the PICA, two distinct PICA with separate origins and distal convergence (arrow). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Extradural origin of the PICA: PICA originates from proximal to the intracranial segment of the VA (Fig. 26). Clinical significance: May change surgical approach. May be origin of the subarachnoid hemorrhage due to associated aneurysm *Tips and Tricks: Trace vertebral artery carefully to look for origin of the PICA! Page 36 of 65

37 Fig. 26: CT angiogram 3D image demonstrates the PICA that takes its origin proximal to the intracranial segment of the vertebral artery, extradural origin of the PICA (arrow). References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Fenestration: Page 37 of 65

38 Extremely rare Clinical significance: May predispose occlusion (thinner vessels)? *Tips and Tricks: Very difficult to catch. Look at thin-slice MIP images!!! Internal carotid artery (ICA) Fenestration: Very rare (Fig. 27) Clinical significance: May be mistaken for an aneurysm. *Tips and Tricks: May be difficult to catch. Look at both MIP and 3D images!!! Page 38 of 65

39 Fig. 27: CT angiography 3D image demonstrates fenestration of the internal carotid artery (arrow). Page 39 of 65

40 References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Persistent Carotid-Basilar Artery Anastomoses: Failure of carotid-vertebrobasilar anastomoses to regress during embryonic development (1). These are the trigeminal (Fig. 28), otic, hypoglossal and proatlantal intersegmental arteries from cephalic to caudal. Clinical significance: It is precence may change surgical approach. May be associated with aneurysm (17). May be responsible for ischemia and cranial nerve neuralgia (1) *Tips and Tricks: Suspect when there is an additional vessel between ICA and BA, with and without BA hypoplasia distal to the anastomosis!!! Be aware they may be seen in various configurations! Fig. 28: CT angiography (a) coronal and (b) axial MIP images show the persistent trigeminal artery, the most common and most cephalic of the persistent carotidvertebrobasilar anastomoses. There is an additional branch between BA and ICA (arrows) that courses lateral to the sella. References: Radiology, Izmir Tepecik Training and Research Hospital - Karabaglar/ Izmir/TR Images for this section: Page 40 of 65

41 Fig. 1: Simple schematic diagrams of the fenestration(f)and duplication(d). Page 41 of 65

42 Fig. 2: Schematic diagram of the double origin of the posterior inferior cerebellar artery (PICA). VA: vertebral artery. Page 42 of 65

43 Fig. 3: CT angiography 3D image shows anterior temporal branch (frontopolar branch), the first branch of the MCA M1 (arrows). Do not call these early braching of the MCA. Look for the big bifurcation (arrowheads). Page 43 of 65

44 Fig. 4: CT angiography 3D image shows bilateral trifurcation of the MCA (arrowheads). There is also trifurcation of anterior cerebral artery (three A2 segments) (arrow). Fig. 5: CT angiography 3D image shows duplication of the MCA, a small branch that originates from ICA (long arrow).there is also ipsilateral A1 hypoplasia (short arrow). Page 44 of 65

45 Fig. 6: CT angiography 3D image shows accessory MCA, a small branch that originates from ACA (arrow).there is also anterior communicating artery fenestration (arrowhead) and MCA trifurcation (double arrows). Fig. 7: CT angiography 3D image shows accessory MCA, originates from ACA at the A1-A2 level (arrow). The vessel courses parallel to the main MCA. This feature helps differentiate it from the recurrent artery of Heubner. Page 45 of 65

46 Fig. 8: CT angiography 3D image shows recurrent artery of Heubner (arrowhead). The course of the artery is not parallel to the main MCA. It is medial lenticulostriate artery and does not have cortical territory. There is also early braching of the left MCA (arrow). Page 46 of 65

47 Fig. 9: CT angiography 3D image shows fenestration of the distal portion of the middle cerebral artery M1 segment (arrow). Fig. 10: CT angiography 3D image shows absence of the left ACA A1 segment (arrow). Page 47 of 65

48 Fig. 11: CT angiography 3D image demonstrates bihemispheric ACA. Dominant A2 segment that supplies both ACA territories has operated aneurysm at the level of furcation (short arrow). The smaller, nondominant A2 segment (arrowhead) courses parallel to the dominant segment. There is small aneurysm at MCA bifurcation (double arrows). Page 48 of 65

49 Fig. 12: CT angiography 3D image demonstrate azygos ACA, a single midline A2 trunk (arrow). Page 49 of 65

50 Fig. 13: CT angiography 3D image demonstrates fenestration of the distal portion of the right ACA A1 segment (arrow). Fig. 14: CT angiography 3D image shows aneurysm formation associated with fenestration of the AcoA (arrow). Arrowheads indicate posterior communicating artery infundibulum. Page 50 of 65

51 Fig. 15: CT angiography 3D image shows absence of the AcoA (arrow). Page 51 of 65

52 Fig. 16: CT angiography 3D image shows prominent, hyperplastic AChA (arrow). Arrowhead indicates prominent PcoA (fetal origin of the PCA, partial). Do not mistake fetal origin of the PCA with hyperplastic AChA because it also originates from ICA, but little bit lower level, but continues with PCA P2 segment (double arrowheads) Fig. 17: CT angiography sagittal thin slice MIP image demonstrates the PcoA arising from the apex of a cone-shaped infundibulum (arrow). The AChA is originating from the supraclinoid ICA above the PcoA (double arrows). Page 52 of 65

53 Fig. 18: CT angiography 3D image demonstrates fenestration of distal portion of the PcoA (arrow). Page 53 of 65

54 Fig. 19: CT angiography 3D image shows prominent PcoA (double arrowheads) with ipsilateral hypoplasia of the PCA P1 segment (arrowhead) (fetal origin of the PCA, partial). There is also basilar artery fenestration (double arrows). Page 54 of 65

55 Fig. 20: CT angiography 3D image demonstrates fenestration of the PCA P1 segment (arrow). Page 55 of 65

56 Fig. 21: (a-d). CT angiography 3D images show various types of basilar artery or vertebrobasilar fenestration (arrows). There is also an aneurysm associated with BA fenestration in d (arrows) Page 56 of 65

57 Fig. 22: CT angiography 3D image demonstrates fenestration of the VA extradural and extraforaminal (V3) segment (arrow). Page 57 of 65

58 Page 58 of 65

59 Fig. 23: CT angiography 3D image shows equal-sized vertebral artery (short arrow) and PICA (double arrows). Vertebral artery has hypoplasia just after its PICA branch (arrowhead). There is also a basilar artery fenestration and associated aneurysm (long arrow). Fig. 24: CT angiography 3D images show variations of the SCA (arrows). (a) Duplication, (b) early bifurcation, (c) SCA and PCA originating as a common trunk, (d) bilateral SCA originating from PCA. Page 59 of 65

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61 Fig. 25: CT angiography 3D image shows double origin of the PICA, two distinct PICA with separate origins and distal convergence (arrow). Fig. 26: CT angiogram 3D image demonstrates the PICA that takes its origin proximal to the intracranial segment of the vertebral artery, extradural origin of the PICA (arrow). Page 61 of 65

62 Fig. 27: CT angiography 3D image demonstrates fenestration of the internal carotid artery (arrow). Page 62 of 65

63 Fig. 28: CT angiography (a) coronal and (b) axial MIP images show the persistent trigeminal artery, the most common and most cephalic of the persistent carotidvertebrobasilar anastomoses. There is an additional branch between BA and ICA (arrows) that courses lateral to the sella. Page 63 of 65

64 Conclusion Vascular variations of the cerebral and cerebellar arteries are common and can be noninvasively evaluated by CT angiography. Radiologist should identify and report these vascular variations because they may have a clinical significance. Personal information Yeliz Pekcevik Izmir Tepecik Training and Research Hospital, Department of Radiology Izmir/Turkey References Dimmick SJ, Faulder KC. Normal variants of the cerebral circulation at multidetector CT angiography. Radiographics 2009; 29: Jayaraman MV, Mayo-Smith WW, Tung GA, et al. Detection of intracranial aneurysms: multi-detector row CT angiography compared with DSA. Radiology 2004; 230: Meaney JF, Sallomi DF, Miles JB. Transhypophyseal primitive trigeminal artery: demonstration with MRA. J Comput Assist Tomogr 1994; 18: Hashimoto M, Urasaki E, Tsujigami S, et al. Ruptured aneurysm associated with partially duplicated posterior communicating artery-case report. Neurol Med Chir (Tokyo). 2002; 42:23-6. Songur A, Gonul Y, Ozen OA, et al. Variations in the intracranial vertebrobasilar system. Surg Radiol Anat 2008; 30: Parmar H, Sitoh YY, Hui F. Normal variants of the intracranial circulation demonstrated by MR angiography at 3T. Eur J Radiol 2005; 56: Lesley WS, Rajab MH, Case RS. Double origin of the posterior inferior cerebellar artery: association with intracranial aneurysm on catheter angiography. AJR Am J Roentgenol 2007; 189: Takahashi T, Suzuki S, Ohkuma H, et al. Aneurysm at a duplication of the middle cerebral artery. AJNR Am J Neuroradiol 1994; 15: Kuwabara S, Naitoh H. Ruptured aneurysm at the origin of the accessory middle cerebral artery: case report. Neurosurgery 1990; 26: Page 64 of 65

65 10. Yamaguchi K, Uchino A, Sawada A, et al. Bilateral anterior cerebral artery territory infarction associated with unilateral hypoplasia of the A1 segment: report of two cases. Radiat Med 2004; 22: Pekcevik Y, Hasbay E, Oncel D. Colloid cyst of the third ventricle associated with anterior cerebral artery trifurcation and agenesis of the corpus callosum: findings on MRI and CT angiography. Pediatr Radiol 2012; 42: Okahara M, Kiyosue H, Mori H, et al. Anatomic variations of the cerebral arteries and their embryology: a pictorial review. Eur Radiol 2002; 12: van Rooij SB, van Rooij WJ, Sluzewski M, et al. Fenestrations of intracranial arteries detected with 3D rotational angiography. AJNR Am J Neuroradiol 2009; 30: van Raamt AF, Mali WP, van Laar PJ, et al. The fetal variant of the circle of Willis and its influence on the cerebral collateral circulation. Cerebrovasc Dis 2006; 22: Katsanos AH, Kosmidou M, Kyritsis AP, et al. Is vertebral artery hypoplasia a predisposing factor for posterior circulation cerebral ischemic events? A comprehensive review. Eur Neurol 2013;70: Oizumi T, Ohira T, Kawase T. Angiographic manifestations and operative findings with 70 cases of hemifacial spasm: relation of common trunk anomalies. Keio J Med 2003; 52: Caldemeyer KS, Carrico JB, Mathews VP. The radiology and embryology of anomalous arteries of the head and neck. AJR Am J Roentgenol 1998;170: Page 65 of 65