Persistent Fetal Carotid –Vertebrobasilar Anastomoses and Other Anomalies-Pictorial Essay Sagar Shetty1, Parangama Chatterjee2, Makarand Kulkarni3, Mehul Vikani4, Murtuza J5, Preeti Kapoor6, Hariprasad Shetty7 Clinical associate, Dept of Radiology, Lilavati Hospital &Research Centre, Mumbai, India
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Consultant, Dept of Radiology,Lilavati Hospital &Research Centre, Mumbai, India
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Asst. Professor, Dept of General Surgery, MGM Hospital, Navi Mumbai, India
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Fellow, Dept of Ophthalmology, Narayan Netralaya, Bangalore, India
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Asso. Professor, Dept of Radiology, MGM Hospital, Navi Mumbai, India
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Asst. Professor, Dept of General Medecine, B.L Cooper Hospital, Mumbai, India
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drsrs87@gmail.com; 2parangamadr@gmail.com; 3makarand_kul@yahoo.com; 4mehulvikani@gmail.com; murtu.95@gmail.com; 6pritikaps@gmail.com; 7harrycool86@gmail.com
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Abstract MRA examination includes a review of three-dimensional and maximum intensity projection images of the intra- and extra cranial arteries to look for anomalies and normal variants like absence, duplication, persistent fetal arteries etc since it plays an important role in management of acute stroke and preoperative planning. Very often, these variants are associated with intracranial malformations like aneurysm, steal, or compression on cranial nerves. Hence, a neuroradiologist should have adequate knowledge of these normal variants which would help in management planning. This pictorial essay reviews various normal anatomical variants and congenital anomalies of internal carotid arteries. Keywords Persistent Trigeminal; Otic, Hypoglossal; Fetal Carotid –Vertebrobasilar Anastomoses; Fenestration; Absent ICA
Introduction MRA examination includes a review of three-dimensional and maximum intensity projection images of the intraand extra cranial arteries to look for anomalies and normal variants like absence, duplication, persistent fetal arteries etc since it plays an important role in management of acute stroke and preoperative planning. Very often, these variants are associated with intracranial malformations like aneurysm, steal, or compression on cranial nerves. This pictorial essay reviews various normal anatomical variants and congenital anomalies of internal carotid arteries. Embryology Padget [1] described the embryology and the various anatomic variations and persistent fetal intracranial anomalies. The forebrain is supplied by the carotid system during the 4mm embryo stage. Hindbrain is supplied by two longitudinal pair of arteries that run along its surface and ultimately join to form the basilar artery. There are four important arterial anastomoses i.e. the trigeminal artery, the otic artery, the hypoglossal artery, and the proatlantal intersegmental artery all of which supply the longitudinal neural arteries via carotid arteries. (Figure. 1). Posterior communicating artery is formed by the anastomosis between distal internal carotid artery and corresponding longitudinal neural artery, during 5-6 mm embryo stage. Later, the presegmental arteries and proatlantal intersegmental arteries regress and obliterate. Otic artery obliterates first which is followed by hypoglossal, trigeminal and lastly the proatlantal intersegmental artery. Until 7-12 mm embryo stage, the International Journal of Advance in Medical Science, Vol. 3, No. 2—November 2015 2327-7238/15/02 045-6 © 2015 DEStech Publications, Inc. doi:10.12783/ams.2015.0302.02
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Sagar Shetty, Parangama Chatterjee, Makarand Kulkarni, Mehul Vikani, Murtuza J, Preeti Kapoor, Hariprasad Shetty
proatlantal intersegmental arteries supply the caudal part of neural arteries after which the vertebral arteries attain function. Approximately at around 7- to 12-mm embryo stage, the basilar artery is formed by union of longitudinal neural arteries. The vertebral arteries are formed by union of multiple longitudinal anastomoses between adjoining cervical intersegmental arteries. (Figure 2). Rarely duplication of vertebral artery takes place if there is any malfunction in union at any level.
FIGURE 1. EMBRYO STAGE, 4 MM. TRIGEMINAL ARTERIES (TA), OTIC ARTERIES (OA), HYPOGLOSSAL ARTERIES (HA), AND PROATLANTAL INTERSEGMENTAL ARTERIES (PA) CONNECT INTERNAL CAROTID ARTERIES TO LONGITUDINAL NEURAL ARTERIES.
FIGURE 2. LONGITUDINAL NEURAL ARTERIES FUSE AND TRIGEMINAL ARTERY, OTIC ARTERY, HYPOGLOSSAL ARTERY, AND PROATLANTAL INTERSEGMENTAL ARTERY REGRESS AND OBLITERATE.
Persistent Trigeminal Artery The incidence of persistent trigeminal artery reported is around 0.2%, though many times this condition goes undiagnosed and unreported since it does not produce any symptoms. Hence considering this fact the incidence might probably reach up to 1% [2]. Persistent trigeminal artery represents about 85% of the carotid-basilar anastomoses [2]. It takes it origin from the cavernous part of internal carotid artery in the region where it exits the carotid canal and enters the cavernous sinus. The trigeminal artery joins the basilar artery in either of two ways [3]. In about 50% of cases, the trigeminal artery pierces the sella turcica, courses in its own groove, and penetrates the dura near the clivus to eventually join the basilar artery between the anterior inferior cerebellar arteries and the superior cerebellar arteries. In the other 50 % of cases, the trigeminal artery egresses from the cavernous sinus, runs along with the trigeminal root, or courses between the sensory trigeminal root and the lateral aspect of the sella, in a groove for the posterior petrosal process, the roof of which is formed by the petroclinoid ligament. It then unites with the basilar artery between the anterior inferior cerebellar arteries and the superior cerebellar arteries. The persistent trigeminal artery links the cavernous internal carotid artery to the basilar artery (Figure 3). It is seldom associated with unilateral or bilateral hypoplastic vertebral arteries. Figures 4, 5, and 6 show MR angiogram images of the same.
FIGURE 3. DIAGRAMATIC REPRESENTATION SHOWING PERSISTENT TRIGEMINAL ARTERY
Persistent Fetal Carotid –Vertebrobasilar Anastomoses and Other Anomalies-Pictorial Essay
FIGURE 4
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FIGURE 5
FIGURE 6 FIGURES 4, 5, 6. MR ANGIOGRAM MIP IMAGES DEPICTING PERSISTENT TRIGEMINAL ARTERY
Persistent Hypoglossal Artery Persistent hypoglossal artery is the second most common type of persistent carotid-vertibrobasilar anastomosis. About 160 cases have been reported so far [2]. The hypoglossal artery arises from internal carotid artery at the level of C1 and C3 then passes through the hypoglossal canal to join the basilar artery [4] (Figure 7). It does not pass though the foramen magnum. One or both of the vertebral arteries may be aplastic or hypoplastic. Figures 8, 9 show MR angiogram images of the same.
FIGURE 7. PERSISTENT HYPOGLOSSAL ARTERY WITH APLASTIC VERTEBRAL ARTERY
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Sagar Shetty, Parangama Chatterjee, Makarand Kulkarni, Mehul Vikani, Murtuza J, Preeti Kapoor, Hariprasad Shetty
FIGURE 8
FIGURE 9
FIGURE 8, 9. MR ANGIOGRAM MIP IMAGES DEPICTING PERSISTENT HYPOGLOSSAL ARTERY
Persistent Otic Artery Till date very few cases have been reported [2], as very often this condition goes undiagnosed. In order to confidently diagnose this condition there are few criteria, mainly being the vessel should originate from petrous part of internal carotid artery i.e. it should be contained within the carotid canal and then course through the internal auditory canal and finally join the proximal basilar artery (Figure 10). A variant of otic artery often directly joins one of the cerebellar arteries.
FIGURE 10. PERSISTENT OTIC ARTERY
Absent Internal Carotid Artery: Congenital absence of internal carotid artery is a rare anomaly. To our knowledge, very few cases have been reported [5]. Frequently, these patients remain asymptomatic as a result of collateral circulation from the Circle of Wills and sometimes by persistent embryological vessels and transcranial collaterals via the ECA. Many theories have been put forward to explain the cause of absence, mainly being mechanical and hemodynamic stress on the embryo and also constriction of amniotic bands [6]. Sometimes these patients present with cerebrovascular insufficiency or complications related to aneurysms of collateral vessels or rarely congenital Horners syndrome [7]. The above is illustrated by Figures 11 and 12.
Persistent Fetal Carotid –Vertebrobasilar Anastomoses and Other Anomalies-Pictorial Essay
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FIGURES 11, 12. MR ANGIOGRAM MIP IMAGES DEPICTING ABSENT LEFT ICA
Fenestration Fenestration is a segmental duplication of an artery resulting into two separate channels. Typical locations for fenestrations are anterior communicating artery, basilar artery and anterior cerebral artery. There are very few reports about fenestration of PCA with associated aneurysm (8, 9), with the exception of a report of fenestrated PCA associated with ruptured aneurysm in a child. (8). To our knowledge, there is only one report of fenestration of superior cerebellar artery (10). The proximal basilar artery is the most frequent site of fenestration and saccular aneurysms frequently arise at the proximal end of the fenestration .The reported incidence of this association is 7% (11) . The defect of the media at the junction of the fenestration and the stresses by the turbulent blood flow may increase the incidence of aneurysms at the fenestration site (9). However, aneurysms can also be seen at sites away from the site of fenestration; the incidence of aneurysms at the site of fenestration is not different from the typical association of other vessel bifurcations with saccular aneurysms. (11). The above is illustrated by Figures 13 and 14.
FIGURE 13. MR ANGIOGRAM MIP IMAGES DEPICTING FENESTRATED RIGHT PCA
FIGURE 14. AXIAL MR T2 WEIGHTED IMAGE SHOWING LEFT ICA ANEURYSM
Conclusion Hence it is very important to identify these normal variants and congenital anomalies as it plays an important role in patient management. Though most of the times these patients are asymptomatic, sometimes they are associated
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Sagar Shetty, Parangama Chatterjee, Makarand Kulkarni, Mehul Vikani, Murtuza J, Preeti Kapoor, Hariprasad Shetty
with intracranial malformations like aneurysm, steal, or compression on cranial nerves. Hence deriving this information is extremely useful as it helps in preoperative planning. ACKNOWLEDGMENTS
My sincere thanks to my teachers Dr. Makarand , Dr. Parangama, and Dr. Priti for teaching me Radiology and my collegues Dr. Mehul , Dr. Murtuza and Dr. Hariprasad for guiding me in writing this article and also providing me with all clinical information of the patients. CONFLICTS OF INTEREST
I hereby state that all the content and pictures used in this article are genuine and every author has contributed equally in writing this article. There are no conflicts of interest including any research funding, other financial support, and material support. REFERENCES
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Padget DH. The development of the cranial arteries in the human embryo Contr Embryol 1948;32:205-261
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Yilmaz E, Erhan I, Dogan T. Primitive persistent carotid-basilar and carotid-vertebral anastomoses: a report of seven cases and a review of the literature. Clin Anat 1995;8:36-43
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Lie TA. Congenital malformations of the carotid and vertebral arterial systems, including the persistent anastomoses. In: Vinken PJ, Bruyn OW, eds. Handbook of Clinical Neurology, vol. 12.
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Brismar J. Persistent hypoglossal artery: diagnostic criteria. Acta Radiol Diagn (Stock/i) 1976;17:160-166
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Afifi AK, Godersky JC, Menezes A, Smoker WR, Bell WE, Jacoby CG.Cerebral hemiatrophy, hypoplasia of internal carotid artery, and intracranial aneurysm: a rare association occurring in an infant.Arch Neurol1987;44:232–235
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Teal JS, Naheedy MH, Hasso AN.Total agenesis of the internal carotid artery.AJNR Am J Neuroradiol1980;1:435–442
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Ryan FH, Kline LB, Gomez C.Congenital Horner’s syndrome resulting from agenesis of the internal carotid artery. Ophthalmology 2000; 107:185–188.
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Lotfi Hacein-bey, Cheryl A Musczynski and Panayiotis N.Varelas. Saccular aneurysm associated with posterior cerebral artery aneurysm manifesting as subarachnoid hemorrhage in a child. American journal of neuroradiology 23:1291-1294, September 2002.
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Akira Uchino, Akira Kato, Yukinori Takase and Sho Kudo.Basilar artery fenestration detected by MR angiography. Radiation medicine Vol 19 No.2 71-74 p.p., 2001
[10] Akira Uchino, Akira Kato, Yukinori Takase and Sho Kudo. Variation of the superior cerebellar artery: MR angiographic demonstration. Radiation medicine Vol 21 No.6 235-238 p.p. 2003 [11] WP Sanders, PA Sorek and BA Mehta. Fenestration of intracranial arteries with special attention to associated aneurysms and other anomalies.AJNR 14:675-680, 1993. Dr. Sagar Shetty MBBS, MD (Radio-Diagnosis) is a team spirited individual with special interest in musculoskeletal, gastrointestinal and chest imaging. He has done his fellowship in Body Imaging from the prestigious King Edward Memorial Hospital, Mumbai. He has also presented various papers in various conferences and has many publications to his name.