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Neuroradiology 17, 105-109 (1979)
© by Springer-Verlag 1979
CASE REPORTS
Persistent Proatlantal Intersegmental Artery and Occipital Artery Originating from Internal Carotid Artery S. Suzuki 1, T. Nobechi 2, I. Itoh 3, M. Yakura 3 and K. Iwashita 3 Department of Radiology1, Tokyo Medical and Dental University, School of Medicine, and Departments of Radiology2 Neurosurgery3, St. Luke's International Hospital, Tokyo, Japan
Summary: A case of a combined anomaly of persistent hypoglossal and proatlantal intersegmental arteries, proved on arteriogram obtained by the insertion of a needle into the common trunk of both arteries, is presented. In addition, a case of anomalous occipital artery arising from the internal carotid artery associated with an intracranial aneurysm and arteriovenous malformation is presented. Based upon analysis of the persistent proatlantal intersegmental artery and the anomalous occipital artery, we conclude that both arteries have an identical embryological origin. Key words: Hypoglossal artery - Proatlantal artery Anomalous occipital artery
Introduction The third and fourth aortic arches appear at the 4mm stage of development of the human embryo, and the first and second aortic arches then regress, leaving two residual segments; the segment originating from the dorsal roots grows cephalad and becomes the internal carotid artery, and the other segment from the ventral roots becomes the external carotid artery [5, 13]. At the 7-mm stage, small paired vessels sprout from the dorsal aortae and run dorsally in the loose mesenchymal tissue between somites; the vessels are called the intersegmental arteries [13, 14, 15]. There are eight pairs of intersegmental arteries in the cervical region. Since the first pair is designated as the proatlantal or suboccipital intersegmental artery, the second pair is called the first cervical intersegmental artery and, therefore, there are seven pairs of cervical intersegmental arteries [5, 14]. At the 12-mm stage
of embryonic development, paired cervical intersegmental arteries are connected by a pair of secondary longitudinal channels, which become the vertebral artery after the first five cervical intersegmental arteries between the dorsal aortae and the longitudinal channels have involuted. The sixth cervical intersegmental artery, however, persists as a trunk for the buds of subclavian and vertebral arteries on both sides [14]. Bilateral vertebral arteries grow cephalad and traverse the foramen magnum, joining each other and forming a single median artery at the level of developing medulla oblongata. The exact manner of development of the basilar artery in the human embryo is not fully clarified but it is said that bilateral longitudinal neural arteries, closely applied to the ventral surface of the hindbrain, fuse to form the basilar artery during the 7-to 12-mm stage of development. The basilar artery eventually interconnects between the single median artery formed by fusion of bilateral vertebral arteries and the cranial end of the basilar artery formed by fusion of the caudal continuations of bilateral posterior communicating arteries which derive from the internal carotid arteries [8]. In the early stage of development the primitive vertebrobasilar arterial system receives blood flow from paired dorsal aortae or internal carotid arteries through a group of temporary, anastomotic arteries; the primitive trigeminal, otic, and hypoglossal arteries are relatively constant among them. The otic artery is first to dissappear and then the hypoglossal. The trigeminal artery finally regresses at the 8-to12mm stage of embryonic development when the posterior communicating artery begins to play the role of main collateral between internal carotid and basilar arteries. These primitive carotid-vertebrobasilar anastomoses occasionaly persist into adult life and are incidentally found on carotid angiogram. 0028-3940/79/0017/0105/$01.00
106
S. Suzuki et al.: Proatlantal and Occipital Arteries from Internal Carotid Artery
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Fig. l a , b, e and d. Case 1. Persistent hypoglossal and proatlantal intersegmental arteries. Left carotid angiography was attempted. a Lateral view. Tip of needle (large arrow) is inserted into an anomalous artery (small arrow) which is bifurcated into hypoglossal artery (crossed arrow) and proatlantal intersegmental artery (arrowheads). b Schematic drawing of a. e Towne view. Hypoglossal artery (crossed arrows) apparently traverses hypoglossal canal, entering posterior fossa, and connects with left vertebral artery. Proatlantal intersegmental artery (arrowheads) runs upward and lateral in course similar to normal occipital artery, fl Schematic drawing of e.
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S. Suzuki et al.: Proatlantal and Occipital Arteries from Internal Carotid Artery
107
Fig. 2. Case 1. The needle tip was directed into left internal carotid artery
The proatlantal intersegmental artery is believed to regress completely by the 12-tol4-mm stage of development [13, 14], though persistence of the artery into adult life due to failure of its involution may sometimes occur. The persistent proatlantal artery is said to arise usually from the internal carotid artery and rarely from the external carotid artery, and connects with the horizontal segment of the vertebral artery [1, 2]. The evolution of the proatlantal intersegmental artery is, however, not as clear as the primitive trigeminal, otic, and hypoglossal arteries. In fact, the proatlantal intersegmental artery is thought by Bloch and Danziger [2] and Padget [14] to contribute to the horizontal or suboccipital segment of the vertebral artery. Furthermore, Lasjaunias et al. [11] recently presented a hypothesis suggesting that the horizontal and more distal segments of the occipital artery are a remnant of the proatlantal intersegmental artery and the occipital artery arising from the internal carotid artery is, therefore, considered the persistent proatlantal intersegmental artery per se. An anomalous anastomosis between the external carotid and ipsilateral vertebral arteries has been reported occasionally [4, 6, 7, 16]. In most of them, the anastomotic channel runs more caudally and joins with the vertebral artery at a level more caudal than the authentic case of the persistent proatlantal artery, and the channel is thought to be a remnant of one of the upper cervical intersegmental arteries. We are presenting a case of a combined anomaly of persistent hypoglossal and proatlantal intersegmental arteries and another case of an anomalous occipital artery arising from the internal carotid
artery in order to support the hypothesis that the persistent proatlantal artery and the anomalous occipital artery may be embryologically identical as suggested by Lasjaunias et al. [11]. Material Case 1. A hydrocephalic girl aged 7 months. Left carotid angiography was first attempted by direct puncture in order to elucidate the etiology of the hydrocephalus. The needle was inserted into an anomalous artery which seemed to originate at the level of the upper margin of the body of the axis and run upwards. It soon bifurcated into two branches, one entering the posterior cranial fossa through the hypoglossal canal and joining the left vertebral artery, the other running backward to the occiput and suboccipital nuchal region (Fig. l). The distal segment of the left vertebral artery and the basilar arterial system are within normal limits. Though the cervical segment of the left vertebral artery can not be identified, the entire course of the right vertebral artery is clearly demonstrated and is essentially normal. Slight movement of the needle resulted in direct insertion of its tip into the left internal carotid artery (Fig. 2). Based upon these findlings, the branch traversing the hypoglossal canal is considered the persistent primitive hypoglossal artery and the other branch of the anomalous artery on Figure 1 the persistent proatlantal intersegmental artery. The common trunk of both branches may be the remnant of the distal part of the ductus caroticus.
108
S. Suzuki et al.: Proatlantal and OccipitalArteries from Internal Carotid Artery
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Fig. 3 a, b, c and d. Case 2. Anomalous occipital artery arising from internal carotid artery is demonstrated on left internal carotid angiogram in patient with intracranial aneurysm and arteriovenous malformation, a Lateral view. Artery (arrows) runs in course similar to normal occipital artery except that it arises here from internal carotid artery, b Lateral view (one second later than a). Distal continuation (arrows) of anomalous artery is identical to persistent proatlantal artery in Case 1 and normal occipital artery. Arteriovenous malformation is seen in left frontal lobe. e Anteroposterior view. Anomalous artery and its branches in cervical and suboccipital regions are indicated by arrows. An aneurysm (crossed arrow) arises from C-1 of left internal carotid artery, d Schematic drawing of angiogram one second later than c with anomalous artery indicated by small arrow
Case 2. A woman, aged 52, with subarachnoid hemorrhage. Left carotid angiography was attempted, obtaining internal carotid angiogram (Fig. 3). In addition to an arteriovenous malformation in left frontal region and a saccular aneurysm in C-1 of the left internal carotid artery, an anomalous artery arises from the internal carotid artery at the level of
the middle of the second cervical vertebra. The artery apparently arises from the back of the internal carotid artery and runs upwards to the space between transverse process of the atlas and the base of the skull. It then turns backwards and runs horizontally, bifurcating into ascending and descending branches. The artery can be interpreted as an 'anomalous
S. Suzuki et al.: Proatlantal and Occipital Arteries from Internal Carotid Artery
occipital artery from the internal carotid artery', as done by Newton et al. [12] and Teal et al. [17]. The present authors, however, consider that the anomalous artery is a persistent proatlantal intersegmental artery since it courses identically to the persistent proatlantal intersegmental artery in Case 1. The left common carotid angiography was performed after operation, revealing none of the arteries arising from the external carotid artery and distributing to the occiput and suboccipital region.
Discussion The angiographic finding, which confirms the persistent hypoglossal artery, is that an anomalous artery arising from the internal carotid artery at the level of the atlas enters the intracranial cavity through the hypoglossal canal and joins the ipsilateral vertebral artery [1, 3, 7, 10]. The persistent proatlantal artery in cases reported in literature originates from the back of the internal carotid artery at a level slightly caudal to the origin of the persistent hypoglossal artery and runs upwards and dorsolaterally to the internal carotid artery. It then connects directly with the horizontal segment of the ipsilateral vertebral artery. The distal course of the vertebral artery is normal but the proximal segment to the anastomotic point is usually hypoplastic or atretic. It is well known that both primitive hypoglossal and proatlantal intersegmental arteries arise from the dorsal root of the 3rd aortic arch (carotid ductus). Persistence of both arteries associated with the involutional disappearance at the caudal end of the ductus caroticus may be the developmental mechanism in Case 1. Absence of a direct communication between the proatlantal artery and ipsilateral vertebral artery may be related to atresia of the latter in the segment distal to the hypoglosso-vertebral anastomosis. An occipital artery arising from the internal carotid artery is a rare anomaly [11, 12, 17]. Its developmental mechanism is not clear mainly due to insufficient understanding of the evolution of the occipital artery in the human embryo. The analysis on the persistent intersegmental artery in Case 1, and the anomalous occipital artery in Case 2, indicates that both are almost identical in course and distribution. The authors conclude therefore, that such an anomalous occipital artery as in Case 2 may be the persistent proatlantal artery per se even though it is not directly connected with the vertebral artery and that the occipital artery in the horizontal and more distal segments may derive from the proatlantal intersegmental artery, as suggested by Lasjaunias et al. [11].
109
References 1. Anderson, R.A., Sondheimer, F.K.: Rare carotid-vertebrobasilar anastomoses with notes on the differentiation between proatlantal and hypoglossal arteries. Neuroradiology 11, 113-118 (1976) 2. Bloch, S., Danziger, J.: Proatlantal intersegmental artery. Neuroradiology 7, 15-17 (19741 3. Birsmar, J.: Persistent hypoglossal artery. Diagnostic criteria. Acta Radiol. [Diagn] (Stockh) 17, 160-166 (1976) 4. Hackett, E. R., Wilson, C. B.: Congenital external carotid-vertebral anastomosis. Am. J. Roentgenol. 104, 86-89 (19681 5. Haughton, V.M., Rosenbaum, A.E.: In: Radiology of the skull and brain, Vol. 2, Book 2, (eds. T.H. Newton, D. G. Potts) pp. 1145-1163. St. Louis: Mosby 1974 6. Huber, G., Piepgras, U.: Ursprung der linken Arteria vertebralis aus der linken Arteria carotis externa. Fortschr. R6ntgenstr. 125, 63-66 (1976) 7. Ishikura, A., Aizumi, S., Izumi, K.: Persistent primitive hypoglossal artery associated with anterior communicating artery aneurysm. Jpn. J. Clin. Radiol. 22, 783-787 (1977) 8. Kier, E.L.: Fetal cerebral arteries: a phylogenetic and ontogenetic study. In: Radiology of the skull and brain, Vol. 2,
Book 1, (eds. T.H. Newton, D.G. Potts) pp. 1089-1130. St. Louis: Mosby 1974 9. Kutsuna, M., Yasui, N., Tani, S., Someda, K., Matsumura, H.: External carotid-basilar anastomosis. Jpn. J. Clin. Radiol. 22, 601-604 (1977) 10. Keller, H. L., Weiss, D.: Ursprung einer das Vertebralisgebiet versorgenden Arteria aus dem Halsabschnitt der rechten Arteria carotid interna. Fortschr. R6ntgenstr. 118, 473-474
(1973) 11. Lasjaunias, P., Th6ron, J., Moret, J.: The occipital artery. Anatomy - normal angiographic aspects - embryological significance. Neuroradiology 15, 31-37 (1978) 12. Newton, T. H., Young, D. A.: Anomalous origin of the occipital artery from the internal carotid artery. Radiology 90, 550-552 (1968) 13. Padget, D. H.: The development of the cranial arteries in the human embryo. Carnegie Inst. Publ. 575. Contributions to Embryology 32, 205-261 (1948) 14. Padget, D.H.: Designation of the embryonic intersegmental arteries in reference to the vertebral artery and subclavian stem. Anat. Rec. 119, 349-356 (19541 15. Patten, B.M.: Human embryology (2nd ed.). p. 626. New York: McGraw-Hill 1953 16. Pinstein, M. L., Gerald, B.: Anomalous communication of the external carotid and vertebral arteries. Radiology 118, 626
(19761 17. Teal, J.S., Rumbaugh, C.L., Segall, H. D., Bergeron, R.T.: Anomalous branches of the internal carotid artery. Radiology
106, 567-574 (1973) Received: 10 August 1978
Dr. Soji Suzuki Department of Radiology Tokyo Medical and Dental University School of Medicine Yushima 1-chome
Bunkyo-ku Tokyo, Japan
Neuroradiology 17, 105-109 (1979)
© by Springer-Verlag 1979
CASE REPORTS
Persistent Proatlantal Intersegmental Artery and Occipital Artery Originating from Internal Carotid Artery S. Suzuki 1, T. Nobechi 2, I. Itoh 3, M. Yakura 3 and K. Iwashita 3 Department of Radiology1, Tokyo Medical and Dental University, School of Medicine, and Departments of Radiology2 Neurosurgery3, St. Luke's International Hospital, Tokyo, Japan
Summary: A case of a combined anomaly of persistent hypoglossal and proatlantal intersegmental arteries, proved on arteriogram obtained by the insertion of a needle into the common trunk of both arteries, is presented. In addition, a case of anomalous occipital artery arising from the internal carotid artery associated with an intracranial aneurysm and arteriovenous malformation is presented. Based upon analysis of the persistent proatlantal intersegmental artery and the anomalous occipital artery, we conclude that both arteries have an identical embryological origin. Key words: Hypoglossal artery - Proatlantal artery Anomalous occipital artery
Introduction The third and fourth aortic arches appear at the 4mm stage of development of the human embryo, and the first and second aortic arches then regress, leaving two residual segments; the segment originating from the dorsal roots grows cephalad and becomes the internal carotid artery, and the other segment from the ventral roots becomes the external carotid artery [5, 13]. At the 7-mm stage, small paired vessels sprout from the dorsal aortae and run dorsally in the loose mesenchymal tissue between somites; the vessels are called the intersegmental arteries [13, 14, 15]. There are eight pairs of intersegmental arteries in the cervical region. Since the first pair is designated as the proatlantal or suboccipital intersegmental artery, the second pair is called the first cervical intersegmental artery and, therefore, there are seven pairs of cervical intersegmental arteries [5, 14]. At the 12-mm stage
of embryonic development, paired cervical intersegmental arteries are connected by a pair of secondary longitudinal channels, which become the vertebral artery after the first five cervical intersegmental arteries between the dorsal aortae and the longitudinal channels have involuted. The sixth cervical intersegmental artery, however, persists as a trunk for the buds of subclavian and vertebral arteries on both sides [14]. Bilateral vertebral arteries grow cephalad and traverse the foramen magnum, joining each other and forming a single median artery at the level of developing medulla oblongata. The exact manner of development of the basilar artery in the human embryo is not fully clarified but it is said that bilateral longitudinal neural arteries, closely applied to the ventral surface of the hindbrain, fuse to form the basilar artery during the 7-to 12-mm stage of development. The basilar artery eventually interconnects between the single median artery formed by fusion of bilateral vertebral arteries and the cranial end of the basilar artery formed by fusion of the caudal continuations of bilateral posterior communicating arteries which derive from the internal carotid arteries [8]. In the early stage of development the primitive vertebrobasilar arterial system receives blood flow from paired dorsal aortae or internal carotid arteries through a group of temporary, anastomotic arteries; the primitive trigeminal, otic, and hypoglossal arteries are relatively constant among them. The otic artery is first to dissappear and then the hypoglossal. The trigeminal artery finally regresses at the 8-to12mm stage of embryonic development when the posterior communicating artery begins to play the role of main collateral between internal carotid and basilar arteries. These primitive carotid-vertebrobasilar anastomoses occasionaly persist into adult life and are incidentally found on carotid angiogram. 0028-3940/79/0017/0105/$01.00
106
S. Suzuki et al.: Proatlantal and Occipital Arteries from Internal Carotid Artery
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Fig. l a , b, e and d. Case 1. Persistent hypoglossal and proatlantal intersegmental arteries. Left carotid angiography was attempted. a Lateral view. Tip of needle (large arrow) is inserted into an anomalous artery (small arrow) which is bifurcated into hypoglossal artery (crossed arrow) and proatlantal intersegmental artery (arrowheads). b Schematic drawing of a. e Towne view. Hypoglossal artery (crossed arrows) apparently traverses hypoglossal canal, entering posterior fossa, and connects with left vertebral artery. Proatlantal intersegmental artery (arrowheads) runs upward and lateral in course similar to normal occipital artery, fl Schematic drawing of e.
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S. Suzuki et al.: Proatlantal and Occipital Arteries from Internal Carotid Artery
107
Fig. 2. Case 1. The needle tip was directed into left internal carotid artery
The proatlantal intersegmental artery is believed to regress completely by the 12-tol4-mm stage of development [13, 14], though persistence of the artery into adult life due to failure of its involution may sometimes occur. The persistent proatlantal artery is said to arise usually from the internal carotid artery and rarely from the external carotid artery, and connects with the horizontal segment of the vertebral artery [1, 2]. The evolution of the proatlantal intersegmental artery is, however, not as clear as the primitive trigeminal, otic, and hypoglossal arteries. In fact, the proatlantal intersegmental artery is thought by Bloch and Danziger [2] and Padget [14] to contribute to the horizontal or suboccipital segment of the vertebral artery. Furthermore, Lasjaunias et al. [11] recently presented a hypothesis suggesting that the horizontal and more distal segments of the occipital artery are a remnant of the proatlantal intersegmental artery and the occipital artery arising from the internal carotid artery is, therefore, considered the persistent proatlantal intersegmental artery per se. An anomalous anastomosis between the external carotid and ipsilateral vertebral arteries has been reported occasionally [4, 6, 7, 16]. In most of them, the anastomotic channel runs more caudally and joins with the vertebral artery at a level more caudal than the authentic case of the persistent proatlantal artery, and the channel is thought to be a remnant of one of the upper cervical intersegmental arteries. We are presenting a case of a combined anomaly of persistent hypoglossal and proatlantal intersegmental arteries and another case of an anomalous occipital artery arising from the internal carotid
artery in order to support the hypothesis that the persistent proatlantal artery and the anomalous occipital artery may be embryologically identical as suggested by Lasjaunias et al. [11]. Material Case 1. A hydrocephalic girl aged 7 months. Left carotid angiography was first attempted by direct puncture in order to elucidate the etiology of the hydrocephalus. The needle was inserted into an anomalous artery which seemed to originate at the level of the upper margin of the body of the axis and run upwards. It soon bifurcated into two branches, one entering the posterior cranial fossa through the hypoglossal canal and joining the left vertebral artery, the other running backward to the occiput and suboccipital nuchal region (Fig. l). The distal segment of the left vertebral artery and the basilar arterial system are within normal limits. Though the cervical segment of the left vertebral artery can not be identified, the entire course of the right vertebral artery is clearly demonstrated and is essentially normal. Slight movement of the needle resulted in direct insertion of its tip into the left internal carotid artery (Fig. 2). Based upon these findlings, the branch traversing the hypoglossal canal is considered the persistent primitive hypoglossal artery and the other branch of the anomalous artery on Figure 1 the persistent proatlantal intersegmental artery. The common trunk of both branches may be the remnant of the distal part of the ductus caroticus.
108
S. Suzuki et al.: Proatlantal and OccipitalArteries from Internal Carotid Artery
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Fig. 3 a, b, c and d. Case 2. Anomalous occipital artery arising from internal carotid artery is demonstrated on left internal carotid angiogram in patient with intracranial aneurysm and arteriovenous malformation, a Lateral view. Artery (arrows) runs in course similar to normal occipital artery except that it arises here from internal carotid artery, b Lateral view (one second later than a). Distal continuation (arrows) of anomalous artery is identical to persistent proatlantal artery in Case 1 and normal occipital artery. Arteriovenous malformation is seen in left frontal lobe. e Anteroposterior view. Anomalous artery and its branches in cervical and suboccipital regions are indicated by arrows. An aneurysm (crossed arrow) arises from C-1 of left internal carotid artery, d Schematic drawing of angiogram one second later than c with anomalous artery indicated by small arrow
Case 2. A woman, aged 52, with subarachnoid hemorrhage. Left carotid angiography was attempted, obtaining internal carotid angiogram (Fig. 3). In addition to an arteriovenous malformation in left frontal region and a saccular aneurysm in C-1 of the left internal carotid artery, an anomalous artery arises from the internal carotid artery at the level of
the middle of the second cervical vertebra. The artery apparently arises from the back of the internal carotid artery and runs upwards to the space between transverse process of the atlas and the base of the skull. It then turns backwards and runs horizontally, bifurcating into ascending and descending branches. The artery can be interpreted as an 'anomalous
S. Suzuki et al.: Proatlantal and Occipital Arteries from Internal Carotid Artery
occipital artery from the internal carotid artery', as done by Newton et al. [12] and Teal et al. [17]. The present authors, however, consider that the anomalous artery is a persistent proatlantal intersegmental artery since it courses identically to the persistent proatlantal intersegmental artery in Case 1. The left common carotid angiography was performed after operation, revealing none of the arteries arising from the external carotid artery and distributing to the occiput and suboccipital region.
Discussion The angiographic finding, which confirms the persistent hypoglossal artery, is that an anomalous artery arising from the internal carotid artery at the level of the atlas enters the intracranial cavity through the hypoglossal canal and joins the ipsilateral vertebral artery [1, 3, 7, 10]. The persistent proatlantal artery in cases reported in literature originates from the back of the internal carotid artery at a level slightly caudal to the origin of the persistent hypoglossal artery and runs upwards and dorsolaterally to the internal carotid artery. It then connects directly with the horizontal segment of the ipsilateral vertebral artery. The distal course of the vertebral artery is normal but the proximal segment to the anastomotic point is usually hypoplastic or atretic. It is well known that both primitive hypoglossal and proatlantal intersegmental arteries arise from the dorsal root of the 3rd aortic arch (carotid ductus). Persistence of both arteries associated with the involutional disappearance at the caudal end of the ductus caroticus may be the developmental mechanism in Case 1. Absence of a direct communication between the proatlantal artery and ipsilateral vertebral artery may be related to atresia of the latter in the segment distal to the hypoglosso-vertebral anastomosis. An occipital artery arising from the internal carotid artery is a rare anomaly [11, 12, 17]. Its developmental mechanism is not clear mainly due to insufficient understanding of the evolution of the occipital artery in the human embryo. The analysis on the persistent intersegmental artery in Case 1, and the anomalous occipital artery in Case 2, indicates that both are almost identical in course and distribution. The authors conclude therefore, that such an anomalous occipital artery as in Case 2 may be the persistent proatlantal artery per se even though it is not directly connected with the vertebral artery and that the occipital artery in the horizontal and more distal segments may derive from the proatlantal intersegmental artery, as suggested by Lasjaunias et al. [11].
109
References 1. Anderson, R.A., Sondheimer, F.K.: Rare carotid-vertebrobasilar anastomoses with notes on the differentiation between proatlantal and hypoglossal arteries. Neuroradiology 11, 113-118 (1976) 2. Bloch, S., Danziger, J.: Proatlantal intersegmental artery. Neuroradiology 7, 15-17 (19741 3. Birsmar, J.: Persistent hypoglossal artery. Diagnostic criteria. Acta Radiol. [Diagn] (Stockh) 17, 160-166 (1976) 4. Hackett, E. R., Wilson, C. B.: Congenital external carotid-vertebral anastomosis. Am. J. Roentgenol. 104, 86-89 (19681 5. Haughton, V.M., Rosenbaum, A.E.: In: Radiology of the skull and brain, Vol. 2, Book 2, (eds. T.H. Newton, D. G. Potts) pp. 1145-1163. St. Louis: Mosby 1974 6. Huber, G., Piepgras, U.: Ursprung der linken Arteria vertebralis aus der linken Arteria carotis externa. Fortschr. R6ntgenstr. 125, 63-66 (1976) 7. Ishikura, A., Aizumi, S., Izumi, K.: Persistent primitive hypoglossal artery associated with anterior communicating artery aneurysm. Jpn. J. Clin. Radiol. 22, 783-787 (1977) 8. Kier, E.L.: Fetal cerebral arteries: a phylogenetic and ontogenetic study. In: Radiology of the skull and brain, Vol. 2,
Book 1, (eds. T.H. Newton, D.G. Potts) pp. 1089-1130. St. Louis: Mosby 1974 9. Kutsuna, M., Yasui, N., Tani, S., Someda, K., Matsumura, H.: External carotid-basilar anastomosis. Jpn. J. Clin. Radiol. 22, 601-604 (1977) 10. Keller, H. L., Weiss, D.: Ursprung einer das Vertebralisgebiet versorgenden Arteria aus dem Halsabschnitt der rechten Arteria carotid interna. Fortschr. R6ntgenstr. 118, 473-474
(1973) 11. Lasjaunias, P., Th6ron, J., Moret, J.: The occipital artery. Anatomy - normal angiographic aspects - embryological significance. Neuroradiology 15, 31-37 (1978) 12. Newton, T. H., Young, D. A.: Anomalous origin of the occipital artery from the internal carotid artery. Radiology 90, 550-552 (1968) 13. Padget, D. H.: The development of the cranial arteries in the human embryo. Carnegie Inst. Publ. 575. Contributions to Embryology 32, 205-261 (1948) 14. Padget, D.H.: Designation of the embryonic intersegmental arteries in reference to the vertebral artery and subclavian stem. Anat. Rec. 119, 349-356 (19541 15. Patten, B.M.: Human embryology (2nd ed.). p. 626. New York: McGraw-Hill 1953 16. Pinstein, M. L., Gerald, B.: Anomalous communication of the external carotid and vertebral arteries. Radiology 118, 626
(19761 17. Teal, J.S., Rumbaugh, C.L., Segall, H. D., Bergeron, R.T.: Anomalous branches of the internal carotid artery. Radiology
106, 567-574 (1973) Received: 10 August 1978
Dr. Soji Suzuki Department of Radiology Tokyo Medical and Dental University School of Medicine Yushima 1-chome
Bunkyo-ku Tokyo, Japan
