Surg Radiol Anat DOI 10.1007/s00276-016-1651-8
ORIGINAL ARTICLE
Infraoptic anterior cerebral artery: case series report and literature review Myoung Soo Kim1 • Sook Young Sim2
Received: 28 October 2015 / Accepted: 13 February 2016 Ó Springer-Verlag France 2016
Abstract An infraoptic course of the precommunicating anterior cerebral artery (A1 segment) is a rare anomaly. We report three patients with an infraoptic A1 diagnosed by computed tomography angiography and we review the literature focusing on embryological development. In all three patients, a left infraoptic A1 that originated from the ophthalmic level of the internal carotid artery was diagnosed incidentally. Only one patient had a normal supraoptic A1. The embryogenesis of this anomaly is unclear. We propose that an error in the development of the definitive ophthalmic artery is possible mechanisms giving rise to this anomaly.
prechiasmatic space; (2) the anomalous artery branches off the internal carotid artery (ICA) at the level of the ophthalmic artery (OA); and (3) the anastomosis between the AComA and the anomalous ACA supplies the vascular territory of the normal ACA [17, 24, 25]. Here, we describe three cases of infraoptic A1 detected by computed tomography (CT) angiography. The possible genesis of this anomaly is discussed and practical considerations when treating an associated aneurysm are discussed.
Keywords Anterior cerebral artery Anomaly Internal carotid artery Computed tomography angiography
Case 1
Introduction Although anomalies of the anterior cerebral artery (ACA)—anterior communicating artery (AComA) complex are commonly identified during imaging studies, an infraoptic A1 is extremely rare. Almost all descriptions of infraoptic ACA in the literature share three features: (1) the anomalous vessel runs beneath the optic nerve and the
& Myoung Soo Kim [email protected] 1
2
Chief of Brain Center, Pohang SM Christianity Hospital, 351 Poscodaero, Namku, Pohang 790-822, Gyeongbuk, Republic of Korea Department of Neurosurgery, Seoul Paik Hospital, Inje University College of Medicine, Seoul, Republic of Korea
Case series
A 69-year-old man presented to his physician complaining of frontal headache. He denied any subjective sensorimotor symptoms and no focal neurological deficits were detected. Brain CT angiography demonstrated unruptured aneurysms located in the right distal ACA and the right cavernous portion of the ICA. The left A1 was shown to arise from the left ICA at the level of the OA. From this anomalous origin, the left ACA projected superomedially between the optic nerves anterior to the chiasm. The infraoptic course of the ACA was connected to the AComA (Fig. 1). There was no left supraoptic A1 segment. The unruptured aneurysm located in the right distal ACA was clipped via an interhemispheric approach. The postoperative course was uneventful. Case 2 A 49-year-old man presented with headache. Neurological examination showed no abnormality. Brain CT angiography demonstrated no abnormal lesion except for the left
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Fig. 1 Infraoptic A1 in 69-year-old man. a Reconstructed computed tomography (CT) angiography reveals an anomalous left anterior cerebral artery (ACA) (dotted arrow infraoptic A1). The left A1 originates from the left internal carotid artery at the level of the ophthalmic artery (white arrow ophthalmic artery) and has a characteristic superomedial course before ascending to join a normally positioned anterior communicating artery. There is no supraoptic A1 segment. b Enhanced CT demonstrates that the infraoptic A1 (white arrow infraoptic A1) is located in the prechiasmatic space (dotted arrows both optic nerves)
A1, which originated from the left ICA at the level of the OA, passed inward below the optic nerve, ascended the prechiasmatic space, and connected to the distal portion of a normal supraoptic left A1 segment (Fig. 2). This patient showed improvement of his headache after medication.
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Fig. 2 a Infraoptic A1 in 49-year-old man. Reconstructed computed tomography (CT) angiography shows an abnormal left anterior cerebral artery (ACA). The left A1 (dotted arrow infraoptic A1) originates from the left internal carotid artery at the level of the ophthalmic artery (white arrowhead origin of ophthalmic artery), has a superomedial course, and joins the distal portion of the left A1. There is a normal supraoptic A1 segment (white arrow supraoptic A1 segment). b Enhanced CT demonstrates left ophthalmic artery and infraoptic A1 (white arrow ophthalmic artery, dotted arrows infraoptic A1)
Case 3 A 39-year-old woman presented with headache. Neurological examination demonstrated no neurological deficit
Surg Radiol Anat
except mild impairment of cognitive function. Past medical history included mitral valve replacement for mitral valve regurgitation and warfarin medication. Brain CT showed a chronic subdural hematoma. Brain CT angiography demonstrated an anomalous proximal ACA. The left A1 originated from the left ICA at the level of the OA, passed superomedially below the optic nerve, ascended the prechiasmatic space and connected with the left AComA (Fig. 3). This patient made an excellent recovery after burrhole surgery for her chronic subdural hematoma.
Discussion The embryogenesis of infraoptic A1 is still controversial. There are three proposed theories in the literature for the origin of this anomaly [16, 23, 25]: (1) the enlargement of the prechiasmal arterial anastomosis [7, 10, 20]; (2) the persistence of the embryonic anastomosis between the primitive maxillary artery and the ACA [4]; and (3) the persistence and enlargement of an embryological anastomotic loop between the primitive dorsal and ventral OAs. There are several prerequisites for the plausibility of an embryogenic mechanism for the existence of an infraoptic A1. In addition to the anomalous artery running below and then medial to the ipsilateral optic nerve, the mechanism must also be able to explain the following three anatomical features: (1) that the origin of the infraoptic A1 is at, or
Fig. 3 Infraoptic A1 in 39-year-old woman. Reconstructed computed tomography angiography reveals an anomalous left anterior cerebral artery (ACA). This vessel originates from the left internal carotid artery at the level of the ophthalmic artery, has a superomedial course, and connects to the anterior communicating artery (white arrow infraoptic A1, dotted arrow origin of ophthalmic artery). Fenestration (white arrowhead) of anterior communicating artery is noted
close to, the level of the OA; (2) the distal anastomosis is in the vicinity of the AComA; and (3) the infraoptic A1 is located in the prechiasmatic space. Although Given and Morris [9] reported an infraoptic A1 with penetration of the ipsilateral optic chiasm, the A1 in case 1 reported by Maurer et al. [15], was not an infraoptic A1. Therefore, all infraoptic A1 reported in the literature are located in the prechiasmatic space. Maurer et al. [15] also reported an infraoptic A1 originating from the ICA close to the lateral margin of the optic chiasm. Therefore, this infraoptic A1 might have originated from a site on the ICA distal to the level of the OA. Isherwood and Dutton [10] proposed the theory of prechiasmal anastomosis. The prechiasmal anastomosis at the medial aspect of the intracranial segments of the optic nerves and at the anterior border of the chiasm consists of the prechiasmal branch of the OA, the superior hypophyseal branch of the ICA, and the chiasmal branches of the ACA. Robinson [20] suggested that an infraoptic A1 might arise from enlargement of an anastomosis between the ACA and the superior hypophyseal vessel proximal to the posterior communicating artery. This theory satisfactorily explains the prechiasmatic location of an infraoptic A1. But the dorsal aspect of the chiasm is vascularized by branches coming from A1 while the ventral aspect receives its supply from the ICA; these vessels realize an anastomotic network between the right and left sides but the dorsal and ventral networks are not really linked and the vessels diameter is very tiny. Therefore, the theory of prechiasmal anastomosis is less likely for formation of infraoptic A1. Bosma [4] also proposed that an infraoptic A1 might arise from developmental failure of the potential anastomosis between the primitive olfactory and the primitive maxillary arteries, both supplying the prosencephalon. Before the 5–6-mm embryonic stage, the primitive maxillary artery, a branch of the ICA arising from its future intracavernous portion, supplies the optic vesicle [19]. This artery normally regresses after the 5–6-mm embryonic stage when other branches of the internal carotid take over responsibility for its territory; in the adult, the primitive maxillary artery persists in the form of small intracavernous arterial branches (posteroinferior hypophyseal artery) supplying the infundibulum. And primitive maxillary artery was originated from vertical portion of intracavernous ICA [14]. After observing an infraoptic A1 originating from the extradural ICA, Akiyama et al. [1] also proposed persistence of the embryonic anastomosis between the primitive maxillary artery and the primitive olfactory artery. However, this theory cannot explain the OA level of the ICA origin in most cases of infraoptic A1. Odake [18] and Sasaki et al. [22] disagreed with this theory because in their case, the primitive maxillary artery was
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located caudal to the primitive dorsal OA from which the normal OA developed. We also do not agree with this theory because Maurer et al. [15] reported an infraoptic A1 originating from the ICA close to the lateral margin of the optic chiasm. The third hypothesis postulates an error in the development of the definitive OA [5]. According to Isherwood and Dutton [10] and Robinson [20], the anomaly of an infraoptic A1 might represent the persistence of an anastomotic loop (around the optic nerve) of the primitive dorsal OA and the primitive ventral OA. Lasjaunias [14] also attribute the presence of an infraoptic A1 to an error in the formation of the adult OA. At the 4-mm embryonic stage, the orbit is vascularized by two OAs: one ventral, arising from the future ACA, and the other dorsal, arising from the intracavernous portion of the ICA. The adult OA is derived from the primitive ventral OA by caudal migration, while the primitive dorsal OA regresses. Failure of this development, with agenesis of the proximal ACA and/or persistence of one or the other primitive arteries, would also explain the formation of an infraoptic A1. Spinnato et al. [23] proposed that the common origin of the OA and the infraoptic A1 was proof of a close relationship, with development of the adult OA accounting for an infraoptic A1. Komiyama et al. [13] described the embryology of OA. Ventral OA originates from the primitive ICA near the origin of the anterior choroidal artery. Therefore we think that ventral OA is more important for formation of infraoptic A1. In most cases of infraoptic A1, caudal migration of the primitive ventral OA stops at, or close to, the OA level of the ICA. However, in some cases of infraoptic A1, reduced caudal migration of the primitive ventral OA results in a caudal origin at the OA level, as in the case reported by Maurer et al. [15]. Although we believe that the vascular anomalies observed in our cases may be related, we are not certain whether they all result from one type of developmental failure in the embryo. The embryogenesis of this anomaly is still controversial, and the explanations that have been offered are hypothetical. However, we do not agree that the embryogenetic origin of an infraoptic A1 is a persistence of the embryonic anastomosis between the primitive maxillary artery and the primitive olfactory artery. Also we do not agree with the theory of prechiasmal anastomosis. The association of an infraoptic A1 with an intracranial aneurysm has been frequently reported [2, 3, 8, 11, 23, 26]. If the associated aneurysm is located distally, the infraoptic A1 seldom poses a problem additional to those involved in clipping of the associated intracranial aneurysm, but simply complicates the meticulous preparation of the neck of the aneurysm [11, 12]. However, failure to recognize this anomaly might result in unnecessary dissection along, and
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possible damage to, the optic apparatus or the inferior frontal lobe during aneurysm repair [6]. Even in patients with a proximal A1 aneurysm, if the aneurysm is small, the optic nerve may not hinder clipping. Awareness of an infraoptic A1 is especially important in patients with a proximal aneurysm, which may be obscured by the optic nerve during craniotomy. Knowledge of the anatomy enables planning for proximal control of an aneurysm and preparedness for more skull-base bone work for better delineation of the vascular anatomy [25]. Sakai et al. [21] reported one case of temporary mild deterioration of visual acuity after clipping of an infraoptic A1 aneurysm. The aneurysm was located on the curved midportion of the infraoptic A1 and extended underneath the right optic nerve. Retraction of the optic nerve during surgery was probably the cause. Removal of the anterior clinoid process and unroofing of the optic canal might facilitate manipulation of the optic nerve. However, clinoidectomy may result to deterioration of visual function. In case of fixed chiasm, optic nerve manipulation also result to visual compromise. Coil embolization can be an alternative treatment option. The presence of the infraoptic A1 can provide a straightforward endovascular approach to the AComA.
Conclusion In conclusion, although an infraoptic A1 is a rare anomaly, it is still important to bear it in mind, because it should be taken into account in planning treatment of an associated pathology. There are three proposed explanations in the literature for this anomaly. We consider that an error in the development of the definitive OA is the most likely explanation for the formation of an infraoptic A1. Acknowledgments This work was supported by research grant from an Inje University College of Medicine. Compliance with ethical standards Conflict of interest We declare that we have no conflict of interest with any organization or institute.
References 1. Akiyama Y, Okada T, Hayashi N, Yokoi T (2010) Infraoptic course of the anterior cerebral artery originating from the extradural internal carotid artery associated with contralateral internal carotid artery agenesis and multiple intracerebral aneurysms. Neurol Med Chir (Tokyo) 50:984–987 2. Al-Qahtani S, Tampieri D, Brassard R, Sirhan D, Mellanson D (2003) Coil embolization of an aneurysm associated with an infraoptic anterior cerebral artery in a child. AJNR Am J Neuroradiol 24:990–991
Surg Radiol Anat 3. Bollar A, Martinez R, Gelabert M, Garcia A (1988) Anomalous origin of the anterior cerebral artery associated with aneurysm– embryological considerations. Neuroradiology 30:86 4. Bosma NJ (1977) Infra-optic course of anterior cerebral artery and low bifurcation of the internal carotid artery. Acta Neurochir (Wien) 38:305–312 5. Brismar J, Ackerman R, Roberson G (1977) Anomaly of anterior cerebral artery: a case report and embryologic considerations. Acta Radiol Diagn (Stockh) 18:154–160 6. Chua MH, Thomas AJ, Fusco MR, Ogilvy CS (2014) An unruptured anterior communicating artery aneurysm with bilateral infraoptic anterior cerebral arteries. Case report and review of the literature. J Cerebrovasc Endovasc Neurosurg 16:368–373 7. Dawson BH (1958) The blood vessels of the human optic chiasma and their relation to those of the hypophysis and hypothalamus. Brain 81:207–217 8. Fujimura M, Seki H, Sugawara T, Tomichi N, Oku T, Higuchi H (1996) Anomalous internal carotid artery-anterior cerebral artery anastomosis associated with fenestration and cerebral aneurysm. Neurol Med Chir (Tokyo) 36:229–233 9. Given CA 2nd, Morris PP (2002) Recognition and importance of an infraoptic anterior cerebral artery: case report. AJNR Am J Neuroradiol 23:452–454 10. Isherwood I, Dutton J (1969) Unusual anomaly of anterior cerebral artery. Acta Radiol Diagn (Stockh) 9:345–351 11. Kilic K, Orakdogen M, Bakirci A, Berkman Z (2005) Bilateral internal carotid to anterior cerebral artery anastomosis with anterior communicating artery aneurysm: technical case report. Neurosurgery 57:E400 12. Klein SI, Gahbauer H, Goodrich I (1987) Bilateral anomalous anterior cerebral artery and infraoptic aneurysm. AJNR Am J Neuroradiol 8:1142–1143 13. Komiyama M (2009) Letter to the editor - embryology of the ophthalmic artery: a revived concept. Interv Neuroradiol 15:363–368 14. Lasjaunias P, Berenstein A, ter Brugge KG (2001) Surgical neuroangiography, vol 1: clinical vascular anatomy and variations, 2nd edn. Springer, Berlin 15. Maurer J, Maurer E, Perneczky A (1991) Surgically verified variations in the A1 segment of the anterior cerebral artery. Report of two cases. J Neurosurg 75:950–953
16. McLaughlin N, Bojanowski MW (2007) Infraoptic course of anterior cerebral arteries associated with abnormal gyral segmentation. Case report. J Neurosurg 107:430–434 17. Mercier P, Velut S, Fournier D, Lescalie F, Guy G, Pillet J, Cronier P (1989) A rare embryologic variation: carotid-anterior cerebral artery anastomosis or infraoptic course of the anterior cerebral artery. Surg Radiol Anat 11:73–77 18. Odake G (1988) Carotid-anterior cerebral artery anastomosis with aneurysm: case report and review of the literature. Neurosurgery 23:654–658 19. Padget DH (1948) The development of the cranial arteries in the human embryo. Contrib Embryol 32:207–261 20. Robinson LR (1959) An unusual human anterior cerebral artery. J Anat 93:131–133 21. Sakai K, Asari S, Fujisawa M, Katagi R (1992) Ruptured aneurysm arising from the anomalous anterior cerebral artery– case report. Neurol Med Chir (Tokyo) 32:846–850 22. Sasaki T, Usami T, Takeda R, Nakagawara J, Sato S, Nakamura J, Suematsu K (1984) Three cases of infra-optic course of the anterior cerebral artery. No Shinkei Geka 12:953–958 23. Spinnato S, Pasqualin A, Chioffi F, Da Pian R (1999) Infraoptic course of the anterior cerebral artery associated with an anterior communicating artery aneurysm: anatomic case report and embryological considerations. Neurosurgery 44:1315–1319 24. Turkoglu E, Arat A, Patel N, Kertmen H, Baskaya MK (2011) Anterior communicating artery aneurysm associated with an infraoptic course of anterior cerebral artery and rare variant of the persistent trigeminal artery: a case report and literature review. Clin Neurol Neurosurg 113:335–340 25. Wong ST, Yuen SC, Fok KF, Yam KY, Fong D (2008) Infraoptic anterior cerebral artery: review, report of two cases and an anatomical classification. Acta Neurochir (Wien) 150:1087–1096 26. Yurt A, Ucar K, Ozer F, Oran I, Arda N (2008) A rare embryologic variation: anterior communicating artery aneurysm associated with carotid-anterior cerebral artery anastomosis or infraoptic course of the anterior cerebral artery. Clin Med Case Rep 1:123–125
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ORIGINAL ARTICLE
Infraoptic anterior cerebral artery: case series report and literature review Myoung Soo Kim1 • Sook Young Sim2
Received: 28 October 2015 / Accepted: 13 February 2016 Ó Springer-Verlag France 2016
Abstract An infraoptic course of the precommunicating anterior cerebral artery (A1 segment) is a rare anomaly. We report three patients with an infraoptic A1 diagnosed by computed tomography angiography and we review the literature focusing on embryological development. In all three patients, a left infraoptic A1 that originated from the ophthalmic level of the internal carotid artery was diagnosed incidentally. Only one patient had a normal supraoptic A1. The embryogenesis of this anomaly is unclear. We propose that an error in the development of the definitive ophthalmic artery is possible mechanisms giving rise to this anomaly.
prechiasmatic space; (2) the anomalous artery branches off the internal carotid artery (ICA) at the level of the ophthalmic artery (OA); and (3) the anastomosis between the AComA and the anomalous ACA supplies the vascular territory of the normal ACA [17, 24, 25]. Here, we describe three cases of infraoptic A1 detected by computed tomography (CT) angiography. The possible genesis of this anomaly is discussed and practical considerations when treating an associated aneurysm are discussed.
Keywords Anterior cerebral artery Anomaly Internal carotid artery Computed tomography angiography
Case 1
Introduction Although anomalies of the anterior cerebral artery (ACA)—anterior communicating artery (AComA) complex are commonly identified during imaging studies, an infraoptic A1 is extremely rare. Almost all descriptions of infraoptic ACA in the literature share three features: (1) the anomalous vessel runs beneath the optic nerve and the
& Myoung Soo Kim [email protected] 1
2
Chief of Brain Center, Pohang SM Christianity Hospital, 351 Poscodaero, Namku, Pohang 790-822, Gyeongbuk, Republic of Korea Department of Neurosurgery, Seoul Paik Hospital, Inje University College of Medicine, Seoul, Republic of Korea
Case series
A 69-year-old man presented to his physician complaining of frontal headache. He denied any subjective sensorimotor symptoms and no focal neurological deficits were detected. Brain CT angiography demonstrated unruptured aneurysms located in the right distal ACA and the right cavernous portion of the ICA. The left A1 was shown to arise from the left ICA at the level of the OA. From this anomalous origin, the left ACA projected superomedially between the optic nerves anterior to the chiasm. The infraoptic course of the ACA was connected to the AComA (Fig. 1). There was no left supraoptic A1 segment. The unruptured aneurysm located in the right distal ACA was clipped via an interhemispheric approach. The postoperative course was uneventful. Case 2 A 49-year-old man presented with headache. Neurological examination showed no abnormality. Brain CT angiography demonstrated no abnormal lesion except for the left
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Fig. 1 Infraoptic A1 in 69-year-old man. a Reconstructed computed tomography (CT) angiography reveals an anomalous left anterior cerebral artery (ACA) (dotted arrow infraoptic A1). The left A1 originates from the left internal carotid artery at the level of the ophthalmic artery (white arrow ophthalmic artery) and has a characteristic superomedial course before ascending to join a normally positioned anterior communicating artery. There is no supraoptic A1 segment. b Enhanced CT demonstrates that the infraoptic A1 (white arrow infraoptic A1) is located in the prechiasmatic space (dotted arrows both optic nerves)
A1, which originated from the left ICA at the level of the OA, passed inward below the optic nerve, ascended the prechiasmatic space, and connected to the distal portion of a normal supraoptic left A1 segment (Fig. 2). This patient showed improvement of his headache after medication.
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Fig. 2 a Infraoptic A1 in 49-year-old man. Reconstructed computed tomography (CT) angiography shows an abnormal left anterior cerebral artery (ACA). The left A1 (dotted arrow infraoptic A1) originates from the left internal carotid artery at the level of the ophthalmic artery (white arrowhead origin of ophthalmic artery), has a superomedial course, and joins the distal portion of the left A1. There is a normal supraoptic A1 segment (white arrow supraoptic A1 segment). b Enhanced CT demonstrates left ophthalmic artery and infraoptic A1 (white arrow ophthalmic artery, dotted arrows infraoptic A1)
Case 3 A 39-year-old woman presented with headache. Neurological examination demonstrated no neurological deficit
Surg Radiol Anat
except mild impairment of cognitive function. Past medical history included mitral valve replacement for mitral valve regurgitation and warfarin medication. Brain CT showed a chronic subdural hematoma. Brain CT angiography demonstrated an anomalous proximal ACA. The left A1 originated from the left ICA at the level of the OA, passed superomedially below the optic nerve, ascended the prechiasmatic space and connected with the left AComA (Fig. 3). This patient made an excellent recovery after burrhole surgery for her chronic subdural hematoma.
Discussion The embryogenesis of infraoptic A1 is still controversial. There are three proposed theories in the literature for the origin of this anomaly [16, 23, 25]: (1) the enlargement of the prechiasmal arterial anastomosis [7, 10, 20]; (2) the persistence of the embryonic anastomosis between the primitive maxillary artery and the ACA [4]; and (3) the persistence and enlargement of an embryological anastomotic loop between the primitive dorsal and ventral OAs. There are several prerequisites for the plausibility of an embryogenic mechanism for the existence of an infraoptic A1. In addition to the anomalous artery running below and then medial to the ipsilateral optic nerve, the mechanism must also be able to explain the following three anatomical features: (1) that the origin of the infraoptic A1 is at, or
Fig. 3 Infraoptic A1 in 39-year-old woman. Reconstructed computed tomography angiography reveals an anomalous left anterior cerebral artery (ACA). This vessel originates from the left internal carotid artery at the level of the ophthalmic artery, has a superomedial course, and connects to the anterior communicating artery (white arrow infraoptic A1, dotted arrow origin of ophthalmic artery). Fenestration (white arrowhead) of anterior communicating artery is noted
close to, the level of the OA; (2) the distal anastomosis is in the vicinity of the AComA; and (3) the infraoptic A1 is located in the prechiasmatic space. Although Given and Morris [9] reported an infraoptic A1 with penetration of the ipsilateral optic chiasm, the A1 in case 1 reported by Maurer et al. [15], was not an infraoptic A1. Therefore, all infraoptic A1 reported in the literature are located in the prechiasmatic space. Maurer et al. [15] also reported an infraoptic A1 originating from the ICA close to the lateral margin of the optic chiasm. Therefore, this infraoptic A1 might have originated from a site on the ICA distal to the level of the OA. Isherwood and Dutton [10] proposed the theory of prechiasmal anastomosis. The prechiasmal anastomosis at the medial aspect of the intracranial segments of the optic nerves and at the anterior border of the chiasm consists of the prechiasmal branch of the OA, the superior hypophyseal branch of the ICA, and the chiasmal branches of the ACA. Robinson [20] suggested that an infraoptic A1 might arise from enlargement of an anastomosis between the ACA and the superior hypophyseal vessel proximal to the posterior communicating artery. This theory satisfactorily explains the prechiasmatic location of an infraoptic A1. But the dorsal aspect of the chiasm is vascularized by branches coming from A1 while the ventral aspect receives its supply from the ICA; these vessels realize an anastomotic network between the right and left sides but the dorsal and ventral networks are not really linked and the vessels diameter is very tiny. Therefore, the theory of prechiasmal anastomosis is less likely for formation of infraoptic A1. Bosma [4] also proposed that an infraoptic A1 might arise from developmental failure of the potential anastomosis between the primitive olfactory and the primitive maxillary arteries, both supplying the prosencephalon. Before the 5–6-mm embryonic stage, the primitive maxillary artery, a branch of the ICA arising from its future intracavernous portion, supplies the optic vesicle [19]. This artery normally regresses after the 5–6-mm embryonic stage when other branches of the internal carotid take over responsibility for its territory; in the adult, the primitive maxillary artery persists in the form of small intracavernous arterial branches (posteroinferior hypophyseal artery) supplying the infundibulum. And primitive maxillary artery was originated from vertical portion of intracavernous ICA [14]. After observing an infraoptic A1 originating from the extradural ICA, Akiyama et al. [1] also proposed persistence of the embryonic anastomosis between the primitive maxillary artery and the primitive olfactory artery. However, this theory cannot explain the OA level of the ICA origin in most cases of infraoptic A1. Odake [18] and Sasaki et al. [22] disagreed with this theory because in their case, the primitive maxillary artery was
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located caudal to the primitive dorsal OA from which the normal OA developed. We also do not agree with this theory because Maurer et al. [15] reported an infraoptic A1 originating from the ICA close to the lateral margin of the optic chiasm. The third hypothesis postulates an error in the development of the definitive OA [5]. According to Isherwood and Dutton [10] and Robinson [20], the anomaly of an infraoptic A1 might represent the persistence of an anastomotic loop (around the optic nerve) of the primitive dorsal OA and the primitive ventral OA. Lasjaunias [14] also attribute the presence of an infraoptic A1 to an error in the formation of the adult OA. At the 4-mm embryonic stage, the orbit is vascularized by two OAs: one ventral, arising from the future ACA, and the other dorsal, arising from the intracavernous portion of the ICA. The adult OA is derived from the primitive ventral OA by caudal migration, while the primitive dorsal OA regresses. Failure of this development, with agenesis of the proximal ACA and/or persistence of one or the other primitive arteries, would also explain the formation of an infraoptic A1. Spinnato et al. [23] proposed that the common origin of the OA and the infraoptic A1 was proof of a close relationship, with development of the adult OA accounting for an infraoptic A1. Komiyama et al. [13] described the embryology of OA. Ventral OA originates from the primitive ICA near the origin of the anterior choroidal artery. Therefore we think that ventral OA is more important for formation of infraoptic A1. In most cases of infraoptic A1, caudal migration of the primitive ventral OA stops at, or close to, the OA level of the ICA. However, in some cases of infraoptic A1, reduced caudal migration of the primitive ventral OA results in a caudal origin at the OA level, as in the case reported by Maurer et al. [15]. Although we believe that the vascular anomalies observed in our cases may be related, we are not certain whether they all result from one type of developmental failure in the embryo. The embryogenesis of this anomaly is still controversial, and the explanations that have been offered are hypothetical. However, we do not agree that the embryogenetic origin of an infraoptic A1 is a persistence of the embryonic anastomosis between the primitive maxillary artery and the primitive olfactory artery. Also we do not agree with the theory of prechiasmal anastomosis. The association of an infraoptic A1 with an intracranial aneurysm has been frequently reported [2, 3, 8, 11, 23, 26]. If the associated aneurysm is located distally, the infraoptic A1 seldom poses a problem additional to those involved in clipping of the associated intracranial aneurysm, but simply complicates the meticulous preparation of the neck of the aneurysm [11, 12]. However, failure to recognize this anomaly might result in unnecessary dissection along, and
123
possible damage to, the optic apparatus or the inferior frontal lobe during aneurysm repair [6]. Even in patients with a proximal A1 aneurysm, if the aneurysm is small, the optic nerve may not hinder clipping. Awareness of an infraoptic A1 is especially important in patients with a proximal aneurysm, which may be obscured by the optic nerve during craniotomy. Knowledge of the anatomy enables planning for proximal control of an aneurysm and preparedness for more skull-base bone work for better delineation of the vascular anatomy [25]. Sakai et al. [21] reported one case of temporary mild deterioration of visual acuity after clipping of an infraoptic A1 aneurysm. The aneurysm was located on the curved midportion of the infraoptic A1 and extended underneath the right optic nerve. Retraction of the optic nerve during surgery was probably the cause. Removal of the anterior clinoid process and unroofing of the optic canal might facilitate manipulation of the optic nerve. However, clinoidectomy may result to deterioration of visual function. In case of fixed chiasm, optic nerve manipulation also result to visual compromise. Coil embolization can be an alternative treatment option. The presence of the infraoptic A1 can provide a straightforward endovascular approach to the AComA.
Conclusion In conclusion, although an infraoptic A1 is a rare anomaly, it is still important to bear it in mind, because it should be taken into account in planning treatment of an associated pathology. There are three proposed explanations in the literature for this anomaly. We consider that an error in the development of the definitive OA is the most likely explanation for the formation of an infraoptic A1. Acknowledgments This work was supported by research grant from an Inje University College of Medicine. Compliance with ethical standards Conflict of interest We declare that we have no conflict of interest with any organization or institute.
References 1. Akiyama Y, Okada T, Hayashi N, Yokoi T (2010) Infraoptic course of the anterior cerebral artery originating from the extradural internal carotid artery associated with contralateral internal carotid artery agenesis and multiple intracerebral aneurysms. Neurol Med Chir (Tokyo) 50:984–987 2. Al-Qahtani S, Tampieri D, Brassard R, Sirhan D, Mellanson D (2003) Coil embolization of an aneurysm associated with an infraoptic anterior cerebral artery in a child. AJNR Am J Neuroradiol 24:990–991
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