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Ruptured anterior communicating artery aneurysms associated with fenestration of the anterior cerebral artery
Surg Neurol 1984;22:371-6
371
Ruptured Anterior Communicating Artery Aneurysms Associated with Fenestration of the Anterior Cerebral Artery Masaru Matsumura, M.D. and Ken Nojiri, M.D. Department of Neurosurgery, Hokushin General Hospital, Nakano, Nagano-ken, Japan
Matsumura M, Nojiri K. Ruptured anterior communicating artery aneurysms associated with fenestration of the anterior cerebral artery. Surg Neurol 1984;22:371-6. T w o patients with ruptured anterior communicating artery aneurysms associated with fenestration of the anterior cerebral artery are reported. In the literature, only 12 angiographic demons'trations of fenestration of the anterior cerebral artery have been reported. All fenestrations were limited to the distal half of the At portion, and seven of the 12 cases wer,= associated with aneurysms. The high incidence of coexisting fenestration and aneurysm suggests that congenital1 factors may play a role in the pathogenesis of cerebral aneurysm. KEYWORDS" Anterior cerebral artery; Cerebral aneurysm; Fenestration; Subarachnoid hemorrhage
Fenestration of cerebraJl arteries is most frequently observed in vertebral and basilar angiograms [1,7,8,12, 16,26]. Angiographically confirmed fenestration of the anterior cerebral arteries is extremely rare [9,11,13,15, 23,28], and there are fi~w reports of the association o f cerebral aneurysms [9,11,15,28]. We now present two patients with ruptured anterior communicating artery aneurysms associated with fenestration of the anterior cerebral artery. Case Reports Case 1
O n July 28, 1983, this 57-year-old man suddenly lost consciousness while talking. Loss of consciousness was followed by vomiting ~Lnd C h e y n e - S t o k e s respiration. Thirty minutes after the attack, he was admitted to our hospital in a semicomatose state. His pupils were isocoric and their reaction to light was sluggish; left hemiparesis and bilateral Babinski reflexes were present. Address reprint requests to: Masaru Matsumura, M.D., Department of Neurosurgery, Gunma University School of Medicine, 3-39-22, Showa-machi, Maebashi-shi, Gunma-ken, 371, Japan.
© 1984 by ElsevierSciencePublishingCo., Inc.
C o m p u t e d tomograms revealed high-density areas in the basal and bilateral Sylvian cisterns, the ventricles, and the right frontal lobe. T h e r e was an oval, slightly dense mass at the interhemispheric fissure (Figure 1). Cerebral angiograms demonstrated a giant aneurysm (25 × 18 mm) on the anterior communicating artery; the distal half of the right A1 portion was fenestrated (Figure 2). An operation was not p e r f o r m e d because of the patient's p o o r condition, and he died due to rebleeding on the eleventh hospital day while in the intensive care unit. Permission for p o s t m o r t e m examination was refused.
Case 2
On September 7, 1983, this 55-year-old man had a sudden attack o f severe headache and nausea; he was admitted to our hospital 6 hours later. O n admission, he was alert, but complained o f severe headache and nausea; there were no focal neurological findings. C o m puted tomograms revealed high-density areas in the basal and both Sylvian cisterns and the interhemispheric fissure (Figure 3). Cerebral angiograms demonstrated a saccular aneurysm at the anterior communicating artery; the distal half of the right A1 portion was fenestrated (Figure 4). T h e left A1 portion was hypoplastic; there were no other aneurysms or arteriovenous malformations. An operation was p e r f o r m e d the next day, and the neck of the aneurysm was clipped. Fenestration of the anterior cerebral artery was confirmed at the operation (Figure 5). His postoperative course was uneventful.
Discussion T h e r e are several reports on fenestration o f the anterior cerebral artery [3,4,9,11,13,15,21,23,27]. A m o n g 350 cases Alpers et al [1] found three (0.8%) exhibiting fenestration o f the anterior cerebral artery. Baptista [3] reported an incidence of 2.9% (12 out of 417) in cases involving adults and 3.4% (3 out o f 87) among children; the incidence reported by von Mitterwallner [25] was 0.8% (3 out of 360); that o f Perlmutter and Rhoton 0090-3019/84/$3.00
372
Surg Neurol 1984;22:371-6
Matsumura and Nojiri
Figure 1. [Above] Case 1: Computed tomogram revealing high-density areas in the basal and bilateral Sylvian cisterns, the ventricles, and the right frontal lobe. A n oval, slightly high-density mass is disclosed at the interhemispheric fissure (arrow).
Figure 2. [Left] Case 1: Right carotid angiogram during compression of the contralateral carotid artery (anteroposterior view). A giant aneurysm at the anterior communicating artery is demonstrated and the right A~ portion is fenestrated (arrow).
Figure 3. [Above right] Case 2: Computed tomogram revealing highdensity areas in the basal and bilateral Sylvian cisterns and in the interhemispheric fissure.
Figure 4. [Below right] Case 2: Right carotid angiogram (A = anteroposterior view; B = oblique view). A saccular aneurysm is demonstrated at the anterior communicating artery (open arrow); the distal half of the right AI portion is fenestrated (solid arrow). Double filling of anterior cerebral arteries from right A1 is seen.
Aneurysm and Fenestration
A
Surg Neurol 1984;22:371-6
B
373
374
Surg Neurol 1984;22:371-6
Matsumura and Nojiri
A
Figure 5. Case 2: (A) Operative view offenestration of the anterior cerebral artery and aneurysm at the anterior communicating artery. (B) Schema of the operative view.
Aneurysm and Fenestration
Surg Neurol 1984;22:371-6
[21] was 4 % (2 out of 50). According to Padget [20], the formation of the anterior cerebral artery occurs at 35 - 1 days in human ,embryos. At this early stage, the arteries are relatively primitive and plexiform. Incomplete fusion of the plexiform anastomosis may result in fenestration o f the anterior cerebral artery [1,23]. The anterior portion of the circle of Willis is the favorite site for accessory vessels, ~nd the anterior communicating artery is most frequently involved [1,14,29]. Interestingly, at autopsy [3,4,21,23] and in angiographic findings [9,11,13,15,23,28], fenestration of the anterior cerebral artery was always limited to the distal half of the AI portion. In reported autopsy [4,27] and the angiographic findings [2,10,14,15,23,24], however, fenestration of the middle cerebral artery was always limited to the proximal half of the M1 portion. Crompton [4] first reported an autopsy case of an aneurysm at the fenestration of the anterior cerebral artery. The aneurysm was located at the proximal end of the fenestration, and a medial defect was noted. Inagawa et al [9] and Yamada et al [28] have recently reported similar cases. Henmati and Kim [7] and Hoffman and Wilson [8] fi3und aneuryms at the proximal end of the fenestrated basilar artery. In both of our cases, the aneurysms were demonstrated at the distal of the fenestration; Ueda et al [24] encountered a similar case. In their patient, the proximal portion of M~ was fenestrated and the aneurysm was located at the bifurcation of the middle cerebral artery. In patients with cerebrovascular diseases, angiographic studies may reveal the existing vascular anomaly [12,14]. On the other hand, a high incidence of coexisting aneurysm or arte;iovenous malformation and vascular anomalies has been reported [15,16,18]. Our re-
375
view of the literature detected 12 angiographic demonstrations of fenestration of the anterior cerebral artery [9,11,13,15,23,28] (Table 1). Seven of the 12 reported cases (58%) were associated with aneurysms. A hemodynamic factor may be involved in the development of aneurysms [5,6,17,19], although the high incidence of coexisting aneurysm and fenestration on one vessel suggests that congenital factors may also play a role in the pathogenesis of cerebral aneurysms [2,4,9,14-16,18,24,28]. When examining cerebral angiograms, care must be taken not to misinterpret the presence of Huebner's artery, duplication of the anterior cerebral artery, looping of the anterior cerebral artery, or looping of the posterior cerebral artery. Looping of the anterior cerebral artery may give the impression of a saccular aneurysm [29]. To avoid misdiagnoses, it is therefore imperative to obtain a half-oblique view or a magnified view.
Conclusion Two cases of ruptured anterior communicating artery aneurysms associated with fenestration of the anterior cerebral artery are presented. Fenestration of the anterior cerebral artery is rare and to our knowledge, only 12 angiographic demonstrations have been reported. In all 12 cases, the fenestration was limited to the distal half of the A1 portion. In seven of the 12 cases there was aneurysmal association. The high incidence of coexisting fenestration and aneurysm suggests that congenital factors may play a role in the pathogenesis of cerebral aneurysms.
Table 1. Twelve Cases of Angiographically Demonstrated Fenestration of the Anterior Cerebral Artery Authors (year) Krayenbiihl and Yasargil (lC'68) Teal et al (1973)
Miyazaki and Tsuruta (1972 Ito et al (1981)
Yamada et al (1982) Inagawa et al (1983)
Matsumura et al (1984)
Age -
-
Sex -
-
49
M
45 32 42 34 37 48 43 70
F F F F F M M F
57 55
M M
Associated lesion -
-
Pseudoazygos pericallosal artery Vascular neoplasm ICA aneurysm ICA aneurysm Meningioma Pituitary adenoma ACA distal aneurysm Aneurysm at the fenestration Aneurysms at the fenestration and MCA trifurcation AComA aneurysm AComA aneurysm
Confirmed at operation No No No Yes No No No No Yes No
No Yes
Abbreviations: ACA = anterior cerebral artery; AComA = anterior communicating artery; ICA = internal carotid artery; MCA = middle cerebral artery.
376
Surg N e u r o l 1984;22:371-6
References 1. Alpers BJ, Berry RG, Paddison RM. Anatomical studies of the circle of Willis in normal brain. Arch Neurol Psychiatry 1959;81:409-18. 2. Baba M, Shimizu T, Kagawa M, Kitamura K, Kobayashi N. A case of multiple anomalies of cerebral vessels. Neurol Surg 1977;5:59-64 [abstract in English]. 3. Baptista AG. Studies on the arteries of the brain. III. Circle of Willis: morphologic features. Acta Neurol Scand 1964;40:398~i 14. 4. Crompton MR. The pathology of ruptured middle-cerebral aneurysms with special reference to the differences between the sexes. Lancet 1962;2:421-5. 5. Ferguson GG. Physical factors in the initiation, growth, and rupture of human intracranial saccular aneurysms. J Neurosurg 1972;37:666-77. 6. Hashimoto N, Handa H, Nagata I, Hazama F. Experimentally induced cerebral aneurysms in rats: Part V. Relation of hemodynamics in the circle of Willis to formation of aneurysms. Surg Neurol 1980;13:41-5. 7. Hemmati M, Kim KS. A ruptured aneurysm at the basilar artery fenestration. Radiology 1979;130:174. 8. Hoffman WF, Wilson CB. Fenestrated basilar artery associated saccular aneurysm. Case report. J Neurosurg 1979;50:262-4. 9. Inagawa T, Yamada T, Takeda T, Taguchi H. Aneurysms of the fenestrated anterior cerebral artery. Report of two cases. Neurol Med Chir (Tokyo) 1983;23:211-5 [abstract in English]. 10. Ito J, Maeda H, Inoue K, Onishi Y. Fenestration of the middle cerebral artery. Neuroradiology 1977;13:37-9. 11. Ito J, Washiyama K, Kim CH, Ibuchi Y. Fenestration of the anterior cerebral artery. Neuroradiology 1981 ;21:277-80. 12. Kawamoto K, Tanaka M, Miki M, Someda K. Fenestration of the vertebrobasilar system. No To Shinkei 1972;24:811-5 [abstract
in English]. 13. Krayenbiihl HA, Yasargil MG. Cerebral angiography. 2nd ed. London: Butterworths, 1968:38-40. 14. Kwak R, Kuwabara K, Niizuma H, Suzuki J. Anomalies of the cerebral artery with intracranial saccular aneurysms. Duplication and fenestration. Neurol Surg 1979;7:691-6 [abstract in English]. 15. Miyazaki Y, Tsuruta J. Clinical studies on the congenital anomalies of the intracranial arteries associated with cerebral aneurysms. Hokkaido Igaku Zasshi 1977;52:111-23 [abstractin English]. 16. Mizukami M, Mine T, Tomita T. Fenestration of the vertebral artery (vertebral diastematoarteria). Coexistence of cerebral aneu-
M a t s u m u r a and N o j i r i
rysm and cerebral arteriovenous malformation. No To Shinkei 1968 ;20:1271-6 [abstract in English]. 17. Nagata I, Handa H, Hashimoto N, Hazama F. Experimentally induced cerebral aneurysms in rats: Part IV. Hypertension. Surg Neurol 1980;14:477-9. 18. Nakajima K, Ito Z, Hen R, Uemura K, Matsuoka S. Congenital anomalies of cerebral artery and intracranial aneurysms. No To Shinkei 1976;28:197-201 [abstract in English]. 19. Nukui H, Nagaya T, Miyagi O, TamadaJ, Kaneko M, Sasaki H, Mitsuka S, Kawafuchi J, Kohno N, Kanoh T. Development of new aneurysm and enlargement of small aneurysm. Report of seven cases. Neurol Med Chir (Tokyo) 1982;22:437-45 [abstract
in English]. 20. Padget DH. The development of the cranial arteries in the human embryo. Contrib Embryol 1948;32:205-61. 21. Perlmutter D, Rhoton AL. Microsurgical anatomy of the anterior cerebral-anterior communicating recurrent artery complex. J Neurosurg 1976;45:259-72. 22. Tanaka M, Matsumoto S. Fenestration of the internal carotid artery. Neurol Med Chir (Tokyo) 1982;22:291-4 [abstract in
English]. 23. Teal JS, Rumbaugh CL, Bergeron RT, Segall HD. Angiographic demonstration of fenestration of the intradural intracranial arteries. Radiology 1973;106:123-6. 24. UedaT, GoyaT, Kinoshita K. Fenestration of the middle cerebral artery associated with an aneurysm. Neurol Med Chir (Tokyo) 1983;23:278-81 [abstract in English]. 25. von Mitterwallner VF. Variationsstatistische Untersuchungen an den basalen Hirngef~issen. Acta Anat (Basel) 1955;24:51-88. 26. Wollschlaeger G, Wollschlaeger PB, Lucas FV, Lopez VF. Experience and results with postmortem cerebral angiography performed as routine procedure of the autopsy. Am J Roentgenol 1967;101:68-87. 27. Wollschlaeger G, WoUschlaeger PB. The circle of Willis. In: Newton TH, Potts DG, eds. Radiology of the skull and brain. Vol 2, book 2. St Louis: CV Mosby, 1974:1180-8. 28. Yamada T, Inagawa T, Takeda T. Ruptured aneurysm at the anterior cerebral artery fenestration. Case report. J Neurosurg 1982;57:826-8. 29. Yasargil MG, FoxJL, Ray MW. The operative approach to aneurysms of the anterior communicating artery. In: Krayenbiihl H, ed. Advances and technical standards in neurosurgery. Vol 2. Vienna: Springer-Verlag, 1975;113-70.
371
Ruptured Anterior Communicating Artery Aneurysms Associated with Fenestration of the Anterior Cerebral Artery Masaru Matsumura, M.D. and Ken Nojiri, M.D. Department of Neurosurgery, Hokushin General Hospital, Nakano, Nagano-ken, Japan
Matsumura M, Nojiri K. Ruptured anterior communicating artery aneurysms associated with fenestration of the anterior cerebral artery. Surg Neurol 1984;22:371-6. T w o patients with ruptured anterior communicating artery aneurysms associated with fenestration of the anterior cerebral artery are reported. In the literature, only 12 angiographic demons'trations of fenestration of the anterior cerebral artery have been reported. All fenestrations were limited to the distal half of the At portion, and seven of the 12 cases wer,= associated with aneurysms. The high incidence of coexisting fenestration and aneurysm suggests that congenital1 factors may play a role in the pathogenesis of cerebral aneurysm. KEYWORDS" Anterior cerebral artery; Cerebral aneurysm; Fenestration; Subarachnoid hemorrhage
Fenestration of cerebraJl arteries is most frequently observed in vertebral and basilar angiograms [1,7,8,12, 16,26]. Angiographically confirmed fenestration of the anterior cerebral arteries is extremely rare [9,11,13,15, 23,28], and there are fi~w reports of the association o f cerebral aneurysms [9,11,15,28]. We now present two patients with ruptured anterior communicating artery aneurysms associated with fenestration of the anterior cerebral artery. Case Reports Case 1
O n July 28, 1983, this 57-year-old man suddenly lost consciousness while talking. Loss of consciousness was followed by vomiting ~Lnd C h e y n e - S t o k e s respiration. Thirty minutes after the attack, he was admitted to our hospital in a semicomatose state. His pupils were isocoric and their reaction to light was sluggish; left hemiparesis and bilateral Babinski reflexes were present. Address reprint requests to: Masaru Matsumura, M.D., Department of Neurosurgery, Gunma University School of Medicine, 3-39-22, Showa-machi, Maebashi-shi, Gunma-ken, 371, Japan.
© 1984 by ElsevierSciencePublishingCo., Inc.
C o m p u t e d tomograms revealed high-density areas in the basal and bilateral Sylvian cisterns, the ventricles, and the right frontal lobe. T h e r e was an oval, slightly dense mass at the interhemispheric fissure (Figure 1). Cerebral angiograms demonstrated a giant aneurysm (25 × 18 mm) on the anterior communicating artery; the distal half of the right A1 portion was fenestrated (Figure 2). An operation was not p e r f o r m e d because of the patient's p o o r condition, and he died due to rebleeding on the eleventh hospital day while in the intensive care unit. Permission for p o s t m o r t e m examination was refused.
Case 2
On September 7, 1983, this 55-year-old man had a sudden attack o f severe headache and nausea; he was admitted to our hospital 6 hours later. O n admission, he was alert, but complained o f severe headache and nausea; there were no focal neurological findings. C o m puted tomograms revealed high-density areas in the basal and both Sylvian cisterns and the interhemispheric fissure (Figure 3). Cerebral angiograms demonstrated a saccular aneurysm at the anterior communicating artery; the distal half of the right A1 portion was fenestrated (Figure 4). T h e left A1 portion was hypoplastic; there were no other aneurysms or arteriovenous malformations. An operation was p e r f o r m e d the next day, and the neck of the aneurysm was clipped. Fenestration of the anterior cerebral artery was confirmed at the operation (Figure 5). His postoperative course was uneventful.
Discussion T h e r e are several reports on fenestration o f the anterior cerebral artery [3,4,9,11,13,15,21,23,27]. A m o n g 350 cases Alpers et al [1] found three (0.8%) exhibiting fenestration o f the anterior cerebral artery. Baptista [3] reported an incidence of 2.9% (12 out of 417) in cases involving adults and 3.4% (3 out o f 87) among children; the incidence reported by von Mitterwallner [25] was 0.8% (3 out of 360); that o f Perlmutter and Rhoton 0090-3019/84/$3.00
372
Surg Neurol 1984;22:371-6
Matsumura and Nojiri
Figure 1. [Above] Case 1: Computed tomogram revealing high-density areas in the basal and bilateral Sylvian cisterns, the ventricles, and the right frontal lobe. A n oval, slightly high-density mass is disclosed at the interhemispheric fissure (arrow).
Figure 2. [Left] Case 1: Right carotid angiogram during compression of the contralateral carotid artery (anteroposterior view). A giant aneurysm at the anterior communicating artery is demonstrated and the right A~ portion is fenestrated (arrow).
Figure 3. [Above right] Case 2: Computed tomogram revealing highdensity areas in the basal and bilateral Sylvian cisterns and in the interhemispheric fissure.
Figure 4. [Below right] Case 2: Right carotid angiogram (A = anteroposterior view; B = oblique view). A saccular aneurysm is demonstrated at the anterior communicating artery (open arrow); the distal half of the right AI portion is fenestrated (solid arrow). Double filling of anterior cerebral arteries from right A1 is seen.
Aneurysm and Fenestration
A
Surg Neurol 1984;22:371-6
B
373
374
Surg Neurol 1984;22:371-6
Matsumura and Nojiri
A
Figure 5. Case 2: (A) Operative view offenestration of the anterior cerebral artery and aneurysm at the anterior communicating artery. (B) Schema of the operative view.
Aneurysm and Fenestration
Surg Neurol 1984;22:371-6
[21] was 4 % (2 out of 50). According to Padget [20], the formation of the anterior cerebral artery occurs at 35 - 1 days in human ,embryos. At this early stage, the arteries are relatively primitive and plexiform. Incomplete fusion of the plexiform anastomosis may result in fenestration o f the anterior cerebral artery [1,23]. The anterior portion of the circle of Willis is the favorite site for accessory vessels, ~nd the anterior communicating artery is most frequently involved [1,14,29]. Interestingly, at autopsy [3,4,21,23] and in angiographic findings [9,11,13,15,23,28], fenestration of the anterior cerebral artery was always limited to the distal half of the AI portion. In reported autopsy [4,27] and the angiographic findings [2,10,14,15,23,24], however, fenestration of the middle cerebral artery was always limited to the proximal half of the M1 portion. Crompton [4] first reported an autopsy case of an aneurysm at the fenestration of the anterior cerebral artery. The aneurysm was located at the proximal end of the fenestration, and a medial defect was noted. Inagawa et al [9] and Yamada et al [28] have recently reported similar cases. Henmati and Kim [7] and Hoffman and Wilson [8] fi3und aneuryms at the proximal end of the fenestrated basilar artery. In both of our cases, the aneurysms were demonstrated at the distal of the fenestration; Ueda et al [24] encountered a similar case. In their patient, the proximal portion of M~ was fenestrated and the aneurysm was located at the bifurcation of the middle cerebral artery. In patients with cerebrovascular diseases, angiographic studies may reveal the existing vascular anomaly [12,14]. On the other hand, a high incidence of coexisting aneurysm or arte;iovenous malformation and vascular anomalies has been reported [15,16,18]. Our re-
375
view of the literature detected 12 angiographic demonstrations of fenestration of the anterior cerebral artery [9,11,13,15,23,28] (Table 1). Seven of the 12 reported cases (58%) were associated with aneurysms. A hemodynamic factor may be involved in the development of aneurysms [5,6,17,19], although the high incidence of coexisting aneurysm and fenestration on one vessel suggests that congenital factors may also play a role in the pathogenesis of cerebral aneurysms [2,4,9,14-16,18,24,28]. When examining cerebral angiograms, care must be taken not to misinterpret the presence of Huebner's artery, duplication of the anterior cerebral artery, looping of the anterior cerebral artery, or looping of the posterior cerebral artery. Looping of the anterior cerebral artery may give the impression of a saccular aneurysm [29]. To avoid misdiagnoses, it is therefore imperative to obtain a half-oblique view or a magnified view.
Conclusion Two cases of ruptured anterior communicating artery aneurysms associated with fenestration of the anterior cerebral artery are presented. Fenestration of the anterior cerebral artery is rare and to our knowledge, only 12 angiographic demonstrations have been reported. In all 12 cases, the fenestration was limited to the distal half of the A1 portion. In seven of the 12 cases there was aneurysmal association. The high incidence of coexisting fenestration and aneurysm suggests that congenital factors may play a role in the pathogenesis of cerebral aneurysms.
Table 1. Twelve Cases of Angiographically Demonstrated Fenestration of the Anterior Cerebral Artery Authors (year) Krayenbiihl and Yasargil (lC'68) Teal et al (1973)
Miyazaki and Tsuruta (1972 Ito et al (1981)
Yamada et al (1982) Inagawa et al (1983)
Matsumura et al (1984)
Age -
-
Sex -
-
49
M
45 32 42 34 37 48 43 70
F F F F F M M F
57 55
M M
Associated lesion -
-
Pseudoazygos pericallosal artery Vascular neoplasm ICA aneurysm ICA aneurysm Meningioma Pituitary adenoma ACA distal aneurysm Aneurysm at the fenestration Aneurysms at the fenestration and MCA trifurcation AComA aneurysm AComA aneurysm
Confirmed at operation No No No Yes No No No No Yes No
No Yes
Abbreviations: ACA = anterior cerebral artery; AComA = anterior communicating artery; ICA = internal carotid artery; MCA = middle cerebral artery.
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Surg N e u r o l 1984;22:371-6
References 1. Alpers BJ, Berry RG, Paddison RM. Anatomical studies of the circle of Willis in normal brain. Arch Neurol Psychiatry 1959;81:409-18. 2. Baba M, Shimizu T, Kagawa M, Kitamura K, Kobayashi N. A case of multiple anomalies of cerebral vessels. Neurol Surg 1977;5:59-64 [abstract in English]. 3. Baptista AG. Studies on the arteries of the brain. III. Circle of Willis: morphologic features. Acta Neurol Scand 1964;40:398~i 14. 4. Crompton MR. The pathology of ruptured middle-cerebral aneurysms with special reference to the differences between the sexes. Lancet 1962;2:421-5. 5. Ferguson GG. Physical factors in the initiation, growth, and rupture of human intracranial saccular aneurysms. J Neurosurg 1972;37:666-77. 6. Hashimoto N, Handa H, Nagata I, Hazama F. Experimentally induced cerebral aneurysms in rats: Part V. Relation of hemodynamics in the circle of Willis to formation of aneurysms. Surg Neurol 1980;13:41-5. 7. Hemmati M, Kim KS. A ruptured aneurysm at the basilar artery fenestration. Radiology 1979;130:174. 8. Hoffman WF, Wilson CB. Fenestrated basilar artery associated saccular aneurysm. Case report. J Neurosurg 1979;50:262-4. 9. Inagawa T, Yamada T, Takeda T, Taguchi H. Aneurysms of the fenestrated anterior cerebral artery. Report of two cases. Neurol Med Chir (Tokyo) 1983;23:211-5 [abstract in English]. 10. Ito J, Maeda H, Inoue K, Onishi Y. Fenestration of the middle cerebral artery. Neuroradiology 1977;13:37-9. 11. Ito J, Washiyama K, Kim CH, Ibuchi Y. Fenestration of the anterior cerebral artery. Neuroradiology 1981 ;21:277-80. 12. Kawamoto K, Tanaka M, Miki M, Someda K. Fenestration of the vertebrobasilar system. No To Shinkei 1972;24:811-5 [abstract
in English]. 13. Krayenbiihl HA, Yasargil MG. Cerebral angiography. 2nd ed. London: Butterworths, 1968:38-40. 14. Kwak R, Kuwabara K, Niizuma H, Suzuki J. Anomalies of the cerebral artery with intracranial saccular aneurysms. Duplication and fenestration. Neurol Surg 1979;7:691-6 [abstract in English]. 15. Miyazaki Y, Tsuruta J. Clinical studies on the congenital anomalies of the intracranial arteries associated with cerebral aneurysms. Hokkaido Igaku Zasshi 1977;52:111-23 [abstractin English]. 16. Mizukami M, Mine T, Tomita T. Fenestration of the vertebral artery (vertebral diastematoarteria). Coexistence of cerebral aneu-
M a t s u m u r a and N o j i r i
rysm and cerebral arteriovenous malformation. No To Shinkei 1968 ;20:1271-6 [abstract in English]. 17. Nagata I, Handa H, Hashimoto N, Hazama F. Experimentally induced cerebral aneurysms in rats: Part IV. Hypertension. Surg Neurol 1980;14:477-9. 18. Nakajima K, Ito Z, Hen R, Uemura K, Matsuoka S. Congenital anomalies of cerebral artery and intracranial aneurysms. No To Shinkei 1976;28:197-201 [abstract in English]. 19. Nukui H, Nagaya T, Miyagi O, TamadaJ, Kaneko M, Sasaki H, Mitsuka S, Kawafuchi J, Kohno N, Kanoh T. Development of new aneurysm and enlargement of small aneurysm. Report of seven cases. Neurol Med Chir (Tokyo) 1982;22:437-45 [abstract
in English]. 20. Padget DH. The development of the cranial arteries in the human embryo. Contrib Embryol 1948;32:205-61. 21. Perlmutter D, Rhoton AL. Microsurgical anatomy of the anterior cerebral-anterior communicating recurrent artery complex. J Neurosurg 1976;45:259-72. 22. Tanaka M, Matsumoto S. Fenestration of the internal carotid artery. Neurol Med Chir (Tokyo) 1982;22:291-4 [abstract in
English]. 23. Teal JS, Rumbaugh CL, Bergeron RT, Segall HD. Angiographic demonstration of fenestration of the intradural intracranial arteries. Radiology 1973;106:123-6. 24. UedaT, GoyaT, Kinoshita K. Fenestration of the middle cerebral artery associated with an aneurysm. Neurol Med Chir (Tokyo) 1983;23:278-81 [abstract in English]. 25. von Mitterwallner VF. Variationsstatistische Untersuchungen an den basalen Hirngef~issen. Acta Anat (Basel) 1955;24:51-88. 26. Wollschlaeger G, Wollschlaeger PB, Lucas FV, Lopez VF. Experience and results with postmortem cerebral angiography performed as routine procedure of the autopsy. Am J Roentgenol 1967;101:68-87. 27. Wollschlaeger G, WoUschlaeger PB. The circle of Willis. In: Newton TH, Potts DG, eds. Radiology of the skull and brain. Vol 2, book 2. St Louis: CV Mosby, 1974:1180-8. 28. Yamada T, Inagawa T, Takeda T. Ruptured aneurysm at the anterior cerebral artery fenestration. Case report. J Neurosurg 1982;57:826-8. 29. Yasargil MG, FoxJL, Ray MW. The operative approach to aneurysms of the anterior communicating artery. In: Krayenbiihl H, ed. Advances and technical standards in neurosurgery. Vol 2. Vienna: Springer-Verlag, 1975;113-70.