Surg Neurol 1992;38:379-82
379
Transoral-Transclival Clipping of a Giant Lower Basilar Artery Aneurysm R.A. de los Reyes, M.D., Allen B. Kantrowitz, M.D., Paul W. Detwiler, M.S., Joseph G. Feghale, M.D., Craig D. Hall, M.D., and William J. Sonstein, M.D. Departments of Neurosurgery, Otolaryngology, and Plastic Surgery, Albert Einstein College of Medicine, New York, New York
de los Reyes RA, Kantrowitz AB, Detwiler PW, FeghaleJG, Hall CD, Sonstein WJ. Transoral-transclivalclipping of a giant lower basilar artery aneurysm. Surg Neurol 1992;38:379-82. The authors discuss the choice of the transoral-transclival approach for the repair of a lower basilar artery aneurysm in a 32-year-old sickle-cell patient. Efficiency of approach and minimization of damage to vital structures support the use of this technique. The risks of cerebrospinal fluid fistula and meningitis are considered. One year after operation, the patient is neurologically intact.
KEY WORDS: Basilar artery aneurysm; Transoral; Transclival
Aneurysms o f the lower basilar artery are among the least accessible and most difficult to treat. Although somewhat accessible via the subtemporal [4-7,9,10, 16,18,19,24] or posterior fossa routes [11,14,23,24, 26], these procedures have serious limitations due to the angle of approach, the presence of cranial nerves and other vital structures along the angle of surgical dissection, and the long working distance. From a purely technical standpoint, the transclival approach to the basilar artery is the most direct, providing a better angle of approach and a field free o f cranial nerves at an equivalent or better working distance [ 1,3,8,12,13,2 2,2 5 ]. Despite some early success with this approach, it was largely discarded due to the complications of cerebrospinal fluid leak and infection [1,12,27]. Recent improvements in the techniques for skull base surgery, antibiotic prophylaxis, and our own experience with this procedure in a previously reported animal model [20] prompted us to reconsider this approach for aneurysms in the inferior basilar region.
Address reprint requests to: R.A. de los Reyes, M.D., Acting Chairman, Department of Neurosurgery, Montefiore Medical Center, 111 East 210th Street, Bronx, New York 10467-2490. Received May 6, 1992; accepted June 12, 1992.
© 1992 by ElsevierSciencePublishingCo., Inc.
Case Report A 32-year-old black male with well-controlled sickle-cell disease presented with a I-week history o f sudden onset o f severe headache. A lumbar puncture revealed xanthochromic cerebrospinal fluid. Computed tomographic (CT) and magnetic resonance imaging (MRI) scans were consistent with a giant, partially thrombosed basilar artery aneurysm (Figures 1 and 2). Cerebral angiography revealed a lower basilar artery aneurysm, just distal to the vertebrobasilar junction (Figures 3 and 4). The neck o f the aneurysm was definable, and the lumen appeared much smaller than on CT and MRI scans confirming that it was partially thrombosed. Also noted were a right internal carotid occlusion, two aneurysms at the right P1-P2 junction, and a fourth aneurysm at the carotidophthalmic bifurcation on the left. Its large size and irregular shape implicated the basilar aneurysm as the offending lesion. In addition, the MRI scan revealed early brain-stem compression. For these reasons, we elected to proceed with surgical clipping for definitive treatment of this aneurysm. After consideration of all possible surgical approaches, the transoral-transclival approach was felt to be the best approach for successfully dealing with this lesion. After induction with general anesthesia, the patient was positioned supine, with his head supported in a doughnut. The face, neck, and right thigh were prepared and draped, and a tracheostomy was performed. For maximum exposure of the clivus, the transoral exposure was extended by mandibulotomy and maxillotomy. The mandibulotomy was p e r f o r m e d via a meatal incision and a stairstep osteotomy. A midline glossotomy would have been added if necessary. A palatal flap was raised. Next, a LeFort I maxillary osteotomy was performed, and the maxilla was segmented by dividing the alveolar arch. By splitting the maxilla, the nasal and oral compartments were rendered confluent. T h e pharyngeal mucosa and musculature were then opened in the midline, exposing the clivus. Electrocautery was used to achieve hemostasis, but sparingly to avoid aggravating flap shrinkage. The 0090-3019/92/$5,00
380
Surg Neurol 1992;37:379-82
de los Reyes et al
Figure 1. Tl-weighted sagittal MR1 showing hyperintense mass indenting the pons at the level of the clivus (arrow).
operating microscope was positioned in the field, and the thickened clivus (Figure 1) was drilled out from foramen magnum to the base of the sella turcica, yielding an 18 × 29-mm dural exposure, the width of which was limited by the hypoglossal canals. The patient's head was rotated 30 degrees to the right, with the surgeon positioned perpendicular to the long axis of the patient. The dura was then incised in the midline with a diamond knife at the inferior aspect of the exposure. The vertebral arteries were identified, and the incision was extended superiorly, exposing the vertebrobasilar junction, neck of the basilar artery aneurysm, and proximal basilar artery. The dome of the aneurysm was not significantly adherent to the dura. Further opening of the dura revealed the thrombosed portion of the aneurysm, arising from the dorsal aspect of the basilar artery, as well as a small daughter aneurysm arising from the neck of the primary aneurysm. Further dissection of the neck was carried out to prepare the neck for clipping. As the clip was closed, a small amount of bleeding occurred from the daughter aneurysm. This was easily controlled. A second clip was applied proximal to the first clip, achieving hemostasis while maintaining the patency of the lumen of the basilar artery. An intraoperative angiogram confirmed proper clip placement. The clips were surrounded with Gelfoam.
The thigh was exposed and a fascia lata graft was harvested to occlude the dural defect. The graft was cut to the appropriate size, tucked intradurally, and covered with fibrin glue and fat. The longus capitus muscle was approximated in the midline, and the pharyngeal mucosa was sutured as completely as possible. Reconstruction of the LeFort I osteotomy was accomplished by miniplate fixation. The palatotomy was sutured, and the mandibulotomy was plated. Postoperatively, the patient awoke promptly and was neurologically intact. For the next 5 days, his head position was maintained at 45 degrees or greater. Lumbar drain was maintained at shoulder height. The lumbar drain was discontinued after day 5. On day 7, the patient developed a 101°F fever. An isotope cisternogram was suggestive ofa cerebrospinal fluid leak. Lumbar drainage was reinstituted, and the patient was started on a third generation cephalosporin. This was continued for 3 weeks, during which time he was afebrile and remained asymptomatic. One year after operation, the patient remains neurologically intact. Discussion Major strides in basilar artery surgery, and neurosurgery in general, were realized in the late 1960s. Improve-
Basilar Artery Aneurysm
Surg Neurol 1992;38:379-82
381
Figure 3. Right vertebral artery angiogram anteroposterior view, showing a vertebrobasilar artery junction aneurysm (solid arrow). The open arrow depicts the right orbit.
Figure 2. Axial CT scan demonstrating a calcified lower basilar artery
Figure 4. Subtraction angiogram (right vertebral artery injection) demonstrating the vertebrobasilar artery junction aneurysm (arrow).
aneurysm (arrow)
ments in neuroanesthesia, controlled hypotension, vascular clamps, high-precision instruments, and the operating microscope contributed to this revolution. Better understanding of the vascular anatomy of the basilar artery, specifically that of the perforating branches, has modified surgical technique to improve operative results [2,5,15]. Subsequently, surgical treatment of posterior circulation aneurysms has become an accepted option, especially when the lifetime risk of an unsecured aneurysm is considered [17,21]. Transclival approaches to the region of vertebrobasilar junction have been a recurring theme in the neurosurgical literature for over 25 years [1,3,8,12,13, 22,25]. Whether transcervical [8,25] or transoral [1,3,12,13,22], the transclival approach to this most difficult area has the obvious attractions of directness of approach and minimal manipulation of cranial nerves and other neurological tissue. On the negative side, however, are the real risks of cerebrospinal fluid fistula formation and meningitis [1,12,27], as well as using a surgical approach that is unfamiliar to most neurosurgeons, As such, the number of cases reported in the literature has
~ ~i!~
382
Surg Neurol 1992;37:379-82
been limited and sporadic. Nevertheless, there are many compelling reasons for reconsidering this approach. Skull base surgery is developing rapidly as a subspecialty. Consequently, the techniques for approach and repair of skull base defects have become more refined. Furthermore, the use of a multidisciplinary approach not only allows each surgeon to focus on the area of her or his expertise, but also enables the cerebrovascular surgeon to perform his or her portion of the operation fresh and relaxed, rather than fatigued from exposing the lesion. While it is true that this patient developed a cerebrospinal fluid leak, we believe that this is attributable to premature removal of the lumbar drain. In the future, removal of lumbar drain following this procedure will be considered after 10 to 14 days. Despite the development of meningitis, at no time was the patient "toxic," and the infection was readily controlled with a third generation cephalosporin. The importance of proper closure of the meningeal incision cannot be emphasized enough. In conclusion, we believe that the lack of disturbance in the level of consciousness, a direct result of the near absence of retraction of neurological tissue, reflects favorably on this approach as compared to the subtemporal or suboccipital approaches. The authors would like to thank Ron L. Alterman, M.D., for his advice during the writing of this manuscript.
References 1. Archer DJ, Young S, Uttley D. Basilar aneurysms: a new transclival approach via maxillotomy. J Neurosurg 1987;67:54-8. 2. Caruso G, Vincentelli F, Giudicelli G, Grisoli F, Xu T, Gouaze A. Perforating branches of the basilar bifurcation. J Neurosurg 1990;73:259-65. 3. Crockard HA, Koksel T, Watkin N. Transoral transclival clipping of anterior inferior cerebellar artery aneurysm using new rotating applier. J Neurosurg 1991;75:483-5. 4. Dorsch NW. Aid to exposure of the upper basilar artery: technical note. Neurosurgery 1988;23:790-1. 5. Drake CG. Further experience with surgical treatment of aneurysms of the basilar artery. J Neurosurg 1968;29:372-92. 6. Drake CG. The surgical treatment of aneurysms of the basilar artery. J Neurosurg 1968;29:436-46. 7. Drake CG. Surgical treatment ofruptured aneurysms ofthe basilar artery. Experience with 14 cases. J Neurosurg 1965;23:457-73. 8. Fox JL. Obliteration of midline vertebral artery aneurysm via basilar craniectomy. J Neurosurg 1967;26:406-12. 9- Fujitsu K, Kuwabara T. Zygomatic approach for lesions in the interpeduncular cistern. J Neurosurg 1985;62:340-3.
de los Reyes et al
10. Hakuba A, Liu S, Nishimura S. The orbitozygomatic infratemporal approach: a new surgical technique. Surg Neurol 1986; 26:271-6. 11. Hammon WM, Kempe LG. The posterior fossa approach to aneurysms of the vertebral and basilar arteries. J Neurosurg 1972;37:339-47. 12. Hayakawa T, Kamikawa K, Ohnishi T, Yoshimine T. Prevention of postoperative complications after a transoral transclival approach to basilar aneurysms. J Neurosurg 1981;54:699-703. 13. Hayakawa T, Kamikawa K, Ohnishi T, Yoshimine T. Transoraltransclival approach to aneurysms of the basilar artery-experience with three cases. Neurol Med Chir (Tokyo) 1981;21:477-84. 14. Heros RC. Lateral suboccipital approach for vertebral and vertebrobasilar artery lesions. J Neurosurg 1986;64:559-62. 15. Inoue T, Kobayashi S, Sugita K. Dye injection method for the demonstration of territories supplied by individual perforating arteries of the posterior communicating artery in the dog. Stroke 1985;16:684-6. 16. Kasdon DL, Stein BM. Combined supratentorial and infratentorial exposure for low-lying basilar aneurysms. Neurosurgery 1979;4:422-6. 17. Kassell NF, Torner JC, Haley EC Jr, Jane JA, Adams HP, Kongable GL. The international cooperative study on the timing of aneurysm surgery. Part 1: Overall management results. J Neurosurg 1990;73:18-36. 18. Kawase T, Toya S, Shiobara R, Mine T. Transpetrosal approach for aneurysms of the lower basilar artery. J Neurosurg 1985;63:857-61. 19. Pitelli SD, Almeida GG, Nakagawa EJ, Marchese AJ, Cabral ND. Basilar aneurysm surgery: the subtemporal approach with section of the zygomatic arch. Neurosurgery 1986;18:125-8. 20. de los Reyes RA, Boehm FH, Ehler W, Kennedy D, Shagets F, WoodruffW, Smith T, AusmanJI. Direct angioplasty of the basilar artery in baboons. Surg Neurol 1990;33:185-91. 21. Rice BJ, Peerless SJ, Drake CG. Surgical treatment ofunruptured aneurysms of the posterior circulation. J Neurosurg 1990; 73:165-73. 22. Saito I, Takahashi H, Joshita H, Usui M, Sasaki T, Sano K. Clipping of vertebro-basilar aneurysms by the transoral transclival approach. Neurol Med Chir (Tokyo) 1980;20:753-8. 23. Salcman M, Rigamonti D, Numaguchi Y, Sadato N. Aneurysms of the posterior inferior cerebellar artery-vertebral artery complex: variations on a theme. Neurosurgery 1990;27:12-20. 24. Solomon RA, Stein BM. Surgical approaches to aneurysms of the vertebral and basilar arteries. Neurosurgery 1988;23: 203-8. 25. Wissinger JP, Danoff D, Wisiol ES, French LA. Repair of an aneurysm of the basilar artery by a transclival approach. Case report. J Neurosurg 1967;26:417-9. 26. Wright DC, Wilson CB. Surgical treatment of basilar aneurysms. Neurosurgery 1979;5:325-33. 27. Yamaura A, Makino H, Isobe K, Takashima T, Nakamura T, Takemiya S. Repair of cerebrospinal fluid fistula following transoral transclival approach to a basilar aneurysm. Technical note. J Neurosurg 1979;50:834-6.
379
Transoral-Transclival Clipping of a Giant Lower Basilar Artery Aneurysm R.A. de los Reyes, M.D., Allen B. Kantrowitz, M.D., Paul W. Detwiler, M.S., Joseph G. Feghale, M.D., Craig D. Hall, M.D., and William J. Sonstein, M.D. Departments of Neurosurgery, Otolaryngology, and Plastic Surgery, Albert Einstein College of Medicine, New York, New York
de los Reyes RA, Kantrowitz AB, Detwiler PW, FeghaleJG, Hall CD, Sonstein WJ. Transoral-transclivalclipping of a giant lower basilar artery aneurysm. Surg Neurol 1992;38:379-82. The authors discuss the choice of the transoral-transclival approach for the repair of a lower basilar artery aneurysm in a 32-year-old sickle-cell patient. Efficiency of approach and minimization of damage to vital structures support the use of this technique. The risks of cerebrospinal fluid fistula and meningitis are considered. One year after operation, the patient is neurologically intact.
KEY WORDS: Basilar artery aneurysm; Transoral; Transclival
Aneurysms o f the lower basilar artery are among the least accessible and most difficult to treat. Although somewhat accessible via the subtemporal [4-7,9,10, 16,18,19,24] or posterior fossa routes [11,14,23,24, 26], these procedures have serious limitations due to the angle of approach, the presence of cranial nerves and other vital structures along the angle of surgical dissection, and the long working distance. From a purely technical standpoint, the transclival approach to the basilar artery is the most direct, providing a better angle of approach and a field free o f cranial nerves at an equivalent or better working distance [ 1,3,8,12,13,2 2,2 5 ]. Despite some early success with this approach, it was largely discarded due to the complications of cerebrospinal fluid leak and infection [1,12,27]. Recent improvements in the techniques for skull base surgery, antibiotic prophylaxis, and our own experience with this procedure in a previously reported animal model [20] prompted us to reconsider this approach for aneurysms in the inferior basilar region.
Address reprint requests to: R.A. de los Reyes, M.D., Acting Chairman, Department of Neurosurgery, Montefiore Medical Center, 111 East 210th Street, Bronx, New York 10467-2490. Received May 6, 1992; accepted June 12, 1992.
© 1992 by ElsevierSciencePublishingCo., Inc.
Case Report A 32-year-old black male with well-controlled sickle-cell disease presented with a I-week history o f sudden onset o f severe headache. A lumbar puncture revealed xanthochromic cerebrospinal fluid. Computed tomographic (CT) and magnetic resonance imaging (MRI) scans were consistent with a giant, partially thrombosed basilar artery aneurysm (Figures 1 and 2). Cerebral angiography revealed a lower basilar artery aneurysm, just distal to the vertebrobasilar junction (Figures 3 and 4). The neck o f the aneurysm was definable, and the lumen appeared much smaller than on CT and MRI scans confirming that it was partially thrombosed. Also noted were a right internal carotid occlusion, two aneurysms at the right P1-P2 junction, and a fourth aneurysm at the carotidophthalmic bifurcation on the left. Its large size and irregular shape implicated the basilar aneurysm as the offending lesion. In addition, the MRI scan revealed early brain-stem compression. For these reasons, we elected to proceed with surgical clipping for definitive treatment of this aneurysm. After consideration of all possible surgical approaches, the transoral-transclival approach was felt to be the best approach for successfully dealing with this lesion. After induction with general anesthesia, the patient was positioned supine, with his head supported in a doughnut. The face, neck, and right thigh were prepared and draped, and a tracheostomy was performed. For maximum exposure of the clivus, the transoral exposure was extended by mandibulotomy and maxillotomy. The mandibulotomy was p e r f o r m e d via a meatal incision and a stairstep osteotomy. A midline glossotomy would have been added if necessary. A palatal flap was raised. Next, a LeFort I maxillary osteotomy was performed, and the maxilla was segmented by dividing the alveolar arch. By splitting the maxilla, the nasal and oral compartments were rendered confluent. T h e pharyngeal mucosa and musculature were then opened in the midline, exposing the clivus. Electrocautery was used to achieve hemostasis, but sparingly to avoid aggravating flap shrinkage. The 0090-3019/92/$5,00
380
Surg Neurol 1992;37:379-82
de los Reyes et al
Figure 1. Tl-weighted sagittal MR1 showing hyperintense mass indenting the pons at the level of the clivus (arrow).
operating microscope was positioned in the field, and the thickened clivus (Figure 1) was drilled out from foramen magnum to the base of the sella turcica, yielding an 18 × 29-mm dural exposure, the width of which was limited by the hypoglossal canals. The patient's head was rotated 30 degrees to the right, with the surgeon positioned perpendicular to the long axis of the patient. The dura was then incised in the midline with a diamond knife at the inferior aspect of the exposure. The vertebral arteries were identified, and the incision was extended superiorly, exposing the vertebrobasilar junction, neck of the basilar artery aneurysm, and proximal basilar artery. The dome of the aneurysm was not significantly adherent to the dura. Further opening of the dura revealed the thrombosed portion of the aneurysm, arising from the dorsal aspect of the basilar artery, as well as a small daughter aneurysm arising from the neck of the primary aneurysm. Further dissection of the neck was carried out to prepare the neck for clipping. As the clip was closed, a small amount of bleeding occurred from the daughter aneurysm. This was easily controlled. A second clip was applied proximal to the first clip, achieving hemostasis while maintaining the patency of the lumen of the basilar artery. An intraoperative angiogram confirmed proper clip placement. The clips were surrounded with Gelfoam.
The thigh was exposed and a fascia lata graft was harvested to occlude the dural defect. The graft was cut to the appropriate size, tucked intradurally, and covered with fibrin glue and fat. The longus capitus muscle was approximated in the midline, and the pharyngeal mucosa was sutured as completely as possible. Reconstruction of the LeFort I osteotomy was accomplished by miniplate fixation. The palatotomy was sutured, and the mandibulotomy was plated. Postoperatively, the patient awoke promptly and was neurologically intact. For the next 5 days, his head position was maintained at 45 degrees or greater. Lumbar drain was maintained at shoulder height. The lumbar drain was discontinued after day 5. On day 7, the patient developed a 101°F fever. An isotope cisternogram was suggestive ofa cerebrospinal fluid leak. Lumbar drainage was reinstituted, and the patient was started on a third generation cephalosporin. This was continued for 3 weeks, during which time he was afebrile and remained asymptomatic. One year after operation, the patient remains neurologically intact. Discussion Major strides in basilar artery surgery, and neurosurgery in general, were realized in the late 1960s. Improve-
Basilar Artery Aneurysm
Surg Neurol 1992;38:379-82
381
Figure 3. Right vertebral artery angiogram anteroposterior view, showing a vertebrobasilar artery junction aneurysm (solid arrow). The open arrow depicts the right orbit.
Figure 2. Axial CT scan demonstrating a calcified lower basilar artery
Figure 4. Subtraction angiogram (right vertebral artery injection) demonstrating the vertebrobasilar artery junction aneurysm (arrow).
aneurysm (arrow)
ments in neuroanesthesia, controlled hypotension, vascular clamps, high-precision instruments, and the operating microscope contributed to this revolution. Better understanding of the vascular anatomy of the basilar artery, specifically that of the perforating branches, has modified surgical technique to improve operative results [2,5,15]. Subsequently, surgical treatment of posterior circulation aneurysms has become an accepted option, especially when the lifetime risk of an unsecured aneurysm is considered [17,21]. Transclival approaches to the region of vertebrobasilar junction have been a recurring theme in the neurosurgical literature for over 25 years [1,3,8,12,13, 22,25]. Whether transcervical [8,25] or transoral [1,3,12,13,22], the transclival approach to this most difficult area has the obvious attractions of directness of approach and minimal manipulation of cranial nerves and other neurological tissue. On the negative side, however, are the real risks of cerebrospinal fluid fistula formation and meningitis [1,12,27], as well as using a surgical approach that is unfamiliar to most neurosurgeons, As such, the number of cases reported in the literature has
~ ~i!~
382
Surg Neurol 1992;37:379-82
been limited and sporadic. Nevertheless, there are many compelling reasons for reconsidering this approach. Skull base surgery is developing rapidly as a subspecialty. Consequently, the techniques for approach and repair of skull base defects have become more refined. Furthermore, the use of a multidisciplinary approach not only allows each surgeon to focus on the area of her or his expertise, but also enables the cerebrovascular surgeon to perform his or her portion of the operation fresh and relaxed, rather than fatigued from exposing the lesion. While it is true that this patient developed a cerebrospinal fluid leak, we believe that this is attributable to premature removal of the lumbar drain. In the future, removal of lumbar drain following this procedure will be considered after 10 to 14 days. Despite the development of meningitis, at no time was the patient "toxic," and the infection was readily controlled with a third generation cephalosporin. The importance of proper closure of the meningeal incision cannot be emphasized enough. In conclusion, we believe that the lack of disturbance in the level of consciousness, a direct result of the near absence of retraction of neurological tissue, reflects favorably on this approach as compared to the subtemporal or suboccipital approaches. The authors would like to thank Ron L. Alterman, M.D., for his advice during the writing of this manuscript.
References 1. Archer DJ, Young S, Uttley D. Basilar aneurysms: a new transclival approach via maxillotomy. J Neurosurg 1987;67:54-8. 2. Caruso G, Vincentelli F, Giudicelli G, Grisoli F, Xu T, Gouaze A. Perforating branches of the basilar bifurcation. J Neurosurg 1990;73:259-65. 3. Crockard HA, Koksel T, Watkin N. Transoral transclival clipping of anterior inferior cerebellar artery aneurysm using new rotating applier. J Neurosurg 1991;75:483-5. 4. Dorsch NW. Aid to exposure of the upper basilar artery: technical note. Neurosurgery 1988;23:790-1. 5. Drake CG. Further experience with surgical treatment of aneurysms of the basilar artery. J Neurosurg 1968;29:372-92. 6. Drake CG. The surgical treatment of aneurysms of the basilar artery. J Neurosurg 1968;29:436-46. 7. Drake CG. Surgical treatment ofruptured aneurysms ofthe basilar artery. Experience with 14 cases. J Neurosurg 1965;23:457-73. 8. Fox JL. Obliteration of midline vertebral artery aneurysm via basilar craniectomy. J Neurosurg 1967;26:406-12. 9- Fujitsu K, Kuwabara T. Zygomatic approach for lesions in the interpeduncular cistern. J Neurosurg 1985;62:340-3.
de los Reyes et al
10. Hakuba A, Liu S, Nishimura S. The orbitozygomatic infratemporal approach: a new surgical technique. Surg Neurol 1986; 26:271-6. 11. Hammon WM, Kempe LG. The posterior fossa approach to aneurysms of the vertebral and basilar arteries. J Neurosurg 1972;37:339-47. 12. Hayakawa T, Kamikawa K, Ohnishi T, Yoshimine T. Prevention of postoperative complications after a transoral transclival approach to basilar aneurysms. J Neurosurg 1981;54:699-703. 13. Hayakawa T, Kamikawa K, Ohnishi T, Yoshimine T. Transoraltransclival approach to aneurysms of the basilar artery-experience with three cases. Neurol Med Chir (Tokyo) 1981;21:477-84. 14. Heros RC. Lateral suboccipital approach for vertebral and vertebrobasilar artery lesions. J Neurosurg 1986;64:559-62. 15. Inoue T, Kobayashi S, Sugita K. Dye injection method for the demonstration of territories supplied by individual perforating arteries of the posterior communicating artery in the dog. Stroke 1985;16:684-6. 16. Kasdon DL, Stein BM. Combined supratentorial and infratentorial exposure for low-lying basilar aneurysms. Neurosurgery 1979;4:422-6. 17. Kassell NF, Torner JC, Haley EC Jr, Jane JA, Adams HP, Kongable GL. The international cooperative study on the timing of aneurysm surgery. Part 1: Overall management results. J Neurosurg 1990;73:18-36. 18. Kawase T, Toya S, Shiobara R, Mine T. Transpetrosal approach for aneurysms of the lower basilar artery. J Neurosurg 1985;63:857-61. 19. Pitelli SD, Almeida GG, Nakagawa EJ, Marchese AJ, Cabral ND. Basilar aneurysm surgery: the subtemporal approach with section of the zygomatic arch. Neurosurgery 1986;18:125-8. 20. de los Reyes RA, Boehm FH, Ehler W, Kennedy D, Shagets F, WoodruffW, Smith T, AusmanJI. Direct angioplasty of the basilar artery in baboons. Surg Neurol 1990;33:185-91. 21. Rice BJ, Peerless SJ, Drake CG. Surgical treatment ofunruptured aneurysms of the posterior circulation. J Neurosurg 1990; 73:165-73. 22. Saito I, Takahashi H, Joshita H, Usui M, Sasaki T, Sano K. Clipping of vertebro-basilar aneurysms by the transoral transclival approach. Neurol Med Chir (Tokyo) 1980;20:753-8. 23. Salcman M, Rigamonti D, Numaguchi Y, Sadato N. Aneurysms of the posterior inferior cerebellar artery-vertebral artery complex: variations on a theme. Neurosurgery 1990;27:12-20. 24. Solomon RA, Stein BM. Surgical approaches to aneurysms of the vertebral and basilar arteries. Neurosurgery 1988;23: 203-8. 25. Wissinger JP, Danoff D, Wisiol ES, French LA. Repair of an aneurysm of the basilar artery by a transclival approach. Case report. J Neurosurg 1967;26:417-9. 26. Wright DC, Wilson CB. Surgical treatment of basilar aneurysms. Neurosurgery 1979;5:325-33. 27. Yamaura A, Makino H, Isobe K, Takashima T, Nakamura T, Takemiya S. Repair of cerebrospinal fluid fistula following transoral transclival approach to a basilar aneurysm. Technical note. J Neurosurg 1979;50:834-6.
