J Neurosurg 76:629-634, 1992
Intraoperative anatomical studies in patients with aneurysms of the anterior communicating artery complex EDGAR NATHAL, M.D., NOBUYUKI YASUI, M.D., TAKESHI SAMPEI, M.D., AND AKIFUMI SUZUKI, M . D .
Department of Surgical Neurology. Research Institute for Brain and Blood Vessels-Akita, Akita, Japan v" The intraoperative anatomical findings of the anterior communicating artery (ACoA) complex in 46 patients with anatomical variations were compared to those in an equal number of patients without variations in order to determine the visualization of the elements of the vascular complex. All patients underwent radical surgery for an ACoA aneurysm by one of three different surgical approaches: transsylvian, anterior interhemispheric, or basal interhemispheric. Visualization of the vascular elements was similar in patients with or without anatomical variations. The differences observed were dependent on the surgical approach selected and on the projection of the aneurysm. It was found that, even when the intraoperative anatomical field and the number of vascular elements visualized are different from those obtained in autopsy studies, the vascular microanatomical characteristics can be confirmed with each surgical approach to the extent necessary to ensure safe clipping ofaneurysms in patients both with and without anatomical variations. KEY WORDS aneurysm 9
9 anterior cerebral artery anatomical study
HE anterior communicating artery (ACoA) is the most frequent site of cerebral aneurysms; consequently, it has been one of the most studied arteries of the cerebral circulation. Some articles based on cadaveric dissections have reviewed the microsurgical anatomy of the anterior cerebral artery (ACA)ACoA complex, thus facilitating the understanding of its anatomical details. 1.~:~ Unfortunately, the fine anatomical view obtained in cadaverie specimens cannot be obtained in the operating room. During surgery, the operative field is mainly dependent on the surgical approach selected and the amount of brain retraction utilized for exposure. Furthermore, in some cases the operative field is obscured by the effects of a recent hemorrhage or a large aneurysm, making it difficult to recognize vascular structures and to preserve small perrotating branches. The present study was undertaken to analyze the intraoperative anatomical findings of the ACoA complex in a series of patients with and without anatomical variations. These patients were treated for an aneurysm of the ACoA complex using one of three different operative approaches: transsylvian, anterior interhemispheric, and basal interhemispheric.
T
Clinical Material and Methods Patient Population Between January, 1985, and March, 1990, a total of 134 patients with aneurysms of the ACoA were surgiJ. Neurosurg. / Volume 76/April, 1992
9
anterior communicating artery
9
cally treated at the Research Institute for Brain and Blood Vessels-Akita. In 46 cases (34.3%) an anatomical variation of the ACoA complex was identified either preoperatively by carotid artery angiography or during surgery (Group 1). The microanatomical findings of this group were compared with those of another 46 cases from the same series in whom no anatomical variation was found (Group 2). These groups were further divided into three subgroups according to the operative approach chosen for clipping the aneurysm; Subgroup A: Lranssylvian; Subgroup B: anterior interhemispheric; and Subgroup C: basal interhemispheric. Table 1 summarizes the size of the aneurysms in both groups. The clinical grade on admission was evaluated using the scale of Hunt and Kosnik. 6
TABLE 1 Distribution of aneurysms by size and patient group* Ancurysm Size 1-5 mm 6-10 mm 11-25 mm > 25 mm totals
Group 1 7 (15.2%) 28 (60.8%)
26 (55.3%)
11 (23.9%)
11 (23.4%)
0 46 (100%)
Group 2 10 (21.2%)
O 47? (100%)
* Group I patients displayed anatomical variations; Group 2 patients had no anatomicalvariations. ~"Includes one patient with two anterior communicating artery aneurysms.
629
E. Nathal, N. Yasui, T. Sampei, and A. Suzuki
Surgical Approaches In every case, surgery was performed by standard methods. The precise surgical technique for each approach has been described elsewhere. 7"~-'~ In brief, in the transsylvian approach, a frontotemporal craniotomy is performed and the dura is opened around the sylvian fissure; the sylvian fissure is then dissected toward the internal carotid artery bifurcation and the dissection is continued along the ACA until the ACoA complex is reached. In the anterior interhemispheric approach, a bifrontal craniotomy is performed, the dura is opened in a W pattern, and the interhemispheric fissure is dissected to the genu of the corpus callosum until the ACA is identified bilaterally; at this point, the patient is repositioned and dissection is continued to the ACoA. In the basal interhemispheric approach, a bifrontal eraniotomy is further extended by bone chisel into the anterior midsection of the frontal base and nasal bones; the dura is opened in the midbasal portion of the right side, parallel to the superior sagittal sinus, and the interhemispheric fissure is dissected. With this approach it is not necessary to reach the genu of the corpus callosum; rather, dissection is performed directly to the ACoA. In all instances, the aneurysm is isolated and the vascular anatomy confirmed before and after neck clipping.
Anatomical Studies The clinical records and bilateral carotid artery angiograms were available for all patients. In addition, the videotapes recorded during the surgical procedure were carefully analyzed and all vascular structures around the ACoA were identified and registered. A separate table of anatomical findings was compiled for every group and subgroup. Also, the surgical results were evaluated in both groups to investigate the impact of the surgical approach and the presence of vascular anomalies on the final outcome. At the time of the patient's discharge, the outcome was classified according to the Glasgow Outcome Scale, defined as follows: total recovery; moderate disability but independent and useful life; severe disability; vegetative state; and death.
FIG, ]. Diagrams showing types of anatomical variations in patientswith anteriorcommunicating artery (ACoA) complex aneurysms (aneurysms not shown). LAI and LA2 = left A~ and A2 segments of the anterior cerebral artery (ACA); RAI and RA2 = right At and A2 segments of the ACA. A and B: Hypoplasia of right (A) and left(B) Aj segments (24 cases). C and D: Duplication (C) and triplication(D) of the ACoA (14 cases). E: Dimpling ofthe ACoA (one case). F: Duplication of the leftAt segment (one case). G: Median
artery of the comus callosum (fivecases). H: Early branching pattern of the A2 segment (three cases). I: Azygous A2 segment (one case). J: Orbitofrontal artery originating from the right At segment (one ~ ) l
Statistical Analysis The results for both groups were compared with Fisher's exact test. Null hypotheses were rejected at a p value of 0.05 or less. Results
raphy. Thirty-four patients (25.3%) had one variation, seven (5.2%) had two variations, and one (0.7%) had three variations.
Anatomical Variations
Microanatomical Findings
Anatomical variations of the ACoA complex were found in 46 (34.3%) of the 134 patients (Fig. 1). The most frequent variations were: hypoplasia of the fight A~ portion of the ACoA (17.9%), duplication or triplication of the ACoA (10.4%), hypoplasia of the left A~ portion (3.7%), and hypoplasia of the median artery of the corpus callosum (3.7%). Most variations could be confirmed preoperatively with stereoscopic angiog-
The microanatomical features of the ACoA complex were studied in 92 patients. The results of the intraoperative anatomical findings for each group and surgical approach are summarized in Table 2. The recurrent artery of Heubner was visualized in 57 cases, originating from the A2 segment of the ACoA in 28 cases (49.1%), from the A] segment in 25 cases (43.9%), and at the level of the ACoA in four cases (7%). The
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J. Neurosurg. / Volume 76/April, 1992
Anterior communicating artery aneuD'sms TABLE 2
Surnrnary of microanatomicalfindings in 92 cases of ACoA complex aneurysm* AnatomicalFinding (arteries)
A
Group 1 B
C
A
Group 2 B
C
No. Percent No. Percent No. Percent No. Percent No. Percent No. Percent rtA~ 6 100 18 94.7 18 85.7 10 76.0 15 83.3 12 80.0 ltA~ 6 100 16 84.2 18 85.7 13 100 13 72.2 15 100 hA, 6 100 19 100 21 100 I3 100 17 94.4 15 100 ItA2 6 100 17 89.4 20 95.2 12 92.3 16 88.8 15 100 n orbitofrontal only 0 -5 26.3 2 9.5 3 23.0 4 22.2 1 6.6 It orbitofrontal only 1 16.6 6 31.5 3 14.2 1 7.6 4 22.2 2 13.3 both orbitofrontal 0 -1 5.2 2 9.5 1 7.6 5 27.7 2 13.3 rt Heubner only 2 33.3 1 5.2 1 4.7 1 7.6 4 222 3 20.0 II Heubner only 0 -3 15.7 3 14.2 2 15.3 2 1I. 1 3 20.0 both Heubner 1 16.6 7 36.8 1 4.7 3 23.0 2 11.1 2 13.3 1p e r f o r a l o r 3 50.0 5 26.3 6 28.5 3 23.0 4 22.2 4 26.6 1 16.6 1 19.0 4 19.0 1 7.6 1 5.5 3 20.0 2 perforators 3 perforators 0 -2 10.5 2 9.5 1 7.6 1 5.5 6 40.0 4 perforators 0 -1 5.2 2 9.5 0 -1 5.5 0 -no. eases 6 19 21 13 18 15 * Group I patients displayed anatomical variations; Group 2 patients had no anatomical variations. Subgroup A = transsylvian approach; Subgroup B = anterior interhemisphericapproach; SubgroupC = basal interhemisphedeapproach. A~and A, = A~and A2portions of the anterior cerebral artery. ACoA = anterior communicating artery.
A~ and A_, segments and the ACoA were the site of origin of small perforating vessels coursing to the adjacent neural structures; these vessels ranged in n u m b e r from one to four (Table 2). W h e n the total n u m b e r of perforating arteries visualized at surgery was compared between groups a n d subgroups, we found a significant difference between the basal interhemispheric approach and the other approaches (p < 0.05). The AI and A2 portions of the ACA were visualized in the majority of cases, even when a hypoplastic A~ segment was present. N o surgical aplasia was encountered, despite some cases in which angiography showed aplasia of one AI segment. A significant difference in the visualization of the left A~ portion was found between the anterior and basal interhemispheric subgroups in G r o u p 2, visualization being better with the basal interhemispheric approach. For the remaining vascular structures, there was no significant difference a m o n g the groups and subgroups studied (Table 2). Similarly, we did not find a significant difference in microanatomical findings between a left or a fight craniotomy with the transsylvian approach.
than in those with Type 1 or 2 (p < 0.05). There was also a correlation between longer operative times and Type 3 aneurysms; however, we did not find a correlation between final outcome a n d the position of the aneurysm.
Surgical Results There were no significant differences in outcome among the three operative approaches utilized for clipping the aneurysms. We also did not find a correlation between the presence of anatomical variations and poor outcome. In our series, outcome was mainly dependent on the patient's clinical grade on admission. Patients with neurological Grades I, II, or III had a better outcome.
Discussion Although ACoA aneurysms are the most frequent type of cerebral aneurysm, j4,~5,~9 no previous studies have compared the anatomical findings according to the surgical approach used in patients with a n d without
Aneurysm Projection In cases operated on by either the anterior or basal interhemispheric approach, the position of the ACoA aneurysm was classified into: Type l, aneurysms located anterior to the bilateral A2 portions of the ACA (24 cases, 32.8%); Type 2, aneurysms located between the bilateral A2 portions of the ACA (43 cases, 58.9%); and Type 3, aneurysms located posterior to the bilateral A2 portions of the ACA (six cases, 8.2%) (Fig. 2). Of all anatomical elements considered in the study, we found that visualization of the artery of H e u b n e r was significantly better in patients with Type 3 aneurysms
J. Neurosurg. / Volume 76/April, 1992
Fro. 2. Diagram illustrating classification of aneurysms according to their projection (as seen through the interhemispheric approaches). See text for description.
~1
E. Nathal, N. Yasui, T. Sampei, and A. Suzuki anatomical variations. The aneurysm origins and projections, and vessel anomalies and their relation to structures located in close proximity to the aneurysm should be confirmed during surgery before the aneurysm is clipped. 3's't2'~3'~6'~':~Unfortunately, the anatomical field is restricted, even with the best approach. Furthermore, in cases of early surgery the anatomy is obscured by the effects of hemorrhage, causing recognition of vascular and neural elements around the aneurysm to become very difficult.
Anatomical Variations The correlation between abnormalities of the circle of Willis and cerebrovascular disease is high; 2-9 this is most noticeable in the anterior part of the circle, where hypoplasia of an A~ segment associated with an ACoA aneurysm is one of the most frequent vascular anomalies) 8 In our series, this finding was present in 21.6% of cases. Duplication or triplication of the ACoA has been reported with an incidence as high as 43.3% in autopsy studies. 5 In our study, it was found in only 11.1% of patients; duplication of a left At portion was present in one case. The occurrence of a median artery of the corpus callosum has been reported with variable incidences ranging from 2% to 13%. t~ It should be identified on preoperative angiograms because during surgery it may be difficult to differentiate between a median artery of the corpus callosum and an early branching pattern of the A2 segment (2.2% in this study), especially when a transsylvian approach is used. The orbitofrontal artery arose from the A: portion in most cases, and originated from the left A~ portion in only one patient. One patient had an azygous A2 pattern; special attention should be given to this particular variation because in such cases the aneurysms are usually positioned high (at the final portion of the anomaly). 4 In patients with multiple variations, the most common pattern was a hypoplastic A~ segment in conjunction with another anomaly.
Microanatomical Findings The introduction of the operating microscope has provided better intraoperative definition of the ACoA complex. As can be seen in Table 2, the incidence of variations in instances where the anatomical structures can be observed differs from that found in autopsy studies. We also found that the presence of anatomical variations did not influence visualization of elements of the ACoA complex; rather, differences were mainly related to the surgical approach selected. Perforating Vessels. In formalin-fixed or polyester resin-injected brains, the number ofperforating arteries originating from the ACoA complex is variable. Therefore, the neurosurgeon must deal with a varying number of these perforators, especially those arising at the distal AI portions or from the ACoA, depending upon the surgical approach utilized. With the transsylvian approach (Fig. 3), some perforators could be found arising from the distal part of the A~ portion on the side 632
FIG. 3. Intraoperative photograph (left) and schematic drawing (right) showing the view obtained with the transsylvian approach. AN = aneurysm; ON = optic nerve; D = dimpling; LAI = left A~ segment; LA2 and RA2 = left and right A: segment.
Fro. 4. Intraoperative photograph (left) and schematic drawing (right) showing the view obtained with the anterior interhemispheric approach. AN = aneurysm; ON = optic nerve; LAI and RA1 = left and right A~ segment; LA2 and RA2 = left and fight A2 segment; LH = left artery of Heubner, LOF and ROF = lea and right orbitofrontal artery.
approached, including in the artery of Heubner. Dissection of the aneurysm may require further confirmation of the contralateral Aj and both A2 portions; however, perforators arising from the posteroinferior or posterosuperior surfaces of the ACoA are not easily visualized unless additional retraction or a gyrus rectus approach ~5is performed. This situation does not cause problems in cases of aneurysms directed anteriorly but, for aneurysms with posterior projection, the risk of perforator occlusion could be high. On the other side, with the anterior interhemispheric approach (Fig. 4), confirmation of the bilateral distal A2 and proximal A3 portions is easily accomplished, and the view of the ACoA complex includes the distal portions of the At segment, the ACoA, and both A2 portions, together with J. Neurosurg. / Volume 76/April, 1992
Anterior communicating artery aneurysms at this lateral point, the artery of Heubner could also fall within the blades of the clip.
Aneurysm Projection Classifying the aneurysm according to their positions (Fig. 2) permits better surgical planning for both isolation of the aneurysm and preservation of perforating vessels. Damage to these arteries may produce serious deficitsY ,.t7 During clipping of Type 1 aneurysms, the perforating vessels arising from the ACoA can be easily confirmed when necessary and rarely interfere with dipping. Conversely, in Type 3 and some Type 2 aneurysms, great care must be taken to spare these perforators during dissection or aneurysmal neck clipping, because visualization is poor and their surgical exposure can be difficult. In the interhemispheric approaches, the artery of Heubner rarely interferes with clipping because it runs laterally from the ACoA complex. Nevertheless, in some cases of Type I and 2 aneurysms, a lateral view of the aneurysm is necessary for clipping in order to ensure preservation of the artery of Heubner.
Surgical Results
FIG. 5. Intraoperative photographs (left) and schematic drawings (right,) showing the view obtained with the basal interhemispheric approach in two anatomical variations. ACoA = anterior communicating artery; AN = aneurysm; ON = optic nerve; RAI and RA2 = right A, and A2 segments; RH = fight artery of Heubner; ROF = right orbitofrontal artery; P = perforator; V = vein. Note the different angle of visualization of the ACoA complex and optic nerve obtained through the anterior (Fig. 4) and basal interhemispheric approaches.
the orbitofrontal artery and perforators arising from the ACoA. With the basal interhemispheric approach (Fig. 5), the field is similar to that of the anterior interhemispheric approach, except that the distal A_~ and proximal A3 portions are not exposed. Also, the angle of vision is different, directed from a lower point and slightly from right to left if the right side is approached. We attribute to this factor the higher rate of visualization of perforated arteries with the basal interhemispheric approach. Artery of Heubner. Intraoperative visualization of the artery of Heubner also depended on the surgical approach. With the transsylvian approach it is not unusual for the origin of the artery of Heubner to appear on the operative side. However, in both the anterior and basal interhemispheric approaches the origin of the artery is not easily visualized, particularly when it is located at the A, portion. Special care must be taken in cases where temporary clips are used because
s Neurosurg. / Volume 76/April 1992
In this study, the main predictor of the final outcome was the patient's clinical grade on admission. Patients who are classified in Grades I, II, or III have a good opportunity for a successful outcome; however, for patients in Grade IV or V the functional prognosis remains unsatisfactory. We did not find a correlation between the surgical approach or the position of the aneurysm and poor outcome in patients with or without anatomical variations. It should be emphasized that variations of the ACoA complex are not simple details to be observed in cadaveric studies; they can be identified on preoperative angiograms and their recognition will allow the neurosurgeon to construct a better operative plan and to save time that is frequently lost in the operating room in defining these anomalies. Selection of the operative approach should depend on personal experience, keeping in mind the most frequent vascular and neural elements to be encountered during dissection. In this study, we were able to demonstrate that visualization of the components of the ACoA complex is lower at surgery than in the cadaver dissection room, and depends on the surgical approach utilized. Nevertheless, the normal microanatomy can be confirmed to the extent necessary to ensure safe clipping of aneurysms arising from this complex in patients with or without anatomical variations.
Acknowledgments We thank Dr. Julio Sotelo for his generous help in reviewing the manuscript. Also, the assistance of Kimio Yoshioka and Yoshitaka Tozawa in preparing the illustrations and photographic material is gratefully acknowledged.
References 1. Dunker RO, Harris AB: Surgical anatomyoftheproximal anterior cerebral artery. J Nenrosurg 44:359-367, 1976
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E. Nathal, N. Yasui, T. Sampei, and A. Suzuki 2. Falconer MA: Surgical treatment of bleeding intracranial aneurysms. J Neural Neurosurg Psychiatry 14:153-186, 1951 3. French LA, Ortiz-Suarez HJ: Anterior communicating artery aneurysms: technique of operation and results. Clia Neurosurg 21:115-119, 1974 4. Fujimoto K, Waga S, Kojima T, et al: Aneurysm of the distal anterior cerebral artery associated with azygos anterior cerebral artery. Aeta Neurosurg 59:65-69, 1981 5. Gomes FB, Dujovny M, Umansky F, et al: Microanatomy of the anterior cerebral artery. Surg Neural 26:129-141, 1986 6. Hunt WE, Kosnik EJ: Timing and perioperative care in intracranial aneurysm surgery. Clin Nearosurg 21:79-89, 1974 7. Ira Z: Anatomical basis of transsylvian approach, in Yasui N, Kamiyama H (eds): Microsurgery of Cerebral Aneurysms. Atlas by Zentaro Ito, M.D. Niigata: NishimuraElsevier, 1985, pp 108-121 8. I1o Z: The microsurgical anterior interhemispheric approach suitably applied to ruptured aneurysms of the anterior communicating artery in the acute stage. Acta Neurochir 63:85-99, 1982 9. Kirgis HD, Fisher WL, Llewellyn RC, et al: Aneurysms of the anterior communicating artery and gross anomalies of the circle of Willis. J Neurosurg 25:73-78, 1966 10. Ogawa A, Suzuki M, Sakurai Y, et al: Vascular anomalies associated with aneurysms of the anterior communicaring artery: microsurgical observations. J Neurosurg 72: 706-709, 1990 11. Perlmutter D, ghoton AL Jr: Microsurgicai anatomy of the anterior cerebral-anterior communicating-recurrent artery complex. J Neurosurg 45:259-272, 1976 12. Pia HW: Aneurysms of the anterior cerebral artery, in Pia HW, Langmaid C, Zierski J (eds): Cerebral Aneurysm. Advances in Diagnosis and Therapy. Berlin: Springer-Verlag, 1979, pp 109-114
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13. Pool JL: Aneurysms of the anterior communicating artery. Bifrontal cmniotomy and routine use of temporary clips. J Neurosurg 18:98-112, 1961 14. Suzuki J, Kodama N, Ebina T, et al: Surgical treatment of anterior communicating artery aneurysms: from the experience of 346 cases, in Suzuki J (ed): Cerebral Aneurysms. Tokyo: Neuron, 1979, pp 238-243 15. VanderArk GD, Kempe LC: Classification of anterior communicating aneurysms as a basis for surgical approach. J Neurosurg 32:300-303, 1970 16. VanderArk GD, Kempe LC, Smith DR: Anterior communicating aneurysms: the gyrus rectus approach. Clin Neurosurg 21:120-133, 1974 17. Webster JE, Gurdjian ES, Lindner DW, et at: Proximal occlusion of the anterior cerebral artery. Arch Neural 2: 19-26, 1960 18. Wilson G, Riggs HE, Rupp C: The pathological anatomy of ruptured cerebral aneurysms. J Neurosurg 11: 128-134, 1954 19. Yasargil MG, Fox JL, Ray MW: The operative approach to aneurysms of the anterior communicating artery. Adv Tech Stand Neurosurg 2:113-170, 1975 20. Yasui N, Suzuki A, Sayama I, et al: [A basal interbemispheric operative approach for anterior communicating artery aneurysms.] Neural Med Chh. 27:756-761, 1987 (Jpn)
Manuscript received March 25, 1991. Accepted in final form September 6, 1991. Address for Dr. Nathal: Division of Surgical Neurology, National Institute of Neurology and Neurosurgery-Mexico, Av. Insurgentes Sur 3877, C.P. 14269, Mexico City, Mexico. Address reprint requests to: Noboyuki Yasui, M.D., Department of Surgical Neurology, Research Institute for Brain and Blood Vessels-Akita, 6,10 Senshu-kubota-machi, Akita 010, Japan.
J. Neurosurg. / Volume 76/April, 1992
Intraoperative anatomical studies in patients with aneurysms of the anterior communicating artery complex EDGAR NATHAL, M.D., NOBUYUKI YASUI, M.D., TAKESHI SAMPEI, M.D., AND AKIFUMI SUZUKI, M . D .
Department of Surgical Neurology. Research Institute for Brain and Blood Vessels-Akita, Akita, Japan v" The intraoperative anatomical findings of the anterior communicating artery (ACoA) complex in 46 patients with anatomical variations were compared to those in an equal number of patients without variations in order to determine the visualization of the elements of the vascular complex. All patients underwent radical surgery for an ACoA aneurysm by one of three different surgical approaches: transsylvian, anterior interhemispheric, or basal interhemispheric. Visualization of the vascular elements was similar in patients with or without anatomical variations. The differences observed were dependent on the surgical approach selected and on the projection of the aneurysm. It was found that, even when the intraoperative anatomical field and the number of vascular elements visualized are different from those obtained in autopsy studies, the vascular microanatomical characteristics can be confirmed with each surgical approach to the extent necessary to ensure safe clipping ofaneurysms in patients both with and without anatomical variations. KEY WORDS aneurysm 9
9 anterior cerebral artery anatomical study
HE anterior communicating artery (ACoA) is the most frequent site of cerebral aneurysms; consequently, it has been one of the most studied arteries of the cerebral circulation. Some articles based on cadaveric dissections have reviewed the microsurgical anatomy of the anterior cerebral artery (ACA)ACoA complex, thus facilitating the understanding of its anatomical details. 1.~:~ Unfortunately, the fine anatomical view obtained in cadaverie specimens cannot be obtained in the operating room. During surgery, the operative field is mainly dependent on the surgical approach selected and the amount of brain retraction utilized for exposure. Furthermore, in some cases the operative field is obscured by the effects of a recent hemorrhage or a large aneurysm, making it difficult to recognize vascular structures and to preserve small perrotating branches. The present study was undertaken to analyze the intraoperative anatomical findings of the ACoA complex in a series of patients with and without anatomical variations. These patients were treated for an aneurysm of the ACoA complex using one of three different operative approaches: transsylvian, anterior interhemispheric, and basal interhemispheric.
T
Clinical Material and Methods Patient Population Between January, 1985, and March, 1990, a total of 134 patients with aneurysms of the ACoA were surgiJ. Neurosurg. / Volume 76/April, 1992
9
anterior communicating artery
9
cally treated at the Research Institute for Brain and Blood Vessels-Akita. In 46 cases (34.3%) an anatomical variation of the ACoA complex was identified either preoperatively by carotid artery angiography or during surgery (Group 1). The microanatomical findings of this group were compared with those of another 46 cases from the same series in whom no anatomical variation was found (Group 2). These groups were further divided into three subgroups according to the operative approach chosen for clipping the aneurysm; Subgroup A: Lranssylvian; Subgroup B: anterior interhemispheric; and Subgroup C: basal interhemispheric. Table 1 summarizes the size of the aneurysms in both groups. The clinical grade on admission was evaluated using the scale of Hunt and Kosnik. 6
TABLE 1 Distribution of aneurysms by size and patient group* Ancurysm Size 1-5 mm 6-10 mm 11-25 mm > 25 mm totals
Group 1 7 (15.2%) 28 (60.8%)
26 (55.3%)
11 (23.9%)
11 (23.4%)
0 46 (100%)
Group 2 10 (21.2%)
O 47? (100%)
* Group I patients displayed anatomical variations; Group 2 patients had no anatomicalvariations. ~"Includes one patient with two anterior communicating artery aneurysms.
629
E. Nathal, N. Yasui, T. Sampei, and A. Suzuki
Surgical Approaches In every case, surgery was performed by standard methods. The precise surgical technique for each approach has been described elsewhere. 7"~-'~ In brief, in the transsylvian approach, a frontotemporal craniotomy is performed and the dura is opened around the sylvian fissure; the sylvian fissure is then dissected toward the internal carotid artery bifurcation and the dissection is continued along the ACA until the ACoA complex is reached. In the anterior interhemispheric approach, a bifrontal craniotomy is performed, the dura is opened in a W pattern, and the interhemispheric fissure is dissected to the genu of the corpus callosum until the ACA is identified bilaterally; at this point, the patient is repositioned and dissection is continued to the ACoA. In the basal interhemispheric approach, a bifrontal eraniotomy is further extended by bone chisel into the anterior midsection of the frontal base and nasal bones; the dura is opened in the midbasal portion of the right side, parallel to the superior sagittal sinus, and the interhemispheric fissure is dissected. With this approach it is not necessary to reach the genu of the corpus callosum; rather, dissection is performed directly to the ACoA. In all instances, the aneurysm is isolated and the vascular anatomy confirmed before and after neck clipping.
Anatomical Studies The clinical records and bilateral carotid artery angiograms were available for all patients. In addition, the videotapes recorded during the surgical procedure were carefully analyzed and all vascular structures around the ACoA were identified and registered. A separate table of anatomical findings was compiled for every group and subgroup. Also, the surgical results were evaluated in both groups to investigate the impact of the surgical approach and the presence of vascular anomalies on the final outcome. At the time of the patient's discharge, the outcome was classified according to the Glasgow Outcome Scale, defined as follows: total recovery; moderate disability but independent and useful life; severe disability; vegetative state; and death.
FIG, ]. Diagrams showing types of anatomical variations in patientswith anteriorcommunicating artery (ACoA) complex aneurysms (aneurysms not shown). LAI and LA2 = left A~ and A2 segments of the anterior cerebral artery (ACA); RAI and RA2 = right At and A2 segments of the ACA. A and B: Hypoplasia of right (A) and left(B) Aj segments (24 cases). C and D: Duplication (C) and triplication(D) of the ACoA (14 cases). E: Dimpling ofthe ACoA (one case). F: Duplication of the leftAt segment (one case). G: Median
artery of the comus callosum (fivecases). H: Early branching pattern of the A2 segment (three cases). I: Azygous A2 segment (one case). J: Orbitofrontal artery originating from the right At segment (one ~ ) l
Statistical Analysis The results for both groups were compared with Fisher's exact test. Null hypotheses were rejected at a p value of 0.05 or less. Results
raphy. Thirty-four patients (25.3%) had one variation, seven (5.2%) had two variations, and one (0.7%) had three variations.
Anatomical Variations
Microanatomical Findings
Anatomical variations of the ACoA complex were found in 46 (34.3%) of the 134 patients (Fig. 1). The most frequent variations were: hypoplasia of the fight A~ portion of the ACoA (17.9%), duplication or triplication of the ACoA (10.4%), hypoplasia of the left A~ portion (3.7%), and hypoplasia of the median artery of the corpus callosum (3.7%). Most variations could be confirmed preoperatively with stereoscopic angiog-
The microanatomical features of the ACoA complex were studied in 92 patients. The results of the intraoperative anatomical findings for each group and surgical approach are summarized in Table 2. The recurrent artery of Heubner was visualized in 57 cases, originating from the A2 segment of the ACoA in 28 cases (49.1%), from the A] segment in 25 cases (43.9%), and at the level of the ACoA in four cases (7%). The
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J. Neurosurg. / Volume 76/April, 1992
Anterior communicating artery aneuD'sms TABLE 2
Surnrnary of microanatomicalfindings in 92 cases of ACoA complex aneurysm* AnatomicalFinding (arteries)
A
Group 1 B
C
A
Group 2 B
C
No. Percent No. Percent No. Percent No. Percent No. Percent No. Percent rtA~ 6 100 18 94.7 18 85.7 10 76.0 15 83.3 12 80.0 ltA~ 6 100 16 84.2 18 85.7 13 100 13 72.2 15 100 hA, 6 100 19 100 21 100 I3 100 17 94.4 15 100 ItA2 6 100 17 89.4 20 95.2 12 92.3 16 88.8 15 100 n orbitofrontal only 0 -5 26.3 2 9.5 3 23.0 4 22.2 1 6.6 It orbitofrontal only 1 16.6 6 31.5 3 14.2 1 7.6 4 22.2 2 13.3 both orbitofrontal 0 -1 5.2 2 9.5 1 7.6 5 27.7 2 13.3 rt Heubner only 2 33.3 1 5.2 1 4.7 1 7.6 4 222 3 20.0 II Heubner only 0 -3 15.7 3 14.2 2 15.3 2 1I. 1 3 20.0 both Heubner 1 16.6 7 36.8 1 4.7 3 23.0 2 11.1 2 13.3 1p e r f o r a l o r 3 50.0 5 26.3 6 28.5 3 23.0 4 22.2 4 26.6 1 16.6 1 19.0 4 19.0 1 7.6 1 5.5 3 20.0 2 perforators 3 perforators 0 -2 10.5 2 9.5 1 7.6 1 5.5 6 40.0 4 perforators 0 -1 5.2 2 9.5 0 -1 5.5 0 -no. eases 6 19 21 13 18 15 * Group I patients displayed anatomical variations; Group 2 patients had no anatomical variations. Subgroup A = transsylvian approach; Subgroup B = anterior interhemisphericapproach; SubgroupC = basal interhemisphedeapproach. A~and A, = A~and A2portions of the anterior cerebral artery. ACoA = anterior communicating artery.
A~ and A_, segments and the ACoA were the site of origin of small perforating vessels coursing to the adjacent neural structures; these vessels ranged in n u m b e r from one to four (Table 2). W h e n the total n u m b e r of perforating arteries visualized at surgery was compared between groups a n d subgroups, we found a significant difference between the basal interhemispheric approach and the other approaches (p < 0.05). The AI and A2 portions of the ACA were visualized in the majority of cases, even when a hypoplastic A~ segment was present. N o surgical aplasia was encountered, despite some cases in which angiography showed aplasia of one AI segment. A significant difference in the visualization of the left A~ portion was found between the anterior and basal interhemispheric subgroups in G r o u p 2, visualization being better with the basal interhemispheric approach. For the remaining vascular structures, there was no significant difference a m o n g the groups and subgroups studied (Table 2). Similarly, we did not find a significant difference in microanatomical findings between a left or a fight craniotomy with the transsylvian approach.
than in those with Type 1 or 2 (p < 0.05). There was also a correlation between longer operative times and Type 3 aneurysms; however, we did not find a correlation between final outcome a n d the position of the aneurysm.
Surgical Results There were no significant differences in outcome among the three operative approaches utilized for clipping the aneurysms. We also did not find a correlation between the presence of anatomical variations and poor outcome. In our series, outcome was mainly dependent on the patient's clinical grade on admission. Patients with neurological Grades I, II, or III had a better outcome.
Discussion Although ACoA aneurysms are the most frequent type of cerebral aneurysm, j4,~5,~9 no previous studies have compared the anatomical findings according to the surgical approach used in patients with a n d without
Aneurysm Projection In cases operated on by either the anterior or basal interhemispheric approach, the position of the ACoA aneurysm was classified into: Type l, aneurysms located anterior to the bilateral A2 portions of the ACA (24 cases, 32.8%); Type 2, aneurysms located between the bilateral A2 portions of the ACA (43 cases, 58.9%); and Type 3, aneurysms located posterior to the bilateral A2 portions of the ACA (six cases, 8.2%) (Fig. 2). Of all anatomical elements considered in the study, we found that visualization of the artery of H e u b n e r was significantly better in patients with Type 3 aneurysms
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Fro. 2. Diagram illustrating classification of aneurysms according to their projection (as seen through the interhemispheric approaches). See text for description.
~1
E. Nathal, N. Yasui, T. Sampei, and A. Suzuki anatomical variations. The aneurysm origins and projections, and vessel anomalies and their relation to structures located in close proximity to the aneurysm should be confirmed during surgery before the aneurysm is clipped. 3's't2'~3'~6'~':~Unfortunately, the anatomical field is restricted, even with the best approach. Furthermore, in cases of early surgery the anatomy is obscured by the effects of hemorrhage, causing recognition of vascular and neural elements around the aneurysm to become very difficult.
Anatomical Variations The correlation between abnormalities of the circle of Willis and cerebrovascular disease is high; 2-9 this is most noticeable in the anterior part of the circle, where hypoplasia of an A~ segment associated with an ACoA aneurysm is one of the most frequent vascular anomalies) 8 In our series, this finding was present in 21.6% of cases. Duplication or triplication of the ACoA has been reported with an incidence as high as 43.3% in autopsy studies. 5 In our study, it was found in only 11.1% of patients; duplication of a left At portion was present in one case. The occurrence of a median artery of the corpus callosum has been reported with variable incidences ranging from 2% to 13%. t~ It should be identified on preoperative angiograms because during surgery it may be difficult to differentiate between a median artery of the corpus callosum and an early branching pattern of the A2 segment (2.2% in this study), especially when a transsylvian approach is used. The orbitofrontal artery arose from the A: portion in most cases, and originated from the left A~ portion in only one patient. One patient had an azygous A2 pattern; special attention should be given to this particular variation because in such cases the aneurysms are usually positioned high (at the final portion of the anomaly). 4 In patients with multiple variations, the most common pattern was a hypoplastic A~ segment in conjunction with another anomaly.
Microanatomical Findings The introduction of the operating microscope has provided better intraoperative definition of the ACoA complex. As can be seen in Table 2, the incidence of variations in instances where the anatomical structures can be observed differs from that found in autopsy studies. We also found that the presence of anatomical variations did not influence visualization of elements of the ACoA complex; rather, differences were mainly related to the surgical approach selected. Perforating Vessels. In formalin-fixed or polyester resin-injected brains, the number ofperforating arteries originating from the ACoA complex is variable. Therefore, the neurosurgeon must deal with a varying number of these perforators, especially those arising at the distal AI portions or from the ACoA, depending upon the surgical approach utilized. With the transsylvian approach (Fig. 3), some perforators could be found arising from the distal part of the A~ portion on the side 632
FIG. 3. Intraoperative photograph (left) and schematic drawing (right) showing the view obtained with the transsylvian approach. AN = aneurysm; ON = optic nerve; D = dimpling; LAI = left A~ segment; LA2 and RA2 = left and right A: segment.
Fro. 4. Intraoperative photograph (left) and schematic drawing (right) showing the view obtained with the anterior interhemispheric approach. AN = aneurysm; ON = optic nerve; LAI and RA1 = left and right A~ segment; LA2 and RA2 = left and fight A2 segment; LH = left artery of Heubner, LOF and ROF = lea and right orbitofrontal artery.
approached, including in the artery of Heubner. Dissection of the aneurysm may require further confirmation of the contralateral Aj and both A2 portions; however, perforators arising from the posteroinferior or posterosuperior surfaces of the ACoA are not easily visualized unless additional retraction or a gyrus rectus approach ~5is performed. This situation does not cause problems in cases of aneurysms directed anteriorly but, for aneurysms with posterior projection, the risk of perforator occlusion could be high. On the other side, with the anterior interhemispheric approach (Fig. 4), confirmation of the bilateral distal A2 and proximal A3 portions is easily accomplished, and the view of the ACoA complex includes the distal portions of the At segment, the ACoA, and both A2 portions, together with J. Neurosurg. / Volume 76/April, 1992
Anterior communicating artery aneurysms at this lateral point, the artery of Heubner could also fall within the blades of the clip.
Aneurysm Projection Classifying the aneurysm according to their positions (Fig. 2) permits better surgical planning for both isolation of the aneurysm and preservation of perforating vessels. Damage to these arteries may produce serious deficitsY ,.t7 During clipping of Type 1 aneurysms, the perforating vessels arising from the ACoA can be easily confirmed when necessary and rarely interfere with dipping. Conversely, in Type 3 and some Type 2 aneurysms, great care must be taken to spare these perforators during dissection or aneurysmal neck clipping, because visualization is poor and their surgical exposure can be difficult. In the interhemispheric approaches, the artery of Heubner rarely interferes with clipping because it runs laterally from the ACoA complex. Nevertheless, in some cases of Type I and 2 aneurysms, a lateral view of the aneurysm is necessary for clipping in order to ensure preservation of the artery of Heubner.
Surgical Results
FIG. 5. Intraoperative photographs (left) and schematic drawings (right,) showing the view obtained with the basal interhemispheric approach in two anatomical variations. ACoA = anterior communicating artery; AN = aneurysm; ON = optic nerve; RAI and RA2 = right A, and A2 segments; RH = fight artery of Heubner; ROF = right orbitofrontal artery; P = perforator; V = vein. Note the different angle of visualization of the ACoA complex and optic nerve obtained through the anterior (Fig. 4) and basal interhemispheric approaches.
the orbitofrontal artery and perforators arising from the ACoA. With the basal interhemispheric approach (Fig. 5), the field is similar to that of the anterior interhemispheric approach, except that the distal A_~ and proximal A3 portions are not exposed. Also, the angle of vision is different, directed from a lower point and slightly from right to left if the right side is approached. We attribute to this factor the higher rate of visualization of perforated arteries with the basal interhemispheric approach. Artery of Heubner. Intraoperative visualization of the artery of Heubner also depended on the surgical approach. With the transsylvian approach it is not unusual for the origin of the artery of Heubner to appear on the operative side. However, in both the anterior and basal interhemispheric approaches the origin of the artery is not easily visualized, particularly when it is located at the A, portion. Special care must be taken in cases where temporary clips are used because
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In this study, the main predictor of the final outcome was the patient's clinical grade on admission. Patients who are classified in Grades I, II, or III have a good opportunity for a successful outcome; however, for patients in Grade IV or V the functional prognosis remains unsatisfactory. We did not find a correlation between the surgical approach or the position of the aneurysm and poor outcome in patients with or without anatomical variations. It should be emphasized that variations of the ACoA complex are not simple details to be observed in cadaveric studies; they can be identified on preoperative angiograms and their recognition will allow the neurosurgeon to construct a better operative plan and to save time that is frequently lost in the operating room in defining these anomalies. Selection of the operative approach should depend on personal experience, keeping in mind the most frequent vascular and neural elements to be encountered during dissection. In this study, we were able to demonstrate that visualization of the components of the ACoA complex is lower at surgery than in the cadaver dissection room, and depends on the surgical approach utilized. Nevertheless, the normal microanatomy can be confirmed to the extent necessary to ensure safe clipping of aneurysms arising from this complex in patients with or without anatomical variations.
Acknowledgments We thank Dr. Julio Sotelo for his generous help in reviewing the manuscript. Also, the assistance of Kimio Yoshioka and Yoshitaka Tozawa in preparing the illustrations and photographic material is gratefully acknowledged.
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Manuscript received March 25, 1991. Accepted in final form September 6, 1991. Address for Dr. Nathal: Division of Surgical Neurology, National Institute of Neurology and Neurosurgery-Mexico, Av. Insurgentes Sur 3877, C.P. 14269, Mexico City, Mexico. Address reprint requests to: Noboyuki Yasui, M.D., Department of Surgical Neurology, Research Institute for Brain and Blood Vessels-Akita, 6,10 Senshu-kubota-machi, Akita 010, Japan.
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