Microsurgical anatomy of the distal anterior cerebral artery

The microsurgical anatomy of the distal anterior cerebral artery (ACA) has been defined in 50 cerebral hemispheres. The distal ACA, the portion beginning at the anterior communicating artery (ACoA), was divided into four segments (A2 through A5) according to Fischer. The distal ACA gave origin to central and cerebral branches. The central branches passed to the optic chiasm, suprachiasmatic area, and anterior forebrain below the corpus callosum. The cerebral branches were divided into cortical, subcortical, and callosal branches. The most frequent site of origin of the cortical branches was as follows: orbitofrontal and frontopolar arteries, A2; the anterior and middle internal frontal and callosomarginal arteries, A3; the paracentral artery, A4; and the superior and inferior parietal arteries, A5. The posterior internal frontal artery arose with approximately equal frequency from A3 and A4 and callosomarginal artery. All the cortical branches arose more frequently from the pericallosal than the callosomarginal artery. Of the major cortical branches, the internal frontal and paracentral arteries arose most frequently from the callosomarginal artery. The distal ACA of one hemisphere sent branches to the contralateral hemisphere in 64% of brains. The anterior portions of the hemisphere between the 5-cm and 15-cm points on the circumferential line showed the most promise of revealing a recipient artery of sufficient size for an extracranial-intracranial artery anastomosis. The distal ACA was the principal artery supplying the corpus callosum. The recurrent artery, which arose from the A2 segment in 78% of hemispheres, sent branches into the subcortical area around the anterior limb of the internal capsule.     

Surgical anatomy of the proximal anterior cerebral artery.

The authors present this study of proximal anterior cerebral arteries in the normal human to provide a clearer basis for strategy in aneurysm surgery. They describe patterns of origin of branches, their subarachnoid course, and parenchymal distribution. Branches that originate from the anterior cerebral artery at the internal carotid bifurcation perfuse the genu and contiguous posterior limb of the internal capsule and the rostral thalamus. Proximal 4-mm branches supply the anterior limb of the internal capsule, the neighboring hypothalamus, anteroventral putamen, and pallidum. The remaining anterior cerebral artery proximal to the communicating artery sends branches to the optic chiasm, the adjacent hypothalamus, and the anterior commissure. Heubner's artery arises directly opposite the anterior communicating artery to supply much of the striatum and internal capsule rostral to the anterior commissure. The anterior communicating artery branches supply the fornix, corpus callosum, septal region, and anterior cingulum. The parenchymal distribution of these end arteries may be surmised from the site of origin named vessels. With this anatomical information one can avoid interruption of blood supply to vital structures when dealing with the anterior cerebral artery and its branches.     

Interhemispheric approach with callosal resection for distal anterior cerebral artery aneurysms. Technical note.

Distal anterior cerebral artery aneurysms are commonly found near the genu of the corpus callosum. While these aneurysms may be surgically obliterated through a variety of approaches, exposure via the interhemispheric fissure is used by many surgeons. Early identification of the afferent artery may be difficult with this approach, however, particularly if the aneurysm lies just beneath the genu of the corpus callosum. The authors have modified the interhemispheric approach to distal anterior cerebral artery aneurysms by electively exposing the feeding artery through a small anterior callosotomy. While this maneuver is not necessary for all distal anterior cerebral artery aneurysms, it can greatly enhance exposure in the region just below the genu of the corpus callosum. Experience with this technique in five patients is reported. In all cases, the limited anterior callosotomy enhanced surgical exposure. No morbidity could be attributed to the callosotomy in any patient. It is concluded that, when the interhemispheric approach is used, anterior callosotomy improves exposure of the region just below the genu of the corpus callosum and may be a useful maneuver when treating distal anterior cerebral artery aneurysms.     

Selective occlusion of blood supply to the anterior perforated substance of the dog: a highly reproducible stroke model

We created a highly reproducible stroke model in dogs by the selective occlusion of middle and anterior cerebral artery branches that penetrate the anterior perforated substance and supply much of the basal forebrain. We also analyzed the anatomic organization of the arterial supply to this region in this animal. Perforators came from anterior communicating artery branches similar to the recurrent artery of Heubner in humans and from the middle cerebral artery at several sites distal to the bifurcation of the internal carotid artery. Although some animals had a single source of the perforating arteries, most had two or more. In 50% of our specimens, the anterior communicating artery was the dominant source of arterial supply, in 21% the middle cerebral artery was dominant, and in 24% neither source dominated. Occlusion of all microscopically visible perforators to the anterior perforated substance reliably resulted in infarction of the internal capsule (100%), caudate nucleus (91%-100%), putamen or globus pallidus (82%-91%), and anterior commissure (73%). Structures involved less frequently in infarctions include the external capsule, claustrum, anterior commissure, and septal nuclei. We believe this anatomic information is useful for understanding why previous focal ischemia lesions in the distribution of the middle cerebral artery in the dog have been highly variable as well as for planning and interpreting future studies in this species. The proposed model of focal ischemia may be of use for the study of stroke.     

Microanatomy of the pericallosal arterial complex

OBJECT: The pericallosal arterial complex supplies the callosal and pericallosal regions, as well as the anterior two thirds of the medial and superomedial aspects of both hemispheres. It is composed of the pericallosal artery (that is, the segment of the anterior cerebral artery located distal to the anterior communicating artery [ACoA]) and the median callosal artery (or third pericallosal artery), which originates from the ACoA. This system was studied in 46 specimens (23 human cadaver heads) injected with colored latex. METHODS: After being injected with colored latex, embalmed, and bleached, the specimens were studied with the aid of optic magnification. The pericallosal artery was found to be divided into four segments (A2-A5 in the proximodistal direction). After giving rise to central, callosal, and cortical branches, it terminated near the splenium of the corpus callosum as the posterior pericallosal artery, or on the precuneus as the inferomedial parietal artery. CONCLUSIONS: The authors propose a logical classification of the different variations in the pericallosal arterial complex based on embryological development. This complex can be considered a hemodynamic solution to an abnormal regression of one of its parts, which is balanced by the development of supplemental channels from other parts.     

Microsurgical anatomy of the anterior communicating artery complex in adult Chinese heads

BACKGROUND: The anterior communicating artery complex, which is composed of anterior cerebral artery (ACA), anterior communicating artery (ACoA), and recurrent artery of Heubner, accounts for the anterior half of the circle of Willis and is a favorite site of aneurysm formation; ACoA accounts for most of intracranial aneurysms. Few authors have studied the microanatomy of the ACA in detail using different specimens; none of these studies involve Chinese specimen. We have studied this area on adult Chinese brain with the aid of surgical microscope. METHODS: The anterior communicating artery complexes of 90 cerebral hemispheres from 45 formalin-fixed cadavers were dissected under microscope. RESULTS: The length and diameter of the recurrent artery and their perforating branches were measured. Their supplying areas, the adjacent structures, and their variations were also recorded. CONCLUSION: The cerebral vessels of native people have many variations in structure. The result of this study is quite different from that of the foreign literatures. The microanatomy of cerebral vessels also provides important data in its morphology for neurosurgeons.     

The perforating branches of the middle cerebral artery. A microanatomical study

The perforating branches (PFB's) of the middle cerebral artery (MCA) were studied in 34 unfixed brain hemispheres which were injected with a polyester resin and dissected under the operating microscope. Five hundred and eight vessels were identified and their site of origin, branching pattern, outer diameter (OD), and length recorded. Four hundred and two PFB's (79%) originated from the main trunk of the MCA before its division; the remaining 106 vessels (21%) had their origin from branches of the MCA as follows: superior trunk, 43 vessels (8.5%); inferior trunk, 30 vessels (6%); middle trunk, four vessels (0.8%); early temporal branch, 27 vessels (5.3%); and early frontal branch, two vessels (0.4%). The number of PFB's in each hemisphere varied from five to 29 (mean 14.9 +/- 0.7 vessels). The great majority of PFB's (96%) originated along the proximal 17 mm of the MCA. The PFB's arising in the first 10 mm had a mean OD of 0.35 +/- 0.01 mm and a mean length of 9.25 +/- 0.19 mm, and those arising from the second 10 mm had a mean OD of 0.47 +/- 0.02 mm and a mean length of 16.67 +/- 1.4 mm. A clear distinction between a medial and lateral group of PFB's was present in only 14 hemispheres (41%). In nine hemispheres (26%), perforating vessels from the anterior cerebral artery (A1 segment) and from the recurrent artery of Heubner replaced the medial group of PFB's of the MCA. In one case this group originated in an accessory MCA. In three hemispheres (9%) a small anastomosis (OD 0.2 mm) was seen between a PFB of the recurrent artery of Heubner and one of the MCA. From a total of 508 PFB's, 255 vessels (50%) originated as single vessels, while 253 vessels (50%) originated as branches of common stems. The OD of the single vessels ranged from 0.1 mm to 1.1 mm (mean 0.39 +/- 0.02 mm), and the length from 3 to 20 mm (mean 10.8 +/- 0.2 mm). The common stems ranged in OD from 0.6 to 1.8 mm (mean 0.87 +/- 0.04 mm), and in length from 1 to 15 mm (mean 4.1 +/- 0.4 mm). The clinical application of these anatomical data to the management of aneurysms and arteriovenous malformations of the MCA, and in the field of interventional neuroradiology is described. The most frequent pathological entities involving the perforating vessels are also discussed.     

Corpus callosal microstructural integrity influences interhemispheric processing: a diffusion tensor imaging study

Normal aging and chronic alcoholism result in disruption of brain white matter microstructure that does not typically cause complete lesions but may underlie degradation of functions requiring interhemispheric information transfer. We examined whether the microstructural integrity of the corpus callosum assessed with diffusion tensor imaging (DTI) would relate to interhemispheric processing speed. DTI yields estimates of fractional anisotropy (FA), a measure of orientation and intravoxel coherence of water diffusion usually in white matter fibers, and diffusivity (), a measure of the amount of intracellular and extracellular fluid diffusion. We tested the hypothesis that FA and would be correlated with (i) the crossed-uncrossed difference (CUD), testing visuomotor interhemispheric transfer; and (ii) the redundant targets effect (RTE), testing parallel processing of visual information presented to each cerebral hemisphere. FA was lower and higher in alcoholics than in controls. In controls but not alcoholics, large CUDs correlated with low FA and high in total corpus callosum and regionally in the genu and splenium. In alcoholics but not controls, small RTEs, elicited with equiluminant stimuli, correlated with low FA in genu and splenium and high in the callosal body. The results provide in vivo evidence for disruption of corpus callosum microstructure in normal aging and alcoholism that has functional ramifications for efficiency in interhemispheric processing.     

Micro-anatomy of collateral perforating branches of the middle cerebral artery

The lenticulostriate arteries are the subject of a microanatomical study on 50 formalin fixed human brains. A single trunk arising from the middle cerebral artery is rarely found. In fact the branches are numerous and they are found to ramify before penetrating the anterior perforated substance. The length of the sphenoidal segment is variable and this aspect is discussed in the light of the literature data. The origin of the perforating branches is spread from the internal carotid artery to the bifurcation branches of the middle cerebral artery (M2 segment). On the other hand lenticulostriate arteries arising from the cortical branches of the middle cerebral artery are often found. These anatomical patterns are of essentially surgical interest. No branches must be damaged during the opening of the Sylvian fissure or during the dissection of an aneurysm in this region.     

Branches of the anterior cerebral artery near the anterior communicating artery complex: an anatomic study and surgical perspective

The anatomy of the branches of the anterior cerebral artery (ACA) near the anterior communicating artery (ACoA) complex were investigated to minimize neurovascular morbidity caused by surgical procedures performed in this region. Thirty-one cadaver brains were perfused with colored silicone, fixed, and studied under the operating microscope. The recurrent artery of Heubner (RAH), orbitofrontal artery (OFA), and frontopolar artery (FPA) were identified as the branches of the ACA arising near the ACoA complex. The OFA and FPA were identified in all hemispheres. Forty-nine (64%) of a total of 77 RAHs arose from the A2 segment. The OFA always arose from the A2 segment, was consistently the smallest branch, and coursed to the gyrus rectus, olfactory tract, and olfactory bulb. The mean distance between the ACoA and the OFA was 5.96 mm. The FPA arose from the A2 segment in 95% of the specimens, and coursed to the medial subfrontal region. The mean distance between the ACoA and the FPA was 14.6 mm. The RAH, OFA, and the FPA are three branches that arise from the ACA near the ACoA complex. These vessels have similar diameters, but can be distinguished by the final destination. Distinguishing these vessels is important since the consequences of injury or occlusion of the FPA and OFA are significantly less than of the RAH.     

Confirmation of blood flow in perforating arteries using fluorescein cerebral angiography during aneurysm surgery

OBJECT: The authors performed fluorescein cerebral angiography in patients after aneurysm clip placement to confirm the patency of the parent artery, perforating artery, and other arteries around the aneurysm. METHODS: Twenty-three patients who underwent aneurysm surgery were studied. Aneurysms were located in the internal carotid artery in 12 patients, middle cerebral artery in six, anterior cerebral artery in three, basilar artery bifurcation in one, and junction of the vertebral artery (VA) and posterior inferior cerebellar artery in one. After aneurysm clip placement, the target arteries were illuminated using a beam from a blue light-emitting diode atop a 7-mm diameter pencil-type probe. In all patients, after intravenous administration of 5 ml of 10% fluorescein sodium, fluorescence in the vessels was clearly observed through a microscope and recorded on videotape. RESULTS: The excellent image quality and spatial resolution of the fluorescein angiography procedure facilitated intraoperative real-time assessment of the patency of the perforating arteries and branches near the aneurysm, including: 12 posterior communicating arteries; 12 anterior choroidal arteries; four lenticulostriate arteries; three recurrent arteries of Heubner; three hypothalamic arteries; one ophthalmic artery; one perforating artery arising from the VA; and one posterior thalamoperforating artery. All 23 patients experienced an uneventful postoperative course without clinical symptoms of perforating artery occlusion. CONCLUSIONS: Because the fluorescein angiography procedure described here allows intraoperative confirmation of the patency of perforating arteries located deep inside the surgical field, it can be practically used for preventing unexpected cerebral infarction during aneurysm surgery.     

Giant aneurysm of the pericallosal artery causing acute subdural hematoma--case report

A 66-year-old female presented with a very rare giant aneurysm of the distal pericallosal artery. She lost consciousness and was admitted. Computed tomography demonstrated a subdural hematoma over the left cerebral convexity and a mass in the frontal lobe. Cerebral angiography disclosed a giant aneurysm located on the distal segment of the right pericallosal artery. The subdural hematoma was removed and the aneurysmal neck was clipped, but she died 15 days after the operation. Autopsy found the giant aneurysm (33 x 30 x 27 mm) on the distal segment of the right pericallosal artery. Highly atheromatous changes were recognized in part of the aneurysmal wall, the arteries near the circle of Willis, and the distal anterior cerebral artery (ACA) adjacent to the aneurysm. There were no anomalous vessels such as azygos ACA. Giant aneurysms situated beyond the genu of the corpus callosum are extremely rare. Atherosclerosis was probably a major etiological factor in this case.     

Surgical strategy for distal anterior cerebral artery aneurysms: microsurgical anatomy

OBJECT: Most distal anterior cerebral artery (ACA) aneurysms arise at the pericallosal-callosomarginal artery (PerA-CMA) junction, which is usually located in the A3 segment of the ACA around the genu of the corpus callosum. Aneurysms in the PerA-CMA junction are divided into two types according to their location: supracallosal and infracallosal. Infracallosal distal ACA aneurysms are defined as those located in the lower half of the A3 segment, which makes it more difficult to gain proximal control. In this study, the authors examined the microsurgical anatomy of the distal ACA region, focusing especially on the relationship between the PerA and CMA located in the lower half of the A3 (infracallosal) segment, and present a surgical strategy for dealing with distal ACA aneurysms. METHODS: The microsurgical anatomy of the distal ACA region was examined in 22 adult cadaveric cerebral hemispheres after perfusion of the arteries and veins with colored silicone. The relationships of the infracallosal segment of the PerA to the CMA and the A2 segment of the PerA to the frontopolar artery were examined. The distance between the nasion and the site at which a parallel line directed along the long axis of the infracallosal PerA just proximal to the origin of the CMA artery crosses the forehead (which we have named the PC point) was also measured. Surgical approaches to distal ACA aneurysms were examined in stepwise dissections. CONCLUSIONS: The PerA-CMA junctions were located in the supracallosal and infracallosal segments of A3 in 36 and 55% of cases, respectively. In the infracallosal region, it was difficult to identify the proximal PerA and to establish proximal control of the vessel. The infracallosal part of the proximal PerA coursed almost parallel to the frontal cranial base, and the PC point was 42.2 +/- 15.9 mm (mean +/- standard deviation) from the nasion. These findings indicate that there is only a limited space in which to access an infracallosal distal ACA aneurysm below the PC point and establish proximal control by the anterior interhemispheric approach. When the approach is made above the PC point, an anterior callosotomy may be necessary to establish proximal control before final aneurysm dissection and clip placement are completed. The PC point is an important surgical landmark in planning the surgical strategy for infracallosal distal ACA aneurysms.     

Parasagittal asymmetries of the corpus callosum

Significant relationships have been reported between midsagittal areas of the corpus callosum and the degree of interhemispheric transfer, functional lateralization and structural brain asymmetries. No study, however, has examined whether parasagittal callosal asymmetries (i.e. those close to the midline of the brain), which may be of specific functional consequence, are present in the human brain. Thus, we applied magnetic resonance imaging and novel computational surface-based methods to encode hemispheric differences in callosal thickness at a very high resolution. Discrete callosal areas were also compared between the hemispheres. Furthermore, acknowledging the frequently reported sex differences in callosal morphology, parasagittal callosal asymmetries were examined within each gender. Results showed significant rightward asymmetries of callosal thickness predominantly in the anterior body and anterior third of the callosum, suggesting a more diffuse functional organization of callosal projections in the right hemisphere. Asymmetries were increased in men, supporting the assumption of a sexually dimorphic organization of male and female brains that involves hemispheric relations and is reflected in the organization and distribution of callosal fibers.     

Partial callosal resection for pericallosal aneurysms.

The surgical treatment of aneurysms that arise at the origin of the pericallosal artery is technically difficult. This report describes a technique that improves the exposure of the proximal vasculature during a craniotomy for pericallosal aneurysms. A portion of the corpus callosum was resected in two patients before the manipulation of their aneurysms. The resection provided excellent exposure of the A2 segment of the anterior cerebral artery, and both aneurysms were clipped safely. Neither patient exhibited signs of hemispheric disconnection. The authors conclude that partial callosal resection improves access to the proximal vessels during procedures for pericallosal aneurysms.     

Extracerebral course of the perforating branches of the anterior communicating artery: microsurgical anatomical study

Damage to the perforating branches arising from the anterior communicating artery, because of their blood supply to the septal nuclei and anterior hypothalamus, explains the memory impairment and the electrolyte disturbances that often follow the surgery of aneurysms located in this part of the circle of Willis. The microsurgical anatomy of these branches was studied on 60 fixed human brains, with special attention to their number, caliber, and vascular territory. The direction of the branches was evaluated, measuring the angle formed by them with the postcommunicating segment of the anterior cerebral artery. The variability of this anatomical region is discussed in light of the literature.     

Aneurysm of peripheral cerebral arteries with developmental anomaly of the anterior cerebral artery

We report a 71-year-old woman who was initially admitted because of a ruptured internal carotid aneurysm, and found to have an aneurysm of the terminal portion (A5 portion) of pericallosal artery. Both of the aneurysms were surgically treated at one stage operation. A saccular aneurysm of the pericallosal artery was verified at operation. Right internal carotid angiography disclosed that medial part of the right anterior cerebral hemisphere was supplied by the right callosomarginal artery, and that unpaired pericallosal artery made a trifurcation at A5 portion, where the saccular aneurysm arose. According to Baptista's classification, anomaly of the anterior cerebral artery (ACA) in this patient was bihemispheric ACA type. Distal ACA aneurysms almost always locate at or near the genu of corpus callosum, either in pericallosal-callosomarginal or in pericallosal-frontopolar junction. In reviewing the literature, we were able to find 14 cases, including ours, of aneurysms located beyond either pericallosal-callosomarginal junction or the genu of corpus callosum. Also the possible role of hemodynamic stress caused by vascular anomaly for aneurysm formation are discussed.     

Ruptured aneurysm at the origin of the median artery of the corpus callosum associated with accessory middle cerebral artery--case report

A 62-year-old male presented with ruptured anterior communicating artery (ACoA) aneurysm manifesting as severe headache associated with the rare combination of median artery of the corpus callosum (MACC) and accessory middle cerebral artery (MCA). Computed tomography demonstrated diffuse subarachnoid hemorrhage. Left carotid angiography demonstrated an anomalous vessel originating from the ACoA complex and passing forward in the interhemispheric fissure between the two companion A2 segments. This vessel was identified as the MACC. Another anomalous vessel originated from the left A1-A2 segment and passed into the sylvian fissure. This vessel was identified as the accessory MCA. Left frontotemporal craniotomy was performed to clip the neck of the aneurysm. After identifying both A1 and A2 segments, accessory MCA, and the MACC, the aneurysm neck was occluded successfully. The ACoA complex is one of the most frequent sites of vascular anomalies. Preoperative and intraoperative care is required to identify the presence of anomalies of the ACoA complex prior to clip placement, to avoid accidental damage or clipping, which may result in severe neurological deficits.     

Two cases of distal anterior cerebral artery aneurysm associated with accessory anterior cerebral artery

An accessory anterior cerebral artery (accessory ACA) is a rare anomalous vessel arising from the anterior communicating artery as a median artery of triplicated ACA. It is considered a large median artery of the corpus callosum and distributes to one or both hemispheres. The cases of an accessory ACA aneurysm are extremely rare; however, we experienced two cases of unruptured aneurysm growing at the distal portion of an accessory ACA. Two females, aged 66 and 67 years, respectively, separately consulted our hospital as a result of chronic headaches. Brain MR angiography and following DSA in the first patient demonstrated a triplicated ACA and an aneurysm located just above the corpus callosum growing from the distal portion of the accessory ACA. MRI and MR angiography in the second patient depicted a triplicated ACA and an aneurysm from the accessory ACA as with the first case. Neck clipping of the aneurysm was performed using an interhemispheric approach in both cases. These aneurysms appeared to present the same intraoperative findings as other unruptured aneurysms growing at the usual positions.