Anatomy of the Callosomarginal Artery Applications to Microsurgery and Endovascular Surgery

SURGICAL ANATOMY

The Anatomy of the Callosomarginal Artery: Applications to Microsurgery and Endovascular Surgery Daniel D. Cavalcanti, MD Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona

Felipe C. Albuquerque, MD Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona

Benjamin F. Silva, MD Department of Neurosurgery, Bonsucesso General Hospital, Rio de Janeiro, Brazil

Robert F. Spetzler, MD Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona

Mark C. Preul, MD Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona Reprint requests: Mark C. Preul, MD, c/o Neuroscience Publications, Barrow Neurological Institute, 350 W. Thomas Road, Phoenix, AZ 85013. E-mail: [email protected] Received, March 5, 2009. Accepted, September 25, 2009. Copyright © 2010 by the Congress of Neurological Surgeons

BACKGROUND: The callosomarginal artery (CMA), the main branch of the pericallosal artery, courses in or near the cingulate sulcus and gives rises to 2 or more major cortical branches. There is confusion about the artery best fitting the definition of “callosomarginal artery.” Distal anterior cerebral artery aneurysms represent 1.5% to 9% of intracranial aneurysms, and most often occur at the origin of the CMA. The microsurgical anatomic features of the CMA, its relationship with the pericallosal artery, and clinical implications are presented. METHODS: The origin, course, branching pattern, and diameter of the CMA and its branches and its relationship with the pericallosal artery were studied in 60 cerebral hemispheres, including cadaveric dissections and angiographic images. RESULTS: The CMA was present in 93.3% of hemispheres studied and arose mainly from A3 (55.2%), a mean of 3.11 ± 1.90 cm from the anterior communicating artery. The mean diameter of the CMA at its origin was 1.53 ± 0.36 mm. The CMA ran 1.28 ± 0.89 cm until its first branch, describing an anterior convex curve backward and upward (60.7%). An average of 3 lesser branches originated from the CMA. The most consistent branch was the posterior internal frontal artery (67.9%). The mean diameter of the CMA branches was 0.93 ± 0.33 mm. CONCLUSION: These morphometric measurements can help neurosurgeons access lesions located in distal intracranial vessels. The vessel coursing the longest pathway in or near the cingulate sulcus and otherwise following Moscow's classic definition should be considered the CMA. KEY WORDS: Anatomic study, Anterior cerebral artery, Callosomarginal artery, Endovascular treatment, Microsurgery Neurosurgery 66:602-610, 2010

DOI: 10.1227/01.NEU.0000365003.25338.62

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he callosomarginal artery (CMA) is considered the largest branch of the pericallosal artery1 and is described in 40% to 85% of hemispheres,1-5 yielding different classifications for this vessel and for the anatomy of the pericallosal artery. Together with the pericallosal artery, the CMA helps supply the anterior two-thirds of the medial and superomedial aspects of both hemispheres. There is some confusion in the nomenclature as to the artery best fitting the definition of “callosomarginal artery.”5 Moscow et al6 defined the CMA as the artery that courses in or near the cingulate sulcus and gives rise to 2 or more major cortical branches. Rhoton supports this definiABBREVIATIONS: ACA, anterior cerebral artery; CMA, callosomarginal artery; DSA, digital subtraction angiogram; ICH, intracerebral hematoma; SD, standard deviation

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tion.1 The confusion exists in that 1 or more large arteries branching from the pericallosal artery often run in the cingulate sulcus and give rise to 2 or more cortical arterial branches.5 Distal anterior cerebral artery (ACA) aneurysms represent 1.5% to 9% of intracranial aneurysms and most often occur at the origin of the CMA.8-10 That location is also one of the preferred sites for traumatic intracranial aneurysms to develop.11-14 The CMA can also supply falx meningiomas. Consequently, the artery can be a route for preoperative tumor embolization.15,16 In 1978, Bogdanović et al17 described the origin, frequency, and course of the CMA. We performed microanatomic dissection of human cadaveric specimens and analyzed digital subtraction angiograms (DSAs) to demonstrate the microsurgical anatomic features of the CMA and its branches and its relationship with the perical-

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CALLOSOMARGINAL ARTERY

losal artery. To the best of our knowledge, this study is the first in the English literature to focus on the microanatomy of the CMA. Clinical cases are presented to demonstrate how knowledge of the anatomy can be used to guide endovascular and microsurgical procedures.

PATIENTS AND METHODS The anatomy of the CMA was studied in 60 human cerebral hemispheres. The study included the dissection of 15 adult cadaveric brains (30 cerebral hemispheres) injected with colored silicone and lightly fixed in a formalin solution, and the analysis of DSAs from 20 patients (30 sides). The mean age of the cadaveric specimens was 72.3 years (range, 47–92 years). There were 9 women and 6 men. The DSAs were performed between August 2008 and May 2009. The mean age of the patients was 57.4 years (range, 35–84 years). There were 7 women and 13 men. The origin and course of the CMA and its relationship with the pericallosal artery were identified in the cadaveric specimens. The length of the main trunk of the CMA (between the origin and first branch) and the distance between the origin of the CMA and the anterior communicating artery were also measured during dissections. The branching pattern of

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the CMA and its branches was evaluated in the specimens and angiograms. The diameter of the vessels in specimens was measured with digital calipers, and the luminal diameter was obtained using the software Web Dominator for angiograms (DR Systems, Inc., San Diego, CA).

RESULTS Origin of the CMA The CMA was present in 93.3% of the 60 cerebral hemispheres studied. In 55.2% of the hemispheres dissected, the CMA arose from the A3 segment of the ACA with 3 different topographies related to the genu of the corpus callosum: at its lower aspect, at its level, and at its upper aspect (Fig. 1; Table 1). The CMA originated from the A4 segment in 24.1% of the hemispheres and from the A2 segment and the anterior communicating artery in 10.3% each. The mean distance from the origin of the CMA to the anterior communicating artery was 3.11 ± 1.90 cm standard deviation (SD) (range, 0–7.1 cm). The mean diameter of the CMA at its origin was 1.53 mm ± 0.36 SD (range, 0.9–2.6 mm) in the dissections and 2.0 mm ± 0.34 SD (range, 1.2–2.5 mm) in the radiologic analy-

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C FIGURE 1. Cadaveric photographs showing that the callosomarginal artery (CMA) most often arose from the A3 segment. A, the CMA originated at the lower aspect of the A3 segment and followed an anterior convex curve. Four main cortical branches (CBs) arose from the CMA: the anterior internal frontal artery (AIFA), a common trunk of the middle internal frontal artery (MIFA),the posterior internal frontal artery (PIFA), and the paracentral artery (PceA). B, in this specimen, the CMA originated from the A3 segment at the level of the genu of the corpus callosum. It also followed the characteristic anterior convex curve and was oriented backward and upward. Only 2 branches arose from the CMA: the MIFA and PIFA. The orbitofrontal artery (OfA), frontopolar artery (FpA), AIFA, PceA, superior parietal artery (SParA), and inferior parietal artery (IParA) arose from the pericallosal artery (PrCA). The common trunk created by the OfA and FpA arising from the pericallosal artery matches Moscow’s definition, thereby leading to the identification of 2 CMAs. C, the CMA arose from the A3 segment at the upper aspect of the genu of the corpus callosum. It followed an anterior convex curve, while oriented backward and upward, into the cingulate sulcus. The MIFA, PIFA, and PceA were branches of the CMA. The common trunk of the FpA and AIFA arising from the pericallosal artery also matches Moscow’s definition. (Used with permission from Barrow Neurological Institute.)

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TABLE 1. Origin of the Callosomarginal Artery in 30 Cadaveric Hemispheresa Origin of CMA

Percentage of Hemispheres

AComA

10.3%

A2

10.3%

A3 Lower aspect of genu

13.8%

Level of genu

24.1%

Upper aspect of genu

17.2%

A4

24.1%

a

CMA; callosomarginal artery; AComA, anterior communicating artery; A2, A3, A4, respective segments of the anterior cerebral artery.

sis. The diameter of the pericallosal artery at the origin of the CMA was slightly smaller than the CMA itself in the dissections (1.42 mm ± 0.32 SD; range, 1.0–2.0 mm) and similar to that of CMA in the angiograms (2.04 mm ± 0.49 SD; range, 1.1–2.9 mm). Configuration of CMA After its origin, the CMA had a characteristic anterior convex curve in 60.7% of the hemispheres studied (Fig. 1). In 25% of the specimens, the CMA ascended with a posteriorly oriented angle with the pericallosal artery. In 7.1% of specimens, the CMA was oriented superiorly and formed a right angle relative to the periA callosal artery. In 3.6% of the specimens, the CMA was oriented anteriorly and formed a right angle relative to the pericallosal artery. In another 3.6% of the specimens, the CMA was oriented upward with an inferior convex curve (Fig. 2). The CMA coursed in the cingulate sulcus parallel to the pericallosal artery in all hemispheres C where it was present. Together, the 2 vessels were positioned to supply the superior frontal gyrus, paracentral lobule, cingulate gyrus, corpus callosum, and precuneus. Branches The mean distance from the origin of the CMA to its first branch was 1.28 cm ± 0.89 SD (range, 0.2–4.9 cm). A mean of 3 branches ± 1.11 SD (range, 2–6) arose from the CMA (Fig. 3). Seven main cortical branches could be identified arising from

the CMA: the orbitofrontal artery, frontopolar artery, anterior internal frontal artery, middle internal frontal artery, posterior internal frontal artery, paracentral artery, and superior parietal artery. The most consistent branch was the posterior internal frontal artery, which was present in 67.9% of the hemispheres studied (Table 2). The middle internal frontal artery was present in 64.3% of the hemispheres, and the paracentral artery was present in 53.6%. The superior parietal artery and the orbitofrontal artery were branches of the CMA in only 7.1% and 3.6% of the specimens, respectively. A total of 19 smaller branches (≥0.3 mm) was found in 14 specimens. Such vessels were classified as cortical branches. Altogether, the mean diameter of CMA branches was 0.93 mm ± 0.33 SD (range, 0.3–1.8 mm) in dissections and 1.31 mm ± 0.34 SD (range, 0.7–2.3 mm) in the radiologic analysis. The middle internal frontal artery was usually the most robust branch of the CMA, with a mean diameter of 1.14 mm ± 0.23 SD (range, 0.8–1.7 mm) in the dissections and of 1.39 mm ± 0.28 SD (range, 0.9–2.0 mm) on the DSAs (Table 3). Common trunks arising from the CMA were observed in 14 hemispheres (Figs. 1A and 3). The most frequent association in a common trunk was between the middle and posterior internal frontal arteries (42.9%). Other associations occurred between the orbitofrontal and frontopolar arteries (14.3%); between the anterior and middle internal frontal arteries (14.3%); among the anterior, middle, and posterior internal frontal arteries (7.14%); between the middle and posterior internal frontal arteries and the paracentral artery (7.14%); between

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D

FIGURE 2. Cadaveric photographs showing unusual configurations of the origin of the CMA. A, in this specimen, the CMA arose in an ascendant, posteriorly oriented angle with the pericallosal artery. B, an inferior convex curve, upwardly oriented CMA. C, an anteriorly oriented CMA describing a square angle with the pericallosal artery. D, a superiorly oriented CMA describing a square angle with the pericallosal artery. (Used with permission from Barrow Neurological Institute.)




TABLE 2. Frequency of Callosomarginal Artery Branches in 56 Cerebral Hemispheresa OfA

FpA

AIFA

MIFA

PIFA

PceA

SParA

3.6%

12.5%

33.9%

64.3%

67.9%

53.6%

7.1%

a

OfA, orbitofrontal artery; FpA, frontopolar artery; AIFA, anterior internal frontal artery; MIFA, middle internal frontal artery; PIFA, posterior internal frontal artery; PceA, paracentral artery; SParA, superior parietal artery.

TABLE 3. Mean Diameter of the Callosomarginal Artery in 56 Cerebral Hemispheresa CMA Branch

FIGURE 3. Seven main CBs could be identified arising from the CMA: OfA,

FpA, AIFA, MIFA, PIFA, PceA, and SParA. This hemisphere illustrates the 4 most common main branches of the CMA: the PIFA, PceA, MIFA, and AIFA. The MIFA and PIFA arise from a common trunk. PrCA, pericallosal artery. Used with permission from Barrow Neurological Institute.

the frontopolar and anterior internal frontal arteries (7.14%); and between the posterior internal frontal artery and paracentral artery (7.14%). The branches of the CMA arose from a common trunk with a frequency of 21.9%. Clinical Cases (Patients 1–3) Three clinical cases of aneurysms involving the pericallosalcallosomarginal junction demonstrate how the vascular anatomy can be used to guide endovascular and microsurgical procedures. The first 2 cases underwent endovascular management at the Barrow Neurological Institute (Figs. 4 and 5). The third patient was treated surgically at the Bonsucesso General Hospital (Fig. 6).

DISCUSSION Anatomy Early studies reported that the CMA occurred in 40% to 56% of specimens.2,4,18 In recent studies, the CMA was found in as many as 85% of specimens.1,3,5,17 In the present study, the CMA was absent in only 4 hemispheres (6.7%). In these cases, the pericallosal artery alone supplied the anterior two-thirds of the superomedial surface of the brain (Fig. 7). Instead, the main cortical branches plus the inferior parietal artery arose from the pericallosal artery. Moscow et al6 defined the CMA as a vessel coursing in or near the cingulate sulcus and giving rise to 2 or more cortical branches. However, as stressed by Ugur et al,5 this definition could lead to the identification of 2 CMAs. In 5 dissected hemispheres in our

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Cadaver Dissections, Mean (Range) (mm)

DSA, Mean (Range) (mm)

Orbitofrontal artery

0.60

0.90

Frontopolar artery

0.93 ± 0.15 (0.8–1.1)

1.0 ± 0.08 (0.9–1.1)

Anterior internal frontal artery

1.1 ± 0.16 (0.9–1.3)

1.2 ± 0.25 (0.9–1.9)

Middle internal frontal artery

1.14 ± 0.23 (0.8–1.7)

1.39 ± 0.28 (0.9–2.0)

Posterior internal frontal artery

1.04 ± 0.32 (0.3–1.5)

1.31 ± 0.33 (0.7–1.8)

Paracentral artery

1.02 ± 0.16 (0.6–1.4)

1.22 ± 0.34 (0.7–1.7)

Superior parietal artery

1.05 ± 0.21 (0.9–1.2)

1.35 ± 0.26 (1.1–1.6)

a

CMA, callosomarginal artery. A CMA was found in 29 hemispheres during anatomic dissections and in 27 hemispheres during analysis of 30 angiograms.

study, 2 vessels fit Moscow’s definition for the CMA (Fig. 1C). In all 5 cases, 1 vessel described a longer course within or near the cingulate sulcus, compared with the other. On the basis of these findings, we propose that Moscow’s definition needs an additional criterion: when 2 or more vessels match the definition for the CMA, the one with the longer course within or near the cingulate sulcus will be defined as the CMA. Krayenbühl and Yaşargil19 found that the CMA arose near the genu of the corpus callosum in 72% of cases. Bogdanović et al17 described the origin of the CMA as being at the level of the genu of the corpus callosum in 81.6% of cases. While studying the anatomic variations of the distal ACA, Ugur et al5 found that the CMA originated from the A3 segment in 64% of hemispheres, from the A2 segment in 18%, from the A4 segment in 12%, and from the anterior communicating artery in 6%. These findings are similar to ours. Rarely, the CMA arises from the A1 segment.20 The variation in the presence and origin of the CMA has yielded 2 main definitions for the origin of the pericallosal artery. Snyckers and Drake21 and Stephens and Stilwell22 consider the pericallosal artery as the segment of the ACA distal to the origin of the CMA. Other authors refer to the pericallosal artery as the segment of the ACA distal to the anterior communicating artery.1,3,8,23,24


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terminates as the paracentral artery. In our study, these last 3 branches typically arose from the CMA (Table 2). Never theless, the 7 main branches (the orbitofrontal, frontopolar, anterior internal frontal, middle internal frontal, posterior internal frontal, paracentral, and superior parietal arteries1,2,5) usually arise from the CMA or the pericallosal artery. Perlmutter and Rhoton,1 however, identified these cortical branches as arising more frequently from the pericallosal artery than from the CMA. They also found that, of the CMAs present, 50% gave rise to 2 major cortical branches, FIGURE 4. Patient 1, a 51-year-old woman with a recurrent aneurysm of the pericallosal-callosomarginal junction after 32% gave rise to 3 cortical branclipping. Angiography showed a large anteroinferiorly oriented aneurysm. The CMA had an anterior convex curve and ches, and 16% gave rise to 4 was oriented backward and upward. The MIFA, PIFA, and PceA branched from the CMA. Thus, thrombosis and occlucortical branches. In 1 hemision of the parent vessel in this patient could result in ischemic stroke in eloquent areas supplied by these branches. The patient sphere, 5 major branches arose underwent endovascular treatment of the lesion. Posttreatment angiography confirmed complete obliteration of the aneurysm and patency of the CMA and PrCA. A, digital subtraction angiogram showing a large anteroinferiorly orifrom the CMA; the middle ented aneurysm. B, immediate posttreatment angiogram showing complete occlusion with detachable coils. (Used with perinternal frontal artery was the mission from Barrow Neurological Institute.) most common branch of the CMA. An inferior parietal artery arising from the CMA was also identified in 1 hemisphere of the The CMA is the widest branch arising from the pericallosal artery. 50 dissected in that study.1 Ugur et al5 found that the posterior interPerlmutter and Rhoton1 found that the mean diameter of the CMA nal frontal and paracentral arteries were the most common branches at its origin was 1.8 mm (range, 1.2–1.7 mm). Likewise Ugur et al5 of the CMA. They also described an anomalous origin of the artery found that the mean diameter at its origin was 1.9 mm (range, of Heubner from the CMA. In another anatomic study, an acces1.2–3.0 mm). Although both studies reported a slightly larger diamsory middle cerebral artery originating from the CMA was described eter for the CMA than we found in the dissections (1.53 mm), coursing over the frontal end of the insula. From it originated corthose values are similar to the mean diameter from our radiologic tical branches to the area supplied by the prefrontal artery.26 analysis (2.0 mm). Moreover, the CMA was always the largest branch of the pericallosal artery in all of the hemispheres we dissected. Pathology Interestingly, the mean luminal diameter of the CMA and its branches Aneurysms arising on the ACA distal to the anterior commuand of the pericallosal artery measured from the angiograms was nicating artery have a mean incidence of 4.4%.8 More commonly, slightly greater than the mean diameter obtained from the specithey occur at the origin of the CMA.8,10,21,27 De Sousa et al8 mens. The advanced age of the cadaveric specimens could explain found that 82.4% of 74 distal ACA aneurysms arose from the orithis difference. Indeed, the caliber of vessels elsewhere within the gin of the CMA. Furthermore, Steven et al10 identified 57% of cerebral circulation has been reported to decrease with age.25 1 67 distal ACA aneurysms at this same site. Compared with our study, Perlmutter and Rhoton also found The reduced dimension of the pericallosal cistern and the that the origin of the CMA was slightly farther from the anterior apposed medial hemispheric surfaces underlie the tendency of communicating artery (mean, 43 mm; range, 12–47 mm). The aneurysms in this region to cause intracerebral hematomas characteristic deep curve at the beginning of the CMA has also (ICHs).28,29 Snyckers and Drake21 found ICH in 48% of their been described in as many as 91.8% of the specimens.17 The precases with a distal ACA aneurysm. Sindou et al30 found ICH in dominance of this configuration was less pronounced in our study 47.4% of their series, in which 42.1% of the aneurysms arose (60.7%). Instead, we identified a CMA ascending with a posterifrom the origin of the CMA. Menovsky et al31 found ICH in half orly oriented angle with the pericallosal artery in one-quarter of of their series of ruptured pericallosal artery aneurysms. the hemispheres; this is a configuration more suitable for naviOthers features of aneurysms at this location are their small gating a catheter through the CMA. size and their association with multiple aneurysms.8,10,27,29,32,33 Snyckers and Drake21 stated that the typical CMA gives rise to Steven et al10 reported that 82% of the distal ACA aneurysms in the anterior, middle, and posterior internal frontal arteries and

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of consciousness, seizures, or a sustained increase in intracranial pressure after a traumatic brain injury and a computed tomographic scan demonstrating intracranial hemorrhage should justify angiography to identify traumatic aneurysms.13,40 Infectious intracranial aneurysms are also uncommon and primarily affect distal arteries. However, infectious aneurysms rarely involve the distal ACA.41 In 2 recent studies that together included 56 infectious aneurysms, only 2 aneurysms (3.6%) arose in the distribution of the distal ACA.42,43 CMA branches can also supply meningiomas at the free edge of the falx. Consequently, the artery can be used as a route for FIGURE 5. Patient 2, a 59-year-old woman with subarachpreoperative embolization of noid hemorrhage, who was admitted to the emergency room. intratumoral vessels.16,44 MeninAngiography showed a superiorly oriented saccular aneurysm giomas located elsewhere along at the pericallosal-callosomarginal junction. The MIFA, PIFA, and PceA branched from the CMA, and the AIFA arose the course of the CMA can be from the PrCA. Endovascular treatment with detachable coils occluded the aneurysm completely. A, angiogram showing supplied by this artery,15 and the superiorly oriented saccular aneurysm at the pericallosal-callosomarginal junction. B, posttreatment angiogram conpreoperative devascularization firming complete aneurysmal obliteration and patency of the CMA and PrCA. cCMA, contralateral CMA; cPrCA, concan be performed as well. An tralateral PrCA. (Used with permission from Barrow Neurological Institute.) arterial feeder arising from the CMA can be catheterized and occluded most safely if the CMA does not give rise to main cortitheir series were less than 10 mm in diameter. They stressed that cal branches to eloquent areas. Roosen and Lins45 described a pria mean of 43% of patients with distal ACA aneurysms harbor mary Ewing sarcoma of the calvaria supplied by the CMA. A rare multiple aneurysms. In a large series of 470 distal ACA aneurysms, intracranial mesenchymal chondrosarcoma involving the superior Lehecka et al29 found that 51% of the ruptured aneurysms and 88% sagittal sinus and supplied by the CMA has also been reported.46 of the unruptured aneurysms were smaller than 7 mm. Associated Occlusion of the CMA can result in a catastrophic condition, aneurysms were identified in 52% of the patients, most often on depending on the number of branches and which are involved. A the middle cerebral artery. On initial computed tomographic careful analysis of the anatomy and variations on preoperative scans, they also encountered ICH in 53% of patients, compared angiograms provides evidence about which vessels and cortical with 25% of patients with ruptured aneurysms located elsewhere.29 areas are at risk. The orbitofrontal artery supplies the olfactory Traumatic intracranial aneurysms are uncommon and represent bulb and tract, gyrus rectus, and medial orbitofrontal lobe. The fewer than 1% of all aneurysms.12,13,34,35 They may occur after a medial and lateral surfaces of the frontal pole are supplied by the blunt or penetrating head injury.7 They are most common in the frontopolar artery.1,47 Disturbance of blood flow in the territory of pediatric population.13,36 The distal ACA is one of the preferred sites 13,37,38 39 the orbitofrontal and frontopolar arteries from orbitofrontal lobe of origin. Nakstad et al postulated that shearing forces lesions is associated with hand grasping.48 The anterior, middle, between the falx, ACAs, and brain during a head injury can lead and posterior internal frontal arteries supply the superior frontal gyrus. to the development of aneurysms. Yang et al34 reported 2 CMA Urinary incontinence can follow injury of the midportion of the aneurysms in a series of 6 traumatic ACA aneurysms that followed superior frontal gyrus and anterior cingulate cortex.49 Whenever blunt craniofacial trauma. In 1 case, the CMA arose from the A4 the CMA gives rise to the posterior internal frontal and paracensegment. This patient presented with ICH and intraventricular tral arteries, its occlusion risks injury to the supplementary motor hemorrhage 29 days after the trauma. In the other patient, who area and paracentral lobule.50 Lesions affecting the supplementary was asymptomatic, the CMA arose from the A3 segment. Barua 11 motor area are associated with transient weakness or neglect of the et al related the development of a traumatic CMA aneurysm after contralateral side51,52 and the development of speech disorders.48,53 a penetrating missile head injury. Acute deterioration in the level

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Surgical Approaches Aneurysms of the CMA and distal ACA are typically managed through a parasagittal craniotomy for an interhemispheric approach. However, the location, diameter, and orientation of the aneurysm will determine the exact position of the cra niotomy. For aneurysms arising at the most proximal A2, a minisupraorbital approach is preferred at our institution.57 At this location, aneurysms likely arise from C the origin of the orbitofrontal or frontopolar arteries, given that FIGURE 6. Patient 3, a 46-year-old woman with subarachthe CMA rarely originates from noid hemorrhage who had an anterosuperiorly oriented saccular aneurysm at the pericallosal-callosomarginal junction. A2. De Sousa et al8 suggest a Three main branches arose from the CMA: a common trunk basal frontal parasagittal cranof the AIFA and MIFA, PIFA, and PceA. Inadvertent clipiotomy with the head fixed in a ping of the parent vessel could have led to a large stroke neutral position for an interhemiincluding the superior frontal gyrus, supplementary motor spheric approach to aneurysms area, and paracentral lobule. The patient underwent microlocated between the anterior surgical clipping of the aneurysm through an anterior intercommunicating artery and the hemispheric approach. Her outcome was uneventful. A, angiogram showing an anterosuperiorly oriented saccular genu of the corpus callosum. aneurysm at the pericallosal-callosomarginal junction. B, For A2 aneurysms that are intraoperative photograph, microsurgical view, showing a bilobulated aneurysm in the pericallosal cistern. C, intraopernot amenable to the minisupraative photograph, microsurgical view, after clipping. orbital approach and for any other distal ACA lesions, we adopt a parasagittal approach and place the craniotomy flap according to the characteristics and topography of the aneurysm. The patient is placed supine on the operating table, the appropriate shoulder is elevated, and the head is placed in the horizontal position and raised 30 to 45 degrees.58 The interhemispheric fissure is parallel to the ground; therefore, the neurosurgeon’s hands can work side by side in the same horizontal plane. Moreover, gravity helps retract the ipsilateral hemisphere. The head is slightly flexed or extended, depending on whether the aneurysm is more distal or proximal, respectively. Because these lesions are primarily approached from the right side, the right side is placed down and a quadrangular craniotomy is fashioned with a single burr hole over the superior sagittal sinus. The bone is cut through either the right frontal and/or parietal bone. Our patient 3 was treated based on these fundamentals (Fig. 6). Kurtsoy et al59 evaluated FIGURE 7. Cadaveric photograph of a left brain hemisphere illustrating the the applicability of the contralateral interhemispheric approach absence of the CMA. The PrCA gives rise to the OfA, FpA, AIFA, MIFA, used with a horizontal head position, as described by Lawton PIFA, PceA, and a common trunk for the SParA and IParA. (Used with peret al.60 They stressed the benefits of minimizing brain retraction, mission from Barrow Neurological Institute.) of obtaining proximal control, and of clipping the neck of the aneurysm without dissecting its dome. When the approach is perMutism and abulia can be associated with injury to this area and formed through the ipsilateral side, the dome is usually the first to the cingulate gyrus.48,54 Paracentral lobule injuries generate artery-aneurysm structure confronted.59 55 weakness of the contralateral lower extremity. Finally, the supeIn a series of 67 patients, Chhabra et al61 reported 28 patients rior parietal artery helps supply the precuneus gyrus, which, if with distal ACA aneurysms approached through a bifrontal basal antedamaged, would place modulation of consciousness at risk.56 rior interhemispheric approach. They concluded that this approach

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provided the shortest and most direct corridor to such aneurysms while facilitating proximal control of the parent A2 segment. Awareness of the arterial anatomy within the interhemispheric fissure and callosal cistern, together with the angiogram obtained at the time of the procedure, can help guide the neurosurgeon. Recognizing one major branch of the CMA or pericallosal artery by its shape, configuration, diameter, and relationship to the other major branches will stepwise lead the dissection to the parent vessel and aneurysm. Endovascular Surgery Although endovascular series are small, coiling of distal ACA aneurysms has evolved. In 1996, Pierot et al62 reported 8 patients with pericallosal artery aneurysms; endovascular treatment was attempted in 7 cases. Only in 2 cases were the aneurysms coiled successfully. In 4 cases, the procedure failed. In 3 of these failed cases, the coils protruded into the parent vessel. In 1 case, the aneurysm was occluded by temporary occlusion of the pericallosal artery. Six years later Menovsky et al31 reported 12 patients who underwent aneurysm coiling. Initially, complete occlusion was achieved in 11 cases. On 6-month follow-up angiography, only 8 aneurysms remained completely occluded. Nguyen et al63 reported a recurrence rate of 52.6% after treating 19 pericallosal aneurysms. Moreover, they stressed that these lesions are associated with a higher rate of periprocedural rupture, compared with intracranial aneurysms located elsewhere. In 2008, Waldenberger et al64 reported complete occlusion in 93.1% of 29 cases of distal ACA aneurysms. Unlike previous reports, they concluded that the endovascular treatment of these aneurysms is feasible, safe, and effective. In our patients 1 and 2, postoperative angiography confirmed complete occlusion of the patients’ aneurysms (Figs. 4 and 5).

CONCLUSION Understanding the anatomy of the CMA and its variations is critical when treating lesions in the interhemispheric region. Many branches of the pericallosal artery can originate from the CMA. Combined with current technology, the morphometric measurements can help endovascular surgeons access lesions located in distal intracranial vessels. We propose an addition to Moscow’s classic definition of the CMAs. The vessel coursing the longest pathway in or near the cingulate sulcus and otherwise following the classic criteria should be considered the CMA. This modification avoids the dilemma created when 2 or more vessels fit the criteria established by Moscow et al.6 Disclosure The authors have no personal financial or institutional interest in any of the drugs, materials, or devices described in this article.

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Anatomy of the Callosomarginal Artery Applications to Microsurgery and Endovascular Surgery

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