Introduction

Pericallosal artery (PcaA) aneurysms, also referred to as distal anterior cerebral artery (DACA) aneurysms, represent 3 to 6% of all intracranial aneurysms in recent clinical trials. Compared to other intracranial aneurysms, PcaA aneurysms are smaller in size, have a high incidence of intracerebral hemorrhage (ICH), and are often associated with other aneurysms. Due to multiple factors, including distal location, small size, small caliber of parent artery, and oftentimes wide-neck incorporating branching arteries, PcaA aneurysms are usually treated with microsurgical clipping as opposed to endovascular treatment.

Major controversies in decision making addressed in this chapter include:

1. 
   

   Whether or not treatment is indicated.

   
   
2. 
   

   Open versus endovascular treatment for ruptured and unruptured PcaA aneurysms.

   
   
3. 
   

   Management of PcaA aneurysms that present with ICH.

   
   
4. 
   

   When should an advanced surgical procedure technique (bypass) be considered?

Whether to Treat

The low incidence of PcaA aneurysms means that they are often underrepresented in clinical trials. In the International Study of Unruptured Intracranial Aneurysms 1 (ISUIA-1) and ISUIA-2, PcaA aneurysms were combined with anterior communicating artery (ACoA) aneurysms. The Unruptured Cerebral Aneurysm Study of Japan (UCAS Japan) listed them in the “other” category, and later defined the overall incidence of DACA aneurysms in UCAS as 4.5% in a follow-up study of Japanese cohorts that also included SUAVe (Small Unruptured Intracranial Aneurysm Verification) study data. This study published by Tominari et al imparted a relatively low rupture risk score (1 point) to PcaA aneurysms compared to middle cerebral artery (MCA) aneurysms (2 points) and ACoA and posterior communicating artery (PCoA) aneurysms (3 points). In contrast, the PHASES aneurysm risk score (Population, Hypertension, Age, Size of aneurysm, Earlier subarachnoid hemorrhage [SAH] from another aneurysm, and Site of aneurysm) combined PcaA aneurysms with ACoA, PCoA, and posterior circulation aneurysm assigning them a 4-point score compared to MCA (2 points) and internal carotid artery (ICA; 0 points) aneurysms ( 1 , 2 in algorithm ). Similarly, ruptured aneurysm trials including the International Subarachnoid Aneurysm Trial (ISAT) and the Barrow Ruptured Aneurysm Trial (BRAT) had a 4.4 and 3.1% incidence, respectively, for PcaA aneurysms, again making the extrapolation of study data to PcaA aneurysms challenging.

As such, much of data regarding risk factors and treatment of PcaA aneurysms are generated from retrospective case series. The largest series of DACA aneurysms to date was published by Lehecka et al and included 470 DACA aneurysms in 427 patients treated in the modern era (1980–2005) from two centers in Finland. The majority (86%) of patients presented with SAH from the DACA aneurysm or another aneurysm. Ruptured DACA aneurysms were larger than unruptured DACA aneurysms (median size 6 and 3 mm, respectively; 1 , 2 in algorithm ). Multiple aneurysms were common and occurred in 52% of patients. Groups were divided into ruptured DACA aneurysms (277 patients), unruptured DACA aneurysms without acute SAH (no history of SAH or recovery after SAH from another aneurysm, 94 patients), and unruptured DACA aneurysms with acute SAH from another aneurysm (56 patients). For the ruptured patients, data were compared to all ruptured patients from a database of 2,243 patients with ruptured aneurysms; DACA aneurysms were smaller (median size 6 vs. 8 mm) and had higher rates of ICH (53 vs. 26%). Fifty-one percent of ruptured DACA aneurysms were less than 7 mm, and 43% were 7 to 14 mm.

In summary, the overall incidence of PcaA aneurysms is low and trials evaluating the risks of rupture and treatment of all intracranial aneurysms may not necessarily represent PcaA aneurysms. The general considerations for aneurysm treatment including patient age, family history, medical comorbidities, psychological factors, and patient preference as well as aneurysm-specific factors such as rupture status, presence of daughter sac or irregular dome configuration, growth over time, and associated aneurysms certainly apply to PcaA aneurysms. However, the smaller size of PcaA aneurysms, especially in ruptured patients, makes decision making in unruptured patients more challenging as there are not clear size thresholds for treatment ( 1 , 2 in algorithm ). One should consider the entire patient in recommending observation or treatment for aneurysms of smaller size (3–7 mm; 7 in algorithm ). For example, a 60-year-old female with a history of smoking and hypertension with a 5 mm, multilobulated PcaA aneurysm is likely at higher risk of rupture than a 60-year-old otherwise healthy male with a 5 mm, saccular PcaA aneurysm. The risk cannot be exactly quantified, but the general considerations defined earlier help counseling the patient about the future risk of rupture.

Anatomical Considerations

The term pericallosal artery is commonly used to define the portion of the ACA distal to the ACoA. The DACA is divided into four segments (A₂–A₅) based on its relationship to the corpus callosum. A₂ begins at the ACoA and courses along the rostrum of the corpus callosum. A₃ curves around the genu until reaching a posterior trajectory. A₄ and A₅ are located above the body of corpus callosum and are divided by the plane of the coronal suture. Together, A2 and A3 are referred to as the ascending segment, and A₄ and A₅ are referred to as the horizontal segment.

Importantly, the origin of the callosomarginal artery (CmaA) on the PcaA does not define the segments of the DACA. The CmaA origin varies, most commonly occurring on the A3 segment, but may be absent in 18% of patients. The PcaA courses along the corpus callosum in the corpus callosum cistern, and the CmaA travels above in or near the cingulate sulcus roughly parallel to the PcaA. The diameter of the CmaA is inversely related to that of the PcaA distal to the CmaA origin with equivalent size seen in 30% of patients and a larger PcaA in 50%. The average diameters of the PcaA and CmaA are 1.9 and 1.8 mm, respectively. Because the falx is thinnest anterior to the genu and gradually thickens posteriorly, the course of the PcaA is below the free margin of the falx, whereas the same is true only for the proximal portion of the CmaA.

Branches of the DACA fall into two categories: central (basal perforating) and cerebral branches, the latter can be further divided into cortical, subcortical, and corpus callosum branches. Central branches originate in A₂ and enter the optic chiasm, lamina terminalis, and anterior forebrain supplying the anterior hypothalamus, anterior commissure, pillars of fornix, and anteroinferior striatum. The subcortical branch (i.e., recurrent artery of Heubner) commonly originates from the A₂ segment supplying the caudate and anteroinferior internal capsule. Both central and subcortical branches are more relevant to ACoA aneurysms.

There are often eight cortical branches from the DACA segments: the orbitofrontal and frontopolar arteries, A₂; anterior and middle internal frontal arteries and CmaA, A₃; the paracentral artery, A₄; and the superior and inferior parietal arteries, A₅. The posterior internal frontal artery can arise from the A₃, A₄, or CmaA. All cortical branches arise more frequently from the PcaA than from the CmaA. The branching pattern of the DACA is variable and provides less anatomical guidance for fissure dissection than MCA aneurysms, for example. Cortical branches supply the superomedial areas of the hemisphere and anastomose with MCA territory laterally and posterior cerebral artery (PCA) territory posteriorly. Anatomical anomalies of the DACA include triplication of the A₂ segments (i.e., accessory A₂), an unpaired A₂ segment (i.e., the azygos ACA), and a bihemispheric ACA (i.e., one ACA with major supply to both hemispheres).

Classification

PcaA aneurysms can be classified according to the DACA segment from where they originate. Aneurysms occur most frequently along the A3 segment (80%) but can occur along the A₂ and horizontal segments. The vast majority of PcaA aneurysms are saccular (98% of ruptured patients and 100% of unruptured patients in the Finnish series), and they tend to occur at branch points. Rarely, the aneurysms are fusiform, traumatic, or mycotic. The proximity of the falx and shear forces with trauma can cause traumatic pseudoaneurysms along the horizontal segment.

Workup

Related posts:

19 Cavernous Carotid Artery Aneurysms 23 Posterior Communicating Artery Aneurysms 24 Anterior Choroidal Artery Aneurysms 26 Middle Cerebral Artery Aneurysms 31 Giant Aneurysms of the Anterior Circulation 33 Dissecting Intracranial Aneurysms of the Anterior Circulation

Stay updated, free articles. Join our Telegram channel

Join