|Year : 2022 | Volume
| Issue : 1 | Page : 35-40
Distal anterior cerebral artery aneurysms: A brief review
Sumeet Narang, Jaspreet Singh Dil, A Raja
Department of Neurosurgery, National Neurosciences Mission, Adarsha Super-Specialty Hospital, Udupi, Karnataka, India
|Date of Submission||22-Aug-2022|
|Date of Decision||24-Aug-2022|
|Date of Acceptance||25-Aug-2022|
|Date of Web Publication||22-Sep-2022|
Dr. Sumeet Narang
Department of Neurosurgery, National Neurosciences Mission, Adarsha Super-Specialty Hospital, Udupi, Karnataka
Source of Support: None, Conflict of Interest: None
Distal anterior cerebral artery (DACA) aneurysms or pericallosal aneurysms are defined as aneurysms arising from any part of the A2 up to the A5 segments of the anterior cerebral arteries. They are relatively uncommon and have unique salient features that are pertinent to its accepted surgical management, hence requiring strong theoretical and conceptual knowledge. The objective of this study is to provide a comprehensive review and discussion on DACA aneurysms, from its nomenclature, anatomical characteristics and its impact on the pathophysiology, to the data on surgical management and outcome, and essential considerations required in the microneurosurgical approach, and to summarise the subject in a sequential and wholesome manner for a neurosurgeon at any stage of the career. Extensive review of available literature and surgical experiences published in indexed journals, was consolidated into concise text. DACA aneurysms represent about 6% of all intracranial aneurysms, and A3 aneurysms are the most common subtype. They have been identified at a mean age of 50 years, women more commonly affected, and found to be associated with other intracranial aneurysms. Patients present with subarachnoid haemorrhage in the distal interhemispheric fissure and pericallosal cisterns along with intracerebral and intraventricular haemorrhage in the vicinity of the frontal lobes, most commonly with Hunt and Hess Grade 2. The majority of such patients managed with surgical clipping had complete occlusion achieved in 67% and favourable outcome achieved in as many as 94%, versus a mortality rate of as high as 70% in conservatively managed cases, making surgical clipping through the interhemispheric approach is the preferred treatment modality. DACA is microsurgically interesting and challenging due to its peculiarities in anatomy. Microsurgical clipping of DACA aneurysms has been proven by literature, and tested by time, to be safe and have a favourable outcome, and hence must be taken up with clarity and vigour.
Keywords: Aneurysm, cerebrovascular, distal anterior cerebral artery, review
|How to cite this article:|
Narang S, Dil JS, Raja A. Distal anterior cerebral artery aneurysms: A brief review. J Cerebrovasc Sci 2022;10:35-40
| Introduction|| |
Intracranial aneurysms are acquired dilatations of arteries within the skull. Aneurysm rupture is the most frequent cause for subarachnoid haemorrhage (SAH), a life-threatening condition that may cause sudden death even before a patient receives medical attention, with a staggering overall mortality rate of as high as 50%. SAH accounts for 5%–10% of all strokes.,
Aneurysms, generalised, commonly occur at branching points of arteries. This is a result of pathobiological factors such as haemodynamic stress on the vessel walls at these junctions, along with other ongoing processes such as inflammation and vascular degeneration and remodelling. Aneurysms could also arise from congenital, traumatic and infective (mycotic aneurysms) aetiology.
The nomenclature and classification of intracranial aneurysms are primarily based on their specific location in the arterial tree, although they can further be classified based on other parameters that affect their surgical complexity, such as size, orientation, aetiology and status (ruptured v/s unruptured of thrombosed, etc.).
Here, the authors present a review of aneurysms of the distal anterior cerebral artery (DACA),,, as further elaborated.
| Microsurgical Anatomy|| |
The anterior cerebral artery
The internal carotid artery on each side terminates at the medial end of the Sylvian fissure, by dividing into the anterior cerebral artery (ACA) (which is the smaller branch) and the middle cerebral artery (MCA). Both ACAs, from their origin, travel a short distance across the optic nerves or optic chiasma and are connected to one another through the anterior communicating artery (ACOM), before ascending superiorly, in the interhemispheric fissure, parallel to the corpus callosum in the pericallosal cistern.
The ACA is divided into five segments as per Fischer,, as follows [Figure 1]:
- A1 Segment: from the origin of the ACA, up to the ACOM
- A2 Segment: from the junction of the A1 and ACOM, up to the region between the rostrum and the genu of the corpus callosum.
The A2 segment gives rise to the following three important branches, namely:
- Recurrent artery of Heubner
- Orbitofrontal artery
- Frontopolar artery.
- A3 Segment: Curving around the genu of the corpus callosum and ending at the rostral part of the body of the corpus callosum.
The A3 segment gives rise to several cortical branches: The anterior, middle and posterior internal frontal arteries, and the callosomarginal artery (CMA), which is the most important branch, identified as the artery which courses in or near the cingulate sulcus. At this very point of the study, it may be noted that the origin of the CMA is the most common site of the presence of the DACA aneurysm.
- A4 Segment and A5 Segment: Together referred to as the horizontal portion of the ACA, running along the superior surface of the corpus callosum, the two being virtually divided by the plane corresponding to the coronal suture.
Based on the above divisions, the ACOM being the key junction, the A1 segment being proximal to it, is referred to as the proximal ACA; and the A2 segment onwards (A2-A5), being distal to it, is called the distal ACA, or, the pericallosal artery.
Hence, DACA aneurysms or pericallosal aneurysms are defined as aneurysms arising from the A2 up to the A5 segment and their branches [Figure 2] and [Figure 3]a, [Figure 3]b, [Figure 3]c, [Figure 3]d, [Figure 3]e, [Figure 3]f.
|Figure 3: (a-f) Anatomical locations of distal ACA aneurysms on angiography|
Click here to view
They are further differentiated and named with respect to their exact location in relation to the ACA and the corpus callosum, as follows:
- A2A or Proximal Pericallosal Aneurysms: aneurysms of the A2 segment and its frontobasal branches
- A3A or Classical Pericallosal Aneurysms: aneurysms of the A3 segment
- AdistA or Distal Pericallosal Aneurysms: aneurysms of the A4-A5 segments and distal cortical branches.
A3A's are the most common as compared to A2A's and AdistA's and were hence titled classical pericallosal or 'loco classico' DACA aneurysms. As mentioned, the origin of the callosomarginal branch of the A3 segment is the most frequent site for aneurysms.
The anatomy of the origin is such that many other aspects are to be taken into consideration in the discussion of DACA aneurysms and microsurgery.
DACA aneurysms are located in the midline as the A2-A5 traverses the interhemispheric fissure, where the falx cerebri separates the two cerebral hemispheres. The arteries run below the free margin of the flax and hence there is crossover of vessels in that narrow fissure. At the same time, the cingulate gyri are adherent to each other, making identification of the corpus callosum an important difficulty.
The venous drainage pattern of the frontal lobes is such that there are ascending veins from the convexity, which drain into the superior sagittal sinus or the superior Sylvian vein; and there are descending veins from the medical surface, which drain into the inferior sagittal sinus or anterior cerebral vein.
The free edge of the dura contains enlarged spaces known as a lacuna, the largest in the posterior frontal region, into which arachnoid granulations protrude.
The bridging veins form a complex network within the narrow interhemispheric fissure, damage to which poses a risk of venous infarction. The pericallosal veins are also located within the fissure and must also be protected.
It is the major transverse commissure connecting the two cerebral hemispheres, which can be identified by its white, transverse fibres. It is anatomically divided into the rostrum, genu, body and splenium. The rostrum, genu and body are supplied by the ACAs and the splenium by the posterior cerebral arteries. The pericallosal artery travels along the corpus callosum throughout its course. However, as the cingulate gyri are adherent and the artery may also traverse the cingulate sulcus, the cingulate gyri and corpus callosum may be mistaken for one another.
The commonly reported anomalies of the ACA and its branches are associated with the presence of DACA aneurysms. They include:
- Azygos ACA – Single trunk distal to the A1 supplying both hemispheres
- Bi-hemispheric ACA – One A2 is hypoplastic
- Triplication – The presence of a middle A2 supplying the corpus callosum.
| Clinical Presentation|| |
Rupture of a DACA aneurysm undoubtedly leads to SAH as the most common presentation, with history of sudden onset of severe headache or loss of consciousness with malignant hypertension. Subarachnoid blood may be seen in the distal interhemispheric fissure and pericallosal cisterns.
However, more than aneurysms in other locations, DACA aneurysm rupture very frequently causes intracerebral haemorrhage in as many as 70% of patients, bleed commonly occurring into the frontal lobes or cingulate gyrus as also noted radiologically., This is due to its presence in the very narrow space available in the interhemispheric fissure and dense adhesions of the medial surfaces of the brain causing bleeding into the adjacent brain and intraventricular haemorrhage (IVH), which has also been noted with significance [Figure 4].
|Figure 4: (a-d) Computed Tomography images following rupture of DACA aneurysms|
Click here to view
Computerised tomography angiography or digital subtraction angiography which is still the standard in use and preferred mode of investigation, has often revealed aneurysms at other sites found in association with a DACA aneurysm.
Patients presenting with symptoms such as headache akin to frontal tumours, have been found to have giant DACA aneurysms on further investigation.
Unique symptoms such as akinetic mutism, bilateral lower limb weakness, behavioural changes, and cognitive deficits have been attributed to DACA aneurysms.
| Microsurgical Management|| |
With a patient presenting in ictus as described above, the primary objective is to address all the problems arising from the initial impact of the SAH and to prevent the expected complication such as cerebral vasospasm and re-bleeding. Microsurgical aneurysm clipping is the definitive preferred mode of treatment, and conservative management has been reported to have a poor outcome. Several series have shown that patients presenting with a low neurological grade at admission, aggressively managed with surgery, have a favourable outcome.
The first detailed report for microneurosurgical clipping of DACA aneurysms came from Yasargil and Carter in 1974. Several aspects of the anatomy of the region contribute to the neurosurgeon's approach to DACA aneurysms. The preferred route of approach for clipping DACA aneurysms is the anterior interhemispheric approach, although other authors have also expressed their perception of advantages obtained using other approaches such as the bifrontal bicoronal with a basal interhemispheric approach., An exception to this is in dealing with more proximal aneurysms, i.e., of the A2 segment, which may be approached unilaterally using a lateral supraorbital approach or a pterional approach.
For the anterior interhemispheric approach, the patient is positioned supine with 20° head-end elevation, and the head is flexed or extended according to the location of the aneurysm, to facilitate the most vertical trajectory which would be optimal for the operating surgeon.
An oblique skin incision is made over the midline just behind the hairline. A bicoronal incision may be employed but it is not necessary. The surgeon must be careful about the underlying superior sagittal sinus and the frontal sinus while performing the craniotomy. The dura is opened as a C-shaped flap, from lateral to medial, with its base over the midline. Care must be taken not to injure the venous lacunae or bridging veins at this point.
The following salient and peculiar features must be stressed on and considered technically, in the surgeon's bid to clip the DACA aneurysm:
- There is an absence of large subarachnoid cisterns in the interhemispheric fissure, as is normally available to the surgeon in the management of the circle of Willis, and the presence of veins draining into the superior sagittal sinus provides a narrow working corridor
- The gain in working space can be obtained by a judicious evacuation of the haematoma in the neighbouring frontal lobe, cingulate gyrus or corpus callosum; and cerebrospinal fluid may be released by puncturing the third ventricle at the lateral border of the craniotomy
- The more proximal the aneurysm, the more it is obstructed from vision by the genu of the corpus callosum. The fundus of the aneurysm may also be embedded in the pia or adherent to the cingulate gyrus
- A judicious incision in the genu or anterior part of the corpus callosum may be needed to approach to the proximal vessel but it is absolutely necessary to first distinguish it from the cingulate gyrus. Other landmarks such as the genu of the corpus callosum and the callosomarginal artery itself may be used in appreciating the surgical anatomy of the region
- Once inside the pericallosal cistern, the pericallosal artery may be identified in the cingulate sulcus itself. The dissection must proceed from distal to proximal, i.e., the parent vessel must be traced towards its origin before proximal control can be attempted or achieved, in contrast to other aneurysms where dissection is proximal to distal
- The sclerotic wall of the aneurysm, the common encounter of a broad base, and the presence of origins of vessels close to the neck lead to difficulty in clip positioning, which poses a risk for ischaemic complications.
It is the golden rule of aneurysm clipping that the proximal vessel, distal vessel and their associated branches, must be visualised, even if it is painstaking to gain that visual. As repeatedly mentioned, the lack of working space makes this a difficult process, especially for more proximal aneurysms, leading to a high risk for intraoperative rupture. For this reason, intraoperative angiogram or use of indocyanine green video angiography is very helpful in appreciating the vascular anatomy and also establishing the side of circulatory dominance of the A1, if it was not possible on pre-operative investigation.
In case, it is difficult to dissect and gain proper visualisation of the neck of the aneurysm and proximal control due to adhesive cingulate gyri following SAH, undue attempts may injure the cingulate gyri or corpus callosum, a pilot clip may be applied to the dome of the aneurysm before continuing dissection.
Temporary clips are very essential and may be needed on the callosomarginal artery itself, especially in the event of intraoperative aneurysm rupture. In such an event, adenosine-induced hypotension and cardiac arrest may be employed to achieve haemostasis. Other aneurysms may be identified during surgery, but are not to be dealt with in the same sitting.
The smallest but most adequate possible clip must be selected for the final clipping of the aneurysm [Figure 5]a and [Figure 5]b.
|Figure 5: (a) Ruptured DACA aneurysm - intra-operative. (b) DACA aneurysm clipped - intra-operative|
Click here to view
| Discussion|| |
Sugar and Tinsley were the first to perform surgery by direct clipping of DACA aneurysms in 1948. Even before Yasargil's pioneering microsurgical techniques, a Finnish series published in 1960, revealed several key points about DACA aneurysms, and subsequent series, including the Cooperative Study of Intracranial Aneurysms in 1966, have almost unanimously corroborated the same findings in the years that followed.,,
With Lehecka's stunning dissertation providing a detailed review of the work of several studies, it has been seen that DACA aneurysms represent about 6% (a range of 2%–9%) of all intracranial aneurysms. Of all DACA aneurysms, 65% are A3As, making them the most common. Sekerci et al. reported 90% of their series to be A3As. As many as 50% of patients have been found to have multiple aneurysms, the MCA bifurcation being the most frequent of the other sites; 23% of patients were found to have associated anomalies of the ACA and only 1% had an associated arteriovenous malformation. As per Shukla et al., the most common site of aneurysm was also the pericallosal (A3 segment) artery noted in 49.2% of patients, and multiple aneurysms were observed in 12.1% of cases.
Anatomically, the average diameter and neck diameter have been reported to be 7 mm and 2.6 mm respectively, and giant DACA aneurysms have been rarely reported.
One major point that must be noted is that because DACA aneurysms are infrequent when compared to aneurysms in other locations, the surgical experience that has been gained, or is available to gain in tackling them, is also less.,, DACA aneurysms come with inherent nuances, which affect patients differently in their presentation, in the technical points that must be taken into consideration in treatment, and by extension, in the outcome, and hence it is these parameters that must be focused on in our discussion of the subject.
DACA aneurysms have been detected at a mean age of 50 years with the number of women affected (60%) being slightly >men (40%). As per Lehecka et al., patients were categorised based on whether they had ruptured or unruptured aneurysms, and those with unruptured aneurysms were further subgrouped based on whether they had SAH or not. Of all patients with ruptured DACA aneurysms who presented with SAH, 25% had both intracerebral haemorrhage (ICH) and IVH and 28% had only ICH, most commonly with bleed into the frontal lobes. Fifteen per cent presented with Hunt and Hess Grade 1 at admission, 32% with Grade 2, 33% with Grade 3, 11% with Grade 4 and 9% with Grade 5. Ninety per cent if these patients were taken up for microneurosurgical aneurysm clipping and 18% of patients were found to have an episode of re-bleeding before treatment was initiated. As per Shukla et al., ICH was observed in 37.1% and IVH in 17.4% of patients. Series of the past had reported low mortality rates following aneurysm clipping but were found to have a selection bias, with studies evaluating more patients with a lower Hunt and Hess Grade at admission.,,
However, as per more recent reviews, of 258 patients with SAH microsurgically treated for ruptured DACA aneurysms, total occlusion was achieved in 67% and there was a surgical mortality rate of only 1%. However, morbidity arising from treatment, such as the development of neurological deficits, occulted in 13%. Seventy-five per cent of patients had a favourable outcome with Glasgow Outcome Scale ≥4 at 1 year. Lee et al. have also documented a good outcome in 94% of 117 cases managed, and the remaining 6% of patients were reported to have presented with Hunt and Hess Grades 4 or 5. Patients' age, Hunt and Hess grade at admission, re-bleeding, presence of ICH, IVH and hydrocephalus preoperatively, have all been noted to be parameters with a significant effect on the outcome. Of the patients who died within 1 year, most deaths were attributed to the primary SAH, whereas no deaths were reported due to re-bleeding from the clipped aneurysm. Here, it is ideal to reiterate that mortality at 1 year following conservative treatment has been reported to be as high as 75%, a totally opposite picture when compared to microsurgical treatment.
Intraoperative rupture of aneurysm occurred in 22% of patients with ruptured aneurysms as compared to only 7% in patients with unruptured aneurysms, but the incidence was as high as 35% among patients with unruptured aneurysms who developed SAH from the rupture of an aneurysm at a different location. The cumulative recurrence rate of SAH from DACA aneurysm is only 1.4%.
No discussion of cerebrovascular intervention is complete without the mention of aneurysm coiling. Endovascular management of DACA aneurysms with acceptable outcomes is indeed possible, although have made up only a small proportion of most patient groups studied, and achievement of complete occlusion does not match that of surgical clipping. Procedural difficulties have been reported due to the same anatomic restrictions and follow-up is limited. Endovascular management is advisable for unruptured fusiform aneurysms, and has to be decided on a case-to-case basis.,,
| Conclusion|| |
DACA aneurysms are not as common as aneurysms at other intracranial locations but are microsurgically interesting and challenging due to their peculiarities in anatomy. Microsurgical clipping of DACA aneurysms has been proven by literature, and tested by time, to be safe and have a favourable outcome, and hence must be taken up with vigour.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]