Surgical clipping of a dissecting aneurysm of the precommunicating segment of the anterior cerebral artery: a case report and review of the literature

Introduction Dissecting aneurysms of the cerebral arteries are uncommon vascular malformations. Neurosurgical treatment remains critical in the management of patients with such vascular pathologies. Case presentation A 20-year-old Caucasian woman presented with a sudden onset of severe headache and loss of consciousness. Computed tomography revealed diffuse subarachnoid hemorrhage, while a computed tomography disclosed a dissecting aneurysm of the precommunicating segment of the right anterior cerebral artery. Cerebral carotid angiography confirmed the presence of the dissecting aneurysm. Due to the peculiar anatomic configuration, endovascular treatment was excluded and surgery was selected. As the left circulation perfused both postcommunicating segments of the anterior cerebral artery and the distal right precommunicating segment was hypoplastic, direct clipping of the right precommunicating segment, close to its origin from the internal carotid artery, was carried out. She recovered after surgery and a late angiography showed the correct positioning of the clip, with regular perfusion of both right and left postcommunicating segments. Conclusions The management of dissecting aneurysms of the cerebral arteries is still controversial. With this report we highlight a possible neurosurgical option among therapeutic strategies for these uncommon vascular lesions.


Introduction
Dissecting aneurysms of the cerebral arteries are infrequent pathological conditions. Most dissecting aneurysms occur in the extracranial vessels and are most commonly due to traumatic events [1].
Nowadays, despite their relatively rare occurrence, intracranial aneurysmal dissections are more frequently diagnosed due to better awareness and increased availability of modern imaging techniques; particular attention has been paid to their pathogenesis, natural history, and optimal management [2]. The etiology and pathogenesis of most dissections involving intracranial vessels are still unclear.
Regarding the neuroimaging, the ACA aneurysmal dissection is more difficult to identify than the vertebrobasilar because of narrower vessel calibers and more curved features. However, key signs include a double lumen, stenosis and dilatation ("pearl and string sign"), stenosis alone ("string sign") or occlusion. Because of the rarity of ACA dissecting aneurysms, there are no standardized treatments described in the pertinent literature. However, conservative, endovascular, and surgical approaches can be taken into account as possible strategies for the management of those rare vascular pathologies.
We here report a case of dissecting aneurysm of the A 1 segment of the ACA which was treated via a direct surgical clipping of the homolateral ACA.

Case presentation
A 20-year-old previously healthy Caucasian woman was admitted to a local hospital because of the sudden onset of severe headache and loss of consciousness. Computed tomography (CT) revealed diffuse subarachnoid hemorrhage (SAH) involving the basal cisterns and the anterior part of the interhemispheric fissure. The SAH was classified as group 3 according to the Fisher's scale [19]. She was then referred to our hospital and, upon admission, a neurological examination showed severe headache and nuchal rigidity (Grade II of the Hunt and Hess scale).
Neuroradiological investigation by means of computed tomography angiography (CTA) disclosed a dissecting aneurysm of the A 1 segment of the right ACA ( Figure 1A-C). Digital subtraction angiography confirmed the presence of the dissecting aneurysm of the A 1 segment of the right ACA originating from the parent vessel with a very acute angle ( Figure 1D). No perforating arteries were clearly detected. Moreover, hypoplasia of the distal part of the right A 1 segment (that is, close to the  anterior communicating artery) was highlighted. Both right and left postcommunicating segments (A 2 ) were perfused from the left ACA, and a balloon occlusion test of the right ICA was performed in order to validate this condition ( Figure 1E).
Because of the characteristic angulation of the aneurysm and the non-accessibility from the opposite site through the anterior communicating arterydue to the hypoplasia of the distal part of the A 1 segment of the right ACA and to the vasospasmit was not possible to perform an endovascular treatment ( Figure 1F). Accordingly, surgery was chosen by means of clipping the right ACA through a right standard pterional craniotomy (Figure 2) [20]. Using a microsurgical technique the dura mater was opened and reflected anteriorly. Afterwards, with sharp arachnoid dissection the sylvian fissure was opened in a distal-toproximal direction in order to achieve cerebrospinal fluid release and brain relaxation; these maneuvers allowed us to reduce brain retraction and to visualize the right ICA, with its bifurcation, and the homolateral optic nerve.
Finally, a vascular clip was positioned at the origin of the right ACA.
Postoperatively, her headache progressively diminished and left-side weakness initially presented (Grade 3 of the Medical Research Council scale); her left-side weakness was relieved by medical therapy with dihydropyridine calcium channel blocker (nimodipine) and corticosteroids. No other medications were used.
CT scans, performed at postoperative days (PODs) 3 and 7, showed a right frontobasal hypodensity areaas per subacute ischemic strokeand progressive resorption of the SAH (Figure 3A-B). Early postoperative CTA-magnetic resonance imaging scans (1 month) confirmed and characterized the right frontobasal subacute ischemia with regular flow of the anterior cerebral circulation ( Figure 3C).
Neurologic examination remained otherwise unchanged and she was discharged on POD 24 without any new neurological defect.
A late postoperative angiography (3 months) showed the correct positioning of the clip, with regular perfusion of both right and left anterior postcommunicating cerebral arteries ( Figure 3D).
Six months after surgical treatment she showed no clinical and/or neurological defects of new onset and resumed her ordinary life.

Discussion
The appropriate management of anterior circulation dissecting aneurysms remains controversial. Conservative treatment could be effective with a good outcome and a low rate of second rupture but, if there is a high risk of rebleeding (growing dissecting aneurysm, giant dissecting aneurysm or dissection associated with uncontrolled hypertension), and/or severe clinical conditions arise, direct treatment of the dissecting aneurysm should be proposed.
Nowadays, multimodal treatment for complex cerebral aneurysms includes two major options: endovascular procedures (that is, coiling, stent-assisted coiling, and flow diversion stents) and direct neurosurgical approach (that is, clipping with or without extra-intracranial bypass).
During the last decade, the management of ruptured and unruptured intracranial aneurysms is moving from neurosurgical clipping to endovascular embolization as the preferred, safe and effective treatment modality.
In our case, endovascular access was unfeasible due to the extremely small size of the parent vessel and the acute angle of origin of the aneurysm. Furthermore, the particular anatomical condition of the right A 2 , perfused by the opposite side, determined the choice of a direct surgical approach by means of a right pterional craniotomy and clipping at the origin of the right A 1 tract. It should be also stressed that other surgical options can be considered. For example, wrapping, that is, wrap the aneurysm with materials (muscle, Teflon®) to promote scarring or trapping, that is, both distal and proximal arterial interruption with direct surgery (ligation or occlusion with a clip) or bypass surgery were not considered. Indeed, in the present case, the left anterior circulation perfused both A 2 segments and the distal part of the right A 1 segment was hypoplastic.
This paper is intended to highlight that vascular neurosurgeons and interventional radiologists must consider a multitude of factors when developing the best treatment option for an individual patient. Optimal management requires a thorough understanding of the anatomy and natural history of such aneurysms as well as risks and benefits related to the different treatment modalities.

Conclusions
The management of cerebral dissecting aneurysms is still controversial. With this report we highlight a possible neurosurgical option among therapeutic strategies for these uncommon vascular lesions.

Consent
Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.