Keywords
posterior cerebral artery (PCA) - aneurysm
Palavras Chave
artéria cerebral posterior - aneurisma
Introduction
Aneurysms of the posterior cerebral artery (PCA) represent ∼ 1% of all intracranial
aneurysms.[1]
[2]
[3]
[4] The surgical approach and dissection of the PCA is technically challenging due to
the complexity of its perforating branches and their intimate relationship with the
cranial nerves and with the upper brain stem.[5]
[6] A precise knowledge of the segmental anatomy of the PCA and its branches is essential
when the surgical or endovascular approach to an aneurysm is planned, particularly
if parent vessel occlusion is contemplated as a temporary control.[7]
[8]
[9]
The aim of the present study is to describe the case of an adult man presenting with
a saccular aneurysm of the right PCA at the posterior half of the postcommunicating
(P2P) segment, and to discuss the technical nuances of the approach and of the clipping
process.
Discussion
Aneurysms of the PCA account for between ∼ 0.7 and 2.3% of all intracranial aneurysms[4]
[10]
[11] and may be associated with innumerous vascular anomalies, such as Moyamoya disease,
arteriovenous malformation, and arterial occlusion, as well as with systemic diseases,
such as bacterial sepsis, tumor emboli, Marfan syndrome, Ehlers-Danlos syndrome, systemic
lupus erythematosus, and head injury.[11]
[12]
[13] Aneurysms of the PCA are usually associated with vertebrobasilar and/or posterior
circulation fusiform or saccular additional aneurysms affecting the midbrain perforating
branches.[4]
[10]
[11] However, distal aneurysms of the PCA located at the P2P segment or at the P2P-P3
junction are an extremely rare disease.
The surgical treatment of aneurysms located at the P2P-P3 junction is challenging,
and most of the cases are currently treated via endovascular route.[7]
[14]
[15]
[16]
[17] Coil embolization, stent-assisted or balloon-assisted coiling, and flow diverters
are the main techniques used to occlude posterior circulation aneurysms.[7]
[14]
[15]
[16]
[17] However, endovascular techniques may not completely exclude saccular dilation, with
persistent neck flow, generally do not resolve mass effect in giant lesions, and present
a risk of occlusion of the small perforating arteries. The operative management allows
a direct approach of the aneurysm, as well as arterial reconstruction with direct
clipping or by-pass techniques, and the removal of mass effect over the nearby structures.[18]
[19]
Great advances have been achieved in the surgical treatment of posterior circulation
aneurysms as the result of a refined anatomical knowledge of the basal cisterns and
of their vascular contents, and of appropriate skull base approaches and clinical
experience.[20]
[21] Several surgical approaches with modifications and combinations have been described
to access the posterior portion of the PCA. However, choosing wisely the appropriate
operative route remains an important step for perfect clipping and requires a precise
understanding of the drawbacks of each approach, as well as of the anatomical variations
of the region. Figueiredo et al[22] showed the appropriateness of four different surgical approaches of the ambient
cistern, as well as the advantages of performing a resection of the parahippocampal
gyrus before clipping distal PCA aneurysms according to their location in the cistern.
Goehre et al[19] affirmed that the subtemporal approach is a suitable route to aneurysms at the P1,
P1-P2 junction, and P2 segments, as well to those located at the anterior portion
of the P3 segment. Through this approach, the cerebrospinal fluid can be released
before retraction is necessary to prevent temporal lobe injury.[19]
In 1997, Seoane et al[23] didactically divided the anatomical segments of the PCA aneurysms in three different
regions/segments. The anterior segment, or S1, is located inside the interpeduncular,
crural and ambient cisterns, and in intimate relationship with the lateral aspect
of the cerebral peduncle, and should be approached via a pterional, a pretemporal,
or a subtemporal route. The middle segment, or S2, is located inside the ambient and
quadrigeminal cisterns, extends from the most lateral aspect of the PCA inside the
quadrigeminal cistern, the so-called collicular point, and is best managed through
the subtemporal approach (usually requiring some parahippocampal gyrus resection)
or through the subtemporal transventricular route. The posterior segment, or S3, is
located inside the quadrigeminal cistern, which includes the collicular point and
extends to the distal branches of the PCA inside the calcarine and parieto-occipital
sulci and should be approached through an occipital interhemispheric route. In the
present case, the aneurysm was located at the P2P-P3 junction and was managed with
a subtemporal approach with limited parahippocampal gyrus resection without neurological
complications.
In conclusion, the management of posterior circulation aneurysms remains challenging
for neurosurgeons due to their deep location, to the difficult exposure, to the numerous
surrounding cranial nerves and perforators, to the narrowness of surgical field, and
to the limited space to operate. In the present case, we presented a distal PCA aneurysm
located at the P2P-P3 junction and highlighted that the subtemporal approach is a
safe and feasible route to appropriately clip this type of intracranial vascular disease.
