Anatomical considerations of sylvian fissure
The extensive spectrum of the neural and vascular structures within the reach of the transylvian approach includes the insula, basal ganglia, lateral ventricle, middle cerebral artery, temporal operculum, uncus, orbit, anterior cranial fossa, optic nerve, internal carotid artery and its branches, lamina terminalis, and interpeduncular fossa
9). From the neurosurgical viewpoint, the sylvian fissure can be considered a gateway connecting the surface to the depth of the anterior part of the brain base including A-ComA
9).
Care, during the procedure without sylvian fissure dissection, should be taken not to injure any vessels and the frontal or temporal cortex. The occurrence of a thick blood clot within the fissure makes the dissection even more difficult. Sylvian fissure has many anatomical variations depending on the citernal size and arachnoidal characteristics10). In some cases, the frontal and temporal lobe are closely approximated on the surface thereby covering the substance of the cistern10). Furthermore, deep within the sylvian fissure, the frontal lobe often protrudes laterally, indenting the temporal lobe10). Failure to recognize this anatomical variation may result in an inadvertent injury to the frontal lobe.
Surgical approach
Many surgeons have proposed different approaches in attempts to improve the surgical outcome. Operative approach of A-ComA can simply be classified into two categories that are lateral approach and anterior approach. The lateral approaches include pterional approach, orbitozygomatic approach, and orbitopterional approach. The anterior approaches consist of anterior interhemispheric approach and subfrontal approach
3). Aneurysm location, direction, and size must be considered to select each operative approaches
3). Yasargil
10) reported excellent surgical results by the pterional approach, and therefore, along with its technial easiness, his approach gained unanimous support and has been widely accepted as a standard procedure. When the aneurysm is positioned high from the anterior clinoid process and it is projected in a superior direction, interhemispheric approach is preferred
5). If large AComA is directed superiorly, orbitozygomatic approach or subfrontal approach are preferred
1,3). But, the choice of approach to AComA has depended largely on the surgeon's preference and experience
1).
Any maneuver that can prolong aneurysm surgery may be detrimental. Rapid clipping of the aneurysm may be the best interest of the patient. Also limiting a vascular manipulation may reduce the risk of spasm and potentially improve outcomes. Solomon8) also commented that he routinely did not dissect sylvian fissure by performing a pterional craniotomy in patients with AComA. He thought that much of the injury associated with AComA surgery derived not from retraction but from small vessel injury. For resection of the gyrus rectus without sylvian fissure dissection, maximal brain relaxation is crucial to the successful exposure of aneurysm without sylvian fissure dissection. The surgeon can angle the microscope from a more oblique trajectory along the frontal lobe with more lateral retraction to the side of spacious sylvian fissure. It is unnecessary either temporal lobe retraction or sylvian fissure splitting. Although we could not compare operative times in patients with sylvian fissure dissection, we believe that eliminating the step of sylvian fissure dissection substantially by gentle lateral basal-frontal retraction to the side of the sylvian fissure may decrease operative times. On the contrary, this approach without sylvian dissection need more surgical experience not only to improve the response to intraoperative rupture but also to visualize anatomy under adverse conditions, and is limited in; 1) aneurysms associated with a large blood clot with mass effect, 2) subarachnoid hemorrhage associated with brain swelling, 3) highly positioned aneurysms, and 4) difficult aneurysms to clip such as large sized aneurysms and complex or postero-inferiorly projecting ACom aneurysms.
In conventional approach with sylvian fissure dissection, there are three disadvantage including time consuming, longer retraction, risk of pial and microvascular injury during sylvian dissection. However, the limited access would in turn increase the tendency toward more significant brain retraction. Considering our surgical experience since 1990, it should be pointed out that an unavoidable prerequisite before trying to perform this approach is to have the precise anatomic knowledge and enough skills to dissect surrounding the aneurysm without using bulky brain retractors.
Complication
Being aware of the technical difficulties and potential morbidity of surgical adjuncts, many surgeons have proposed different approaches in attempts to decrease the surgical complication rates.
Hoeoek et al.6) reported 0-3% of anosomia at the Acom-A surgery. Aydian et al.2) observed 3% of the olfactory nerve dysfunction. In our series, there were no procedure-related complications except for olfactory dysfunction (2.96%), which was similar to conventional transsylvian approach. It is well known that the nerve can be pulled out from the cribriform plate when retraction exceeds a certain degree, and that even a moderate strain of compression on cranial nerves may result in temporary or permanent damage.
and Jong Moon Kim, M.D.
