| Objective:The pterional-transsylvian (PT-TS) approach is one of the most versatile and useful approaches in neurosurgery. It is used to treat pathological features arising from the circle of Willis and surrounding vicinity, such as the sellar, parasellar, and subfrontal regions. Lesions originating from the orbit, medial sphenoid ridge, uncus, and insula may also be treated with this approach. The principle of the PT-TS approach consists of leaving the brain undisturbed by using natural planes and spaces to expose surgical targets in the basal cisterns without significant brain retraction. In order to achieve this ideal state, the neurosurgeon must have an intimate knowledge of the anatomical structure of the Sylvian fissure. The purpose of this study was to supply the clinical anatomical materials to neurosurgeon and define the importance of the protection of middle cerebral artery and lenticulostriate arteries by research the microsurgical anatomy of the Sylvian fissure.Methods: Ten color latex-injected, formalin fixed cadaver heads (twenty sides) without obvious intracranial disease were used in this study. Each head was fixed rigidly in a head holder in a position simulating the standard PT-TS approach. The procedures were performed using microsurgical instruments and a surgical microscope. Splitting the Sylvian fissure using the operating microscope under 5–20x magnification to observe the morphology and middle cerebral artery, lenticulostriate artery, early branches, middle cerebral artery bifurcation situation, the variability. Take out the brain observe the composition of the Sylvian fissure, measure and record internal carotid artery diameter at the just-bifurcated region, the anterior cerebral artery diameter at its origin, anterior cerebral artery at its origin, middle cerebral artery diameter at its origin. Measure the length of the anterior horizontal ramus , the anterior ascending ramus the posterior ramus and records, observation of composition of the insula, and measure the length of circular sulcus and insula sulcus. Particular attention was paid to the perforators arising from the M1 portion of the MCA. The division of the main trunk and the secondary trunks was studied and documented.Results:The Sylvian fissure was divided into large Sylvian fissure and small Sylvian fissure, the large Sylvian fissure was 60%, Small Sylvian fissure was 40%.Measurement of lateral fissure:Length of stem of Sylvian fissure is average 35.0mm (range 28.3-47.1mm),length of anterior horizontal ramus is 10.8mm(range 7.6-24.3mm), length of anterior ascending ramus is 11.7mm (range 6.6-18.4mm),length of posterior ramus is 53.7mm (range 37.6-62.2mm).Distance from near Sylvian point to precentral sulcus, central sulcus and postcentral sulcus is 8.9mm(range 7.12-11.36mm), 21.7 mm (range 17.9-25.1mm ), 26.5mm (range 24.1-30.5mm) respectively.Insula morphology and measurement:Insula was pyramid shape, there was a circular sulcus around and separated from the cerebral cortex. Limen insulae width of an average was 21.36mm (16.3-29.8mm). The central island sulcus of 70% of cerebral hemisphere start from the limen insulae, 30% of the cerebral hemisphere began between 5mm (4.5-10.5mm) behind the limen insulae. Length of anterior limiting sulcus was 18.3mm(13.1-24.9mm),superior limiting sulcus was 38.9mm(36.1-49.8mm), inferior limiting sulcus was 32.6mm(26.5-43.7mm)Anterior perforated substance:The anterior perforated substance lies just medial to the limen insulae and serves as an important surgical landmark. The point of entrance of the most lateral LSA was the lateral limit of the anterior perforated substance. The mean distance from the point of entrance of the most lateral LSA into the anterior perforated substance to the medial border of the limen insulae was 11.2mm(range 7.8-18.3mm). The most lateral LSA originat -ed from the M1 segment prior to bifurcation in 7 of 20 hemispheres, from the inferior trunk in 8, and from the superior trunk in 5.Middle cerebral artery:Diameter of the origin was average 3.2mm(2.1-3.8mm), in 90% middle cerebral artery the bifurcation of middle cerebral artery was at the level of, or distal to the limen insula, and it was proximal to the insula in the remaining 10%. Among 20 cerebral hemispheres MCA trunk of 17(85%) cerebral hemispheres were bifurcated. In these bifurcated MCAs 6(20%) hemispheres had superior trunk dominant;7(35%) hemispheres had inferior trunk dominant and in 4(20%) superior and inferior trunks were equal. 3 (15%) MCAs underwent trifurcation. Among trifurcated MCAs 2(10%) superior trunk dominant, middle trunk dominant was 5%and inferior trunk dominant was 0%. Length of M1 segment of MCA was 20mm average(12-28mm),prebifuecation was 15.8mm(6.5-29.2).MCA gave off perforators in all of the cerebral hemispheres, Quantity from the 2-18 range, with an average 11.The perforate arteries of the MCA were divided into medial, middle, and lateral groups. The medial group exit in 10 MCA, ranged in number from 1 to 4, outer diameter 0.18mm(0.12-1.06mm).The medial group number was 1-8,outer diameter was 0.48mm(0.14-1.02mm)exit in all MCA. The lateral group number 1-8,outer diameter was 0.98mm(0.32-1.46mm).The lateral group perforate arteries were developed and big in diameter, Nearly 30% of the lateral group lenticulostriate arteries originate from the pre- or postbifurcation trunks 4.3mm(3-5mm). Some branches arise directly on the bifurcation.An accessory MCA was found, arising from A1 segment. The accessory MCA coursed parallel to the A1 segment in a posterolateral direction to reach the anterior perforated substance. There, the accessory MCA gave rise to perforators in the middle and anterior zones of this region, territory that usually would be supplied by the recurrent artery of Heubner. The accessory MCA followed the direction of the sylvian fissure, where it was located anteriorly, to the branches of the MCA near the roof of the fissure. The accessory MCA bifurcated into anterior branch and posterior branch, the anterior branch sent branches to supply the posterior and lateral portions of the orbital gyri, the posterior branch supply the pars triangularis and opercularis of the inferior frontal gyrus and precentral gurus.Conclusion:The Sylvian fissure was divided into large Sylvian fissure and small Sylvian fissure. It is important for a neurosurgeon to have a good understanding of the microsurgical anatomy of the insula. Knowing of the insular microanatomy is helpful to avoiding neurological complications after the surgery in the insula. The true bifurcation of the middle cerebral artery sometimes occur proximal to the the limen insulae. The anterior perforated substance lies just medial to the limen insulae and serves as an important surgical landmark. Lateral group lenticulostriate arteries arising from a short distance between the prebifurcation to postbifurcation, some arise from the bifurcation. So we should pay attention to these perforaters in the operation. Temporary clipping of the MCA during surgery was not absolutely safe, as perforators in the segment distal to the clip would be devoid of blood supply. Temporary clipping if found to be essential should be applied as distally as possible in the M1 segment. Further, exposure of the MCA should be done along the lateral border, as there are no perforators on this surface. An accessory MCA may increase the difficulty of exposing lesions in the vicinity of the optic chiasm. the accessory MCA is that the vessel is not a hypertrophic change in the recurrent artery of Heubner. Patients with this anomaly may, have an increased risk for developing aneurysms and other neurovascular complications. An accessory MCA can be associated with aneurysms at its junction with the anterior cerebral artery.
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