Variations of shape, length, branching, and end trunks of M1 segment of middle cerebral artery

Introduction: The middle cerebral artery is divided into four segments: proximal M1, insular M2, opercular M3 and cortical M4. M1 extends from the bifurcation point of ACI at ACA and ACM to the insula threshold, laterally from chiasma opticum, laterally from tractus opticus and caudally from trigonum olfactorium, directed laterally, dorsally and rostrally. Early division of the M1 segment into the fi nal trunk is possible at any of the fi rst points of the limb insulae. Material and methods: The study of the micromorphological and morphometric characteristics of the M1 segment was performed in 25 brain (50 ACM preparations) obtained from autopsy of both sexes of different ages without pathological changes. For the removal of the brain from the skull we used the usual technique of obduction. Results: This segment was arch-shaped, in 32 (64%) arteries, rarely S-shaped, in 12 (24%) arteries, much less straight alignment, in 6 (12%) arteries. The average length of the M1 segment of the S shape was 20.6±3.31mm, with a 19.8mm 4.41mm arch shape, while the straight shape was 16.9±3.62mm. The average S-shaped diameter was 2.7±0.51mm, arched 2.6±0.47mm, straight form 2.6±0.36mm. Variations of M1 branching were: common in 38 cases, early branching in 12 cases, joint trunk with cortical branch in 9 cases, lateral cortical branch in 21 cases, fi nal bifurcation in 24 cases, fi nal trifurcation in 13 cases, duplication in 1 case and M1 accessory in just 1 case. Conclusion: True bifurcation refers to the division of the M1 segment into two fi nal trunks. In cases where the strong joint cortical branch trunk divides from segment M1, while dividing into two terminal trunk immediately after ACM knee formation, it is described as false branching of M1 segment into three terminal branches. Research Article Variations of shape, length, branching, and end trunks of M1 segment of middle cerebral artery Valvita Reçi* and Sadi Bexheti Department of Anatomy, Faculty of Medical Sciences, University of Tetova, Republic of North Macedonia Received: 29 October, 2019 Accepted: 21 November, 2019 Published: 22 November, 2019 *Corresponding author: Valvita Reçi, MD, PhD, Department of Anatomy, Faculty of Medical Sciences, University of Tetova, Republic of North Macedonia, E-mail: valvitareci@hotmail.com


Introduction
Middle cerebral artery (ACM), in addition to anterior cerebral artery (ACA), is the largest, lateral branch of the internal carotid artery, a. carotis interna (ACI) [1]. It is divided into the fusion of the carotid cistern (cisterna carotica) and the Sylvii cistern of the lateral hull of the large brain (cisterna fossae lateralis cerebri). Further down of its path, lies at the outer cavity of the large brain (fossa lateralis cerebri), between the temporal and frontal lobe of the telencephalon. On the surface of the insula, where the ACM is located, it is divided into two, three or more primary trunks, which are further subdivided and from which the cortical (leptomeningeal) branches will be separated. After exiting the operculo-insular region, through Sylvius furrow, the breeze-shaped cortical branches head toward their vascularization fi eld [2][3][4] (Figure 1). It is accepted to divide the ACM into four parts: the proximal part, pars sphenoidalis s. horisontalis (segmentum M1), insular, pars insularis (segmentum M2), opercular, pars opercularis (segmentum M3) and cortical, pars corticalis (segmentum M4) [5].
The proximal (M1) segment extends from the ACI and ACM bifurcation point to the insula threshold (limen insulae). The M1 segment of the ACM extends laterally from the chiasma opticum, rostrally from the tractus opticus and caudally from the trigonum olfactorium, directed laterally, dorsally and rostrally.
Dorsally to the M1 segment is the outer part of the substantia perforata anterior, the prepiriform part of the cortex of large brain and stria olfactoria lateralis, while the posterior edge of the small wing of the sphenoidal bone (ala minor ossis sphenoidalis) is rostrally to the artery. At the level of the limen insulae the M1 segment immediately turns dorsally and caudally and forms the ACM knee. Early division of the M1 segment into the terminal trunk is possible at any of the fi rst points of the insula. 2.5% to 21% of cases are described [6][7][8] (Figure 2). topographic ratios of the surrounding arteries are shown in the diagrams prepared in advance.
For evaluating the signifi cance of the obtained data we used descriptive and statistical analytical methods, especially the determination of absolute and relative frequencies, as well as the arithmetic mean with standard deviation, as well as the quadratic test and Studen T-test for evaluating the signifi cant differences. All data attempted are tabular and graphical.

Material and Methods
The study of the micromorphological and morphometric

Results and Discussion
We studied the M1 segment of the ACM in 50 arteries. This segment was in most cases arch-shaped, in 32 (64%) artery (I), rarely in S-shaped, in 12 (24%) artery (II), whereas much less frequently it had straight alignment, in 6 (12%) of arteries (III) ( According to the other authors data [12,14] Other authors cite extreme values of 2.4mm to 4.6mm, on average 3.0mm, 3.9mm, respectively [9][10][11]. It is evident that there are differences between the data from different authors.
Our obtained data are slightly smaller, however, all of our measurements were made on gelatin-injectable preparations using reliable measurement software and the results are accurate. Measurements in native preparations as well as blood vessels in angiography could not be more accurate than our data. Other authors [13][14][15] also do not provide data on the forms of the M1 segment, and also in the literature there is no data on the size of different morphological types of the M1 segment.

Variations of length, branching and trunk of segment M1
We describe two length variations of M1 segment: 1) Common M1 segment, which most commonly ends at the level of the insula threshold (limen insulae), in 38 (76%) hemispheres, at the place where the knee is formed, a fl exure of 90˚. Its length was from 15.1mm to 28.2mm (21.2±3.54mm on average). The diameter of the M1 segment in these cases ranged from 1.8mm to 3.6mm (2.6±0.45 on average). The artery then immediately turns backwards and above, and passes into the M2 insular segment through the insula cortex, where it gives the upper and lower common trunk of the cortical branches ( Figure.  2) Early branching of the M1 segment was observed in 12 (24%) hemispheres. In these cases, the short M1 segment gives the fi nal branch in front of the ACM knee, medially from the limen insulae. The length of this segment, measured from carotid bifurcation to ACM terminal branching, ranged from 11.8mm to 16.5mm (14.9±1.2mm on average). The diameter of        We also describe three possible variations of M1 segment branching: 1a) Separation of the strong common trunk of cortical branches of the M1 segment that we have encountered in 9 (18%) cases (Figure 7). 1b) Individual leptomeningeal branches larger than 1.0 mm in diameter, are also directly separated from the M1 segment into 21 (42%) hemispheres, most often a. anterior temporalis, a. temporalis media and a. frontobasalis. The most constant and smallest cortical branch of the M1 segment, smaller than 1.0 mm in diameter, was a. polaris temporalis, which was present in 47 (94%) cases (Figure 8 C,  2c) The fi nal lower trunk of the M1 segment with a larger caliber has been more frequently present, in 24 (48%) cases ( Figure 8 F) (Table 3) (Graph 4).
All data on variations of length, branching and trunks of M1 segment are presented in tabelar and graphical way (Table   3) (Graph 4).

Conclusion
Most authors emphasize that true branching ("true bifurcation") belongs to the division of the M1 segment into two almost identical end-trunks. On the other hand, in cases where the strong common trunk of cortical branches divides from the M1 segment, while the rest of the artery continues its course and divides into two terminal trunks immediately after the formation of ACM knee, dorsally and caudally by the limen insulae, is described as false branching of M1 segment into three terminal branches. Some authors even mention also the trifurcation, sometimes and the tetrafurcation ACM, respectively, the existence of three or four fi nal trunks. By doing so, while the false branching is immediately proximal to the fi nal branching, it gives the wrong impression of the existence of three terminal ACM trunks.