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Morphologic Variations of end Trunks of M1 Segment of Middle Cerebral Artery

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 field (Figure 1) [2-4].

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 first points of the insula. 2.5 to 21% of cases are described ( Figure 2) [6][7][8].

Material and Methods
The study of the micromorphological and morphometric characteristics of the M1 segment of the middle cerebral artery and its branches was performed in 25 brain (50 ACM preparations) obtained from autopsy of both sexes (11 females and 14 males), aged different (from 46 to 84 years, 68.4 on average) without pathological changes of brain structures. For the removal of the brain from the skull we used the usual technique of abduction.
Microdissection of the trunk and injected perforant branches of the M1 segment of ACM and all measurements were done on the Leica MZ6 stereomicroscope. All the preparations were photographed with the SX170IS digital camera, and all details were recorded under a stereomicroscope using the Leica DFC295 digital camera. For the morphometric analysis, Leica Interactive Measurements software was used (Figure 3.5). The perforant branches of the M1 segment of the ACM and the topographic ratios of the surrounding arteries are shown in the diagrams prepared in advance.
For evaluating the significance 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 significant differences. All data attempted are tabular and graphical.
Our measurements have shown that the mean diameter of the S-shaped M1 segment was 2.7 ± 0.51 mm, from 1.9 to 3.5 mm, respectively. The M1 arc-shaped segment had an average diameter slightly smaller, 2.6 ± 0.47 mm, from 1.8 to 3.6 mm. Similar diameter values also had the straight shape of the M1 segment, without curves, averaging 2.6 ± 0.36 mm, from 1.9 to 2.9 mm. In all 50 observed hemisphere, the mean diameter of the M1 segment was 2.6 ± 0.47 mm, from 1.8 to 3.6 mm ( Table 2.) (Graph 3).
Other authors cite extreme values of 2.4 mm to 4.6 mm, on average 3.0 mm, 3.9 mm, 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 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 [13][14][15].

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 flexure of 90˚. Its length was from 15.1 to 28.2 mm (21.2 ± 3.54 mm on average). The diameter of the M1 segment in these cases ranged from 1.8 to 3.6 mm (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 ( Fig. 4.8 A, 4.1, 4.2) ( Table 3) (Graph 4).
2) Early branching of the M1 segment was observed in 12 (24%) hemispheres. In these cases, the short M1 segment gives the final 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 11.8 to 16.5 mm (14.9 ± 1.2 mm on average). The diameter of the M1 segment in these cases ranged from 1.9 to 3.5 mm ( 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, 4.2) (   All data on variations of length, branching and trunks of M1 segment are presented in tabelar and graphical way (Table 3) (Graph 4).