Introduction
Although the wrinkles of the outermost layer of the brain vary among people and even between two right and left hemispheres, anatomical folds such as Sylvian fissure and central sulcus are more stable (the so-called anatomical landmarks) and their differences among individuals are not significant. Indeed, Sylvian fissure is the most recognizable part of the outer layer of the brain and thus Sylvian fissure and central sulcus are the main anatomical indices during brain surgery. Moreover, detailed knowledge of their size and distance from other anatomical indices such as the frontal pole, and detailed information about the distance of important locus from these markers are necessary, especially for specific surgeries such as frontal and temporal lobectomy. Nowadays, different complex apparatuses exist for image guided surgery [1,2]. Because of setting of these systems for patients before the start of surgery, their accuracy may be decreased after skull incision and removal of CSF due to small changes in the brain position [3,4]. Thus, no assistive devices can replace the surgeon’s anatomical knowledge.
Although brain wrinkles become more visible in imaging techniques such as MRI [5-14], they sometimes have inaccuracies [15-19]. Furthermore, recognizing them during surgery is very difficult due to being covered by vessels and arachnoid and small accessible space to the brain surface [20]. Therefore, the study of fixed area in wrinkles and skull surface and their anatomical relations and distances for diagnosis of other wrinkles during brain surgery are vital, as transsulcal and transfissural methods are used to reach the lesion in many of the surgeries [21,22]. Indeed, brain wrinkles are similar to hallways and corridors which guide the surgeons to the underlying lesions [23]. In the present study, the cerebral surface landmarks in human fresh autopsy specimens were investigated.

Methods and Materials/Patients
Samples
After receiving the legal license from the head of Forensic Medicine Center of Rasht, 37 fresh autopsy brains were enrolled from December 2015 to June 2016. Among them, four samples were excluded due to various reasons such as direct trauma to the brain surface. All samples were fresh and death had occurred no more than two days before.

Measurements
Some surface markers were measured using scale in millimeter at both sides. These markers included length of central sulcus from beginning near the longitudinal fissure to the end slightly above the posterior branch of the Sylvian fissure (Figure 1A), length of Sylvian fissure just at the outer surface of the brain (only the posterior branch of Sylvian fissure) from beginning in in the place of trifurcation to horizontal anterior branch, ascending anterior branch and posterior branch to the end at the temporal lobe (Figure 1B), distance of frontal pole (the most anterior area of frontal lobe in the sideview of brain hemispheres) to midpart of longitudinal fissure (Figure 1C) and thickness of upper, middle, and lower temporal gyri (Figure 1D).

 

Statistical Analysis
Data were analyzed using SPSS (Version 19), length difference equal to or more than five millimeter (mm) in central sulcus, posterior branch of Sylvian fissure and distance of central sulcus to frontal pole and thickness difference equal to or more than one mm in temporal lobe gyri between right and left hemispheres were considered as significant difference.

Results
Totally, 66 hemispheres belonging to 33 cadavers, eight females (24.2%) and 25 males (75.8%) were evaluated. Mean age of the samples was 45.93 years old. The measured parameters are presented in table 1.
In this study, 13 and 11 samples (n=24, 72.8%) had longer length of Sylvian fissure in the right and left sides and nine samples showed no difference between two sides. In the central sulcus, nine and 18 samples (n=27, 81.8%) had longer length in the right and left sides and six samples had similar length in two sides. Distance of frontal pole to longitudinal fissure in 12 samples was longer in the right compared to that in the left side. This distance in 13 cases was longer in left side against right side (totally 25 samples, 75.7%). In eight samples, this distance was equal in both sides. Upper
 

 

temporal gyrus was thicker in 13 samples at right side and 16 samples at left side (n=29, 87.7%) and four samples showed no difference between two sides. About middle temporal gyrus,  10 and 13 samples (n=23, 69.6%) were thicker in the right and left sides and 10 samples had similar thickness in two sides. Finally, the thickness of lower temporal gyrus in 11 samples was greater in right compared to the left side. This thickness in 11 cases was greater in left side against the opposite side (totally 22 samples, 66.6%). In 11 samples, this thickness was equal in both sides.

Discussion
In the study of Vannier and colleagues, quantitative associations of MRI of brain cortex with real cadaver brains were evaluated [24]. But several studies were performed on the cadaver brains [25, 27-29], mostly on the formalin fixed brains. Harkey et al. evaluated five formalin fixed brains for their surface wrinkles [30]. In another study, the anatomy of middle temporal part of 26 formalin fixed brains (52 hemispheres) was studied [31] and in continuation of that work with similar authors, the areas around the Sylvian fissure in 60 formalin fixed hemispheres and 12 cadaver brains were investigated [32]. Although the study of Ribas et al. on the 16 formalin fixed brain [23] was a fully described and exact study with evaluation of several anatomical indices of brain surface, our evaluated parameters were not investigated, neither in their studies nor in the other above mentioned studies.
In the present study, difference in mean length of Sylvian sulcus between hemispheres was less than one mm (75.61 mm and 74.55 mm for right and left sides, respectively) which can be ignored. Mean of the central sulcus was 94.85 mm in the right side and 97.24 mm in the left side, which the difference was not significant. Mean distance of central sulcus to the right frontal pole was 81.27 mm and to the left frontal pole was 82.36 which was not a significant different taken together. Thickness of upper temporal gyrus in the left side was 15.33 mm and in the right side was 14.66 mm, which showed no significant difference. Mean thickness of middle gyrus of temporal lobe was 16.42 mm in the left side and 16.63 in the right side and
this difference was not significant. About the lower gyrus of temporal lobe, mean thickness was 10.30 in the right side and 10.7 in the left side and this difference can be ignored. Totally, no significant differences were detected in the measured value between right and left brain hemispheres.

Funding
None

Conflicts of Interest
The authors declare that they have no conflicts of interest.

Authors' Contribution
Conception and Design: Mehryar Mashouf
Data Collection: Maryam Kiaee
Drafting the Article: Maryam Kiaee, Elham Bidabadi
Critically Revising the Article: Mehryar Mashouf, Elham Bidabadi
Reviewed Submitted Version of the Manuscript: Mehryar Mashouf, Elham Bidabadi
Approved the Final Version of the Manuscript: Mehryar Mashouf

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Comments
Technological progress made neurosurgery more safe and effective. Functional MRI, tractography, neuronavigation, brain stimulation and the others are important tools for a neurosurgeon, but all these resources are as nothing without a deep and comprehensive anatomical knowledge. The best way to study and learn the anatomy is specimen and anatomy lab. For this reason, this paper goes in the right direction. It might be interesting to extend this study with more surgical consideration with regard to surgery of gliomas.