ANTERIOR INCISURAL SPACE (AIS): ITS TOPOGRAPHY AND SIZE IN THE CRANIAL CAVITY. POSITION OF THE BASILAR ARTERY APEX IN AIS

Objective: to explore microsurgical anatomy of the anterior incisural space (AIS), its topography and size in the skull, and to assess the topography of the basilar artery apex in AIS and find possible craniometric correlations.

Materials and methods. In this anatomical study, we used 100 non-fixed heads of people who died from somatic pathology without diseases of the central nervous system. All heads were dissected using standard methods. Then we modelled the topography of the tentorial incisure (TI) in the skull  by cutting off the hemispheres at the level of the brain stem in parallel to the free margin of TI. We measured  length and width of TI, analyzed its topography in the cranial cavity, performed TI morphometry, and  measured cranial indices and angular parameters of the skull base relief. Morphometric analysis of our data  was conducted by calculating coefficients and indices. Data analysis was performed using the STATISTICA  Statsoft. Microsurgical anatomy of the AIS and TI was studied using the operating microscope MBS-10 and digital video camera Sony HDR-CX560 E. The photos were taken with a 2–8-fold magnification.

Results. Results. AIS length varied between 14 and 24 mm, whereas its width was between 24.0 and 36.0 mm. Almost half of all TI samples (42%) had AIS with a length of 17–19 mm. In all series of measurements, the length of the AIS was minimal – 14 mm (6%); 15–16 mm (19%), medium – 17–19 mm (42%), large – 20–22 mm (24%) and maximum – 23–24 mm – 9%. AIS were divided by TI types into four groups: A, B, C,  and D. Minimum and small AIS were grouped into into ‘short-size AIS’ [14–16] mm, while large and maximum AIS were grouped into ‘long-size AIS’ [20–24] mm. The proportions of short AIS, long AIS, and medium AIS were 25%, 33%, and 42%, respectively. In group A, long-size AIS were found in 53.68% of samples; in garup B, long-size AIS were found in 3.7% of samples, in group C, there were only large AIS–33.3%; in group D, the maximum size of 24 mm was more frequent – 18.2 %, but the total number of samples with large AIS  was two times lower–27.3% than in group A. Group A (sub- and brachycephaly) had the highest percentage of long AIS with a length of 20–24 mm (~54% of cases). The position of the BA in the AIS depends on the AIS length and clivus tilt.

Conclusion. The size and topography of the AIS in the cranial cavity vary significantly; this must be taken into account when planning neurosurgical approaches. The concept of limited AIS boundaries, their structural flexibility in terms of surgical approach is the basis for choosing an optimal approach or its direction. The size  of the AIS, its anatomical structure, and topography of the borders, access paths through AIS, possibility of  manipulations with the content and boundaries of the AIS, the degrees of freedom or limits in acceptable surgical corridors, etc. should be taken into account when planning surgical intervention and choosing an  optimal approach. 

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