gms | German Medical Science

Objective: For a comparative analysis we aimed to define the anatomical presentation of the Sylvian fissure (SF) on plain CT scans. Based on Yasargils’ descriptions of different intraoperative anatomical variations of the (SF) an adaptation of the appearance on CT scanning was done in our earlier work. In the current study we determined the distribution of the defined SF types in a normal population and analyze special features of the middle cerebral artery (MCA) in relation to the SF types.

Method: A total of 250 cranial CT scans and an additional 100 CT angiography datasets from patients with normal intracranial findings, who were examined for various issues at our university hospital were reviewed. Five SF types were defined, 1: Straight wide; 2: straight narrow; 3: Wide with herniation of the frontal or temporal lobe, 4: Narrow with herniation of the frontal or temporal lobe; 5: Herniation of temporal and frontal lobe. Length, diameter and branches of the MCA were measured and compared to the SF types. Statistical analysis was done using the Fisher's exact and Chi-square test (SPSS 19). Statistical significance was estimated as p-value <0.05.

Results: We analyzed data of 141 male and 109 female patients (mean age 53.9 y; range 9-91 y). In total, SF 1 was observed in 46 (18.4%), SF 2 in 27 (10.8%), SF 3 in 72 (28.8%), SF 4 in 70 (28%) and SF 5 in 35 patients (14%). Intra-individual symmetric appearance of the SF types was observed in 224 patients (89.6%). N=180 patients (72%) were <70 y/o. In this group the SF 1 was observed in 21 (11.6%), SF 2 in 25 (13.8%), SF 3 in 42 (23.3%), SF 4 in 62 (34.4%) and SF 5 in 30 patients 16.6%. Mean length of the M1 segment was 16.4mm and mean diameter was 2.6mm. A bifurcation was observed in 55.5%, trifurcation in 14.8% and an early M2 branch or false bifurcation in 29.6%. Subgroup analysis showed that M1 length was greater in the narrow SF types (1vs2 and 3vs4), however, without statistical significance.

Conclusions: In this CT imaging based anatomical study, we could show that a twisted and narrow SF (type 4&5) occurred more frequently in patients younger than 70y/o due to brain atrophy with increasing age. The anatomical condition might influence the size and configuration of the proximal medial cerebral artery, which in turn will influence the surgeon’s choice of the approach to the SF. Preoperative evaluation on the basis of the presented data may help to decide for a transsylvian approach or an opening of the SF from its offspring.