Analysis of a bleeding mechanism in patients with the sylvian arachnoid cyst using a finite element model

The sylvian arachnoid cyst (AC) is a common benign disease; however, it sometimes leads to subdural or intracystic hemorrhage without major trauma. The reason of easy bleeding of the AC is not fully understood. The purpose of this study was to investigate the bleeding mechanism of the sylvian AC in biomechanical aspect and suggest treatment guidelines.

A finite element (FE) model of normal male adult head/brain was developed and validated by comparison with cadaveric experimental studies. Based on the normal FE model, two sylvian AC models with different sizes (mean size, 55.5 cm(3); large size, 75.2 cm(3)) were developed. To simulate the interface between the dura mater and the arachnoid membrane, spot-weld constraints were assigned. The vulnerability of vein rupture was forecasted with calculated shear force at the spot-weld elements (SFSW). Simulation was performed for four different loading directions.

The newly developed normal FE models showed reliable biomechanical responses comparable with the cadaveric experiments. The sylvian AC model showed significantly increased SFSW compared with normal model. As AC size increased, higher shear force was generated at the spot-weld element of outer wall of sylvian AC regardless of impact directions.

Outer wall of sylvian AC receives higher shear force comparing with normal brain, which is a possible cause of vulnerability to bleeding. Although the size-reducing surgery may decrease bleeding risk of sylvian AC, clinicians need to consider the rare incidence of AC bleeding and unsatisfactory volume reduction in many cases of fenestration.