The effect of aneurismal-wall mechanical properties on patient-specific hemodynamic simulations:two clinical case reports

Hemodynamic factors such as the wall shear stress play an important role in the pathogenesis and treatment of cerebral aneurysms. In present study, we apply computational fluid-structure interaction analyses on cerebral aneurysms with two different constitutive relations for aneurismal wall in order to investigate the effect of the aneurismal wall mechanical properties on the simulation results. We carry out these analyses by using two patient-specific models of cerebral aneurysms of different sizes located in different branches of the circle of Willis. The models are constructed from 3D rotational angiography image data and blood flow dynamics is studied under physiologically representative waveform of inflow. From the patient models analyzed in this investigation, we find that the deformations of cerebral aneurysms are very small. But due to the nonlinear character of the Navier-Stokes equations, these small deformations could have significant influences on the flow characteristics. In addition, we find that the aneurismal-wall mechanical properties have great effects on the deformation distribution of the aneurysm, which also affects the wall shear stress distribution and flow patterns. Therefore, how to define a proper constitutive relation for aneurismal wall should be considered carefully in the hemodynamic simulation.

Application of Keyhole Microneurosurgery in China

INTRODUCTIONMicroneurosurgery made its debut in the early 1960s. It became popular in the medical field and became a primary operation method in neurosurgery since it improved the efficacy of neurosurgery with a less surgery-related injury. Over the past five decades, the accumulation of experience of microsurgery, improvement of microsurgery techniques, refined micro-instruments, and advanced preoperative diagnostic imaging allowed the evolution of microneurosurgery techniques and further reduced surgery-related trauma.

PATIENT-SPECIFIC BLOOD DYNAMIC SIMULATIONS IN ASSESSING ENDOVASCULAR OCCLUSION OF INTRACRANIAL ANEURYSMS

According to recent studies, there are various potential predictors for surgical outcome for cerebral aneurysms. An accurate surgical outcome assessment would help make better-informed decisions and avoid the risk of rebleeding. It is well known that hemodynamic factors play an important role in the pathogenesis and treatment of intracranial aneurysms. In this article, a computational fluid dynamic analysis is applied to one patient-specific model of the cerebral aneurysm located at the tip of basilar artery, by which the differences of hemodynamic parameters before and after endovascular treatment may be evaluated. Based on the model, we show that the flow behavior near the neck of the aneurysm sees great differences after endovascular treatment as compared with that before treatment, which also affects the wall shear stress and the displacement distribution. In addition, our whole simulation process is based on a series of CFD commercial software packages, which are easily available for doctors to implement such a method in their daily practice. These results would be used to assess the outcome of endovascular treatment for the aneurysm occlusion.

EFFECTS OF PARENT ARTERY SEGMENTATION AND ANEURISMALWALL ELASTICITY ON PATIENT-SPECIFIC HEMODYNAMIC SIMULATIONS

It is well known that hemodynamics and wall tension play an important role in the formation, growth and rupture of aneurysms. In the present study, the authors investigated the influence of parent artery segmentation and aneurismal-wall elasticity on patient-specific hemodynamic simulations with two patient-specific cases of cerebral aneurysms. Realistic models of the aneurysms were constructed from 3-D angiography images and blood flow dynamics was studied under physiologically representative waveform of inflow. For each aneurysm three computational models were constructed： Model 1 with more extensive upstream parent artery with the rigid arterial and aneurismal wall, Model 2 with the partial upstream parent artery with the elastic arterial and aneurismal wall, Model 3 with more extensive upstream parent artery with the rigid wall for arterial wall far from the aneurysm and the elastic wall for arterial wall near the aneurysm. The results show that Model 1 could predict complex intra-aneurismal flow patterns and wall shear stress distribution in the aneurysm, but is unable to give aneurismal wall deformation and tension, Model 2 demonstrates aneurismal wall deformation and tension, but fails to properly model inflow pattern contributed by the upstream parent artery, resulting in local misunderstanding Wall Shear Stress （WSS） distribution, Model 3 can overcome limitations of the former two models, and give an overall and accurate analysis on intra-aneufismal flow patterns, wall shear stress distribution, aneurismal-wall deformation and tension. Therefore we suggest that the proper length of extensive upstream parent artery and aneurismal-wall elasticity should be considered carefully in establishing computational model to predict the intra-aneurismal hemodynamic and wall tension.

Management of intracranial invasive olfactory neuroblastoma

Background Olfactory neuroblastoma （ONB） is a rare tumor that often arise from the nasal cavity. The aim of this study was to investigate the clinical characteristics and treatments of intracranial invasive ONB. Methods Between July 2001 and August 2005, 5 patients with intracranial invasive ONB were treated in our department. Their clinical features, radiological and pathological characteristics, and surgical treatments were analyzed. Among the 5 patients, 1 received transnasal biopsy, and 4 were operated through the transfrontal or extended bifrontal approaches to reconstruct the skull base. After the operation, all the patients received radiotherapy, and one received chemotherapy. They were followed up for 6 to 45 months. Results The ONB was resected totally in the 4 patients. In all the patients, nasal obstruction was alleviated without cerebrospinal fluid leakage. The visual acuity was improved in 3 patients, who had a decreased visual acuity before the operation. Two patients had metastasis into the lumbosacral spinal canal 6 and 8 months after the operation, one of them received a second operation and the other died. Conclusion ONB has no specific symptoms. Intracranial ONB should be resected as far as possible, and treated by radiotherapy after the operation.