Jean Paul Lejeune

Biomechanical wall properties of human intracranial aneurysms resected following surgical clipping (IRRAs Project)

BACKGROUND AND PURPOSE Individual rupture risk assessment of intracranial aneurysms is a major issue in the clinical management of asymptomatic aneurysms. Aneurysm rupture occurs when wall tension exceeds the strength limit of the wall tissue. At present, aneurysmal wall mechanics are poorly understood and thus, risk assessment involving mechanical properties is inexistent. Aneurysm computational hemodynamics studies make the assumption of rigid walls, an arguable simplification. We therefore aim to assess mechanical properties of ruptured and unruptured intracranial aneurysms in order to provide the foundation for future patient-specific aneurysmal risk assessment. This work also challenges some of the currently held hypotheses in computational flow hemodynamics research. METHODS A specific conservation protocol was applied to aneurysmal tissues following clipping and resection in order to preserve their mechanical properties. Sixteen intracranial aneurysms (11 female, 5 male) underwent mechanical uniaxial stress tests under physiological conditions, temperature, and saline isotonic solution. These represented 11 unruptured and 5 ruptured aneurysms. Stress/strain curves were then obtained for each sample, and a fitting algorithm was applied following a 3-parameter (C(10), C(01), C(11)) Mooney-Rivlin hyperelastic model. Each aneurysm was classified according to its biomechanical properties and (un)rupture status. RESULTS Tissue testing demonstrated three main tissue classes: Soft, Rigid, and Intermediate. All unruptured aneurysms presented a more Rigid tissue than ruptured or pre-ruptured aneurysms within each gender subgroup. Wall thickness was not correlated to aneurysmal status (ruptured/unruptured). An Intermediate subgroup of unruptured aneurysms with softer tissue characteristic was identified and correlated with multiple documented risk factors of rupture. CONCLUSION There is a significant modification in biomechanical properties between ruptured aneurysm, presenting a soft tissue and unruptured aneurysms, presenting a rigid material. This finding strongly supports the idea that a biomechanical risk factor based assessment should be utilized in the to improve the therapeutic decision making.

Outcome in 53 patients with spinal cord cavernomas

BACKGROUND Prevalence of cerebral cavernomas in the general population is close to 0.5%. In contrast, SCCs are rare. The aim of this study was to determine the outcome of SCC in a large sample of patients. METHODS Clinical and neuroradiologic findings were retrospectively collected in a multicentric study. Diagnosis was based on pathologic criteria or MR findings. RESULTS Fifty-three patients were included (26 males, 27 females). Mean age at onset of symptoms was 40.2 years (11-80 years). Initial symptoms were progressive (32) or acute myelopathy (20). One case was asymptomatic. Triggering factors were found in 14 of the patients (26%). Clinical symptoms were related to spinal cord compression (27) and hemorrhage (22). Spinal cord cavernoma was thoracic in 41 cases and cervical in 12. Mean size of the lesions was 16.3 mm (3-54 mm). In the 40 surgical patients, long-term follow-up was available in 37 cases for a mean time of 7.3 years (0.4-50 years). During the follow-up period, 20 patients improved, 6 remained on their preoperative baseline, and 11 got worse. Surgical improvement was more often found in posterior rather than anterior location. Using McCormick classification, 22 patients were autonomous (grades 1-2), 12 handicapped (grade 3), and 3 bedridden (grade 4) at the end of the follow-up. CONCLUSIONS This study has defined clinical and MR patterns of spinal cavernomas. Surgery lastingly improved more than half of the patients.

Intracranial Aneurysmal Pulsatility as a New Individual Criterion for Rupture Risk Evaluation: Biomechanical and Numeric Approach (IRRAs Project)

BACKGROUND AND PURPOSE: The present study follows an experimental work based on the characterization of the biomechanical behavior of the aneurysmal wall and a numerical study where a significant difference in term of volume variation between ruptured and unruptured aneurysm was observed in a specific case. Our study was designed to highlight by means of numeric simulations the correlation between aneurysm sac pulsatility and the risk of rupture through the mechanical properties of the wall. MATERIALS AND METHODS: In accordance with previous work suggesting a correlation between the risk of rupture and the material properties of cerebral aneurysms, 12 fluid-structure interaction computations were performed on 12 “patient-specific” cases, corresponding to typical shapes and locations of cerebral aneurysms. The variations of the aneurysmal volume during the cardiac cycle (ΔV) are compared by using wall material characteristics of either degraded or nondegraded tissues. RESULTS: Aneurysms were located on 6 different arteries: middle cerebral artery (4), anterior cerebral artery (3), internal carotid artery (1), vertebral artery (1), ophthalmic artery (1), and basilar artery (1). Aneurysms presented different shapes (uniform or multilobulated) and diastolic volumes (from 18 to 392 mm3). The pulsatility (ΔV/V) was significantly larger for a soft aneurysmal material (average of 26%) than for a stiff material (average of 4%). The difference between ΔV, for each condition, was statistically significant: P = .005. CONCLUSIONS: The difference in aneurysmal pulsatility as highlighted in this work might be a relevant patient-specific predictor of aneurysm risk of rupture.