Short summary

With the present study, we wish to 1) develop a quantitative indentation based method of measuring the viscoelastic properties of meningioma specimen ex vitro 2) predict qualitative perioperative consistency with pre-operative Magnetic Resonance Elastography (MRE) measured viscoelasticity and verify the results with rheometry measured viscoelasticity in meningiomas

Rationale

Meningioma resection is complicated by variations in tumor consistency. Meningiomas are common intracranial tumors with an estimated prevalence of 50.4 - 70.7/100 000 in the US population 1, 2. The incidence in Nordic countries is approx. 1.9 for males and 4.5 for females per 100.000 3, 4, with a similar incidence in the US population 5. The preferred treatment of symptomatic meningiomas is surgical resection 6. The consistency of meningiomas is a major factor for operative strategy and patient counseling 7. Meningiomas span from soft tumors, almost entirely removable by suction, to hard masses requiring piece-meal resection or ultrasonic aspiration 8. The resectability of meningiomas depend on several factors including tumor location, consistency and adherence to surrounding tissue. The resection grade has prognostic implications as it is associated with recurrence rate 9, 10. Hard meningiomas are often technically challenging to remove and the risk of iatrogenic incidences may increase. The introduction of less invasive techniques such as endoscopic approaches augments the need for pre-operative acquisition and knowledge about tumor consistency, as hard tumors are impossible to resect minimally invasively 11-14. These challenges have motivated several, generally unsuccessful attempts to predict the consistency of meningiomas using Magnetic Resonance Imaging (MRI) techniques 7. Magnetic Resonance elastography (MRE) is a novel imaging technique that allow quantification of mechanical properties that determine tissue consistency. Brain MRE research is still at a pre-clinical stage, but technical advances, improved understanding of soft tissue rheological impact, and larger samples are likely to enable future clinical introduction. Magnetic resonance elastography is a phase contrast based MRI technique that image the spread of mechanical waves in tissues. The acquired data can be used to display several aspects of tissue mechanics such as elastic and viscoelastic behavior, tissue damping properties etc. The acquired parameters are related to haptic properties such as consistency that can be evaluated by touch. Simplified MRE can be described in three stages (figure 1) 15-17. First, stress is introduced by mechanical waves that causes tissue excitation (i.e. deformation). Image accusation apply phase contrast MRI sequences to record the propagation of waves in tissues. Inversion describes a series of complex mathematical operations that extract information about tissue properties including the complex shear modulus (G*) which has an elastic component called the storage modulus (G'), and a viscous component termed the loss modulus (G''). The shear modulus phase angle describes the relative contribution of G' and G'' to G*. Because soft tissues are viscoelastic they display a non-linear stress strain response. This has several implications to acquisition strategies 18. Murphy et al. 19 correlated the median storage modulus (G') of 12 meningiomas with intraoperative consistency grading. MRE measured stiffness correlated significantly with the surgeons' assessment (p = 0.023). However, some degree of overlapping data points and a semi quantitative analytic approach limits the direct translational value of the study. Huges et al. 20, applied a higher resolution MRE technique in their study on meningioma consistency and mechanical heterogenicity. The correlation between surgical grading and MRE measured consistency (G') was significant (p = 0.02). The positive predictive value (PPV) and specificity for detecting hard and heterogeneous tumors were 100% 20. In predicting homogeneity, MRE had a specificity of 78% and a PPV of 75%. In predicting a soft consistency, PPV was 86% but the specificity was only 33% 20. MRE had 60% specificity in ruling out hardness 20.

Description of the cohort

Patients scheduled for surgical resection of an intracranial meningioma

Collaborating researchers and departments

Department of radiology, Mayo Clinic

Department of Radiology (OUH)

Food lab, SDU