İnbh’da Pia-Araknoid Kompleksinin Patofizyolojik Mekanizmaya Olan Etkisinin Volumetrik İncelenmesi

Abstract

Introduction and Objective: Normal pressure hydrocephalus (NPH) is a significant disease characterized by enlarged ventricles and a triad of walking, cognition, and micturition disorders. The first hypothesis developed for this disease, first proposed by Solomon Hakim, is based on Pascal's law, suggesting that the growth on the ventricular surface increases the effective expansive force due to the water hammer effect, resulting in tension in the white matter and the emergence of symptoms. In recent years, its importance has been better understood with epidemiological studies reporting a prevalence of up to 3% in the population over 65 years of age. In NPH, where surgery plays a significant role in treatment, the complication rates of V/P shunt have been reported up to 38%, making it essential to understand the pathophysiology correctly to make the right clinical decision.

Most studies on the pathophysiology of the disease consider increased ICP, periventricular CSF leakage, and impaired cerebral perfusion as the most critical mechanisms in the development of NPH, based on the effective expansive force applied to the ventricles. However, there are fewer studies investigating the contribution of gray matter damage to the pathophysiological mechanism, and the arachnoid trabecula and pial integrity have not been studied in this context. Moreover, although the presence of jet flow in the cisterns, vallecula, and proximal sylvian cistern in NPH has been demonstrated, it is unclear how this jet flow contributes to the pathophysiology. The aim of this study is to test the Arachnoid Traction and Pial Dehiscence hypothesis (briefly Pial-Arachnoid Dehiscence hypothesis), which we claim could be one of the main mechanisms of cortical gray matter damage in iNPH, using MRI volumetry methods.

Material and Method: The patient group consisted of 72 iNPH patients diagnosed and operated by a multidisciplinary team at Hacettepe University Faculty of Medicine, Department of Brain and Nerve Surgery between 01.06.2019-01.12.2022. Eight patients with thin sections (number of sections >50) were excluded, and the MRI images of the remaining 64 patients were converted to nifti format using MRIcroGL software and uploaded to the volbrain software. Eight patients whose images could not be processed by the volbrain software and seven patients with incorrect volumetry were excluded from the study. The patient group consisted of 49 patients. The control group was formed by selecting patients over 55 and under 85 years old with high-resolution MRIs who presented with complaints of dizziness, headache, and syncope at Hacettepe University Faculty of Medicine outpatient clinic between 01/3/2021 and 01/03/2023. Sixteen patients were selected, maintaining the male/female ratio. 3D Axial T1 MPRAGE images obtained from GE's SIGNA Architect device belonging to Hacettepe University Faculty of Medicine, Department of Radiology, were used for the patients' MRI images.

All images were processed by denoising, coarse inhomogeneity correction, MNI space registration, fine inhomogeneity correction, intensity normalization, intracranial cavity discrimination, gray-white matter and CSF discrimination, and finally, gray matter (and deep nuclei) segmentation according to the Neuromorphometrics atlas, obtaining volumetric data.

Results: Our results showed that the highest change in fluid compartments in iNPH was a 317.37% increase in lateral ventricles, followed by a 102.99% increase in the size of the 3rd ventricle. Cortical gray matter volume reduction in the patient group was recorded at 10.51%, while subcortical gray matter volume reduction was 16.15%. No statistically significant difference was found between white matter volumes. The highest volume reduction among cortical gray matter lobes occurred in the temporal and occipital lobes (respectively -11.24, -10.31, p<0.05). In the patient group, a significant cortical volume reduction was observed in the perisylvian region, particularly a 27.22% reduction in the frontal operculum and a 19.68% reduction in the Heschl Gyrus. Additionally, a statistically significant volume reduction was observed in the area surrounding the vallecula.

Discussion and Conclusion: In our study, the volume loss in the perisylvian region was shown to be consistent with the literature . Furthermore, examining the cortical volume loss in the perisylvian region with its anatomical features showed that the jet flow of fluid exiting the ventricles and the resulting barotrauma could indeed be a contributing factor to cortical volume loss in iNPH. However, direct evidence of pial dehiscence was not demonstrated in our study. In conclusion, it was not possible to reach a definitive judgment on the accuracy of the Arachnoid Trabecular Traction and Pial Dehiscence hypothesis, but our findings have formed the belief that the hypothesis and the outcomes it describes play a significant role in iNPH pathophysiology. It has been concluded that further studies on the subarachnoid CSF system and arachnoid trabecular features are needed for a better understanding of iNPH pathophysiology.