Human Arachnoid Granulation Topography and Surface Area Quantification: Significance for PTC

Abstract

Abstract: : Purpose: 1.) To measure en–face surface area of human arachnoid granulations (AGs) on a standardized superior view of the brain. 2.) To topographically map distribution of AGs. 3.) To correlate these measurements with donor age. AGs are small herniations of the arachnoid membrane associated with cerebrospinal fluid (CSF) drainage into venous sinuses. Increased resistance across AGs with associated increased CSF pressure is implicated in the pathogenesis of pseudotumor cerebri (PTC). In addition to providing topographic and age–related data, these measurements provide input to our in vitro CSF outflow model. The model uses cells cultured from AG caps seeded onto filter membranes. A flow perfusion system is used to measure hydraulic conductivity of a confluent monolayer of these cells at normal and increased pressures, simulating conditions of PTC. Extrapolating this data to physiologic conditions in vivo will use the surface area quantification data. Methods: Brain images were taken with accompanying autopsy reports within 24 hours post–mortem. To control glare, these brains were submerged in water with attached ruler. The 35mm Nikon FM2 camera with its Nikon 52–55mm micro lens were stabilized at a fixed distance. Film (100ASA Kodak Elite Chrome) was processed as color slides and digitized into TIF format. Two pictures were taken from each sample: the brain and the superior sagittal sinus. Adobe Photoshop was used to identify AGs and create a segmented image. Twenty fiducial points were identified in a standard method for each cerebral hemisphere, and an average hemisphere template was calculated. Each segmented image is transformed to the standard template. The transformed images are used to calculate a probability–of–occurrence map that depicts the spatial distribution of AG. Results: Images have been obtained from 30 brains. Preliminary analysis of 5 of these has been performed. This has revealed an average AG surface area of 2.25 +/– 0.7 cm². Topographical distribution was primarily along the longitudinal fissure. Conclusions: We have determined preliminary averages of human AG surface area, and of topographical distribution. These measurements provide age–related topographical and quantification data as well as data for the CSF perfusion model outflow calculations. Additional data on more brain specimens will achieve more accurate measures of AG surface area and distribution and allow correlation with more independent variables.

Keywords: visual impairment: neuro-ophthalmological disease • imaging/image analysis: non-clinical • pump/barrier function