Extra-axial collections are collections of fluid within the skull, but outside the brain parenchyma. This is of questionable clinical significance. Two recent papers illustrate the complexities of using brain atrophy as a marker for neurodegeneration. 2022 Nov 15;8(6):532-539. eCollection 2022 Dec 29. An arachnoid cyst is a noncancerous fluid-filled sac that grows on the brain or spinal cord. CSF is also found centrally within the ventricles. Understand the future of immersive. window._wpemojiSettings={"baseUrl":"https:\/\/s.w.org\/images\/core\/emoji\/13.0.1\/72x72\/","ext":".png","svgUrl":"https:\/\/s.w.org\/images\/core\/emoji\/13.0.1\/svg\/","svgExt":".svg","source":{"concatemoji":"https:\/\/www.greenlightinsights.com\/wp-includes\/js\/wp-emoji-release.min.js?ver=5.7.2"}};!function(e,a,t){var n,r,o,i=a.createElement("canvas"),p=i.getContext&&i.getContext("2d");function s(e,t){var a=String.fromCharCode;p.clearRect(0,0,i.width,i.height),p.fillText(a.apply(this,e),0,0);e=i.toDataURL();return p.clearRect(0,0,i.width,i.height),p.fillText(a.apply(this,t),0,0),e===i.toDataURL()}function c(e){var t=a.createElement("script");t.src=e,t.defer=t.type="text/javascript",a.getElementsByTagName("head")[0].appendChild(t)}for(o=Array("flag","emoji"),t.supports={everything:!0,everythingExceptFlag:!0},r=0;r