====== Extra axial ======


Extra-[[axial]] is a descriptive term to denote lesions external to the [[brain parenchyma]], in contrast to [[intra-axial]] which describes lesions within the brain substance. 
===== Radiographic features =====


Often it is trivially easy to distinguish an intra-axial from an extra-axial mass. In many cases, especially when the mass is large and associated with parenchymal changes, such as oedema, localisation can be more difficult. A number of features are helpful in suggesting that a mass or lesion is extra-axial, including: 

    subarachnoid space
        CSF cleft sign
        widening of adjacent subarachnoid space/cistern
         intervening pial arteries or veins
    brain parenchyma
        absence of a claw sign
        intervening cortex between mass and white matter
        white matter buckling sign
    bone and meninges
        
dural tail sign
        
erosion or invasion/destruction of bone

hyperostosis
((https://radiopaedia.org/articles/extra-axial-1)).