Measurements of intracranial fat prolapse. According to Birchall et al,6 intracranial fat prolapse is defined as a distance of orbital fat behind the boundary of superior ophthalmic fissure (red line) on axial CT image. The lateral margin of the SOF is identified at the most inner border of the sphenoid wing (green arrow), while the medial margin is indicated at the most anterior border of sphenoid body groove (yellow arrow).