“Papilledema”: Neuroradiologic Evaluation of Optic Disk Protrusion with Dynamic Orbital CT

Abstract

Current-generation CT scanners enable the visualization in vivo of structures and substructures that were previously unobservable. Certainly the orbit and optic nerve/sheath complex have demonstrated a great number of pathologic and normal anatomic variations. It has been found in patients with elevated intracranial pressure that what was previously thought to be simple papilledema in fact masks a surprisingly large component of optic papilla protrusion. There may be a variable amount of increased intercellular/axonal fluid within the optic disk in patients with increased intracranial pressure; however, a significant factor in the “swollen disk” is the simple transmission of pressure along the optic nerve sheath to the papilla, causing it to bulge. Further investigations with dynamic CT reveal that there is decreased perfusion of the optic disk in the active phase of severe increased intracranial pressure in patients with papilledema and/or protrusion as compared with normal control subjects. This depressed flow pattern seems to originate subacutely and appears to resolve in certain patients after normalization of the elevated pressure. These findings apparently indicate that clinical intervention in cases of intracranial hypertension to restore the hemodynamic status of the optic disk would be timely, and thereby avert irreversible damage. This suggests and supports the theory that increased intracranial pressure may lead to rapid vision loss by the mechanical mechanism of pressure projected directly to the junction of the optic nerve and optic nerve head, leading to decreased perfusion, ischemia, axonal flow stasis, and resultant optic nerve atrophy.