Papilledema is an ophthalmoscopic diagnosis and refers to swelling of the optic disc. The MRI appearance relates to the dural anatomy of the optic nerve, which is continuous with the subarachnoid space, thereby allowing increased intracranial pressure (ICP) to be transmitted to the optic disc. The causes are protean, a veritable Augean stable of conditions (see below), the most common of which would be an intracranial mass or collection. In most cases, the papilledema is bilateral, however can be unilateral in Foster Kennedy syndrome and its pseudovariants.
Note however that with the advent of motion correction (e.g. BLADE) sequences, CSF in the dural sheath over the optic nerve is much more frequently seen, and caution should be shown when reporting this. Flattening or bulging of the optic nerve head is probably a more specific sign.
The differential is also broad for the fundoscopic findings, although most have quite different MRI appearances. These include:
- optic neuropathy
- malignant hypertension
- optic nerve papillitis
- optic nerve tumors
Possible etiologies of papilledema
- intracranial masses
- primary CNS malignancies
- cerebral metastases
- extra-axial collection
- meningeal disease
- idiopathic intracranial hypertension also known as pseudotumor cerebri
- progressive stenosis of the optic canals and compressive optic neuropathy - rare but can occur in certain skeletal dysplasias such as progressive diaphyseal dysplasia
Possible imaging differential considerations include: