Teaching neuroimages: massive cerebral edema after CT myelography: an optical illusion.

A 74-year-old woman underwent myelography with iohexol to exclude a CSF leak. Three days later, her son noticed mild facial asymmetry and took her back to the hospital. Neurologic status was at baseline except for minimal left nasolabial flattening. Initial head CT appeared to show diffuse cerebral edema (figure, A), but the following morning the appearance had normalized (figure, B). Based on the spontaneous clinicoradiologic improvement, we hypothesize that an illusion of cerebral edema was caused by residual iohexol. Although not reported with iohexol, older agents can cause hyperdense gray matter and can accumulate in sulci.