The patient had initially presented with a longstanding headache of several months' duration, plus unsteadiness and vomiting for the past few days. Papilledema was noted on physical examination.

The MR study shown here is one of many performed for the follow-up of diffuse leptomeningeal glioneuronal tumor, diagnosed by immunostaining of biopsy specimens from the dura and brain. After the patient started receiving cobimetinib (MEK inhibitor) treatment, he improved slowly but remarkably. This was mirrored in later follow-up MR studies (not shown), where the meningeal enhancement had all but vanished.