Surgical observation of the agenesis of the foramen of Magendie.

We report a young girl who presented with headache and back pain. Dynamic MRI revealed no cerebrospinal egress from the median aperture (Foramen of Magendie) of the fourth ventricle and syringomyelia. A posterior cranial fossa exploration was performed and agenesis of the median aperture was observed. Following surgical penetration of the posterior aspect of the fourth ventricle and at the most recent follow-up examination, this patient's syringomyelia had resolved, as had her symptoms. Agenesis of the foramen of Magendie may be a rare cause of inhibition of normal cerebrospinal egress from the fourth ventricle with resultant syringomyelia.