Rhombencephalosynapsis and a Chiari II malformation.

Rhombencephalosynapsis is an anomaly of the hindbrain characteristically presenting with cerebellar fusion and absence of cerebellar vermis on magnetic resonance imaging. Its association with spinal anomalies has not been reported previously. We report a unique case, a 22-year-old man with cerebellar fusion associated with a cervicothoracic meningomyelocele, diastematomyelia, tethering of the spinal cord, and dorsal dermal sinuses. In addition, cerebellar tonsillar herniation and tectal beaking similar to that seen in Chiari II malformations were present. These findings suggest that rhombencephalosynapsis can be associated with spinal malformations and, furthermore, that cases with the common features of rhombencephalosynapsis and a Chiari II malformation can exist. Such an association likely represents a new anomaly of the hindbrain and spine.