Sonographic appearance of the ventriculus terminalis cyst in the neonatal spinal cord.

The ventriculus terminalis or "fifth ventricle" is an ependyma-lined residual lumen of the caudal portion of the spinal cord (the conus medullaris). We present the cases of three neonates with asymptomatic cystic dilatation of the ventriculus terminalis as seen on spinal sonography. Over a 4 year period (1996-1999), we prospectively found three cases in which spinal sonograms demonstrated cystic dilatation of the ventriculus terminalis of the conus medullaris in normal term neonates. Sonograms of the lumbosacral spine of two of the infants demonstrated cystic dilatation of the ventriculus terminalis of the conus medullaris. The third infant had cystic dilatation at the distal tip of the conus medullaris at the origin of the filum terminale. No other abnormalities were noted. The three infants have remained asymptomatic during clinical follow-up periods of up to 3 years. Cystic dilatation of the ventriculus terminalis is an unusual but normal anatomic variant of the conus medullaris that can be visualized on spinal sonograms in neonates.