Dimyelia, diplomyelia, and diastematomyelia.

Four types of rare human spinal cord duplications are reported. (1) Dimyelia, a complete duplication of the spinal cord, was observed in a female stillborn dicephalus dibrachius. Histologically the two spinal cords showed symmetric medial hemihypoplasia that included the roots. (2) Diplomyelia, an isolated accessory spinal cord without roots at the ventral lumbosacral level, was observed in a newborn female with a cardiovascular malformation. (3) Complex diastematomyelia: a 9-day-old boy had Arnold-Chiari malformation and an additional diastematomyelia with thoracic meningomyelocele; the left branch of the cord showed further complex multifurcations. (4) Typical diastematomyelia was observed in a stillborn female, born to an adolescent mother at 34 weeks of gestation. The term dimyelia is used to express the condition of total duplication of the spinal cord, by analogy to the term dicephalus in the case of duplicitas. Diastematomyelia means a lateral bifurcation of the spinal cord, independent of whether or not the branches show completely differentiated cord structures with four columns and segmental roots. The term diplomyelia, on the other hand, should be limited to cases of an isolated accessory spinal cord, ventral or dorsal to the normal cord.