Split cord malformations have been classically called diastematomyelia and diplomyelia. These malformations account for 3.8% of all Complex Dysraphic States (CSD). In 1992, Pang et al. suggested that terms such as diastematomyelia and diplomyelia be abandoned to introduce the term “split cord malformation” (SCM). They also proposed categorizing these abnormalities into two types based on the state of the dural tube and the nature of the median septum.
Type I SCM consists of two hemicords contained within individual dural tubes, separated by a bony or osteocartilaginous septum that extends from the vertebral body to the neural arches. This rigid median septum is entirely extradural.
In type II SCM, a common dural tube houses both hemicords, and there is no rigid median septum. These main features of the two types of SCM never overlap, and the classification can be made readily by preoperative neuroimaging studies
The cutaneous stigmata of diastematomyelia type II are similar to those of type I - hypertrichosis is a remarkable telltale signature. The radiological hallmark is represented by a single dural sac housing both hemicords. Diastematomyelia type II may be difficult to appreciate on sagittal MR images, coronal and axial MR images clearly depict the cord splitting. The fibrous septum may be very thin and usually is appreciated best with high-resolution coronal or axial T2-weighted MR images