Diastematomyelia¶

Definition¶

Diastematomyelia (split cord malformation) is a type of spinal dyspraphism characterized by the spinal cord being split longitudinally into two hemicords by a bony, cartilaginous, or fibrous septum. Each hemicord contains a central canal, a dorsal horn, and a ventral horn. The split most commonly occurs in the lower thoracic or lumbar spine.

Classification — Pang¶

Type I — Two hemicords in separate dural tubes = 2 dural sacs, separated by a rigid osseocartilaginous septum (bony spur). This type is more likely to cause tethering and neurological symptoms. Vertebral anomalies are also more commonly associated.

Type II — Two hemicords within a single shared dural tube = 1 dural sac, separated by a fibrous band. This type is less likely to cause symptoms.

Imaging Findings¶

MRI¶

Sagittal — The cord appears to "split" into two hemicords over a segment, then reunite below the split. A low-lying conus is common.
Axial — Two hemicords visible within the thecal sac, either in separate dural tubes (Type I) or a single tube (Type II)
The bony septum in Type I may be visible as a low-signal structure between the hemicords
Associated tethered cord, hydromyelia, and segmentation anomalies are common

CT¶

Best modality for demonstrating the bony septum (Type I) — a bony spur extending from the posterior vertebral body to the posterior elements
Associated vertebral anomalies (hemivertebra, butterfly vertebra, block vertebra)

Clinical Pearl

On axial MRI, diastematomyelia shows two hemicords within the thecal sac — the "split cord" appearance. The critical surgical question is whether a bony septum is present (Type I), because the septum must be removed to untether the cord. CT is the best modality for demonstrating the bony spur if MRI findings are equivocal.

Key Points¶

Spinal cord is split into two hemicords by a septum
Type I (bony septum, separate dural tubes) is more symptomatic than Type II (fibrous band, single tube)
CT best demonstrates the bony septum; MRI evaluates the hemicords and associated anomalies
Lower thoracic and lumbar spine are most commonly affected
Associated with tethered cord, segmentation anomalies, and scoliosis

References¶

Pang D, Dias MS, Ahab-Barmada M. Split cord malformation: Part I: A unified theory of embryogenesis for double spinal cord malformations. Neurosurgery. 1992;31(3):451-80. Available from: https://pubmed.ncbi.nlm.nih.gov/1407428/
Pang D. Split cord malformation: Part II: Clinical syndrome. Neurosurgery. 1992;31(3):481-500. Available from: https://pubmed.ncbi.nlm.nih.gov/1407429/
Trapp B, Freddi TAL, Hans MOM, et al. A practical approach to diagnosis of spinal dysraphism. RadioGraphics. 2021;41(2):559-575. Available from: https://pubmed.ncbi.nlm.nih.gov/33449837/
Kleinrok J, Kleinrok K, Popiela TJ. Split cord malformation - a simple, current classification based on CT and MRI neuroimaging studies. Pol J Radiol. 2025;90:e46-e54. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC11891551/
Jiblawi A, Chanbour H, Tayba A, Khayat H, Jiblawi K. MRI characteristics of split cord malformation. Cureus. 2021;13(9):e18328. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC8553275/
Gaillard F, et al. Diastematomyelia. Reference article, Radiopaedia.org. Available from: https://radiopaedia.org/articles/diastematomyelia