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Split Cord Malformation

Tsai, Tobias J., MD; Michaud, Linda J., MD, PT

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American Journal of Physical Medicine & Rehabilitation: September 2013 - Volume 92 - Issue 9 - p 839
doi: 10.1097/PHM.0b013e3182328440
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A 22-mo-old girl was referred to pediatric rehabilitation clinic for left-foot pronation. Her past medical history was notable for constipation. She had an absent left patellar tendon reflex, and her left plantar response was upgoing. Her gait was notable for left-foot pronation. Brain magnetic resonance image was unremarkable. Lumbosacral spine magnetic resonance image showed splitting of the distal spinal cord into two hemicords with separate central canals, beginning at T12–L1 (Fig. 1). The hemicords reunited at L3. There was tethering of the cord with the conus terminating in a lipoma extending from L5 through S5.

FIGURE 1
FIGURE 1:
T2-weighted axial fast-spin echo magnetic resonance image of the lumbar spine shows the two hemicords.

The term split cord malformation (SCM) was proposed by Pang et al.1 as common nomenclature for the double spinal cord conditions historically known as diastematomyelia and diplomyelia. Diastematomyelia is most frequently referred to as a condition in which two hemicords, each with its own central canal and pia mater, inhabit their own dural tube and are separated by a dural-sheathed rigid, bony median septum. Diplomyelia is referred to as a condition in which two hemicords share a single dural tube but are separated by a nonrigid fibrous septum. Both conditions may share the same embryogenetic mechanism.1 Early in development, adhesions between ectoderm and endoderm can form an endomesenchymal tract that splits the notochord, forming two hemineural plates and hemineural tubes. Mesoderm may then associate with the endomesenchymal tract. If the mesoderm surrounds each hemineural tube, the formation of a bony septum and the condition now known as SCM type I occurs. Otherwise, a single dural sac develops, and the remains of the endomesenchymal tract create a nonrigid fibrous septum and the condition now known as SCM type II. Both conditions are associated with spinal cord tethering and have clinical implications. This patient does not have a bony septum and was given a diagnosis of SCM type II.

This patient’s most striking abnormality on examination was unilateral foot pronation. Unilateral findings in conjunction with combined upper- and lower-motor neuron signs have often been reported in SCM, including eight patients with left–right functional discrepancy in the seminal paper published by Pang.2 Treatment is surgical and may include detethering and/or resection of a fibro-osseus septum. This patient’s constipation resolved after detethering, and her gait has been stable postoperatively. In retrospect, her constipation was likely caused by a neurogenic bowel. Split cord malformation should be considered in the differential diagnosis of patients with suspected tethering lesions for whom early detection may allow preservation of function.

ACKNOWLEDGMENTS

We thank William S. Ball, MD, for interpretation of the MRI.

REFERENCES

1. 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: 451–80
2. Pang D: Split cord malformation: Part II: Clinical syndrome. Neurosurgery 1992; 31: 481–500
© 2013 by Lippincott Williams & Wilkins