sabato 23 maggio 2009
Figure 1: Myelogram of the thoracolumbar spine demonstrates a vertical linear cleft within the distal cord dividing it into two hemicords. Vertebral and rib abnormalities are noted in the lower thoracic spine.
Figure 2: Axial post myelogram CT image of the thoracic spine shows two hemicords.
Figure 3: Axial T2-weighted MR of the thoracic spine shows two hemicords.
Diastematomyelia is characterized by a sagittal division of the spinal cord into two hemicords, each with one central canal, dorsal horn, and ventral horn. An osseous or fibrous septum separates the two hemicords. The condition represents a disorder of neural tube fusion with the persistence of mesodermal tissue from the primitive neurenteric canal acting as the septum or cleft. 85% of clefts occur in the thoracolumbar spine between T9 and S1. The hemicords typically reunite above and below the cleft.
Two types of diastematomyelia have been defined:
- Type 1 diastematomyelia: each hemicord has its own dural sheath
- Type 2 diastematomyelia: both hemicords are covered by a common dural sheath
Congenital spinal deformities are seen in approximately 85% of patients with diastematomyelia. Intersegmental laminar fusion is considered virtually pathognomonic for the condition. Scoliosis, tethered cord, spinal dysraphism, and syringohydromyelia are also commonly associated.
Diastematomyelia occurs in 5% of patients with congenital scoliosis. The diagnosis is typically made in childhood, and is much more common in females. The clinical presentation varies from asymptomatic to neurologic abnormalities indistinguishable from other causes of a tethered cord. Cutaneous stigmata, most commonly a “fawn’s tail” hair patch, may indicate the level of diastematomyelia. The treatment of symptomatic patients is excision of the bony spur or septum and lysis of the adjacent adhesions.