DIASTEMATOMYELIA

Diastematomyelia (split cord or myeloschisis) is the sagittal division of the spinal cord into two hemicords each containing:

• A central canal.
• One dorsal horn and nerve roots.
• One ventral horn and nerve roots.

ETIOLOGY

• Congenital malformation as a result of a split notocord.
• Female predominance (85%) (1).

PATHOLOGY

1. Two hemicords each covered by a layer of pia within a single subarachnoid space and dural sac (60%). No bony spur or fibrous band.
2. Two hemicords each with its own pial, subarachnoid and dural sheath (40%). Fibrous band (25%) or bony spur (75%).

ULTRASOUND

• Lower thoracic / upper lumbar > upper thoracic > cervical spine.
• 82% of septae are located between T1 and T5 (2).
• Scoliosis (50-75%).
• Spina bifida over multiple levels.
• Widened interpedicular distance (splaying of the posterior elements in an axial plane).
• Narrow disc with hemivertebrae, block vertebrae or butterfly vertebrae.
• Bony spur (echogenic focus) through the center of spinal canal.
• Isolated or...
• Associated with other vertebral defects including:
• Spina bifida.
• Kyphoscoliosis.
• Hemivertebra.
• Butterfly vertebra.
• Absent vertebrae.
• Sagittal clefted vertebrae.
• There may be an associated lipomeningocele or rare teratoma of the cord (3).
• Cutaneous signs of occult dysraphism include (4):

- Hypertricosis (hairy patch) 56%

- Capillary hemangioma 26%

- Dermal sinus 22%

- Subctaneous lipoma 11%.

• Associations – High association with a low lying conus (tethered cord) with thickened filum terminale (40%).

- Hydromyelia of one or both hemicords.

- Lipoma of the filum terminalis.

- Intradural lipoma.

- Fibrous bands.

Diastematomyelia
Arrow: central bony bar

REFERENCES

1. Silverman FN, Kuhn JP (eds). Caffey’s X-ray pediatric diagnosis: An integrated imaging approach 1993;Mosby St Louis:pg 133-134 and 318-319.
2. Pang D. Split cord malformation: Part II. Clinical syndrome. Neurosurgery 1992;31:481-500
3. Seeds JW, Powers SK. Early prenatal diagnosis of familial lipomeningocele. Obstet Gynecol 1988;72:469-471.
4. Winter RK, McKnight L, Byrne RA et.al. Diastematomyelia: prenatal ultrasound appearance. Clin Rad 1989;40:291-294
5. Sepulveda W, Kyle PM, Hassan J et.al. Prenatal diagnosis of diastematomyelia: case reports and review of the literature. Prenat Diagn 1997;17:161-165.