Diastematomyelia of the thoracic spinal cord

CLINICAL HISTORY

A 40-year-old man presented with upper and lower back pain. His symptoms worsened over the course of a month. The patient denied any bowel or bladder dysfunction, radiating symptoms, or motor deficits.

FINDINGS

Axial T2-weighted MR images (Figures 1 and 2) reveal a longitudinally split thoracic spinal cord with cerebrospinal fluid intervening between the two hemicords (arrow). The left hemicord is slightly larger than the right hemicord. No bony spurs were identified along the course of the split cord. A sagittal T1-weighted image (Figure 3) shows bony fusion of the bodies of the T10 and T11 vertebrae.

DIAGNOSIS

Diastematomyelia of the thoracic spinal cord with associated vertebral body fusion.

DIFFERENTIAL DIAGNOSIS

The differential diagnosis includes diplomyelia, tethered spinal cord, thickened filum terminale, neurenteric cysts, congenital dermal sinus tract, anterior sacral meningocele, spinal lipomas, and dermoid and epidermoid tumors.

DISCUSSION

Diastematomyelia refers to a pathologic longitudinal splitting of the spinal cord and the intradorsal nerve roots into two columns. Separation into the two hemicords may be due to a bony spur, cartilaginous separation or fibrous band with a usual asymmetry in size of the hemicords.

Two types of diastematomyelia have been described. Each accounts for roughly 50% of the observed cases. Type I refers to a split cord that is surrounded by a normal undivided arachnoid-dural sleeve without a septum. Type II refers to a split cord in which each hemicord is invested by a separate dural sleeve that is divided by a fibrous, cartilaginous, or bony septum.¹

Diastematomyelia usually occurs in the lower thoracic and upper lumbar regions and 85% of the time is associated with bony abnormalities including spina bifida, widened interpediculate distances, hemivertebrae, and scoliosis. There are also associated cutaneous manifestations of the dorsal midline including telangectasias, atrophic skin, hemangiomas, and subcutaneous lipomas.^1,2

Patients present with a wide range of severity in their signs and symptoms, including clinically silent lesions and gait disturbance, lower extremity weakness, progressive paraparesis, and bladder and bowel dysfunction.³ Diastematomyelia is best evaluated with MRI in conjunction with CT. Diagnostic ultrasound is the modality of choice for prenatal detection, typically during the early to mid third trimester, allowing for an early surgical intervention and usually a good prognosis.

Submitted by Neil M. Gupta, M.D., radiology resident, and Michael I. Firestone, M.D., assistant professor of radiology at St. Francis Hospital in Hartford, CT.

BIBLIOGRAPHY

1. Barkovich AJ, Naidich TP. Congenital anomalies of the spine; pediatric neuroimaging. New York: Raven Press; 1990:227-271.
2. Grossman R, Yousem D. The requisites: neuroradiology, 2nd ed. Philadelphia: Mosby; 2003:462-465.
3. Scotti G, Musgrave MA, Harwood-Nash DC, et al. Diastematomyelia in children: metrizamide and CT metrizamide myelography. AJR 1980;135:1225-1232.