Denouement and Discussion: Occult Spinal Dysraphism (Tethered Cord, Diastematomyelia, and Spinal Lipoma)
Figure 1. Photograph of the newborn's back shows a copious, localized hair tuft over the lumbar area.
Figure 2. Axial ultrasonographic scan at the level of L1 demonstrates division of the spinal cord into 2 portions (arrows).
Figure 3. Midsagittal ultrasonographic scan shows the spinal cord (arrow) to be tethered posteriorly by a lipoma (arrowheads).
Figure 4. Magnetic resonance imaging in the coronal plane (T1-weighted) demonstrating a split spinal cord (arrows) from diastematomyelia and a small lipoma (arrowhead).
The term dysraphism means incomplete fusion of a raphe. The skin and the nervous system share a common ectodermal origin. Differentation of the neural ectoderm from the epithelial ectoderm occurs during the third to the fifth week of gestation. Cleavage occurs concurrently with formation and closure of the neural tube.1 The embryologic concurrence of events explains simultaneous occurrence of "occult" dysraphic lesions and minor malformations of the skin. Awareness of the cutaneous manifestations of underlying spinal cord malformations is critical because dysraphic malformations can cause damage from tethering of the spinal cord.
While during early fetal life the spinal cord occupies the entire length of the vertebral column, differential growth results in progressive ascent of the conus medullaris. In the newborn, the conus medullaris can be at the level of L2/L3 but by the age of 3 months is at the level of L1/L2, as in adults. Tethering of the cord prevents the progressive ascension of the conus with continued somatic growth and anchors the conus at or below the L2 level. Flexion of the normal spine is associated with upward movement of the cord and if the cord is fixed or tethered, traction injuries occur and there is damage to the lower cord and conus.2
Split cord malformations are anomalies in which the spinal cord is cleft over a portion of its length by either a fibrocartilaginous or a bony septum originating from the posterior part of the vertebral body. The terms diastematomyelia and diplomyelia have created confusion; hence, they have been superseded by the term spilt cord malformation. The malformation results from disarry of midline axial integration during gastrulation, producing a split neural tube.3 In both types of malformation there is a tethering element that results in neurologic deterioration.4
The neurologic symptoms result from flexion and extension movements of the cord that produce traction and trauma from the impaling septum. The clinical presentations of occult spinal lesions vary. Clinical signs could appear at birth or be delayed until adulthood. Tethering from any cause may produce back, leg, or groin pain, progressive lower extremity sensorimotor dysfunction, urinary dysfunction from neurogenic bladder, bowel incontinence or constipation, lower extremity orthopedic deformities, and progressive scoliosis.5
Dysraphism should be diagnosed and surgically repaired before symptoms and signs of irreversible neurologic impairment are evident. Cutaneous abnormalities, such as hypertrichosis, a dimple, or a lipoma, might be the only clues to an underlying tethered cord. This is particularly seen in newborn infants with spinal dysraphism; 71% to 100% of patients have these signs.6,7 A high index of suspicion should occur when any of the above-mentioned cutaneous abnormalities is present so that spinal dysraphism can be recognized and managed to prevent irreversible neurologic impairment.
Accepted for publication October 23, 2000.
Corresponding author: Monica Epelman, MD, Department of Diagnostic Imaging, Hospital for Sick Children, 555 University Ave, Toronto, Ontario, M5G 1X8, Canada.
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