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Neuroradiology Case of the Week

Case 303

M. F. Boomsma, M.D.
Antonius Ziekenhuis, Nieuwegein, The Netherlands

Clinical Presentation: A 40-year-old woman presented at the neurologist with a headache. In patient's history there had been delayed motor development as she could not walk before the age of two. She showed normal mental development. Early childhood diagnostic imaging would have showed a meningocele, but imaging results could not be retrieved. Physical examination revealed increased hair growth (hairy patch) in the cervical region consistent with a meningocele. The neck was very short. There was impaired flexibility of the neck and an increased muscle tone was present. Neurological evaluation revealed echopraxis, in which actions on one side were unwillingly followed by actions on the other side.

Imaging Findings: MR imaging showed a superior position of the atlas in relation to the dens axis and there was no fusion of the arcus posterior of C1 and C2. The cerebellar tonils were low situated. A meningocele at this level was present and the cord showed a split cord malformation, consistent with diastematomyelia Pang type II.

Diagnosis: Cervical diastematomyelia (Pang type II split cord malformation)

Discussion: Diastematomyelia is an anomaly of notochord development. The notochord is a cellular rod that defines the embryonic primitive axis and provides rigidity to the embryo. It induces the ectoderm to develop the neural tube and crest and actuates the induction of the mesodermal germ layer to form spinal axis mesenchymal elements [1].
     Diastematomyelia is a rare congenital anomaly that results in the "splitting" of the spinal cord in a longitudinal (sagittal) direction. It can be detected by prenatal sonography, newborn sonography, CT or MR [2,3,4]. Females are affected much more commonly than males. This condition can occur in the presence of an osseous (bone), cartilaginous or fibrous septum in the central portion of the spinal canal which then produces a complete or incomplete sagittal division of the spinal cord into two hemicords. When the split does not reunite distal to the spur, the condition is referred to as a diplomyelia (which is a "true duplication" of the spinal cord.) This condition may be an isolated phenomenon or may be associated with other segmental anomalies of the vertebral bodies such as spina bifida, kyphoscoliosis, butterfly vertebra, hemivertebra and block vertebrae which are observed in a high proportion of cases. Scoliosis is usually identified in more than half of these patients. Diastematomyelia occurs in 85% between 9th thoracic and 1st sacral levels of the spinal column with most being at the level of the upper lumbar vertebra. Cervical diastematomyelia is a very rare entity. The extent (or length of spinal cord involved) varies from one affected individual to another.
     In Pang type I split cord malformation (SCM) approximately 50% of patients with diastematomyelia, the two hemicords, not necessarily symmetric, are each covered by an intact layer of pia arachnoid, and travels through it's own subarachnoid space surrounded by it's own dural sac. Each hemicord has its own anterior spinal artery, central canal, anterior and posterior horn. This form of diastematomyelia is accompanied by a bony spur or fibrous band and is more often symptomatic than type II. The other 50% of patients, Pang type II SCM, do not have a bony spur or a fibrous band that passes through the two hemicords. These cases are less often symptomatic, unless hydromyelia or tethering is present. Vertebral anomalies are less severe (usually butterfly vertebrae), and nerve roots may become adherent to the dura and tether the cord (meningocele manque).
     Clinically, prenatal sonography can already identify diastematomyelia. Presentation is usually in childhood and adult presentation is uncommon. Gender distribution in the pediatric population F>>M, 80-94%, in adults M < F 1:3.4. Mild cases show cutaneous stigmata on the back indicating the diastematomyelia level. In more severe cases kyphoscoliosis, neurological and musculoskeletal disorders can occur (kyphoscoliosis, orthopedic foot problems (especially club foot), urological dysfunction). Late onset or previously stable patients may become symptomatic following relatively minor back injury or surgery requiring spinal manipulation. More than 90 % of patients stabilize or improve after surgery. Surgery can consist of releasing the tethered cord, spur resection and dural repair for progressive symptoms. Scoliosis is rarely affected by surgical untethering.
     In this patient after MR imaging, further investigation of the vertebral anomalies was advised by means of conventional radiographs or CT. MR imaging findings however enabled the neurologist to explain the clinical findings and patient was reassured. No further actions were undertaken.

References:

1. Ross JS, Brant-Zawadzki M, Moore KR, Crim J, Chen MZ, Katzman GL. Diagnostic Imaging. Spine, Amirsys I:56-59.
2. Anderson NG, Jordan S, MacFarlane MR, Lovell-Smith M. Diastematomyelia: diagnosis by prenatal sonography. AJR Am J Roentgenol. 1994 Oct;163(4):911-4. [Medline]
   
3. Unsinn KM, Geley T, Freund MC, Gassner I. US of the spinal cord in newborns: spectrum of normal findings, variants, congenital anomalies, and acquired diseases. Radiographics. 2000 Jul-Aug;20(4):923-38. [Medline]
4. Arredondo F, Haughton VM, Hemmy DC, Zelaya B, Williams AL The computed tomographic appearance of the spinal cord in diastematomyelia. Radiology. 1980 Sep;136(3):685-8. [Medline]