Spinal dysraphism

Spinal dysraphisms refer to a broad group of malformations affecting the spine and/or surrounding structures in the dorsum of the embryo. They are a form of neural tube defect.

Terminology

The term dysraphism implies that the cause of the abnormality is due to anomalous midline fusion and should not be used interchangeably with the term tethered cord, which refers to a constellation of clinical deficits, often but not invariably caused by spinal dysraphism ¹¹.

Epidemiology

The overall prevalence of spinal dysraphism varies somewhat between different populations but is generally approximately 1/1000 pregnancies ¹². The prevalence at birth is lower, primarily influenced by regional and cultural differences in termination rates ¹².

Established risk factors include ¹²:

• maternal obesity

• maternal pregestational diabetes

• maternal use of various drugs (e.g. carbamazepine, valproic acid)

• maternal hyperthermia (e.g. fever) ¹³

Folic acid supplementation is protective ¹².

Pathology

The neural tube is formed by the lengthwise closure of the neural plate, in the dorsum of the embryo.

The upper part of the neural tube forms the forebrain, midbrain and hindbrain. The lower part of the neural tube forms the spinal canal. Dysraphism results when the neural plate does not fuse completely in its lower section.

Classification

Although spinal dysraphism can be classified in a variety of ways, most commonly it is broadly divided into two different clinicoradiological entities based on whether or not the skin is intact (closed) or the abnormality communicates through a cutaneous defect (open) with associated loss of CSF ^8,9,14:

• open spinal dysraphism

  • myelomeningocele (98% of open spinal dysraphism)

  • myelocele

  • myeloschisis

  • hemimyelomeningocele

  • hemimyelocele

• closed spinal dysraphism

  • with subcutaneous mass

    • lipoma with dural defect

      • lipomyelomeningocele

      • lipomyelocele/lipomyeloschisis

    • terminal myelocystocele

    • meningocele

    • limited dorsal myeloschisis

  • without subcutaneous mass

    • posterior spina bifida (isolated defect of the posterior vertebral arch)

    • intradural lipoma

    • filar lipoma

    • tight filum terminale

    • persistent terminal ventricle

    • disorders of midline notochordal integration

      • dorsal dermal sinus

      • dorsal enteric fistula

      • neurenteric cyst ^5,6

      • split cord malformations

        • diastematomyelia

        • diplomyelia

    • disorders of notochordal formation

      • caudal regression syndrome

      • segmental spinal dysgenesis

Associations

Associated abnormalities of mesenchymal development occur often. Hence, lipomas and/or teratomas may be associated with any type.

Spinal dysraphism is also associated with many other syndromes including ¹²:

• trisomies (trisomy 13, 18, 21)

• single gene abnormalities (e.g. Meckel-Gruber syndrome, Waadenburg syndrome)

History and etymology

Dysraphism is formed from the Greek root raphe which means ridge or seam.

See also

• rachischisis totalis