this is a localised dilatation of the central canal of the spinal cord (hydromyelia) which produces a fluid-filled sac or diverticulum which then protrudes through the cord and the defective dorsal dura between the posterior parts of the vertebra. the sac is lined by ependyma and is covered by meninges and skin. it is usually located at the lower end of the neural tube when it is called a terminal myelocystocele. it may occasionally arise from the ventral aspect of the spine.


the lesion is rare and its most common presentation is of a subcutaneous mass. the appearance of a cyst within a cyst is typical. the inner cyst is the hydromyelic sac and the outer cyst the dura and skin. cervical myelocystoceles may be associated with hydrocephalus and the arnold-chiari malformation. terminal myelocystoceles are associated with hypogastric ventral wall defects which may include vesical exstrophy. vertebral abnormalities and deficiences may be noted.

differential diagnosis

the differential diagnosis of a subcutaneous paraspinal cyst includes: cystic hygroma, when seen in the cervical region; however, this abnormality is often septate, extends laterally, and may be associated with hydrops and chromosomal anomalies (turnerís syndrome, trisomies 21 and 18), unlike the isolated myelocystocele. a closed simple meningocele with a small spinal defect may present in a similar fashion, without associated cranial features. larger neural tube defects, however, are more likely to demonstrate hydrocephalus and the arnold-chiari malformation, and raised maternal serum and amniotic fluid alpha-fetoprotein concentrations may enable the correct diagnosis.

sonographic features

subcutaneous paraspinal cystic mass ‘cyst within a cyst’ appearance.

hydrocephaly and arnold-chiari type ii malformation may be seen if lesion is in cervical region.

ventral wall defects may be seen with terminal myelocystoceles.

associated syndromes


bhargava r, hammond di, benzie rj, ventureyra ecg, higgins mj, martin dj prenatal demonstration of a cervical myelocystocele prenat diagn 12: 653-659