Diastematomyelia

Longitudinal clefting of the spinal cord, which is divided into two hemi-cords.¹ 

Unknown. Prenatal diagnosis has been reported for few isolated cases thus far.

Several hypotheses have been formulated:

1. Retention of the neurenteric canal that transiently connects the yolk sac to the amnion via the primitive knot. This knot migrates distally to the region of the coccyx, where it disappears. If an accessory canal develops, it would split the neural ectoderm with underlying endoderm and result in a midline fistula. The fistula eventually disappears, but not until abnormal vertebral and neural elements have been formed.²  
2. Presence of a dorsal and ventral cleft that severs the neural plate near the midline, resulting in separate closure of the two hemicords. Mesenchymal tissue filling the gap results in mesodermal and bony abnormalities.³ 
3. Excessive dilatation of the neural tube resulting in subdivision of the cord and internal penetration by mesodermal structures originating from the vertebral body.⁴ 

Unknown. Rare case of autosomal dominance are reported.⁵

The spinal cord and the intradorsal nerve roots are split into two columns. Diastematomyelia may occur with spina bifida or with a closed spine. In cases of the latter, the cleft of the cord is associated with a mass attached anteriorly to the vertebral body and posteriorly to the dura mater. This mass may be a bony, fibrous or cartilaginous septum that partially or completely subdivides the vertebral canal. Each hemicord usually has a distinct arachnoid membrane with a common dura. Diastematomyelia may involve a single vertebra or extend to several vertebral segments. The cleft may be found at any level, but in most cases is found in the lower thoracic or upper lumbar regions.

The anomalies that have been described in association with diastematomyelia include:

1. Open spina bifida.
2. Closed abnormalities of the vertebrae: scoliosis, kyphosis, hemivertebrae, butterfly vertebra.
3. Cutaneous manifestations on the dorsal midline consisting of telangiectasias, atrophic skin, hemangiomas, subcutaneous lipomas and cutaneous nevi. Among the cutaneous nevi, the most characteristic is the nevus pilosus: a large patch of long silky hairs which is situated over the site of the cleft in the cord in 50-70% of cases. The location of the cutaneous abnormality, however, is not necessarily indicative of the level of the lesion.
4. Orthopedic deformities of the feet, especially clubfoot, are found in approximately half of patients. 

The risk of recurrence is unknown. Autosomal dominant transmission has been described in rare cases.⁶ The majority of cases occur in females (M:F = 1:3).

Diastematomyelia may occur in association with spina bifida. Diastematomyelia as a closed neural defect has been antenatally diagnosed in a few cases, most of which were associated with vertebral abnormalities. In some of these cases, the condition was inferred by demonstration of an alteration in vertebral morphology. It seems unlikely that cases with neither spina bifida nor bony alterations of the vertebrae will be identified even by expert sonography.

The available reports describe the following characteristic findings:

•  In a coronal section, widening of the spinal canal, similar to what is encountered in spina bifida. 
• In a transverse section of the affected vertebrae, the presence of three instead of two posterior ossification centers, with the central one protruding both posteriorly towards the skin and anteriorly towards the spinal canal.
• Intact soft tissues overlying the spine.

Identification of an echogenic posterior focus in the spinal canal is considered a highly specific prenatal sign of diastematomyelia. ^{7, 8, 9, 12, 13}  This finding has been detected prospectively in 0.06% of 10,070 obstetric sonograms. In all cases, the prenatal diagnosis was confirmed after delivery.¹¹

The main obstacle to antenatal diagnosis of diastematomyelia is distinguishing it from open spina bifida and hemivertebra.¹²
The available experience suggests that the appearance of the spine in coronal and sagittal sections is non-diagnostic, while the transverse section that demonstrates three ossification centers is strongly indicative of diastematomyelia.^11-13 Demonstrating the integrity of the soft tissues overlying the abnormal vertebrae and of the intracranial anatomy can also help to rule out spina bifida. Amniotic fluid alpha-fetoprotein concentration and acetylcholinesterase can be assessed if an associated spina bifida can not ruled out by sonography alone. 
 

If there is familial history of diastematomyelia, a fetal sonogram should be carried out to attempt to predict a recurrence. We would recommend a careful sonographic assessment of the spine in the transverse plane at 18-20 weeks' gestation. However, the exact sensitivity of even targeted examinations in predicting this condition is uncertain. It is likely that it is only possible to detect cases associated with significant vertebral abnormalities. We have found vaginal sonography extremely useful in fetuses with a posterior spine. 

It is unlikely that diastematomyelia without spina bifida can be recognised in standard sonographic examinations.

The presence of diastematomyelia does not influence prognosis when spina bifida is present. When diastematomyelia presents as a closed neural tube defect, the prognosis for neurological function may be enhanced by early surgical removal of the septum, dural reconstruction into a single tube, excision of associated developmental masses and division of the tethered filum. Most of the cases identified antenatally thus far had a good outcome. Sepulveda¹¹ reviewed 15 cases diagnosed antenatally. Information on the postnatal outcome of diastematomyelia without additional abnormal findings was available from six cases. Of these, one had severe orthopedic problems, including a spinal deformity, shortening of one leg and a small foot. All the remaining were free from both neurologic and orthopedic sequelae, although one underwent spinal surgery. 

For cases with open spinal defects, the reader is referred to the chapter on spina bifida.
Counselling patients with a prenatal diagnosis of diastematomyelia without evidence of either spina bifida or other vertebral anomalies is difficult. Although the outcome is usually favorable, neurosurgical and orthopedic surgery may be necessary, and there is a chance of neurologic compromise.
We believe therefore that termination of pregnancy could be considered as an option, particularly if associated anomalies that are likely to worsen the outcome are present, such as severe scoliosis and clubfoot.
In continuing pregnancies, standard obstetric care is recommended.

1. Guth Kelch AN, Jones RA, Zierski J: Diastematomyelia. Dev Med Child Neurol (Suppl) 13:137-138, 1971.
2. Bremer JL: Dorsal intestinal fistula. Accessory neuroenteric canal: diastematomyelia. Arch Pathol 54:132-138, 1952.
3. Padget DH: Neuroschisis and human embryonic maldevelopment. J Neuropathol Exp Neurol 29:192, 1970.
4. Gardner WS: Diastematomyelia and the Klippel-Feil syndrome: relationship to hydrocephalus, syringomyelia, meningocele, meningomyelocele and miencephalus. Clev Clin A 31:19-44, 1964.
5. Carter CO: Spinal dysraphism: genetic relation to neural tube malformations. J Med Genet 13:343-50, 1976.
6. Carter CO: Spinal dysraphism: genetic relation to neural tube malformations. J Med Genet 13:343-50, 1976
7. Winter RK, McKnight L, Byrne RA, Wright CH: Diastemamyelia: prenatal ultrasonic appearances. Clin Radiol 40:291-4, 1989.
8. Anderson NG, Jordan S, McFarlane MR, Lovell-Smith M: Diastematomyelia: diagnosis by prenatal sonography. Am J Roentgenol 163:911-4, 1994.
9. Sepulveda W, Kyle PM, Hassan J, Weiner E: Prenatal diagnosis of diastematomyelia: case reports and review of the literature. Prenat Diagn 17:2, 161-5, 1997.
10. Has R, Yuksel A, Buyukkurt S, Kalelioglu I, Tatli B.Prenatal diagnosis of diastematomyelia: presentation of eight cases and review of the literature. Ultrasound Obstet Gynecol. 2007 Nov;30(6):845-9.
11. Allen LM, Silverman RK. Prenatal ultrasound evaluation of fetal diastematomyelia: two cases of type I split cord malformation. Ultrasound Obstet Gynecol. 2000 Jan;15(1):78-82.

Please note that the maximum upload size is 5MB, and larger images and video clips can be sent to [email protected].