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1999-07-15-18 Diastematomyelia © Pilu  www.thefetus.net/


Diastematomyelia

Gianluigi Pilu, MD

Bologna, Italy 

Synonyms: Split cord, occult spinal dysraphism, diplomyelia with bony spur.

Definition: Longitudinal clefting of the spinal cord that is divided into two hemi-cords[1].

CODES = MESH Diastematomyelia BDE 0292 ICD9 742.51 CDC 742.52

Prevalence:

Unknown. Prenatal diagnosis has been reported for 15 cases thus far.

Pathology:

The spinal cord and the intradorsal nerve roots are splitted into two columns. Diastematomyelia may occur with spina bifida or with a closed spine. In the latter case 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 subdivides partially or completely the vertebral canal. The hemicords usually have a distinct arachnoid membrane each 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 at the lower thoracic or upper lumbar regions.

Associated anomalies

The anomalies that have been described in association with diastematomyelia[2],[3]  include:

1) open spina bifida.

2) closed abnormalities of the vertebrae: scoliosis, kiphosis, 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, that is situated over the site of the cleft in the cord in 50-70% of the cases. The location of the cutaneous abnormality, however, is necessarily indicative of the level of the lesion;

4) Orthopedic deformities of the feet, especially clubfoot, are found in approximately half of the patients.

Pathogenesis

Several hypothesis 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;[4]

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;[5]

3) excessive dilatation of the neural tube resulting in subdivision of the cord and internal penetration by mesodermal structures originating from the vertebral body.[6]

The vertebral column and the spinal cord have the same length up to the third month of embryonal life, after which growth proceeds with a different speed. The vertebral column lengths more rapidly, and at birth the conus medullaris is at the level of the lower margin of the second lumbar vertebra. This different growth continues up to the age of 5 years, when the conus medullaris reaches the upper margin of the body of the second lumbar vertebra.

Diastematomyelia acts as a restraint that slows the normal growth of the spinal cord by impeding the upward migration of the neural elements, with progressive neurologic deficits in the limbs. 

Etiology:

Unknown, rare case of autosomal dominance[7].

Recurrence risk

The risk of recurrence is unknown. Autosomal dominant transmission has been described in rare cases.[8] The great majority of cases occur in females (M:F = 1:3).

Diagnosis

Diastematomyelia may occur in association with spina bifida. The experience with the antenatal diagnosis of diastematomyelia as a closed neural defect is limited to a few cases, most of which were associated with vertebral abnormalities. In some of these cases, demonstration of an alteration in vertebral morphology allowed to infer the condition. It seems unlikely that cases without either spina bifida or bony alterations of the vertebrae will be identified even by expert sonography.

The available reports describe the following characteristic findings: 1) in a coronal section, widening of the spinal canal, similar to the one encountered in spina bifida; 2) in a transverse section of the affected vertebrae, the presence of three in stead of two posterior ossification centers, the central one protruding both posteriorly towards the skin and anteriorly towards the spinal canal; 3) intact soft tissues overlying the spine (Figure 1).

Identification of an extra-echogenic posterior focus in the spinal canal is considered an highly specific prenatal sign of diastematomyelia.[9],[10],[11] This finding has been detected prospectively in 0.06% of 10,070 obstetric sonograms. In all cases, the prenatal diagnosis was confirmed after delivery.[12]

Fig. 1: Diastematomyelia in a second trimester fetus. In a sagittal scan (left) an irregularity of the spinal contour is seen. The soft tissues appear intact, but a bony spur is seen projecting posteriorly. In a axial plane (right) three posterior ossification center are seen, the central one protruding both posteriorly and anteriorly towards the spinal canal. The soft tissue appear intact.

Differential diagnosis

Antenatally, the diagnostic problem is distinguishing diastematomyelia from open spina bifida and hemivertebra.

The available experience suggests that the appearance of the spine in coronal and sagittal sections is aspecific, while the transverse section that demonstrates three ossification centers is strongly indicative of diastematomyelia.[13] Demonstrating the integrity of the soft tissues overlying the abnormal vertebrae and of the intracranial anatomy can be of further help in ruling out spina bifida. Amniotic fluid alpha-fetoprotein concentration and acetylcholinesterase can be assessed if the doubt of an associated spina bifida can not ruled out by sonography alone.

Implications

A familial history of dyastematomyelia indicates a fetal sonogram in the attempt to predict a recurrence. The exact sensitivity of even targeted examinations in predicting this condition is however uncertain. It is likely that only those cases associated with significant vertebral abnormalities are amenable to detection. We would recommend an examination at 18 weeks. We have found vaginal sonography extremely useful in fetuses with a posterior spine.

Implications for sonographic screening

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

Implications for targeted examination

In a fetus at risk for diastematomelia careful sonographic assessemt of the spine in the transverse plane is reommended.

Prognosis

The presence of diastematomyelia has no influence on the 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 tethering filum. Most of the cases identified antenatally thus far had a good outcome. Sepulveda[14] 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 remaning were free from both neurologic and orthopedic sequelae, although one underwent spinal surgery.

Obstetrical management

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 favourable, 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.

References

[1] Guth Kelch AN, Jones RA, Zierski J: Diastematomyelia. Dev Med Child Neurol (Suppl) 13:137-138, 1971.

[2] Schut L, Sutton NL, Duhaine AC: Congenital neurological disorders of the lumbar spine presenting in the adult. In: The adult spine: Principles and Practice. Frymover W.J., Editor-in-chief., New York. Raven Press, 1991.

[3] Rothman RH, Simeone FA: Anomalie congenite del rachide In: Il Rachide. Bologna. Gaggi Ed., 1978.

[4] Bremer JL: Dorsal intestinal fistula. Accessory neuroenteric canal: diastematomyelia. Arch Pathol 54:132-138, 1952.

[5] Padget DH: Neuroschisis and human embryonic maldevelopment. J Neuropathol Exp Neurol 29:192, 1970.

[6] Gardner WS: Diastematomyelia and the Klippel-Feil syndrome: relationship to hydrocephalus, syringomyelia, meningocele, meningomyelocele and miencephalus. Clev Clin A 31:19-44, 1964.

[7] Carter CO: Spinal dysraphism: genetic relation to neural tube malformations. J Med Genet 13:343-50, 1976.

[8] Carter CO: Spinal dysraphism: genetic relation to neural tube malformations. J Med Genet 13:343-50, 1976

[9] Winter RK, McKnight L, Byrne RA, Wright CH: Diastemamyelia: prenatal ultrasonic appearances. Clin Radiol 40:291-4, 1989.

[10] Anderson NG, Jordan S, McFarlane MR, Lovell-Smith M: Diastematomyelia: diagnosis by prenatal sonography. Am J Roentgenol 163:911-4, 1994.

[11] 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.

[12] 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.

[13] 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.

[14] 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.

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