Split Notochord Syndrome: A Rare Variant.

Split notochord syndrome represents an extremely rare and pleomorphic form of spinal dysraphism characterized by a persistent communication between the endoderm and the ectoderm, resulting in splitting or deviation of the notochord. It manifests as a cleft in the dorsal midline of the body through which intestinal loops are exteriorized and even myelomeningoceles or teratomas may occur at the site. A rare variant was diagnosed on autopsy of a 23+4-week-old fetus showing a similar dorsal enteric fistula and midline protruding intestinal loops in thoracolumbar region. The anteroposterior radiograph showed a complete midline cleft in the vertebral bodies from T11 to L5 region, and a split in the spinal cord was further confirmed by ultrasonography. Myelomeningocele was erroneously reported on antenatal ultrasound. Thus, awareness of this rare anomaly is necessary to thoroughly evaluate the cases of such spinal defects or suspected myelomeningoceles.

INTRODUCTION

Split notochord syndrome (SNS) represents an extremely rare and pleomorphic form of spinal dysraphism characterized by a wide spinal defect and a persistent communication between endoderm and ectoderm.[12] In its basic form, it consists of a neural tube defect with an endo-ectodermal fistula opening in the dorsal aspect, varying in location from distal ileum/cecum or in the large intestine.[3] Several variants have been reported with gastrointestinal tracts such as dorsal enteric fistula or diverticulum, imperforate anus, duplicated colon, and central nervous system (CNS) including meningocele, neurenteric cysts, duplicated spine, or sacral agenesis. Less frequent presentations include bladder exstrophy, bladder or urethral duplication, and teratomas.[45]

CASE REPORT

Less than 35 cases have been reported in the literature till now, and one such case was examined on routine fetal autopsy done in the Anatomy Department of Government Medical College, Chandigarh, India. The mother, a primigravida, was admitted for termination of pregnancy considering the antenatal ultrasound which reported a myelomeningocele in the lower thoracolumbar region. The gestational age of the fetus was 23+4 weeks (crown-rump length 17.85 cm). There was no history of fever or exposure to any teratogenic agents. The family history was unremarkable, with no consanguinity reported.

OBSERVATIONS

Gross observations

The fetus presented with following anomalies:

A big gap in the vertebral column in the thoracolumbar region. Protuberant bony mass (sacrum) in the lumbosacral region [Figure 1a]

Figure 1

Gross observations of fetus showing midline herniating loop measuring 2.9 cms (right arrow), enteric fistulous opening (left arrow), protuberant bony mass (star) (Figure 1a and 1b). Superficial dissection of back showing posterior midline thoracolumbar diastasis with herniating bowel loops (star) and dorsal enteric fistula (left arrow) (Figure 1c and 1d)

Midline herniating loop – In thoracolumbar region, 5.7 cm from the root of neck, measuring 2.9 cm from its attachment to the dorsum [Figure 1a and b]

Enteric fistulous opening – 0.2 cm and 0.6 cm to the right of the first [Figure 1a].

On dissection of back

Superficial [Figure 1c]

Skin – Normal

Posterior midline thoracolumbar diastasis of vertebral column (2.6 cm × 2.0 cm) with herniating distal ileal loops

Dorsal enteric fistula

Deep [Figure 1d]

Complete splitting of spinal cord

Protuberant bony mass – Sacrum with slight posterior convexity.

Radiographic findings

Anteroposterior [Figure 2a]

Figure 2

Midline vertical cleft (T11–L5) (a), flattening of vertebral concavity (b)

Complete midline vertical cleft in T11–L5 vertebral bodies

Butterfly appearance due to lateral fanning of the hemivertebrae

Lateral [Figure 2b] – Flattening of the concavity of vertebral column.

Ultrasound findings

Split cord in the lower thoracic and lumbar region with the presence of overlapping bowel loops

Normal spinal cord contour in the cervical and upper thoracic level [Figure 3a and b].

Figure 3

Ultrasonography findings: Lower thoracic - split cord (a), lower thoracic, upper lumbar: Bowel loops (b)

DISCUSSION

Spinal dysraphisms consist of a wide variety of congenital malformations resulting from defective embryogenesis of the spinal cord and vertebrae. Spinal dysraphisms show a relatively uniform incidence in all ethnic groups, with no geographic and socioeconomic variations. SNS is usually discovered in the 1st year of life affects both sexes and mostly involve cervical or thoracic regions.[2] Owing to its pleomorphism, this condition has rarely been identified prenatally, with only two cases reported in the last 20 years.[12] The malformations featuring spinal dysraphisms can occur as isolated lesions or in combination with a wide range of anomalies of both CNS and other systems. The SNS belongs to a group of complex occult spinal dysraphisms out of the open (spina bifida cystica) and closed (spina bifida occulta) varieties of spinal dysraphisms. The most common occult forms of spinal dysraphism are lipomas, split cord malformations (diastematomyelia and diplomyelia), dermal sinuses and dermoid tumors, myelocystoceles, tight filum terminale, neuroenteric cysts, and caudal agenesis.[6]

The pathogenesis of the condition is not completely known. One hypothesis for the SNS refers to the persistence or partial obliteration of an accessory neurenteric canal that connects the yolk sac and the amniotic cavity in the 3rd week of gestation. The most widely accepted theory suggests a primary midline notochordal integration defect and paraxial mesoderm changes resulting in split notochord, which is not completely separated from primitive intestine. This leads to herniation of endoderm and underlying primitive intestine which adhere to the dorsal ectoderm and eventually rupture.[3] No clear etiology has been documented, but approximately 50% of the cases are related to maternal nutritional deficiency, especially folic acid. The use of supplementary folic acid may reduce neural tube defects by up to 72.68%. Other causes are zinc and Vitamin A deficiency, high nitrates or Vitamin A excess, altered carbohydrate metabolism (e.g., diabetes mellitus, hyperinsulinemia).[7]

The importance of genetic factors is evidenced by a 3-fold higher incidence in consanguineous marriages as well as monozygotic twins. The role of the Sonic Hedgehog gene (shh) on chromosome 7q36 acting as a morphogen for dorsoventral patterning of somites, anteroposterior polarity of limb, and left-right asymmetry has been documented.[8]

The present case represents a case of SNS located in the lower thoracic (T11) to lumbar region. Myelomeningocele was erroneously reported on the prenatal ultrasound done at 23+4 weeks of gestation. However, the lesions are so different from each other with such a wide range of associated anomalies that each one might be considered a unique variant.[5910]

Although the anomaly is grossly evident at birth, the prenatal recognition of the condition can help in prompt management of such cases. The present case was not diagnosed prenatally. Appropriate and detailed preoperative imaging studies, combining nuclear magnetic resonance and contrast fistulography, are of utmost importance for proper surgical planning and management may vary from case to case.[911] A poor prognosis for survival has been described in the literature, with only 12 survivors being reported.

CONCLUSION

SNS is an extremely rare disorder with <35 cases described in literature before the present case. This report demonstrates that awareness of this rare anomaly is necessary as it can be suspected prenatally whenever a spinal defect is detected together with gastrointestinal variants. This calls for thorough evaluation of cases of hemivertebrae and suspected myelomeningoceles.

The study was supported by Government Medical College and Hospital, Chandigarh, India.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.