DR. NISHANT SINGLADNB RESIDENT, RADIOLOGY

HINDUJA HOSPITAL, MUMBAI.

DR. PRAVEEN WALIDNB RESIDENT, RADIOLOGY

HINDUJA HOSPITAL, MUMBAI

Neural tube defects are one of the most commoncongenital malformations observed in clinicalpractice. The spectrum includes Anencephaly ,encephalocoele, craniorachischisis totalis, spinabifida aperta , meningomyelocoele,lipomeningomyelocoele, diastometamyelia ,caudal agenesis.

USG: ACRANIA WITH FROG EYE APPEARANCE

3D ULTRASOUND : ANENCEPHALY

T2 HASTE: SPLAYING OF VERTEBRAL LAMINAE AND ANENCEPHALY WITH FROG EYE APPEARANCE

USG: SPLAYING OF THORACIC SPINE

SPECIMEN SHOWING CRANIORACHISCHISIS TOTALIS

INFERIOR VERMIAN HYPOPLASIA

USG: OCCIPITAL MENINGOCOELE AND ABSENT CORPUS CALLOSUM AND SQUARING OF ANTERIOR HORNS

MRI T2 HASTE : SHOWS EXENCEPHALY USG : SHOWS EXENCEPHALY

USG : FLOATING CRANIAL CONTENTS & AMNIOTIC BANDS

USG : LEMON & BANANA SIGN

MRI HASTE : SACRAL MENINGOMYELOCELE

3D USG: SACRAL AGENESIS

USG: SACRAL MENINGOMYELOCELE

T2 HASTE TONSILLAR HERNIATION

Neural tube defects (NTD) occur because of a defect in the neuralation process. Since the anterior and posterior neuropores close last, they are the most vulnerable to defects. NTDs can be classified as open or closed types.

Open NTDs : Involve the entire CNS and are due to failure of primary neuralation. Neural tissue is exposed with associated cerebrospinal fluid (CSF) leakage.

Closed NTDs : are localized and confined to the spine and result from a defect in secondary neuralation . Neural tissue is not exposed and the defect is fully epithelialized , although the skin covering the defect may be dysplastic

PATHOPHYSIOLOGY: Two distinct processes appear to be involved in the formation of the neural tube: primary

neuralation and secondary neuralation (ie, canalization).[6] The neural plate and the notochord are formed during early embryonic development. The neural groove develops by the third gestational week. Subsequently, the neural folds form bilaterally.

Open NTDs have been suggested to result from defective primary neuralation while defective secondary neuralation gives rise to closed NTDs. Another possible explanation is that open NTDs (spina bifida in particular) result from defects in either primary or secondary neuralation, depending on their site being cranial or caudal to the posterior neuropore (ie, upper and lower spina bifida, respectively).

EPIDEMIOLOGY: 1 case in 1,200-1,400 live births, female predominance

RADIOGRAPHY:

Show structural vertebral anomalies such as hemivertebra, butterfly vertebra, or incomplete fusion of posterior elements.

Plain radiographs of patients with myelomeningocele demonstrate incomplete fusion of posterior elements and increased interpedicular distance.

ULTRASONOGRAPHY:

MENINGOCOELE AND MYELOMENINGOMYELOCOELE: These are most common forms of spinal dysraphism. A meningocele represents a

herniation of distended meninges only, whereas in a myelomeningocele, part of the spinal cord and or nerve roots lie within the herniated sac. Ultrasonography shows an anechoic lobulated sac that is continuous with a low-lying tethered cord.

SPINA BIFIDA: Findings include widening of the posterolateral spinal ossification centers, an absence of

the continuity of the skin over the spine, and a bulging sac past the dorsal skin line. Suggestive cranial findings include the presence of ventriculomegaly; small head size; an elongated cerebellum with obliteration of cisterna magna from a Chiari II malformation (the banana sign); and scalloping of the frontal skull region (the lemon sign).

ANENCEPHALY:

Morphologcial spectrum within anencephaly ranges from holocrania (severest form) to merocrania (mildest form).

Anencephaly may be sonographically detectable as early as 11 weeks. Ultrasound findings include : 1. No tissue above the orbits and absent calvarium : parts of the occipital bone and mid brain may be present

2. If a small amount of neural tissue is present it is then termed exencephaly. 3. A "frog eye" or "mickey mouse" appearance may be seen when seen in the coronal plane due to

absent cranial bone / brain and bulging orbits. 4. Polyhydramnios. CRANIORACHISCHISIS: Craniorachischisis = Anencephaly + contiguous bony defect of the spine and exposure of neural

tissue. The face and orbits are normally formed.

AMNIOTIC BAND SEQUENCE WITH EXENCEPHALY:

Amniotic bands are thin fibrous bands causing regional constrictions, amputations and disruption of cranial bone formation .The brain tissue is covered by only a vascular layer of epithelium, and can be slowly degraded by the amniotic fluid and degenerate into anencephaly.The brain tissue is covered by only a vascular layer of epithelium, and can be slowly degraded by the amniotic fluid and degenerate into anencephaly.

MRI: Usually HASTE T2 or SSFSE sequence is used , which is very fast and thus prevents motion

artifacts. Arnold-Chiari II malformations are noted in nearly all cases of myelomeningocele. The small posterior fossa, low insertion of the tentorium, and downward displacement of cerebellar tissue and medulla through a widened foramen magnum and cervicomedullary kink is noted. A low cord invariably occurs with a myelomeningocele

1.Dias MS, Li V. Pediatric neurosurgical disease. Pediatr Clin North Am. Dec 1998;45(6):1539-78,

2.Dirks PB, Rutka JT. The neurogenetic basis of pediatric neurosurgical conditions. In: Albright L, 3.Pollack I, Adelson D, eds. Principles and Practice of Neurosurgery. New York: Thieme Medical Publishers; 1999:. 23-4.

4.Harris LW, Oakes WJ. Open neural tube defects. In: Tindall GT,Cooper PR, Barrow DL, eds. The 5.Practice of Neurosurgery. Baltimore: Williams & Wilkins; 1996:. 2779-89.