Dr/Ahmed Bahnassy

Consultant Radiologist

Riyadh Military Hospital

Why US spines ?

Spinal ultrasound (SUS) is becoming increasingly accepted as a first line screening test in neonates suspected of spinal dysraphism .

Challenging MRI

The advantages of SUS are not only a diagnostic sensitivity equal to MRI but that, unlike MRI, SUS can be performed portably, without the need for sedation or general anaesthesia.

In addition, MRI is highly dependent on factors affecting resolution, including patient movement, physiological motion from cerebral spinal fluid (CSF) pulsation and vascular flow, factors that do not affect SUS . New generation high frequency ultrasound machines

with extended field of view capability now permit imaging of high diagnostic quality in young babies.

When to perform ?

SUS is possible in the neonate owing to a lackof ossification of the predominantly cartilaginousposterior arch of the spine . The quality ofultrasound assessment decreases after the first3–4 months of life as posterior spinous elementsossify, and in most children SUS is not possiblebeyond 6 months of age. However, the persistingacoustic window in children with posterior spinaldefects of SD enables ultrasound to be performedat any age

When to request US spines ?Current RCR guidelines are thatall neonates with a hairy patch or sacral dimple should undergo SUS . However, while more than 90% of patients with occult SD have a cutaneous abnormality over the lower spine , a cutaneous marker may have a low yield in predicting the presence of a clinically significant abnormality. In a recent review of 200 SUS examinations performed over an 11-year period, SD was found in less than 1% of cases when a cutaneous marker was the only clinically detectedabnormality .

Gastrulation stage

Neurulation stage

Retrogressive differentiation and relative cord ascent

Formation of the ventriculus terminalis, the

caudal portion of the conus medullaris, and the filum terminale through the processes of canalization and retrogressive

differentiation.

Sonographic examination of the neonatal spine is performed with the infant in a warm room lying in a prone, lateral decubitus, or semi-erect position.

Feeding the infant before examination helps him

or her to relax. Placing a towel under the infant’s pelvis will flex

the spine enough to separate the midline posterior arches .

.

A high frequency (7- to 15-MHz) linear-array transducer should be used .. higher frequency transducers are beneficial for optimization of superficial structures such as skin lesions and sinus tracts.

Extended field-of-view (EFOV) imaging is

an additional feature that can demonstrate the whole neonatal spine from T12 to the coccyx

• Mark T 12 in transverse plane (presence of ribs witnessing)

• Then count downwards to end of cord.

Alternatively by

Locating the last lumbar vertebra, L5, byevaluating the lumbosacral junction. Thencount cephalad to the conus medullaris.

Locating the last ossified vertebral body,the first coccygeal segment. Then count thefive sacral segments cephalad into thelumbar vertebra.

The spinal cord lies in the spinal canal within anechoic CSF of the subarachnoid space. Surrounding

the canal is the dura mater, which is shown by anechogenic line dorsal and ventral to the canal. The

cord is lined with the arachnoid sheet, which exhibits an echogenic line parallel to the cord’s surface.

Caudally, the lumbar enlargement tapers, forming the conus medullaris, which extends and becomes the filum terminale.

Filum teminale

The filum terminale images as an echogenic cordlike structure that is surrounded by echogenic nerve roots of the cauda

equina. For that reason, separation of the two is difficult.

However, the filum terminale is commonly more echogenic than the surrounding cauda equina.

The filum terminale normally measure less than or equal to 2 mm.

Cord

On a sagittal image, the spinal cord appears asa hypoechoic cylindrical structure with two echogeniccomplexes centrally. These represent thecentral echo complex. The normal cord lies onethird to one half of the way between the dorsal andventral walls of the spinal canal On a transverse image, the cervical spinal cordappears as an oval shape, whereas the thoracic andlumbar portions are more circular.

Conus level

The level of the conus usually ends between T12 and L1 or L2 .If it ends at the L2-L3 disk space or

lower, it is abnormal, and one should explore for any tethering masses. However, it must be noted that a normal cord may lie around L3, mainly in preterm infants.

The normal position of the cord should be centralin the spinal canal. The spinal cord is held in placeby echogenic dentate ligaments passing laterallyfrom each side of the cord.

The normal spinal cord produces a rhythmic movement

• Standard views

Cystic ventriculus terminalis (normal variant)

Cystic distension of distal spinal canal (normal variant )

Size smaller than

5 mm and stability over time

distinguish this normal variant

from small syrinx.

Filar cyst (normal variant)

criteria for filar cyst:

location just below

conus medullaris, fusiform shape, well defined, thin walled, and hypoechoic.

Pseudo-masses

• Clumped nerve roots..

• Use 2 planes..to see the whole length of nerve root.

Dysmorphic coccyx

• Cartilagenous angulated lesion.

• Not dermal sinus track.

Three processes can lead to congenital anomalies:

First, premature separation of the skin ectoderm from the neural tube can lead to entrapment of mesodermal elements, such as fat.

Second, failed neurulation leads to dysraphisms,

such as myelomeningocele(overt or closed )

Last ,anomalies of the filum terminale, such as fibrolipomas and caudal regression syndrome caused by disembryogenesis of the caudal cell mass

Classification

Congenital spinal dysraphisms can be classified on the basis of the presence or absence

of a soft-tissue mass and skin covering .

Those without a mass include tethered cord,

diastematomyelia, anterior sacral meningocele,

and spinal lipoma.

Those with a skin covered soft-tissue mass include lipomyelomeningocele and myelocystocele.

And those with a back mass but without skin covering include myelomeningocele and myelocele

Lipoma

Dorsal dermal sinus track

Tethered cord

Sonographically, tethered cord is diagnosedin neonates by the presence of a low-lyingconus (below the L2–L3 disk space) andlack of normal nerve root motion during realtimesonography

Search for cause

Intradural lipoma

• Hyperechoic dural mass..

• Tethered cord.

Thick filum terminale

Fatty filum

Lipoma of filum terminale

Tethered cord

L3

Diastematomyelia

• Echogenic spur between two hemicords in transverse image.

Caudal regression syndrome

• Blunted conus medullaris.

• Fatty filum• Absence of sacral

vertebrae and coccyx .

Myelomeningocele

• Cystic mass (CSF)

• +tethered cord

• +neural elements.

• +soft tissue mass

Unilocular meningocele

Lipomyelomenimgeocyle

Neuroblastoma

Sacrococcygeal teratoma

Other renal anomalies

Conclusion• Spinal ultrasound (SUS) is becoming

accepted as a first line screening test in neonates with high sensitivity and specificity.

• Recognizing normal anatomy ,variants and congenital anomalies early in life help in futur planning of management .