neonatal spine normal
in the neonate, the cartilaginous vertebral components make ultrasound excellent for:
- assessing suspected neural tube defects. particularly closed defects.
- guiding lumbar puncture and spinal intervention.
ultrasound of a normal neonatal spine sagittally at the level of conus medullaris.
the central canal of the cord continues distally as filum terminale.
note that the nerve roots in cauda equina are laying in the dependant aspect of the thecal sac.
avoid using the spinous processes to calculate level because they angle caudally.
sagittal neonatal sacrum ultrasound image.
ultrasound of a normal neonatal spine. transverse plane.
image sequence from superior to inferior.
schematic of the neonatal spine showing approximate transverse ultrasound probe levels corresponding to the adjacent images.
panoramic view from lower thoracic to the buttock
scan protocol
role of ultrasound
ultrasound is a cost effective, readily accessible tool to investigate the neonatal spine.
it is the premier tool for screening for most suspected neonatal spinal abnormalities from the first few hours of life.
it requires no ionizing radiation or sedation. generally, ultrasound can be used as a stand alone tool to investigate for spinabifida occulta, cord tethering, masses, infection and the degree of clinically obvious abnormalities.
indications
- posterior mid-line cysts/masses
- mid-line skin dimples – often called a ‘sacral pit’.
– babies with tiny mid-line skin defects low in the sacro-coccygeal region at the upper buttock cleft, will generally be normal.
– larger or higher clefts are more likely associated with spinal abnormalities.
- tufts of hair
- visible haemangioma / skin discolouration
- anal atresia / stenosis
- guidance for lumbar puncture
- post injury / trauma
- post surgical – follow up or complication
- infection / abscess
limitations
caution needs to be exercised with open (or near-open) neural tube defects. if scanning is required in these circumstances, sterile technique should be observed, ideally with a sterile gel stand-off so minimal pressure is required. sterile water/saline may be appropriate rather than gel. this should be discussed with the managing physician.
generally, if available, mri is the modality of choice for open neural tube defects, including small csf leaks.
patient preparation
- prone, head, slightly higher than the feet to better fill the lower csf space.
- a rolled towel (or similar) under the baby’s abdomen to slightly widen the posterior inter-spinous spaces.
if using ultrasound to guide a spinal tap, the more erect you are able to position the baby, the more csf will be visible, avoiding a ‘dry-tap’.
equipment setup
- a high frequency, linear array transducer. minimum 8mhz. ideally a large footprint to offer more length of the image field.
- you may also require a smaller footprint, higher frequency probe to assess fistulae or for procedural needle guidance.
- ‘panorama’ function is useful to demonstrate the relationship of anatomy/pathology.
- warm room.
- warm gel.
- warm hands.
- dim lighting
- bribery: a soothing parent or assistant, food, pacifier (dummy). glycerine (glucose syrup) can be useful to dip the pacifier, or a maternal finger, in to encourage quiet sucking..
remember, a warm, quiet relaxed baby leads to a quicker easier scan with more accurate results.
common pathology
- spina bifida and its sequelae.
- low conus medullaris – cord tethering
- arachnoid cysts / pseudomenigoceles
- intra-thecal lipomata
- skin – thecal sac fistula
- haemangioma
- haematoma
- complicated csf ( infection or bleeding)
- vertebral agenesis, malformation or malalignment
scanning technique
begin with a survey scan (this will take less than a minute) followed by a detailed assessment.
survey
- firstly in transverse, sweep from the mid thoracic region to the sacro-coccygeal region.
– are the posterior neural arches, paired and uniform.
– are there any obvious, gross pathologies.
- next, a sagittal sweep from one side to the other.
– depending on your transducer footprint as to how many passes you require to cover the anatomy.
– are there any obvious, gross pathologies.
detail scanning
- is the cord and csf space uniform in shape?
there are two primary methods to determine the level of conus.
- identify the 12th rib, and thus t12 and count down.
- identify the lumbo-sacral junction and count up from l5.
normal conus position is: no lower than the top of l3 in a term infant or the bottom l3 in a pre-term infant.
– be cautious of variation in the number of lumbar vertebrae.
* if the level cannot be accurately determined, a radio-opaque marker (ball bearing or similar) may by fixed to the skin over conus, and a plain x-ray performed. this should only be performed if there is sufficient clinical concern. ensure the baby is flat when the marker is applied to eliminate error from relative movement of the skin-spine.
- identify filum terminale.
normal filum terminale ultrasound image.
– it should appear as thin closely related parallel lines extending from conus to the lowest reaches of the thecal space (approximately s2).
– filum is approximately 2mm in diameter.
– a filar cyst (ventriclus terminalis) is an commonly seen anatomical variant. it will be seen as a focal fusiform thickening of filum, usually close to conus.
examine cauda equina
transverse ultrasound view of normal symmetry of cauda equina surrounding the tip of conus and the filum.
longitudinal ultrasound view of normal cauda equina
the nerve roots comprising cauda equina should lie in the dependent portion of the thecal sac.
– should see gentle oscillating movements with the baby’s cardiac pulsations and respiration.
– symmetry. look for asymmetry indicative of pathology (space occupying mass or unilateral abnormality)
the nerve roots comprising cauda equina should lie in the dependent portion of the thecal sac.
– should see gentle oscillating movements with the baby’s cardiac pulsations and respiration.
– symmetry. look for asymmetry indicative of pathology (space occupying mass or unilateral abnormality)
- examine the bony anatomy
– particular attention should be paid to the integrity the posterior neural arches in the transverse plane.
– check the vertebral bodies for alignment, shape and symmetry in both transverse and sagittal planes.
- examine the dimple
– if there is a dimple or skin defect, this should be carefully examined with a high frequency probe to look for a skin – thecal sac fistula.
– use minimal pressure so as not to compress and thus obscure a fistula tract.
– an anatomical variant is a thin hypoechoic fibrous band from the dimple to the coccyx. this is of no clinical signifigance. most true fitsulae will be higher than the coccygeal region.
– if csf is leaking, an mri should be performed.
basic hardcopy imaging
- t12 – s2 posterior bony arches in transverse.
- transverse cord, conus and nerve roots.
- longitudinal distal cord with conus and labelled vertebral numbers (t12, l1, l2 etc).
- longitudinal at the ‘dimple’.
– if necessary, m-mode (or capturing a cine loop) can be used to document normal or abnormal motion of the cord or nerve roots.
– appropriate documentation of any pathology identified.