Ossified vertebral body appears echogenic

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  Cartilaginous tip at spinous process appears hypoechoic

Cervical : Upper 7 vertebrae

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  C1 (atlas): No body, spinous process; circular shape

  
  
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  C2 (axis): Body with bony peg (dens/odontoid process)

  
  
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  C3-C6 similar in size, shape; C7 marked by longest spinous process

Thoracic : 12 vertebrae, which articulate with ribs

Lumbar : 5 vertebrae

Sacrum : Fusion of 5 segments

Coccyx : Fusion of 3-5 segments

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  Cartilaginous coccyx is hypoechoic

  
  
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  Ossified coccygeal vertebral bodies have rounded central nucleus rather than square contour, as in sacrum

Hypoechoic with central echogenic complex

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  Suspended within thecal sac, anchored to dura by denticulate ligaments, and surrounded by cerebral spinal fluid (CSF)

  
  
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  Central spinal canal: CSF-containing space throughout length of cord; contiguous with ventricular system

  
  
  
  
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    Typically do not see fluid in canal unless dilated (syrinx)

  
  
  
  
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  In contrast to brain, gray matter (which is roughly H-shaped) is on inside with white matter on periphery of cord

2 widened segments : Cervical enlargement (C3-T2) and lumbar enlargement (T9-T12)

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  Cord tapers to diamond-shaped point ( conus medullaris ), normally ends between T12 to L2-L3 disc space, most common at T12-L1

Filum terminale : Connective tissue extension of pia mater extending inferiorly from conus

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  Fuses distally into dura, attaches to dorsal coccyx

  
  
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  Should be < 2 mm in diameter

  
  
  
  
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    Hypoechoic center with more echogenic outer margin

    
    
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    Dorsal extension within thecal sac toward coccyx

  
  

Caudaequina : “Horse’s tail” of lumbar, sacral, coccygeal nerve roots below conus

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  Multiple, linear, diverging nerve roots drape dependently within thecal sac, undulate with each CSF pulsation

Thecal sac usually ends at S2

Nonossified posterior elements provide ample acoustic window in newborns

Spinal cord is best visualized by US within 1st month after birth for term infants

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  Transverse scan of cord possible in older infant as cartilaginous gap in vertebral ring allows penetration of US beam

Indications include

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  Clinical suspicion of caudal regression syndrome or cord abnormality (e.g., tethered cord, diastematomyelia, syrinx)

  
  
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  Skin findings associated with spinal dysraphism and tethered cord, including midline discoloration or dimple, skin tags, hair tufts, hemangiomas

  
  
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  Looking for hematoma or other abnormality after unsuccessful lumbar puncture

Document level of conus medullaris termination in all cases

Real-time evaluation and cine loop documentation of nerve root oscillation with CSF pulsations

Infants are preferably scanned in prone position using high-frequency (9- to 12-MHz) linear transducer

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  Decubitus position is adopted to calm struggling baby by bottle or breast feeding

Scan both longitudinally and transversely

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  Longitudinal images are ideally obtained in midline sagittal plane

  
  
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  In older infants with greater spine ossification, it may be necessary to obtain images in slightly off-midline parasagittal plane parallel to spinous processes

Focus is generally on distal end of cord but prudent to scan from craniocervical junction to coccyx

Ways to determine vertebral level where conus terminates

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  Count upward after defining lumbosacral junction

  
  
  
  
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    Lumbar vertebral bodies typically lie in horizontal plane in prone infant, while sacral vertebral bodies lie at angle

    
    
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    For more clear delineation of L5-S1, accentuate lumbar lordosis by elevation of shoulders

    
    
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    Extended field of view often facilitates identifying vertebral level and gives “big picture” of cord

  
  
  
  
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  Count downward from 12th rib

Craniocervical junction can be assessed by scanning base of skull through foramen magnum

Tethered cord

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  Conus terminates at or above inferior L2 vertebra in ≥ 98% of normal population

  
  
  
  
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    Conus at normal position by term to 2 months of age

  
  
  
  
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  Conus terminating below L2-L3 disc is abnormal

  
  
  
  
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    Significance questionable in absence of signs/symptoms particularly in preterm infants

    
    
    
    
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      Consider follow-up scan after infant attains corrected age of 40-weeks gestation

    
    
    
    
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    Important to evaluate appearance of nerve roots and filum terminale as well as conus level

  
  
  
  
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  Conus located over mid L3 or lower, or with lack of normal nerve-root pulsations, requires further evaluation with MR

  
  
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  Filum terminale thickened (> 2 mm at L5-S1 on axial/transverse images)

  
  
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  Cord may appear taut or directly apposed to dorsal thecal sac

  
  
  
  
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    Lack of conus/nerve root motion with CSF pulsations

    
    
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    Lack of dependent ventral shift of conus/nerve roots when prone

  
  
  
  
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  Look for associated lipoma (echogenic mass)