Imaging Evaluation Of Patients With Spinal Deformity

General

• evaluation of spinal deformity requires assessment of:
  • central spinal canal contents
  • paraspinal soft tissue
  • osseous structures

MRI

• noninvasive and improved soft-tissue contrast ---> largely replaced both myelography and CT myelography

CT Myelography

Advantages

• minimally invasive procedure accomplished in an outpatient setting
• spot film myelogram prior to the CT scan ---> dynamic visualisation of the central spinal canal
  • dynamic cord or nerve root impingement from spinal deformities or extradural masses (i.e., disc herniations, synovial cysts,
    degenerative facet disease, and epidural hematomas)
  • visualisation of neural structures in a dependent, weight-bearing position during flexion, extension, or side bending
    ---> cord or nerve root impingement might be better seen than on subsequent nondependent axial CT scanning
• superb depiction of subtle bony detail
• directly visualise and characterise ossific and calcific lesions
• indirect visualization of the spinal cord
  • assessment of both cord position and enlargement
• unlike MRI, claustrophobia not a clinical problem
• dynamic myelographic visualization of multilevel central stenosis in the lumbar spine cannot be
  achieved with routine MRI.

Disadvantages

• invasive procedure
  • percutaneous puncture of the sub-arachnoid space
    ---> risk of contrast reaction and spinal-tap headache
  • most common adverse reactions:
    • headache, nausea, dizziness, neck pain, and vomiting
    • most of these reactions mild
    • less common when using second-generation non-ionic contrast agents Omnipaque or Isovue
    • incidence of spinal-tap headache ---> directly related to the size of the spinal needle employed
      using a 26-gauge spinal needle < 4%
• relative lack of soft-tissue contrast ---> less sensitive & specific than MRI
• imaging limited to the axial plane
  
  • problematic evaluating patients with spinal deformities and complex curvatures

Magnetic Resonance Imaging

Advantages

• inherent soft-tissue contrast
• non invasive imaging of the entire spine including the spinal cord and spinal canal contents
• examination of choice in infection, neoplasms, degenerative lumbar disc disease, and spinal deformities
• multiplanar imaging capability ---> visualization of complex anatomy
  
  • nature and degree of cord compression, atrophy, and associated intrinsic cord abnormalities, such as syrinx and atrophy
• superior patient comfort and lack of ionizing radiation
  
  • sedation may be required in young patients or in those with claustrophobia

MRI parameters

• dependent on the suspected or known clinical diagnosis

T1-weighted (T1W) images

• scoliosis ---> multiple images in various planes often adequate
• screening for Arnold-Chiari malformation, cord syrinx, cord tethering, and cord neoplasms
  • if neoplasm --> proton density (PDW) and T2-weighted (T2W) images necessary
• choice of imaging planes depends on the type of deformity present
  • in patients with significant spinal deformity --> necessarily imaged in at least two different anatomic planes

Scoliosis

• routine evaluation with conventional X-rays
• advanced imaging techniques to detect intraspinal abnormalities
  • myelography, CT, MRI
• congenital scoliosis ---> 50% spinal cord abnormalities
  • Arnold-Chiari malformation, cord syrinx, cord tethering, diastematomyelia and cord neoplasms
• goals of complete spinal axis imaging
  
  • identify of correctable causes of scoliosis --> should be treated prior to surgical correction of the curve
    • intramedullary spinal cord tumours may present as scoliosis without neurologic signs
      ---> any patient with an unusual, painful, or rapidly progressing curve should undergo MRI
      ---> any patient with scoliosis and progressive neurologic findings MRI mandatory
  • patients with congenital scoliosis ---> spinal dysraphism and segmentation anomalies
    • MRI recommended for the following conditions:
      1. patients undergoing a spinal stabilisation procedure
      2. patients complaining of back or leg pain
      3. patients with neurologic signs
      4. patients with lumbo-sacral kyphosis, radiographic evidence of diastematomyelia or widening of
         the interpedicular distance, or a congenital bar with contra lateral hemivertebra

Tethered cord syndrome

• position of the conus medullaris tip abnormally low
• often associated with intraspinal abnormalities such as fibrous bands, bony or cartilaginous spurs, a thickened filum terminale,
  or intradural lipomas, which tether the conus medullaris at an abnormally low position in the spinal canal
• normal adult conus tip located at the L1 to L2 level
• variable in childhood
  
  • acceptable lower limits of normal at L2-L3 at the age of 2 and the L2 level at the age of 12 years
• clinical manifestations include gait difficulty, leg weakness, enuresis, muscle atrophy, back pain, and cutaneous manifestations
• skin manifestations include hypertrichosis, lipoma, hemangioma, or an overlying area of thin, atrophic skin
• foot deformities such as talipes equinovarus, calcaneovalgus, pes planus, and pes cavus may be associated
• usually presents in childhood with incontinence and hyporeflexion
• later presentation may also occur and sometimes exacerbated by growth spurts, acute disc herniation, or trauma resulting in
  greater stress to the tethered cord
• Yamada and colleagues have demonstrated diminished mitochondrial function in stretched and tethered spinal cords resulting in
  lowered oxidative metabolism and, therefore, functional deterioration of nerve cells
  ---> release of tethered cords may result in clinical improvements

MRI

• replaced CT myelography
• axial and sagittal T1W images ---> excellent screening for tethered cord
  
  • axial T1W or T2W images often necessary to determine the exact position of the tip of the conus relative to the immediately
    adjacent nerve roots of the cauda equina
  • dependence on sagittal images alone may be misleading because the immediately adjacent cauda equina nerve roots may
    merge imperceptibly with the adjacent conus and result in the false impression of a low-lying conus
  • use of axial images avoids this problem
  • filum terminale lipomas or lipomatous infiltration easily identified as areas of increased signal intensity on T1W images

Diastematomyelia

• midline sagittal clefting of the spinal cord
• may involve the conus medullaris, the filum terminale, or both
  • results in two hemicords each consisting of a single dorsal and ventral horn giving rise to ipsilateral nerve roots
  • 50% ---> split cord associated with splitting of the dural sac
  • other 50% ---> a split cord contained within a single dural sac
• Diplomyelia ---> rare phenomenon
  • true duplication of the spinal cord with each hemi-cord containing a central canal and two dorsal and two ventral horns
• cleft usually composed of a fibrous or osteocartilaginous septum arising from the dorsal aspect of a vertebral body and extending dorsally into the central spinal canal to divide the two hemicords
  • fibrous or osteocartilaginous septum uncommon in those cases associated with a single dural sac
  • location of spurs variable most commonly in the lower thoracic and lumbar region
  • length of the cleft also variable, but in most cases, the hemicords unite below the cleft
  • occasionally may extend into the conus, filum terminale, or roots of the cauda equina
• usually associated with:
  • cord tethering and thickening of the filum terminale
  • myelomeningocele and lipomyelomeningocele
  • segmental anomalies of the vertebral column
    • widened spinal canal, hemivertebrae, butterfly vertebrae, laminar anomalies, spina bifida, and intersegmental fusions
• clinically:
  • may present with symptoms related to cord tethering ---> motor weakness, gait disturbance, sensory deficits, bladder dysfunction
  • orthopedic deformities also common, including clubfoot and scoliosis
  • cutaneous manifestations such as lipomas, hairy patches, and dermal sinuses
• radiologic evaluation
  • plain film ---> segmental vertebral anomalies, widened spinal canal, central osseous spur
  • Plain CT ---> similar findings
  • CT myelography ---> assessment of the spur & nature of the cord splitting & surrounding dural sac(s)
• MRI ---> most complete evaluation
  • superior soft-tissue contrast
  • ability to image any desired plane
  • can assess the nature and length of the diastematomyelia
  • detect associated soft-tissue abnormalities
  • axial and coronal T1W images best for showing the degree of cord duplication and the associated fibrosis or osteocartilaginous spur,
  • lipomas are easily seen as areas of bright signal intensity on T1W images
  • if severe scoliosis or kyphosis ---> imaging in oblique axial or oblique coronal planes
  • detailed views of the nerve roots exiting the hemicords obtained using either T1W axial images or T2W images
  • syringohydromyelia ---> low signal intensity on T1W images & increased signal intensity on T2W images
  • shows the spurs and septa separating the hemicords

Chiari's malformations

• increased frequency in patients with spinal deformities

Chiari I malformation

• downward displacement of the cerebellar tonsils through the foramen magnum, with the forth ventricle
  remaining in normal position
• if symptomatic ---> present in late childhood or adulthood with symptoms and signs related to hind brain compression
  • headache, neckache, weakness, numbness, vertigo, and cranial nerve palsies
  • associated syringomyelia occur in 30% to 50%
• MRI diagnosis ---> downward cerebellar tonsil migration > 5 mm below the plane of the foramen magnum
  • anterior kinking of the inferior medulla and upper cervical cord, decreased size of the cisterna magna, and constriction of the subarachnoid space at the craniovertebral junction possibly related to local adhesions and arachnoidal scarring

Chiari II malformation

• downward displacement of the cerebellar vernus and tonsils into the spinal canal together with caudal displacement of the
  brainstem and elongation of the fourth ventricle
• nearly always associated with myelomeningocele ---> recognised early in life
• present with neurologic findings related to hydrocephalus or to brainstem or cerebellar compression
• MRI findings on axial and sagittal images
  
  • caudally displaced brainstem and cerebellar vermis, hydrocephalus, medullary kinking, enlargement of the foramen magnum,
    tectal beaking, and inferior displacement of the fourth ventricle
  • cerebellum usually elongated and projects superiorly through a hypoplastic tentorial incisura to form a pseudomass

Syringomyelia

• cystic cavitation of the spinal cord
  • may be congenital, post-traumatic, or associated with spinal cord tumors or infection

Hydromyelia

• dilation of the central canal of the cord possibly related to CSF flow obstruction in the region of the foramen magnum or outlet of the fourth ventricle
• hydromyelia ---> dilation of the central canal lined by the ependyma
• syringomyelia ---> dissection of CSF into the parenchyma of the spinal cord
• overlap of these two entities considerable, and distinction on the basis of MRI not possible
  ---> combined term syringo-hydromyelia often used
• syrinx cavities associated with
  
  • a number of congenital spine anomalies diastematomyelia, Chiari I and II malformations, Klippel- Fiel syndrome, and myelomeningocele
  • commonly associated with scoliosis ( 25% to 62% )
    • result from neuromuscular abnormalities produced by syringomyelia
• MRI
  • procedure of choice for evaluation of syringomyelia
  • replaced CT myelography
  • best performed using sagittal and axial T1W images
    • cord syrinx --> decreased signal intensity on T1W images and increased signal intensity on T2W images
    • walls of these cavities smooth in appearance
  • differential dg.: benign cyst versus a tumor cyst and post-traumatic myelomalacia may be difficult

Degenerative scoliosis

• deformity presenting de novo in the adult
• varying descriptive terms "collapsing scoliosis" or "senescent lumbar scoliosis"
  • to be distinguished from an adult with scoliosis that started prior to skeletal maturity
• caused by a number of factors
  
  • disc degeneration, osteoporosis, fracture, leg-length discrepancy, and osteomalacia
  • frequently in patients with prior lumbar surgery (lumbar decompression and fusion)
• similarities and differences in adults with adult-onset scoliosis and those with idiopathic scoliosis
  
  • adult-onset scoliosis --> older mean age 60 versus 42
    --> equal sex distribution versus female predominance
    --> both groups present with low back and leg pain;
    --> 90% symptoms indicative of spinal stenosis compared with 31%
• high-quality preoperative imaging to detect all areas of significant central, subarticular (lateral recess), and lateral
  (foraminal or nerve root canal) spinal stenosis

Myelography

• valuable dynamic information to severity of the central stenosis at each level

MRI

• preferred method
• can differentiate the many complicating soft-tissue processes with degenerative scoliosis
  • disc herniation, synovial chondroma, synovial cyst, hypertrophied ligamentum flavum, and epidural hematoma
  • axial and sagittal PDW1 and T2W images --> excellent views of the central spinal canal contents and allow accurate assessment of both the presence and severity of multilevel central spinal stenosis
• T2W images show each nerve root --> central, subarticular recess, and lateral (foraminal) spinal stenosis
• degree of central spinal stenosis based on the percentage of constriction of the thecal sac
  • sac constricted to 30% of normal --> severe central stenosis
• observe whether any CSF surrounds the nerve roots
  
  • if little or no CSF on axial T2W images at the level of maximum constriction -->stenosis severe
  • correlates well with obstruction of flow of contrast on myelography

Subarticular lateral recess stenosis

• occurs within the central spinal canal
• involves the root traversing the motion segment (S1 root at L5-S1 level)
• nerve pressed dorsally by a disc bar against the superior ventral edge of the lamina or the medial edge of the superior articular process of that segment

Lateral spinal stenosis

• occurs within the nerve root canal
• involves the exiting nerve root within the foramen
• stenosis occurs in an up-down or front-back direction
  • Up-down stenosis
    • common at L5-S1
    • occurring because of posterolateral osteophytic spurs (uncinate spurs) projecting from the L5 vertebrae into the caudal aspect of the L5-S1 foramen
    • results in compression of the L5 ganglion, which occupies a position within the ventral and superior half of the foramen
  • Front-back stenosis
    • hypertrophy of the superior articular process and adjacent ligamentum flavum results in anteroposterior stenosis of the foramen
• occur in patients with adult-onset degenerative scoliosis
• occurs most commonly on the concave side of the curvature
• usually the result of degenerative disc space narrowing and associated osteophytic spurring at the disc margin which results from
  increased stress loading on the concave side of the curve

Sagittal reformatted images in CT myelography

• aids in the diagnosis and quantification of these types of lateral spinal stenoses