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
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:
patients undergoing a spinal stabilisation procedure
patients complaining of back or leg pain
patients with neurologic signs
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
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
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