Imaging of the Spine and Spinal Cord

The vertebral column is the most important anatomical and functional axis of the body, consisting of 7 cervical, 12 thoracic, and 5 lumbar vertebrae and limited cranially by the skull and caudally by the sacrum. The vertebral column provides structural support and protection for the spinal cord, which is housed in the spinal canal. The vertebral column and the spinal cord may be affected by various diseases, in which different imaging methods are important for correct diagnosis and management. Radiographs and CT scans are useful in evaluating bony structures, especially in excluding fractures and checking hardware. Additionally, CT scans also provide information on soft tissues. MRI is performed for evaluation of tumors, infection, disk herniations, and other soft tissue abnormalities including acute ligamentous or spinal cord injury.

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Radiography

Overview

Before the advent of CT and MRI, X-ray imaging was widely used to study the bones of the spine.

Views and spine structures:

  • Frontal view (anteroposterior (AP) or posteroanterior (PA)):
    • Spinous processes: hyperdense structures over the midline
    • Pedicles: round, lucent circles on both sides of the spinous processes
    • Facet joints 
    • Vertebral body heights and intervertebral disk spaces
  • Posterior oblique view:
    • Parts of the spine are represented as parts of a dog.
    • “Scottie dog” sign
  • Open-mouth (odontoid) view: alignment of C1 lateral masses and C2 vertebra
  • Lateral view:
    • Evaluation of spinal alignment
    • Vertebral body heights and intervertebral disk spaces

Normal radiographic findings

  • Bones:
    • Appear white (radiodense)
    • Certain pathologies can differ in radiodensity.
  • Normal spine:
    • Cervical and lumbar lordosis (anterior convexity) 
    • Thoracic kyphosis (posterior convexity)
  • Spinal alignment:
    • The spinous processes, pedicles, and laminae of the vertebrae must be checked for adequate positioning.
    • Vertebral lines should be parallel:
      • Anterior vertebral line: connects the anterior margins of the vertebral bodies
      • Posterior vertebral line: connects the posterior margins of the vertebral bodies
      • Spinolaminar line: connects the posterior margins of the spinal canal
      • Interspinous line: connects the tips of the spinous processes
  • Soft tissues: cannot be clearly seen (radiolucent) unless they an contain abnormal density (such as calcification)

CT

Overview

A CT scan can evaluate both bone and soft tissue structures.

  • Indications for spinal CT scan:
    • Trauma setting in cases such as: 
      • Glasgow Coma Scale score < 15
      • Unstable vital signs
      • Acute paralysis
    • For evaluation before or after surgery, especially if there is a contraindication to MRI
    • Malignancy 
    • To guide some procedures (e.g., CT-guided epidural injection)
  • Contraindications: pregnancy

Normal CT findings

Anatomy:

  • Bone appears hyperdense (> 250–700 Hounsfield units) 
  • Most vertebrae have common structures: 
    • Body 
    • Pedicles 
    • Transverse processes
    • Spinous process
    • Spinal canal (where the spinal cord lies) 
  • Vertebrae also differ in shape and structures according to their anatomic position.
  • Spinal cord density on CT (in Hounsfield units): 
    • Gray matter > white matter > CSF 
    • Note: Evaluation of gray versus white matter is more difficult in the spinal cord than in the brain.

Different planes can be used: 

  • Axial
  • Sagittal 
  • Coronal

MRI

Overview

MRI provides superior visualization of intraspinal anatomy.

  • Indications for spinal MRI:
  • Spinal cord injury:
    • Hemorrhage
    • Spinal cord contusion
    • Edema
    • Compression by a bony fragment
    • Acute traumatic disk herniation
    • Ligamentous injury
  • Low back pain: 
    • Disk herniation 
    • Malignancy 
    • Infections (e.g., osteomyelitis or abscess) 
  • Neural tube defects 
  • Spinal cord disease (e.g., multiple sclerosis)
  • Relative and absolute contraindications: 
    • Ferromagnetic implants: can move or overheat, causing injury
    • Electrical or mechanical devices:
      • Cochlear implants
      • Pacemakers
      • Drug/insulin infusion pumps
    • Claustrophobia: treated with sedatives
    • Allergy to contrast agent: may manifest as anaphylaxis
    • Abnormal renal function: if contrast agent is needed

Normal MRI findings

Anatomy:

  • Most vertebrae have common structures: 
    • Body 
    • Pedicles 
    • Transverse processes
    • Spinous process
    • Spinal canal
  • Shape and structures of vertebrae differ according to their anatomic position.
  • Intervertebral disk: The nucleus pulposus should be contained within the annulus fibrosus.

On T2-weighted images:

  • Nucleus pulposus: hyperintense (high water content, which is T2 hyperintense)
  • Annulus fibrosus: hypointense (due to the high collagen content)

Different planes can be used:

  • Axial
  • Sagittal 
  • Coronal

Tissue appearance on MRI

Table: Tissue appearance on MRI
Tissue T1-weighted images T2-weighted images
Fluid (e.g., CSF) Dark Bright
White matter Light gray Dark gray
Gray matter Gray Light gray

Clinical Correlation

Compression fracture

  • Vertebral compression fracture: most common type of osteoporotic fracture
  • Most common sites:
    • T7–T8
    • T12–L1
  • Kummell disease: delayed vertebral body collapse, which is a rare complication of osteoporotic compression fractures and suggests avascular necrosis
  • X-ray:
    • Wedge-shaped vertebral body: compression of the superior and/or anterior surface
    • +/– Kyphosis
    • Kummell disease is seen with air in the vertebral body representing avascular necrosis.
  • MRI or CT considered if further evaluation (acuity or instability of wedge fracture) is needed.
Compression fractures

Compression fractures:
A lateral thoracic spine radiograph shows multiple severe vertebral body compression fractures (vertebra plana; small arrows) characteristic of multiple myeloma (among other etiologies). At T11 and T12 (open arrows), mild vertebral sclerosis is a result of treatment and healing.

Image: “Multiple myeloma: imaging evaluation of skeletal disease” by Sexton C, Crichlow C. License: CC BY 2.0

Burst fracture

  • Vertebral compression injuries affect the cervical, thoracic, and lumbar areas, with high-energy axial loading:
    • From above, via the skull
    • From below, via the pelvis or feet
  • Body of the vertebra breaks up or bursts in an AP plane.
  • X-ray: 3-column unstable fracture of the vertebral body 
  • CT:
    • 3-column unstable fracture of the vertebral body 
    • Vertebral body retropulsion 

Jefferson fracture

  • Bone fracture of C1 (atlas)
  • X-ray:
    • Seen on open-mouth X-ray
    • Lateral displacement of the lateral masses of C1 away from the dens (> 6 mm indicates ligament injury) 
  • CT: seen as C1 fractures involving the anterior and the posterior arches of C1

Hangman’s fracture

  • Traumatic spondylolisthesis of C2 (axis) 
  • X-ray: 
    • Bilateral fractures of the lamina and pedicles of C2
    • Anterior displacement of the C2 vertebral body (anterolisthesis of C2 on C3)
Radiography shows dens fracture on c2

Radiography shows dens fracture on C2 (type III Hangman’s fracture):
There is also significant anterior subluxation of C2 on the C3 vertebral body.

Image: “An unusual presentation of an atypical hangman’s fracture” by Yilmaz F, Akbulut S, Kose O. License: CC BY 2.0

Chance fracture

  • “Seatbelt fractures”
  • Flexion-distraction injury of the spine, often in the thoracolumbar area
  • Seen in both X-ray and CT (more accurate details):
    • Involvement of the: 
      • Vertebral body
      • Pedicles 
      • Spinous process
    • ↑ Interspinous distance 
  • MRI used for associated ligament and/or cord injury assessment.
Chance fracture on ct

Chance fracture on CT (images at the time of injury):
Images reveal a Chance-type injury with an associated L2 compression fracture of the right vertebral body (a), a horizontal split of the right L2 pedicle (b), and the splitting and distraction of the left L2 transverse processes, left L2 pedicle, and L2 middle column (c), resulting in asymmetrical kyphoscoliosis.

Image: “Asymmetrical pedicle subtraction osteotomy for progressive kyphoscoliosis caused by a pediatric Chance fracture: a case report” by Scoliosis and Spinal Disorders. License: CC BY 4.0

Spondylosis, spondylolysis and spondylolisthesis

  • Imaging is performed to evaluate back pain and is commonly limited early, unless the patient exhibits red flags such as fever, trauma history, or neurologic findings.
  • Spondylosis: 
    • Degeneration/osteoarthritis of the vertebral column
    • X-ray:
      • Loss of height of the disk space 
      • Sclerosis of the end plates 
      • Vacuum phenomenon: gas within the disk space
      • Facet degenerative changes: bony osteophytes
  • Spondylolysis:
    • Defect (stress fracture or separation) in the pars interarticularis (a bone connecting one facet joint to another)
    • Children and adolescents most susceptible
    • Majority in L5
    • X-ray: break seen in pars interarticularis
    • MRI:
      • Detects bone marrow edema in the pedicle and pars region (early sign of injury)
      • Important to detect early bone stress reaction to prevent defects.
    • SPECT can be used, but it has a risk of radiation exposure.
  • Spondylolisthesis: 
    • Slippage of a vertebra forward in relation to the vertebra below it
    • Often accompanies spondylolysis (especially in bilateral defects)
    • Common in lumbar area
    • X-ray (lateral radiograph):
      • Anterior displacement of a vertebra relative to that below it
      • Disruption of vertebral lines

Disk herniation

  • Herniation of the nucleus pulposus (beyond the annulus fibrosus) into the spinal canal through a defect:
    • Protrusion: base wider than herniation dome 
    • Extrusion: base narrower than herniation dome
  • X-ray: limited benefit
  • MRI: 
    • Both CT and MRI are sensitive, but MRI can identify other pathologies in the spine (inflammatory, vascular disorders).
    • No ionizing radiation
Disk herniation on mri

Disk herniation on MRI:
T2-weighted MRI showing L5–S1 disk herniation into the spinal canal and degenerative disk changes (loss of T2 signal intensity and loss of disk-space height)

Image: “Spinal-disc-protrusion-l5” by Damato. License: Public Domain

Sacroiliitis

  • Inflammation of the sacroiliac joint(s)
  • X-ray:
    • 1st-line test
    • Sclerosis of the iliac side of the sacroiliac joint
    • Irregular joint end plate
  • CT:
    • Detects erosions, bone sclerosis, ankylosis
    • Significant radiation 
  • MRI:
    • Most sensitive test
    • Early changes are detected when other imaging studies are negative.
    • Can show bone marrow edema and disease severity

Vertebral metastatic lesions

  • Metastatic involvement of the vertebral spine
  • Bone: 3rd most frequent site of metastasis
    • Predominantly osteoblastic (↑ irregular bone trabeculae): prostate, small-cell cancer, carcinoid
    • Predominantly osteolytic (↑ bone destruction): non-small-cell cancer, renal cell carcinoma, thyroid cancer
    • Mixed: breast cancer
  • X-ray:
    • Initial test
    • Osteolytic lesions: radiolucent lesions (“lytic” = “lucent”)
    • Osteoblastic lesions: radiopaque lesions 
  • CT and MRI: help determine complications such as spinal cord compression, impending pathologic fractures

Tumors

MRI is the study of choice for spinal tumors.

  • Meningioma:
    • An intradural, extramedullary spinal tumor that arises from the meninges.
    • Usually isointense to gray matter on T1 and T2
    • Intense and homogeneous enhancement 
    • Compresses the cord
  • Ependymoma: 
    • Centrally located mass within the cord (intramedullary)
    • Isointense to hypointense lesion on T1
    • Hyperintense lesion on T2
    • Intense and inhomogeneous enhancement
Meningioma on mri

Meningioma on MRI:
A and B: The T1- and T2-weighted images both show slightly lower intensity than that of the cord, revealing a homogeneous lesion.
C: Contrast-enhanced MRI shows the high homogeneous signal intensity of the tumor.

Image: “The surgical treatment for spinal intradural extramedullary tumors” by Ahn DK, Park HS, Choi DJ, Kim KS, Kim TW, Park SY. License: CC BY 2.0

Vertebral osteomyelitis and diskitis

  • Infection of the bones of the spine from direct inoculation (trauma), hematogenous or contiguous spread
  • X-ray:
    • Used as adjunct to MRI
    • Changes noted when disease is advanced
  • MRI:
    • Most sensitive test
    • T1-weighted images: decreased signal intensity in the disk and vertebral bodies, with less well defined end plate 
    • T2-weighted images: increased disk signal intensity (can have increased vertebral body signal intensity)
    • After contrast administration: 
      • Vertebral body and disk enhancement
      • +/– ring enhancement indicating abscess formation
  • CT done when MRI is not available or is contraindicated.
Vertebral osteomyelitis on mri

Vertebral osteomyelitis on MRI:
Enhanced T1-weighted MRI showing vertebral osteomyelitis involving the L1 and L2 vertebral bodies. Of note, the relative sparing of the intervertebral disk space can typically be seen with mycobacterial infection.
(a): Sagittal view
(b): Axial view

Image: “Vertebral Osteomyelitis Caused by Mycobacterium abscessus Surgically Treated Using Antibacterial Iodine-Supported Instrumentation” by Kato S, Murakami H, Demura S, Yoshioka K, Hayashi H, Yokogawa N, Fang X, Tsuchiya H. License: CC BY 3.0

Epidural abscess

  • Accumulation of pus between the outer meningeal layer and the vertebral column
  • MRI:
    • With contrast: preferred method
    • Detects early changes and details regarding location and extent
    • T2-weighted images:
      • Hyperintense mass with rim enhancement and a hypointense center
      • If diffusion restriction series are obtained, abscesses tend to show increased signal.
Epidural abscess on mri

Epidural abscess on MRI: L4–5 infectious spondylitis in a male patient:
A: Sagittal T1- and T2-weighted and contrast MRI shows L4–5 epidural abscess with compression of neural elements.
B: After treatment, sagittal T2-weighted MRI at 6-month follow-up demonstrates the disappearance of the abscess.
C: Sagittal CT reveals L4–5 disk space narrowing leading to spontaneous fusion.

Image: “Minimally invasive endoscopic treatment for lumbar infectious spondylitis: a retrospective study in a tertiary referral center” by Yang SC, Fu TS, Chen HS, Kao YH, Yu SW, Tu YK. License: CC BY 2.0

Spinal cord transection

  • Traumatic spinal cord injury: most occur with injury to the vertebral column (bone fracture, joint dislocation, ligament tear, or intervertebral disk herniation)
  • MRI:
    • Loss of cord continuity
    • +/– compression by bony fragments 
Mri of spinal cord injury

MRI of spinal cord injury:
Spinal cord transection at the T6 injury level (arrow) noted in a patient who had a fall from 300 feet.

Image: “Survival following a vertical free fall from 300 feet: the crucial role of body position to impact surface” by Weckbach S, Flierl MA, Blei M, Burlew CC, Moore EE, Stahel PF. License: CC BY 2.0, cropped by Lecturio.

Multiple sclerosis

  • CNS disease characterized by immune-mediated inflammatory demyelination
  • MRI:
    • Test of choice
    • Demyelination would be seen:
      • T1: Lesions are isointense or hypointense.
      • T2: Lesions are hyperintense.
      • T1 + contrast: Active areas of demyelination show contrast enhancement (incomplete ring enhancement can be seen).
Tumefactive multiple sclerosis on mri

Tumefactive multiple sclerosis on MRI:
C3 cervical intramedullary lesion (arrow) that is hyperintense on T2-weighted images (A), is isointense on T1-weighted images (B), and has areas of contrast enhancement (C).

Image: “Figure 1: Initial MRI” by Mamilly A, Aslan A, Adeeb N, et al. License: CC BY 3.0

References

  1. Amini, B., Metwalli, Z. A. (2014). Musculoskeletal. In Elsayes, K. M., Oldham, S. A. (Eds.), Introduction to Diagnostic Radiology. McGraw-Hill. https://accessmedicine.mhmedical.com/content.aspx?bookid=1562&sectionid=95878512
  2. Hansebout, R., Kachur, E. (2021). Acute traumatic spinal cord injury. UpToDate. Retrieved May 6, 2021, from  https://www.uptodate.com/contents/acute-traumatic-spinal-cord-injury
  3. Peel, T., McDonald, M. (2021). Vertebral osteomyelitis and discitis. UpToDate. Retrieved May 6, 2021, from https://www.uptodate.com/contents/vertebral-osteomyelitis-and-discitis-in-adults
  4. Sexton, D., Sampson, J. (2021). Spinal epidural abscess. UpToDate. Retrieved May 6, 2021, from https://www.uptodate.com/contents/spinal-epidural-abscess
  5. Tsoi, C., et al. (2019). Imaging of sacroiliitis: current status, limitations and pitfalls. Quantitative Imaging in Medicine and Surgery 9:318–335. https://doi.org/10.21037/qims.2018.11.10
  6. Wasserman, P. L., Pope, T. L. (2011). Imaging of joints. In Chen, M. M., Pope, T. L., Ott, D. J. (Eds.), Basic Radiology, 2nd ed. McGraw-Hill. https://accessmedicine.mhmedical.com/content.aspx?bookid=360&sectionid=39669015
  7. Yu, H. M., Hoffe, S. (2021). Epidemiology, clinical presentation, and diagnosis of bone metastasis in adults. UpToDate. Retrieved May 6, 2021, from https://www.uptodate.com/contents/epidemiology-clinical-presentation-and-diagnosis-of-bone-metastasis-in-adults

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