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)
Spinal X-ray showing vertebral lines
Image: “X-ray of vertebral lines” by Mikael Häggström. License: CC0
Lateral view of vertebral column showing the normal curvature (cervical and lumbar lordosis; thoracic kyphosis)
Image by Lecturio.
Left: Lateral cervical spine X-ray showing normal alignment at C1–2, no significant prevertebral edema, appropriate alignment of the cervical spine, and normal interspinous distances
Image: “C1-C2 Lat” by Lucien Monfils. License: CC BY 3.0
Right: Lateral cervical spine x-ray showing C1 (blue outline) and C2 (red outline)
X-ray of thoracic spine (frontal on the left and lateral on the right):
Image: “Complete Recovery of Thoracic Myelopathy after Eleven Months of Paraplegia: A Case Report” by Malaysian Orthopaedic Journal. License: CC BY 3.0
The frontal view demonstrates no significant scoliotic curvature, a normal vertebral body height, and a normal-appearing trachea. The lateral view is slightly limited because of overexposure, which prevents complete visualization of the lower thoracic spine, although the visualized vertebral elements are unremarkable.
Lumbosacral X-ray:
Image: “Tarlov cyst: Case report and review of literature” by Prashad B, Jain AK, Dhammi IK. License: CC BY 2.0
The lumbosacral area is shown in an anteroposterior X-ray (A) and a lateral X-ray (B).
These images demonstrate normal sacroiliac joints, appropriate spinal alignment, and no height loss of the intervertebral disk space.
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)
- Trauma setting in cases such as:
- 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
CT image viewing planes:
Image by Lecturio.
The slices through this model demonstrate how axial, coronal, and sagittal images correlate with the patient’s anatomy.
Spinal CT views:
Image: “Sacral Stress Fracture following the Bone Union of Lumbar Spondylolysis” by Case Reports in Medicine. License: CC BY 4.0
Right (a) and left (b) parasagittal reconstructed CT image of the lumbar spine
(c): Axial CT image at L5 level, which shows a displaced fracture of the left/inferior vertebral body of C5.
Coronal view of the spine
Image: “Figure 1” by Clemente, M.A., et al. License: CC BY 4.0, cropped by Lecturio.
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
Intervertebral disk
Image: “Intervertebral disc” by Phil Schatz. License: CC BY 4.0
Sagittal T1-weighted MRI of the cervical spine
Image: “Possible gabapentin and ketamine interaction causing prolonged central nervous system depression during post-operative recovery following cervical laminoplasty: a case report” by Elyassi AR, Long RP, Bejnarowicz RP, Schoneboom BA. License: CC BY 2.0
Coronal T2-weighted MRI of the cervical spine shows defective ossification of vertebral bodies.
Image: “Significant traumatic atrophy of the spinal cord in connection with severe cervical vertebral body hypoplasia in a boy with Larsen syndrome: a case report and review of the literature” by Al Kaissi A, Altenhuber J, Grill F, Klaushofer K. License: CC BY 3.0
Axial T1-weighted MRI:
Image: “Paravertebral Burkitt’s Lymphoma in a Child: An Unusual Presentation” by Hoyoux C, Forget P, Piette C, Dresse MF, Florkin B, Rausin L, Thiry A. License: CC BY 3.0
In this image, A points to a dorsal paravertebral mass and B points to tumor spread.
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:
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.
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
X-ray of burst fracture of T12
Image: “Figure 1” by Akiki Alian. License: Public Domain
Sagittal CT of burst fracture of T12
Image: “Figure 1” by Akiki Alian. License: Public Domain
Burst fracture on CT:
Image: “Earthquake-related versus non-earthquake-related injuries in spinal injury patients: differentiation with multidetector computed tomography” by Dong ZH, Yang ZG, Chen TW, Chu ZG, Wang QL, Deng W, Denor JC. License: CC BY 2.0
Cross-sectional image shows burst fracture of T12 (arrow) and the spinal canal narrowing degree of 1 (constriction of ⅓ of the spinal canal).
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
Jefferson fracture:
Image: “Injuries of the upper cervical spine: A series of 28 cases” by Basu S, Chatterjee S, Bhattacharya MK, Seal K. License: CC BY 2.0, cropped by Lecturio.
a: Open-mouth X-ray shows lateral subluxation of C1–C2 (arrow).
b: Axial CT scan with fracture on the left side (arrow)
Jefferson fracture on CT:
Image: “CT of Jefferson fracture” by Michael Utz, Shadab Khan, Daniel O’Connor & Stephen Meyers. License: CC BY 4.0
Multiple fractures involving the anterior and posterior arches of C1 are seen on axial (a) and coronal (b) CT scans.
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 (type III Hangman’s fracture):
There is also significant anterior subluxation of C2 on the C3 vertebral body.
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
- Involvement of the:
- MRI used for associated ligament and/or cord injury assessment.
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.
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
Spondylolisthesis of L5 on S1 on radiography:
Image: “Spondylolistheses annotated” by Don’tKnowItAtAll. License: Public Domain
Lateral X-ray showing disruption of the center line and anterior displacement of the lumbar spine over sacral vertebrae
Spondylolysis on X-ray:
A break in the pars interarticularis (arrow) with associated anterior spondylolisthesis
Image: “Image-guided lumbar facet joint infiltration in nonradicular low back pain” by Chaturvedi A, Chaturvedi S, Sivasankar R. License: CC BY 2.0, cropped by Lecturio.
Lumbar spondylolysis in MRI:
Image: “Lumbar spondylolysis in juveniles from the same family: a report of three cases and a review of the literature” by Yamada A, Sairyo K, Shibuya I, Kato K, Dezawa A, Sakai T. License: CC BY 3.0
Note the effusion in the pars defects and in the adjacent facet joints.
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:
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)
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
Bilateral sacroiliitis on radiography (arrows):
Image: “The assessment of the spondyloarthritis international society concept and criteria for the classification of axial spondyloarthritis and peripheral spondyloarthritis: A critical appraisal for the pediatric rheumatologist” by Burgos-Vargas R. License: CC BY 2.0, edited by Lecturio.
There is subchondral sclerosis of the iliac bone, joint surface irregularities, which include some erosions on both sides, and joint space narrowing of the hips.
Sacroiliitis on MRI:
Image: “ASAS definition for sacroiliitis on MRI in SpA: applicable to children” by Pediatric Rheumatology Online Journal. License: CC BY 4.0
a: Arrows point to focal spots of bone marrow edema (BME) on the right sacroiliac (SI) joint
b: Arrows show active sacroiliitis with bilateral high signal in the joint space and BME on the sacral side of the SI joint
c: Fat-saturated T1-weighted image showing bilateral synovitis and active lesion on the left side (arrows)
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
Metastasis seen as an osteolytic lesion on X-ray:
Image: “Spinal cord compression: an unusual presentation of hepatocellular carcinoma” by Nangolo HT, Roberto L, Segamwenge IL, Voigt A, Kidaaga F. License: CC BY 2.0
Thoracic spine X-ray in a patient with hepatocellular carcinoma showing osteolytic left L1 lesion with missing pedicle (blue line)
Metastatic disease (affecting the spine) on MRI:
Image: “Lung cancer metastasis to the scapula and spine: a case report” by Demetrious J, Demetrious GJ. License: CC BY 2.0
MRI sagittal T1-weighted image reveals scattered foci of decreased signal intensity reflective of metastatic disease affecting the cervical and thoracic spine regions.
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:
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.
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:
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
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: 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.
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:
Spinal cord transection at the T6 injury level (arrow) noted in a patient who had a fall from 300 feet.
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:
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).
References
- 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§ionid=95878512
- 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
- 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
- Sexton, D., Sampson, J. (2021). Spinal epidural abscess. UpToDate. Retrieved May 6, 2021, from https://www.uptodate.com/contents/spinal-epidural-abscess
- 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
- 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§ionid=39669015
- 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
