Spine and Pelvis
Myelography
Anatomy
Students should be able to identify the following structures on radiographic images:
Spinal canal, medulla oblongata, conus medullaris, cauda equina, intervertebral foramina.
Routine Projections (ARRT Required)
General Fluoroscopic Myelography
CR Location & Positioning
- SID: 40 inches (100 cm)
- Patient position: Prone or lateral recumbent for spinal puncture; table may be tilted during imaging
- Adjustments: Flex spine to widen interspinous spaces; head hyperextended in Trendelenburg to prevent contrast entering the ventricles
- CR: Directed per level of interest (usually L3 for lumbar, T7 for thoracic, C4 for cervical)
- Patient instructions: Remain still; communicate any discomfort; avoid flexing neck after injection
- Exposure: Per radiologist protocol (fluoroscopic and spot imaging under aseptic technique)
Evaluation Criteria
- Coverage (what anatomy must be included and how you verify it’s complete): Area of spine where contrast was introduced (lumbar, thoracic, or cervical) demonstrated with contrast column visible
- Rotation checks (how symmetry or alignment tells you if positioning is correct): Spine aligned and centered, symmetric pedicles and vertebral bodies
- Motion checks (how sharpness confirms patient cooperation/exposure timing): Sharp bony outlines, no blurring from patient motion or table tilt
- Technique checks (what contrast density, soft tissue visibility, and artifacts to look for): Proper exposure for contrast visualization; collimation visible
- Clinical aim (when applicable, e.g., reflux, obstruction, displacement, etc.): Visualization of subarachnoid space and spinal cord outline to detect blockages, extrinsic compression, or deformity
Contrast Media
- Type: Nonionic, water-soluble iodinated agents (e.g., iohexol [Omnipaque], iopamidol [Isovue])
- Dosage: 9–15 mL injected intrathecally
- Absorption: Begins within 30 minutes; usually radiographically undetectable after 24 hours
- Precautions: Verify correct vial; store intrathecal agents separately; never use ionic contrast for myelography
- Injection Site: L3–L4 interspace (lumbar puncture) most common; C1–C2 or cisterna magna used only when indicated
Hows & Whys of Myelography
Anatomy
- What is the subarachnoid space?
The fluid-filled space between the arachnoid and pia mater containing cerebrospinal fluid (CSF). - What is the conus medullaris?
The tapered end of the spinal cord, usually near L1–L2. - What is the cauda equina?
A bundle of spinal nerves extending below the spinal cord into the lumbar and sacral regions.
Positioning
- Why is the lumbar puncture typically done at L3–L4?
Because the spinal cord ends around L1–L2, puncturing lower reduces risk of injury. - Why is the patient’s spine flexed for lumbar puncture?
Flexion widens the interspinous spaces, making needle insertion easier. - Why is the head hyperextended when tilting the table head-down?
To prevent contrast medium from entering the cranial cavity and ventricles. - Why is the Trendelenburg position used?
To allow contrast to flow under gravity to the cervical or thoracic region being examined.
Technique & Image Evaluation
- How can you confirm that a contrast vial is approved for intrathecal use?
Check the manufacturer label; only vials marked “For Intrathecal Use” are safe for injection into the subarachnoid space. Using a non-intrathecal agent can cause severe neurotoxicity. - How should the sterile skin preparation be performed before spinal puncture?
The prep should start at the intended puncture site and move outward in concentric circles, pushing microorganisms away from the insertion point to maintain a clean center. - How do you determine if a sterile field or package has been compromised?
Any tear, puncture, moisture, broken seal, or evidence of prior opening indicates contamination, and the item must be replaced before use. - How should a sterile tray be opened?
Place it on a clean surface and open the flaps away from your body first, then the sides, and the last flap toward you, keeping hands above waist level and avoiding contact with sterile contents. - How can you tell if the patient is rotated on the image?
Unequal spacing of pedicles or asymmetric alignment of the vertebral column. - How can you tell if the contrast column is adequate?
The subarachnoid space and nerve root sleeves should appear sharply outlined without voids. - How can you tell if contrast leaked outside the subarachnoid space?
Contrast appears irregularly shaped or displaced, often pooling in soft tissues. - How can you verify that the image shows the correct spinal level?
Landmarks such as vertebral body counting and intervertebral disk levels confirm positioning.
Clinical Applications
- Why is myelography still performed despite MRI availability?
It remains useful for patients with MRI contraindications such as pacemakers or metal fusion rods. - Why is nonionic contrast required?
To prevent neurotoxicity that could result from ionic contrast entering the spinal canal. - Why is the patient kept semi-upright during recovery?
To prevent contrast from flowing cranially and to reduce post-procedure headaches. - Why must patients stay hydrated after the procedure?
Fluids aid contrast absorption and help replenish cerebrospinal fluid volume.
