LESI LESI Fluoroscopy and Imaging Guidance 2 — Questions and Answers
Question 1: Digital subtraction angiography (DSA) during transforaminal LESI offers what advantage over standard fluoroscopy?
- It shows disc morphology in real time
- It enhances detection of intravascular contrast uptake by subtracting the bony background (Correct answer)
- It measures epidural spread volume
- It identifies the conus medullaris level
Correct answer: It enhances detection of intravascular contrast uptake by subtracting the bony background
DSA subtracts the static bony fluoroscopic image, leaving only contrast flow visible, which makes small volumes of intravascular contrast uptake far more detectable than with standard fluoroscopy.
Question 2: Which imaging modality is used for LESI guidance when fluoroscopy is contraindicated (e.g., pregnancy)?
- CT guidance
- Ultrasound guidance (Correct answer)
- MRI-guided injection
- Blind landmark technique
Correct answer: Ultrasound guidance
Ultrasound guidance avoids ionizing radiation and can be used for lumbar ESI when fluoroscopy is contraindicated, particularly in pregnancy, using real-time visualization of the ligamentum flavum and epidural space.
Question 3: The 'loss of resistance' technique during ESI uses which substance to confirm epidural entry?
- Iodinated contrast only
- Air or preservative-free normal saline (Correct answer)
- Steroid injectate itself
- Gadolinium
Correct answer: Air or preservative-free normal saline
The loss of resistance technique uses air or preservative-free saline in a syringe; the plunger meets resistance in the ligamentum flavum and suddenly loses resistance as the needle enters the epidural space.
Question 4: A posterior epidural spread pattern without filling of nerve root sheaths on fluoroscopy after interlaminar injection suggests which problem?
- Intravascular injection
- Needle tip in the posterior epidural fat only without adequate anterior spread toward the nerve root (Correct answer)
- Intrathecal injection
- Subdural injection
Correct answer: Needle tip in the posterior epidural fat only without adequate anterior spread toward the nerve root
Posterior-only contrast spread without anterior flow toward nerve root sleeves suggests the needle may be too posterior, limiting injectate access to the target anterior epidural space where nerve roots are located.
Question 5: Radiation dose reduction during fluoroscopic LESI can be achieved by all of the following EXCEPT:
- Using pulsed fluoroscopy rather than continuous
- Collimating the beam to the area of interest
- Increasing distance between the image intensifier and the patient (Correct answer)
- Using last-image hold rather than live fluoroscopy for static checks
Correct answer: Increasing distance between the image intensifier and the patient
Increasing the distance between the image intensifier and the patient actually increases radiation dose to the patient; the intensifier should be kept as close to the patient as possible to minimize dose.
Question 6: Which finding on post-injection fluoroscopy confirms an intrathecal injection rather than epidural injection?
- Contrast outlining nerve root sleeves bilaterally
- Myelographic pattern with contrast outlining the entire thecal sac and nerve roots filling uniformly (Correct answer)
- Rapid vascular washout of contrast
- Unilateral foraminal spread
Correct answer: Myelographic pattern with contrast outlining the entire thecal sac and nerve roots filling uniformly
An intrathecal injection produces a myelographic contrast pattern with the contrast outlining the thecal sac and filling the subarachnoid space around all nerve roots in a uniform, dense pattern.
LESI LESI Fluoroscopy and Imaging Guidance 2
Digital subtraction angiography (DSA) during transforaminal LESI offers what advantage over standard fluoroscopy?