LESI LESI Techniques and Approaches 2 — Questions and Answers
Question 1: During transforaminal LESI, which fluoroscopic view is used to confirm the needle tip is in the posterior (not anterior) epidural space?
- AP view showing the needle at the 6 o'clock position of the foramen
- Lateral view confirming the needle tip is posterior to the posterior vertebral body line (Correct answer)
- Ipsilateral oblique view showing the 'Scotty dog' eye
- Caudal tilt AP view
Correct answer: Lateral view confirming the needle tip is posterior to the posterior vertebral body line
The lateral fluoroscopic view allows the physician to confirm that the needle tip is posterior to the posterior vertebral body margin, ensuring correct epidural rather than anterior disc or vascular placement.
Question 2: The paramedian interlaminar approach to lumbar epidural injection differs from the midline approach primarily in that:
- It accesses the epidural space through the neural foramen
- The needle is angled medially and cephalad, bypassing the spinous process (Correct answer)
- It is performed without fluoroscopic guidance as standard of care
- It requires a larger-gauge needle for reliable loss of resistance
Correct answer: The needle is angled medially and cephalad, bypassing the spinous process
The paramedian approach angles the needle from a lateral starting point medially and cephalad, avoiding the spinous process and often encountering a thinner ligamentum flavum.
Question 3: An inadvertent subdural injection during LESI differs clinically from an intrathecal injection because:
- It deposits injectate between the dura and arachnoid, not within the CSF (Correct answer)
- It immediately produces total spinal anesthesia due to direct CSF dilution
- It is easily identified by free aspiration of cerebrospinal fluid
- It has no clinical significance and self-resolves within minutes
Correct answer: It deposits injectate between the dura and arachnoid, not within the CSF
The subdural space lies between the dura mater and arachnoid mater; injected material does not freely mix with CSF, producing a variable and often delayed neurological picture distinct from true intrathecal injection.
Question 4: When performing a caudal epidural injection, the 'pop' or loss of resistance typically occurs as the needle passes through which structure?
- The posterior sacral ligament overlying the sacrum
- The sacrococcygeal ligament connecting the coccyx to the sacrum
- The sacrococcygeal membrane covering the sacral hiatus (Correct answer)
- The posterior longitudinal ligament of the lower sacrum
Correct answer: The sacrococcygeal membrane covering the sacral hiatus
The sacrococcygeal membrane (homologue of the ligamentum flavum) covers the sacral hiatus; piercing it produces the characteristic 'pop' signaling entry into the sacral epidural canal.
Question 5: Which fluoroscopic view is most useful for identifying the sacral hiatus before performing a caudal epidural injection?
- Anteroposterior (AP) view
- Lateral view (Correct answer)
- Ipsilateral oblique view
- Caudal tilt AP view
Correct answer: Lateral view
The lateral view clearly delineates the sacral hiatus, the sacrococcygeal junction, and the depth of the sacral canal, guiding correct needle angulation and depth.
Question 6: During transforaminal LESI setup, the C-arm is obliqued ipsilaterally until which classic landmark is visualized?
- The spinous process is centered over the disc space
- The 'Scotty dog' silhouette of the vertebra with the pedicle as the eye (Correct answer)
- The interlaminar space reaches its maximum opening
- The contralateral pedicle overlaps the midline
Correct answer: The 'Scotty dog' silhouette of the vertebra with the pedicle as the eye
The oblique view creates the 'Scotty dog' appearance where the pedicle represents the eye; the needle targets the inferior aspect of this eye (the superior foramen) for safe entry.
Question 7: What is the primary advantage of the interlaminar approach over the transforaminal approach for LESI when bilateral radiculopathy is present?
- More precise delivery to a single targeted nerve root
- Lower risk of intravascular injection into radicular arteries
- Better bilateral spread of injectate to cover both sides simultaneously (Correct answer)
- Easier visualization of correct needle placement under fluoroscopy
Correct answer: Better bilateral spread of injectate to cover both sides simultaneously
The interlaminar approach deposits steroid in the midline posterior epidural space, allowing bilateral spread to address bilateral or diffuse radicular symptoms with a single injection.
LESI LESI Techniques and Approaches 2
During transforaminal LESI, which fluoroscopic view is used to confirm the needle tip is in the posterior (not anterior) epidural space?