LESI LESI Anatomy and Neuroanatomy 2 — Questions and Answers
Question 1: In the lumbar spine, the exiting nerve root at L4-L5 passes through which foramen?
- L3-L4 foramen
- L4-L5 foramen
- L5-S1 foramen
- L4 nerve exits at the L3-L4 foramen (Correct answer)
Correct answer: L4 nerve exits at the L3-L4 foramen
In the lumbar spine, each nerve root exits below its named vertebra, so the L4 nerve root exits through the L3-L4 neural foramen.
Question 2: The cauda equina is the collection of nerve roots below the conus medullaris that float in which fluid?
- Synovial fluid
- Interstitial fluid
- Cerebrospinal fluid (Correct answer)
- Lymphatic fluid
Correct answer: Cerebrospinal fluid
The cauda equina nerve roots are suspended in cerebrospinal fluid within the thecal sac below the conus medullaris.
Question 3: Which lumbar level has the narrowest epidural space, making interlaminar injection most technically demanding there?
- L1-L2
- L2-L3
- L3-L4
- L5-S1 (Correct answer)
Correct answer: L5-S1
The L5-S1 interlaminar space can be narrow due to overlapping laminae and large spinous processes, making access more challenging.
Question 4: The dorsal root ganglion (DRG) of a lumbar nerve root is typically located where within the neural foramen?
- Medial (just outside the thecal sac)
- In the middle of the foramen (Correct answer)
- At the lateral exit of the foramen
- Outside the foramen entirely
Correct answer: In the middle of the foramen
The dorsal root ganglion is typically positioned in the mid-portion of the neural foramen, making it susceptible to compression by foraminal stenosis.
Question 5: Which artery, if inadvertently injected during LESI, can cause catastrophic spinal cord ischemia?
- Anterior spinal artery
- Artery of Adamkiewicz (Correct answer)
- Posterior spinal artery
- Iliolumbar artery
Correct answer: Artery of Adamkiewicz
The artery of Adamkiewicz (arteria radicularis magna) is the dominant blood supply to the lower spinal cord and inadvertent injection can cause paraplegia.
Question 6: The width of the lumbar epidural space is greatest at which location within the canal?
- Anteriorly at the posterior longitudinal ligament
- Laterally in the lateral recesses
- Posteriorly at the midline (Correct answer)
- At the intervertebral foramen
Correct answer: Posteriorly at the midline
The posterior midline of the lumbar epidural space is typically the widest point, averaging 5-7 mm, which is why interlaminar injections target this region.
LESI LESI Anatomy and Neuroanatomy 2
In the lumbar spine, the exiting nerve root at L4-L5 passes through which foramen?