CNIM Somatosensory Evoked Potentials (SSEP) 1 — Questions and Answers
Question 1: What is the primary neural pathway monitored by upper extremity SSEP during intraoperative monitoring?
- Dorsal column-medial lemniscal pathway (Correct answer)
- Spinothalamic tract
- Corticospinal tract
- Rubrospinal tract
Correct answer: Dorsal column-medial lemniscal pathway
Upper extremity SSEPs monitor the dorsal column-medial lemniscal pathway, which carries proprioception and fine touch from the periphery to the cortex.
Question 2: Which SSEP component is considered the most clinically significant cortical response when monitoring median nerve stimulation?
- N9
- N13
- N20 (Correct answer)
- P25
Correct answer: N20
The N20 is the primary cortical response generated in the contralateral primary somatosensory cortex and is the most clinically significant component for median nerve SSEP monitoring.
Question 3: A 50% decrease in SSEP amplitude combined with a 10% increase in latency is generally considered:
- Normal physiological variation
- A minor technical artifact
- A significant alarm criterion requiring intervention (Correct answer)
- A sign of electrode failure
Correct answer: A significant alarm criterion requiring intervention
A 50% amplitude decrease with a 10% latency increase meets the standard CNIM alarm criteria and requires immediate notification of the surgical team.
Question 4: Which electrode placement is used to record the Erb's point potential during median nerve SSEP?
- Ipsilateral to stimulation at the clavicle (Correct answer)
- Contralateral to stimulation at the clavicle
- Midline cervical spine
- Contralateral parietal scalp
Correct answer: Ipsilateral to stimulation at the clavicle
Erb's point (N9) is recorded ipsilateral to the stimulation site over the brachial plexus at the clavicle, representing a peripheral nerve potential.
Question 5: What does the P37 component represent in lower extremity SSEP monitoring via posterior tibial nerve stimulation?
- Lumbar spinal cord response
- Cortical response at the vertex (Correct answer)
- Peripheral nerve action potential
- Brainstem response
Correct answer: Cortical response at the vertex
The P37 is a positive cortical potential recorded at the vertex (Cz) representing activation of the primary somatosensory cortex after posterior tibial nerve stimulation.
Question 6: During SSEP monitoring, the N13 potential recorded at the cervical spine represents activity originating from:
- The peripheral nerve
- The dorsal horn of the cervical spinal cord (Correct answer)
- The thalamus
- The somatosensory cortex
Correct answer: The dorsal horn of the cervical spinal cord
The N13 is a stationary potential generated in the dorsal horn of the cervical spinal cord and serves as a subcortical reference point in SSEP monitoring.
CNIM Somatosensory Evoked Potentials (SSEP) 1
What is the primary neural pathway monitored by upper extremity SSEP during intraoperative monitoring?