The value of intraoperative neurophysiological monitoring for microsurgical removal of conus medullaris lipomas: a 12-year retrospective cohort study

Suess, Olaf; Mularski, Sven; Czabanka, Marcus A; Cabraja, Mario; Hammersen, Stefanie; Kombos, Theodoros

doi:10.1186/s13037-014-0035-4

Patient Safety in Surgery

Table 3 Results of the MEP, SEP and EMG monitoring

From: The value of intraoperative neurophysiological monitoring for microsurgical removal of conus medullaris lipomas: a 12-year retrospective cohort study

MEP (n = 30), technical feasibility: 86.7% (26/30)
Motor strength - 24 hours post surgery					motor strength - 3 months post surgery
Intraoperative findings	+	=	−		+	=	−	Σ
Uneventful	1	16	2		6	13	0	19 (73.1%)
Reversible	0	4	1	→	1	4	0	5 (19.2%)
Irreversible	0	0	2		0	0	2	2 (7.7%)
SEP (n = 30), technical feasibility: 66.7% (20/30)
Sensory status - 24 hours post surgery					sensory status - 3 months post surgery
Intraoperative findings	+	=	−		+	=	−	Σ
Uneventful	0	6	3		1	5	3	9 (45.0%)
Reversible	0	4	2	→	0	5	1	6 (30.0%)
Irreversible	0	4	1		0	5	0	5 (25.0%)
Free-run EMG (n = 30), technical feasibility: 100% (30/30)
Motor strength - 24 hours post surgery					motor strength - 3 months post surgery
Intraoperative findings	+	=	−		+	=	−	Σ
Uneventful	0	0	0		0	0	0	0/30
Bursts/salves	2	22	6	→	8	20	2	30/30
Trains	0	4	6		0	7	3	10/30
Triggered EMG (n = 432)
Before tx removal							after tx removal, before dura closure
Stimulation success	No. of nerve roots			changes during tx removal			No. of nerve roots
Yes	260 (60.2%)			+81/-11*			330 (76.4%)
No	172 (39.8%)		→	−81/+11*		→	102 (23.6%)

MEP: Correlation between the transcranial evoked MEP results (unchanged, reversible changes, irreversible changes) and the postoperative muscle strength, as a change in at least one of the recorded muscle groups L3-S5 (BMRC grade improved, unchanged, worse) within 24 h post-op and in the follow-up exam 3 months post-op. uneventful = amplitude and latency within individual limits; reversible potential changes (p.c.) = at least one and then no longer reaching these criteria at the latest by the end of the operation; irreversible p.c. = continuous exceeding of amplitude reduction > 50% or latency prolongation > 15% after spontaneous initiation.
SEP: Correlation between the tibialis SEP events (unchanged, reversible changes, irreversible changes) and the postoperative sensory status, as a subjective change in at least one dermatome L3-S5 (improved, unchanged, worse) within 24 h post-op and in the follow-up exam 3 months post-op. uneventful = amplitude and latency within individual limits; reversible p.c. = at least one and then no longer reaching these criteria at the latest by the end of the operation; irreversible p.c. = continuous exceeding of amplitude reduction > 50% or latency prolongation > 15% after spontaneous initiation.
Free-run EMG: Correlation between the events of the free-running EMG (uneventful, volleys/bursts, trains) and the postoperative muscle strength, as a change in at least one of the recorded muscle groups L3-S5 (BMRC grade improved, unchanged, worse) within 24 h post-op and in the follow-up exam 3 month post-op.
Triggered EMG: Number (n) of the stimulated nerve roots and stimulation success before and after removal of the tumor (tx). * = number of stimulation gains during the operation, ** = number of stimulation losses during the operation.

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