Somatosensory evoked potential alert due to intraoperative stroke during intraoperative neuromonitoring for transforaminal lumbar interbody fusion surgery
1Department of Clinical Neurophysiology, Jaslok Hospital and Research Centre, Maharashtra, India
2Department of Neurology, Jaslok Hospital, Maharashtra, India
Correspondence to Poornima Amit Shah Department of Clinical Neurophysiology, Jaslok Hospital and Research Centre, Mumbai, Maharashtra 400026, India Tel: +22-40173206,7 E-mail: doc_prk@yahoo.com
• Received: January 30, 2025 • Accepted: April 25, 2025
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We report the case of somatosensory evoked potential loss during a transforaminal interbody fusion during exposure following a transient rise in blood pressure. The topography of signal loss and elimination of technical causes led to the inference of left sided stroke which was confirmed as a left thalamocapsular hemorrhagic infarct on postoperative magnetic resonance imaging. Use of intraoperative neuromonitoring in this lumbar fixation surgery helped to identify it intraoperatively and prevented undue alternative surgical decision making.
The incidence of perioperative stroke varies with the type of surgery. The risk of perioperative stroke in spine surgery is around 0.05-0.1%.1,2 The risk factors for perioperative stroke are advanced age, history of cerebrovascular disease, ischemic heart disease, congestive heart failure, atrial fibrillation, and renal disease.3 Stroke may present as delayed awakening from anesthesia. It may not be possible to differentiate whether the stroke was intraoperative or while awakening from anesthesia.
CASE
A 62-year male presented with significant neurogenic claudication and backpain of few months’ duration. He had no past medical history. No family history of cerebro-vascular accidents. He was admitted for a planned lumbar spine decompression surgery. Pre-operative investigations done were within normal. Pre-operative examination had normal vital parameters, no neurological or systemic deficits. He was taken up for surgery under intraoperative neuromonitoring (IONM).
Transcranial motor‑evoked potential (TcMEP) and somatosensory‑evoked potential (SSEP) were planned for IONM using NIM‑Eclipse System (Medtronic, Minneapolis, MN, USA). The patient was placed in prone position.
Total intravenous anesthesia (TIVA) was used in the form of propofol, fentanyl and ketamine. Neuromuscular block was given only for intubation.
Corkscrew electrodes were placed at motor (M)1, M2, M3, and M4 for linked quadripolar stimulation using double train of 8 pulses, 75 μs duration each, 250 Hz at 180 volts after ascertaining the threshold. Recording was done using paired needle electrode, placed bilaterally in the abductor pollicis brevis (control), iliopsoas, vastus medialis, adductor longus, tibialis anterior, and gastrocnemius and abductor halluces.
Bilateral median SSEP (control) and bilateral tibial SSEPs were recorded. Stimulation was done using paired needle electrodes (upto 30 mA, 200 μs, and 4.7 Hz). Recording was done using corkscrew electrodes placed at Fz, Cz, C3’, and C4’ (30-300 Hz bandpass, 300 averages).
Initial baselines was taken prior to incision. During exposure, a rise in blood pressure was noted upto 160/110 mmHg for a few minutes after which abrupt loss of right median and right tibial SSEPs was noted (Fig. 1). Systematic trouble shooting confirmed all impedances less than 5 kOhms and adequacy of stimulation. Anesthesia would induce global changes.4,5 The hemibody topography of signal loss indicated the only possibility of stroke. TcMEPs were well preserved (Fig. 2). Surgeon was informed about the incident. Decision was taken to finish the surgery as planned as quickly as possible. No new changes were noted in the IONM till end of surgery. Magnetic resonance imaging brain was advised suspecting a stroke which revealed a 2.2 × 1.7 cm left thalamocapsular bleed with surrounding mild edema (Fig. 3). There was no angiographic abnormality. Five to 6 hours later when fully out of anaesthesia the patient had mild right sided parasthesia and few hours later he had mild right upper limb weakness. Examination revealed right pronator droop with a mute right plantar and slurred speech, with rest of the neurology examination being normal.
DISCUSSION
Perioperative stroke is very rare. Perioperative stroke can be defined as any embolic, thrombotic, or haemorrhagic cerebrovascular event with motor, sensory, or cognitive dysfunction lasting at least 24 hours, transient ischaemic attack, or within 30 days after surgery.6,7 Their occurrence is most common in cardiac and vascular neurosurgeries.
Overall, they are rare and occur in 0.1-1.9% of non-cardiac and non-vascular.8 Haemorrhagic strokes are even rarer, forming 1-4% of these.9 Risk factors for intra-operative and peri-operative stroke include conventional risk factors like age, sex, past history of stroke/transient ischaemic attack, hypertension, cardiac arrhythmias, ischemic heart disease, smoking, diabetes mellitus, and obesity. General anaesthesia also carries higher risk of peri-operative stroke than other forms of anaesthesia. Our patient had no such risk factors pre-operatively (apart from age and male sex which are non-modifiable).
Risk factors for haemorrhagic strokes are hypertension, cerebral vascular malformations, use of blood thinners. Also blood pressure almost always spikes up during a stroke (ischemic and haemorrhagic both) as a reactionary response. In our case, when the blood pressure spiked up and SSEPs on the right side were lost minutes later- a stroke was correctly suspected as the most likely culprit. As soon as the surgeon was alerted a decision was made to complete the surgery at the earliest and blood pressure control was achieved.
As the thalamus is a major relay centre for the tracts of Goll and Burdach, the loss of SSEP was of localising value. Sparing of TcMEP would suggest initial sparing of pyramidal tracts by the bleed. As was also seen clinically when the patient first complained of paraesthesia. He later complained of arm weakness and slurred speech (which is when the intracerebral bleed size would have increased due to cytotoxic oedema).
To the best of our knowledge, this is the first report in India of intraoperative stroke during non-cardiovascular surgery accurately identified by neuromonitoring.10 Here IONM provided the surgeon assurance to proceed with the planned surgery with timely precise identification and clinical correlation of signal loss.
Notes
Conflicts of Interest
None.
Funding
None.
Fig. 1.
Illustration of absent right median and right Tibial SSEP-red trace-baseline, black trace-current average, and green trace-previous average. SSEP, somatosensory‑evoked potential.
Fig. 2.
TcMEP-left and right panel-top to bottom-iliopsoas, adductor longus, vastus medialis, tibialis anterior, gastrocnemius, abductor hallucis, and abductor pollicis brevis. Sweep speed-100 ms/div. TcMEP, transcranial motor‑evoked potential.
Fig. 3.
SWI image showing well defined intraparenchymal haemorrhage in the left thalamocapsular region just extending into the posterior aspect of basal ganglia and left subthalamus with surrounding mild perilesional edema. SWI, susceptibility weighted imaging.
References
1. Bekelis K, Desai A, Bakhoum SF, Missios S. A predictive model of complications after spine surgery: the National Surgical Quality Improvement Program (NSQIP) 2005-2010. Spine J 2014;14:1247-1255.
2. Schoenfeld AJ, Ochoa LM, Bader JO, Belmont PJ Jr. Risk factors for immediate postoperative complications and mortality following spine surgery: a study of 3475 patients from the National Surgical Quality Improvement Program. J Bone Joint Surg Am 2011;93:1577-1582.
6. Yan X, Pang Y, Yan L, Ma Z, Jiang M, Wang W, et al. Perioperative stroke in patients undergoing spinal surgery: a retrospective cohort study. BMC Musculoskelet Disord 2022;23:652.
10. Legatt AD, Laarakker AS, Nakhla JP, Nasser R, Altschul DJ. Somatosensory evoked potential monitoring detection of carotid compression during ACDF surgery in a patient with a vascularly isolated hemisphere. J Neurosurg Spine 2016;25:566-571.
Somatosensory evoked potential alert due to intraoperative stroke during intraoperative neuromonitoring for transforaminal lumbar interbody fusion surgery
Fig. 1. Illustration of absent right median and right Tibial SSEP-red trace-baseline, black trace-current average, and green trace-previous average. SSEP, somatosensory‑evoked potential.
Fig. 2. TcMEP-left and right panel-top to bottom-iliopsoas, adductor longus, vastus medialis, tibialis anterior, gastrocnemius, abductor hallucis, and abductor pollicis brevis. Sweep speed-100 ms/div. TcMEP, transcranial motor‑evoked potential.
Fig. 3. SWI image showing well defined intraparenchymal haemorrhage in the left thalamocapsular region just extending into the posterior aspect of basal ganglia and left subthalamus with surrounding mild perilesional edema. SWI, susceptibility weighted imaging.
Fig. 1.
Fig. 2.
Fig. 3.
Somatosensory evoked potential alert due to intraoperative stroke during intraoperative neuromonitoring for transforaminal lumbar interbody fusion surgery
