Fall 2021

Fall 2021

Contributed by:
Saman Zafar MD1, Evgeny Shelkov BSN CNIM1, Oleg Modik PhD CNIM1, Steven Karceski MD1, Pegah Afra MD1.
1Department of Neurophysiology, New York Presbyterian Hospital Weill Cornell Medical Center, New York.

Case Presentation

A 70-year-old female presented with a 4-week history of mid thoracic back pain radiating anteriorly to the abdomen, and hyperesthesia in the skin above the umbilicus. Neurological examination showed otherwise normal strength and normal reflexes. MRI showed an avidly enhancing intra-medullary mass. She was advised a T8 laminectomy with tumor resection using Total IV Anesthesia (TIVA) and Intra-Operative Neuromonitoring.

After ultrasound identification of tumor, T8 laminectomy along with partial T7 and partial T9 laminectomies, the dura and arachnoid mater were retracted. Tumor was seen at the spinal cord surface, just right of the midline. After a right paramedian incision, planes were developed rostral and caudal to the tumor and piecemeal resection of tumor was done. Pathology later revealed a WHO Grade II Ependymoma.

For intraoperative monitoring, spinal cord monitoring with Somatosensory Evoked Potentials (SSEP) of bilateral median and posterior tibial nerves, and transcranial Motor Evoked Potentials (TcMEPs) were requested.

Regarding the SSEPs: Bilateral Median and bilateral posterior tibial SSEPs remained stable with no change throughout the procedure.

Regarding the Transcranial Motor Evoked Potentials (Tc-MEPs), reproducible baseline responses were obtained with transcranial electric stimulation (C3-C4 anodal stimulation with 200-260 V, 5 pulses with ISI 3 ms, PW 75usec) from bilateral hand muscles (APB, ADM) and bilateral lower extremity muscles (Quad, GN, TA, EDB and AH).

During piecemeal resection of the thoracic spinal cord tumor, there was loss or reduction in amplitude of 8/10 of lower extremity muscles: bilateral Quad, bilateral GN, bilateral TA and AH ( R. AH >50% loss). Bilateral EDB MEPs and bilateral upper limb MEPs remained intact.


Right MEPs: the MEPs are from the right upper limb (first 2 columns, APB and ADM) and right lower limb (Quad, TA, Gastr, EDB and AH). All MEPs were intact at baseline- (green arrow) and the first change was noted at 15:06 (red arrow).

 


Left MEPs: the MEPs are from the left upper limb (first 2 columns, APB and ADM) and left lower limb (Quad, TA, Gastr, EDB and AH). All MEPs were intact at baseline- (green arrow) and the first change was noted at 15:06 (red arrow).

 

Question 1: What could have caused the loss of MEPs during the case?

  1. Systemic causes (e.g. hypotension, anesthesia, hypothermia)
  2. Direct Cord Trauma
  3. Anterior Spinal Cord Ischemia
  4. Local cord edema and traction
Answer: (click here)

Correct answer: Local cord edema and traction (D.)

Consider the upper limb evoked potentials as controls in this case, as the level of the surgery is caudal to the brachial plexus. The upper limb MEPs and SSEPs remain unchanged, therefore, a systemic cause such as the level of anesthesia is not the answer. The change in both LE MEP is BELOW the known lesion, indicating a focal rather than a systemic cause.

Question 2: What immediate decision should be made, based on the IOM findings?

  1. It is reassuring that all MEPs are not lost. Continue surgery
  2. Abandon further resection completely.
  3. Consider lowering sedation/anesthesia and waking up the patient to assess lower limb function.
  4. Hold surgery for now. Reassess after 15 minutes.
Answer: (click here)

Correct answer: Hold surgery for now. Reassess after 15 minutes. (D.)

There has been significant loss of lower limb MEPs, occurring at a time of active intramedullary tumor resection, imply-ing a local compromise to the descending motor pathways. It is important to inform the surgeon, trouble-shoot possi-ble causes for the change, and consider what options might help in minimizing the risk of post-operative paraplegia.

Lowering anesthesia and briefly waking up the patient to check lower limb function is sometimes an option (Stagnara Wake-up Test). The major limitations of the procedure the challenges of waking the patient and reliably following the surgeon’s commands. (2) The risks of patient movement on the table include patient injury, dislodged lines and tubes.

Considering spinal cord edema and traction as the best possible cause of the change in MEPs, the best immediate op-tion is to hold surgery for some time, release any cord traction, consider steroids and increasing the mean arterial pressure to reduce edema and improve perfusion to the spinal cord, and reassess in 15 minutes.

In this case, the MEPs partially improved, surgery proceeded, and the patient had no post-operative motor deficits.

 

References

  1. Husain, Aatif M., editor. A Practical Approach to Neurophysiologic Intraoperative Monitoring. Second edition, Demos Medical, 2015.
  2. Eggspuehler A, Sutter MA, Grob D, Jeszenszky D, Dvorak J. Multimodal intraoperative monitoring during surgery of spinal deformities in 217 patients. Eur Spine J. 2007;16 Suppl 2(Suppl 2):S188‐S196. doi:10.1007/s00586-007-0427-6

 

Last updated: July 5, 2022

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