Viet Nguyen, MD

All Publications

• Positive pharmacologic provocative testing with methohexital during cerebral arteriovenous malformation embolization. Clinical imaging Bican, O., Cho, C., Lee, L., Nguyen, V., Le, S., Heit, J., Lopez, J. 2018; 51: 155–59

  Abstract

  A middle-aged patient underwent staged endovascular embolization of a Spetzler-Martin grade V right parietal arteriovenous malformation(AVM).In the fifth endovascular embolization, after methohexital 10 mg injection into a right posterior choroidal artery feeding the AVM nidus, there was an immediate change in the electroencephalogram (EEG) with simultaneous loss of motor evoked potentials (MEPs) in the bilateral upper and lower extremities and a delayed change in somatosensory evoked potential responses (SSEPs). No embolization was made and procedure was terminated. This case demonstrates the utility of intraoperative neurophysiologic monitoring (IONM) with pharmacologic provocative testing in predicting and mitigating the risks prior to the proposed embolization.

  View details for DOI 10.1016/j.clinimag.2018.02.014

  View details for PubMedID 29501883

• Retrospective Waveform Analysis of Transcranial Motor Evoked Potentials (MEP) to Identify Early Predictors of Impending Motor Deficits in Spinal Surgeries. The Neurodiagnostic journal Le, S., Nguyen, V., Ekwueme, A. C., Cho, S. C., Lee, L., López, J. 2017; 57 (1): 53-68

  Abstract

  Although there are guidelines analyzing transcranial motor evoked potentials (MEP) waveform criteria, they vary widely and are not applied universally during intraoperative neurophysiologic monitoring (IONM). The objective is to generate hypotheses to identify early and reliable MEP waveform characteristics prior to complete loss of MEP to predict impending motor spinal cord injuries during spinal surgeries. The ultimate goal is to enhance real-time feedback to prevent injury or detect reversible spinal cord damage.Fifteen true positive cases of persistent intraoperative MEP loss and new postoperative motor deficits were retrospectively identified from 2011 to 2013. Waveform characteristics of latency, amplitude, duration, phases, and area-under-the-curve (AUC) were measured, and an intraoperative spinal cord index (ISCI) was calculated for 5 traces prior to complete MEP loss. ISCI = [amplitude x duration x (phases+1) x AUC]/latency.Out of 22 muscles in 15 cases, latency increased in 2, duration decreased in 12, amplitude decreased in 13, AUC decreased in 13, and ISCI decreased in 14. In 11 out of 15 cases (73%), ISCI dropped > 40% in at least one muscle before MEP were completely lost. Thirteen cases had concurrent somatosensory evoked potentials (SSEP) changes, 9 out of 13 had > 50% decrease in SSEP: 2 out of 9 changed before MEP, 5 out of 9 simultaneously, and 2 out of 9 after.In these cases of motor injury, smaller and simpler MEP waveforms preceded complete loss of signal. An ISCI 40% drop could be tested as a warning threshold for impending motor compromise in future prospective studies and lead to eventual standardization to predict irreversible postoperative deficits.

  View details for DOI 10.1080/21646821.2017.1257330

  View details for PubMedID 28436812

• Diagnostic Utility of Intraoperative Neurophysiological Monitoring for Intramedullary Spinal Cord Tumors: Systematic Review and Meta-Analysis. Clinical spine surgery Azad, T. D., Pendharkar, A. V., Nguyen, V., Pan, J., Connolly, I. D., Veeravagu, A., Popat, R., Ratliff, J. K., Grant, G. A. 2017

  Abstract

  Systematic review and meta-analysis.The aim of this study was to systematically evaluate the diagnostic utility of intraoperative neurophysiological monitoring (IONM) for detecting postoperative injury in resection of intramedullary spinal cord tumors (IMSCT).Surgical management of IMSCT can involve key neurological and vascular structures. IONM aims to assess the functional integrity of susceptible elements in real time. The diagnostic value of IONM for ISMCT has not been systematically evaluated.We performed a systematic review of the PubMed and MEDLINE databases for studies investigating the use of IONM for IMSCT and conducted a meta-analysis of diagnostic capability.Our search produced 257 citations. After application of exclusion criteria, 21 studies remained, 10 American Academy of Neurology grade III and 11 American Academy of Neurology grade IV. We found that a strong pooled mean sensitivity of 90% [95% confidence interval (CI), 84-94] and a weaker pooled mean specificity of 82% (95% CI, 70-90) for motor-evoked potential (MEP) recording changes. Somatosensory-evoked potential (SSEP) recording changes yielded pooled sensitivity of 85% (95% CI, 75-91) and pooled specificity of 72% (95% CI, 57-83). The pooled diagnostic odds ratio for MEP was 55.7 (95% CI, 26.3-119.1) and 14.3 (95% CI, 5.47-37.3) for SSEP. Bivariate analysis yielded summary receiver operative characteristic curves with area under the curve of 91.8% for MEPs and 86.3% for SSEPs.MEPs and SSEPs appear to be more sensitive than specific for detection of postoperative injury. Patients with perioperative neurological deficits are 56 times more likely to have had changes in MEPs during the procedure. We observed considerable variability in alarm criteria and interventions in response to IONM changes, indicating the need for prospective studies capable of defining standardized alarm criteria and responses.

  View details for DOI 10.1097/BSD.0000000000000558

  View details for PubMedID 28650882

• Fentanyl-induced suppression of transcranial Motor Evoked Potentials (tcMEPs) Anaesthesia Cases Bican, O., López, J., Cho, S. C., Nguyen, V., Le, S., Lee, L. 2016; 0241
• In Vivo Imaging of Human Sarcomere Twitch Dynamics in Individual Motor Units NEURON Sanchez, G. N., Sinha, S., Liske, H., Chen, X., Viet Nguyen, V., Delp, S. L., Schnitzer, M. J. 2015; 88 (6): 1109-1120

  Abstract

  Motor units comprise a pre-synaptic motor neuron and multiple post-synaptic muscle fibers. Many movement disorders disrupt motor unit contractile dynamics and the structure of sarcomeres, skeletal muscle's contractile units. Despite the motor unit's centrality to neuromuscular physiology, no extant technology can image sarcomere twitch dynamics in live humans. We created a wearable microscope equipped with a microendoscope for minimally invasive observation of sarcomere lengths and contractile dynamics in any major skeletal muscle. By electrically stimulating twitches via the microendoscope and visualizing the sarcomere displacements, we monitored single motor unit contractions in soleus and vastus lateralis muscles of healthy individuals. Control experiments verified that these evoked twitches involved neuromuscular transmission and faithfully reported muscle force generation. In post-stroke patients with spasticity of the biceps brachii, we found involuntary microscopic contractions and sarcomere length abnormalities. The wearable microscope facilitates exploration of many basic and disease-related neuromuscular phenomena never visualized before in live humans. VIDEO ABSTRACT.

  View details for DOI 10.1016/j.neuron.2015.11.022

  View details for Web of Science ID 000368443900008

• Neuromonitoring: EMG, SSEP and MEP Neurosurgery Tricks of the Trade: Spine and Peripheral Nerves Nguyen, V., Lopez, J. R. edited by Nader, R., Berta, S. Thieme. 2014; 1st edition: Chapter 88
• Peripheral Nerve Surgery A Practical Approach to Neurophysiologic Intraoperative Monitoring Nguyen, V., Jones, E. edited by Husain, A. M. Demos Medical Publishing. 2014; 2nd edition: 163–179
• Detection of inferolateral trunk syndrome by neuromonitoring during catheter angiography with provocative testing. Journal of neurointerventional surgery Le, S., Dodd, R., López, J., Nguyen, V., Cho, S. C., Lee, L. 2013; 5 (2)

  Abstract

  It is not uncommon that endovascular balloon test occlusion (BTO) is performed to assess collateral blood flow and risk of injury of permanent occlusion of the internal carotid artery (ICA). This case is the first reported of detection and reversal of the inferolateral trunk (ILT) syndrome in an awake patient during provocative BTO; prompt recognition of the syndrome effectively prevented permanent neurologic deficits.The case of a 42-year-old woman is reported who had a left sphenoid wing meningioma with extension into the cavernous sinus and who underwent awake catheter angiography with provocative BTO of the ICA. Serial examinations by intraoperative monitoring neurologists and neurointerventionalists detected acute progressive left retro-orbital pressure followed by sudden inability to adduct the left eye, or a left medial rectus palsy, indicative of the ILT syndrome which led to immediate balloon deflation and resolution of the deficits. The hypothesis was that hypoperfusion of the ILT, an arterial branch of the ICA which provides blood supply to several cranial nerves (CN) III, CN V1 and CN V2, caused her acute symptoms.Although cerebral ischemia is a well known complication of endovascular procedures, CN ischemia is a rare potential risk. Knowledge of cerebrovascular anatomy and serial examinations prevented neurologic deficits; this case underscores the added utility of examinations by intraoperative monitoring neurologists and interdisciplinary collaboration.

  View details for DOI 10.1136/neurintsurg-2011-010236

  View details for PubMedID 22345146