Anterior Transthoracic Surgery with Motor Evoked Potential Monitoring for High-Risk Thoracic Disc Herniations: Technique and Results

OBJECTIVE: To present our experience with anterior transthoracic surgery for high-risk thoracic disc herniations (TDHs) using motor evoked potential monitoring (MEPm).

METHODS: We estimated surgical risk based on clinical and radiologic characteristics, including anteroposterior (AP) spinal canal occupation (SCO), AP spinal cord compression (SCC), residual AP spinal cord diameter (RSCD), and intramedullary signal changes (ISC). We analyzed Anand, ASIA, and Nurick scores, anesthesiologic, neurophysiological, and surgical reports. We considered > 50% MEP signal deterioration significant.

RESULTS: Out of 435 anterior transthoracic procedures, 77 concerned high-risk TDH(s): 69 single-level, 8 multilevel, 61 with clinical myelopathy, 6 with merely ISC. Mean SCO and SCC were 55.4% and 54.0% for single-level, 31.8% and 33.9% for multilevel cases. ISC were present in 64% of single-level and 50% of multilevel cases, calcifications in 87% of single-level and 84% of multilevel TDHs. We initially performed 23 mini-transthoracic approaches (miniTTAs) and 24 thoracoscopic microdiscectomies (TMDs), more recently 29 TMDs (23 giant TDHs) and 1 transaxillary mini-TTA. Overall, 72 patients had reliable MEP signals. Isolated lower extremity MEP signal deteriorations (n = 21) correlated with maximal TDH AP diameter, SCO, SCC, and ISC. ASIA and Nurick scores improved in 45% and 66% respectively. One patient became paraplegic. MEP signal deterioration had 100% sensitivity, 75% specificity, and 19% positive predictive value during and 44% at the end of surgery.

CONCLUSIONS: Maximal TDH AP diameter, SCO, SCC, (sub) total calcification, and ISC correlate with lower extremity MEP signal deterioration. In experienced hands, TMD with MEPm support is a safe, efficient procedure for high-risk TDHs.