Attenuation of Motor Evoked Potentials Following Prone Positioning

Background and Importance: Of utmost importance for successful neurosurgical operations is proper patient positioning. This is particularly the case for operations conducted in the prone position, which is associated with several potential complications. Case Presentation: Here we report the case of a 52-year-old male patient who underwent endoscopic discectomy for L5-S1 herniated disc. Following placement in the prone position, Motor Evoked Potentials (MEP) were significantly asymmetric, with those from the left side being disproportionately low considering his clinical presentation. MEP recordings were ameliorated when the patient was placed in the supine position. Considering the nervous and vascular anatomy of the area, a peripheral insult is highly unlikely to be the cause of the neurophysiological profile of this patient. Instead, compression of the dural sac due to biomechanical alterations of the contents of the spinal canal is the most possible pathogenetic mechanism. Conclusion: Proper patient positioning is of paramount importance for the success of a neurosurgical operation. Still, even if all precautions are taken, it is possible that insults to neuronal structures can be due to biomechanical alterations of the contents of the spinal canal, secondary to prone positioning.