The incidence of anatomic variations of the vertebral artery V2 segment is high. Potentially dangerous conditions can be detected on preoperative imaging.
From a practical standpoint, three warning values, based on delay in latency of Peak V, were established for use during surgery: an initial one at 0.4 millisecond ("watching" signal) at the safety limit; a second one at 0.6 millisecond (risk "warning" signal), which is the mean value corresponding to the group of patients without postoperative hearing loss; and an ultimate one at 1 millisecond ("critical" warning), before irreversibility. These warnings should help the surgeon to avoid or correct maneuvers that are dangerous for hearing function, which is mandatory in functional surgery.
Intradural disc herniation (IDH) is very rare. Most diagnoses were surgical but with the improvements in magnetic resonance imaging (MRI) it has become possible to preoperatively diagnose intradural migration of disc in some cases. We report a case with very specific imaging features in MRI, well correlated with the surgical findings.
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