The central myelin-peripheral myelin transitional zone of the nervus intermedius and its implications for microsurgery in the cerebellopontine angle.

The central myelin-peripheral myelin transitional zone, also referred to as the "Obersteiner-Redlich zone (ORZ)" or "glial/Schwann junction" of the nervus intermedius, is thought to play a role in the pathophysiology of nervus intermedius neuralgia (NIN). To evaluate the location and histological features of the ORZ of the nervus intermedius (NI), 10 NI specimens from five fresh cadavers were microscopically analyzed for structural differences between their central and peripheral myelin segments. The ORZ was analyzed under a light microscope, and the exact location of the ORZ was confirmed by immunohistochemical staining using an oligodendroglial antibody. The total diameter of the NI showed a mean of 0.62 mm. The cisternal segment of the NI from the brain stem to the porus acusticus internus had a mean length of 13.97 mm. The mean extent of central myelin was 0.5 mm from the brain stem on the medial side and 0.33 mm on the lateral side. Moreover, the mean length of the ORZ was 0.279 mm on the medial side and 0.134 mm on the lateral side. The distance between the brain stem and the most distal point of central myelin that could be detected was 0.67 mm. Accordingly, the ORZ of the NI appears closer to the brain stem compared to the other cranial nerves. The exact location of the ORZ may play a role in diagnostic preoperative imaging, in the planning of surgical procedures for NIN, and may offer suitable landmarks for surgeons performing microvascular decompression in NIN treatment.