Transition zone (nerve)
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The transition zone of a nerve, also known as the Obersteiner-Redlich zone, describes a region of a few millimeters where the myelin sheath changes from a central to peripheral type as enveloping glial cells are replaced by Schwann cells.
Transition zone locations 1:
- CN V: 4 mm from root entry zone
- CN VII: 2 mm from root entry zone
- CN VIII: 10 mm from root entry zone
- CN IX: 1.5 mm from root entry zone
The transition zone is susceptible to mechanical irritation and is implicated in neurovascular compression syndromes such as trigeminal neuralgia (CN V), hemifacial spasm (CN VII), vestibular paroxysmia (CN VIII) and glossopharyngeal neuralgia (CN IX). The location of the transition zone relative to the root entry zone for a cranial nerve can be useful in understanding whether a contacting vessel is likely to cause neuralgia or not 1.
The transition zone is often attributed to being the site of origin of vestibular schwannomas, however this has been shown to be an erroneous myth across multiple studies 2,3.
History and etymology
The zone is eponymously attributed to Emil Redlich (1866-1930) and Heinrich Obersteiner (1847-1922), Austrian physicians.