Microanatomy of the Central Myelin-Peripheral Myelin Transition Zone of the Trigeminal Nerve

Abstract

The data definitively prove that the root entry zone (REZ, nerve-pons junction) and TZ of the trigeminal nerve are distinct sites and that these terms should never be used interchangeably. The measurements showed that the central myelin occupies only the initial one-fourth of the trigeminal nerve length. If trigeminal neuralgia is caused exclusively by vascular compression of the central myelin, the problem vessel would always have to be located in this region. However, it is well known that pain from trigeminal neuralgia can resolve after vascular decompression at more distal sites. This suggests that the effects of surgical decompression are caused by another mechanism.

Microvascular Decompression for Trigeminal Neuralgia in Patients with and without Prior Stereotactic Radiosurgery

“…This area of the nerve differs from the more distal extent by being myelinated by oligodendroglia (16). This location of treatment has been thought to produce more reliable and possibly more long-lasting pain relief due to the radiation sensitivity of oligodendroglial myelin (15), although this remains controversial (14).…”

Pathology of the Trigeminal Nerve

“…The axons of the root entry zone of the trigeminal nerve are coated with central nervous system myelin, which extends up to 5 mm along the root into the prepontine cistern. 10,26,27 In consequence, the junction between central nervous system myelin and peripheral nervous system myelin, which is approximately 2 mm in length, is located some distance away from the pons. Examination of trigeminal nerve roots from patients with compression of the nerve root by an overlying blood vessel has revealed focal demyelination in the region of compression, 10,27,28 which results in the abnormal generation of ectopic sensory impulses with subsequent spread to adjacent fibers, so that spontaneous nerve activity increases.…”

Trigeminal neuralgia: Assessment with T2 VISTA and FLAIR VISTA fusion imaging

“…The theory proposes that neuralgia occurs because of compression of the centralperipheral myelin transitional zone (TZ) of the trigeminal nerve by a vessel [15]. However, surgical decompression is not performed exclusively at this site in the case of TN.…”

“…There are several studies on the length of the central myelin portion of the sensory root of the human trigeminal nerve [15,20]. Peker et al [15] revealed that the central-peripheral myelin TZ is located a mean of 1.13 mm from the REZ (the precise nerve-pons junction) on the medial aspect of the nerve, and 2.47 mm from the REZ on the lateral aspect. Therefore, central myelin demyelination can be extended to the cisternal segment, and is not limited to the REZ.…”