Tag: DREZ

Acta Neurochirurgica (2026) 168:103

This paper argues that the physiologic target for microvascular decompression (MVD) in hemifacial spasm (HFS) is the full extent of the centrally myelinated facial root exit zone (fREZ), from the pontomedullary sulcus (root exit point) to the transitional zone, rather than the shorter REZ segment often emphasized. The authors critique recent anatomical definitions and highlight histological and intraoperative evidence supporting a longer susceptible CMP.

The manuscript details four fREZ segments (RExP, attached segment, root detachment point, TZ), presents frequency data of culprit compressions concentrated on the attached segment, and stresses diagnostic-imaging and surgical implications. Adopting the expanded fREZ map and subfloccular approach is presented as essential to reduce failed MVDs for HFS.

Target definition problem: Equating the cranial nerve REZ with just the short segment between the brainstem surface and the TZ does not accurately represent the physiologically vulnerable central myelin portion (CMP) of the facial nerve in hemifacial spasm surgery.

Facial CMP length: The facial nerve’s exposed centrally myelinated fibers extend proximally along the pontine surface and are considerably longer (about ~1 cm) than the commonly measured brainstem-to-TZ segment.

Expanded fREZ anatomy: A practical surgical definition divides the facial root exit zone (fREZ) into four parts—RExP (root exit point at the pontomedullary sulcus), AS (attached segment adherent to the pons), RDP (root detachment point), and distal TZ (2–3 mm beyond RDP).

Physiologic susceptibility zone: The vulnerable target for MVD in HFS is the entire exposed centrally myelinated facial segment from the pontomedullary sulcus (RExP) to the TZ, not only the short “REZ” segment near the brainstem edge.

Compression distribution: Culprit neurovascular compression in HFS occurs most often along the AS (~80%), less at RExP (~10%) and RDP–TZ (~10%), and only rarely on the distal cisternal portion (typically with severe distortion).

Imaging implication: Diagnostic imaging interpretation for HFS should assess the most proximal fREZ (RExP and AS) rather than focusing only distal to the RDP.

Surgical failure mechanism: Failed MVD can result when decompression is directed at more distal facial nerve portions, missing persistent compression at the true proximal anatomical target.

Approach to access target: A subfloccular approach helps reach the proximal fREZ by tracking glossopharyngeal fibers to the brainstem, supporting effective decompression of the susceptible proximal segment.