Tag: Surgical targeting

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Defining the target for hemifacial spasm –regarding microvascular decompression

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.

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Clinical Evaluation of Cingulum Bundle Connectivity for Neurosurgical Hypothesis Development

Neurosurgery 86:724–735, 2020

The cingulum bundle (CB) has long been a target for psychiatric neurosurgical procedures, but with limited understanding of the brain networks being impacted. Recent advances in human tractography could provide a foundation to better understand the effects of neurosurgical interventions on the CB; however, the reliability of tractography remains in question.

OBJECTIVE: To evaluate the ability of different tractography techniques, derived from typical, human diffusion-weighted imaging (DWI) data, to characterize CB connectivity described in animalmodels. This will help validate the clinical applicability of tractography, and generate insight on current and future neurosurgical targets for psychiatric disorders.

METHODS: Connectivity of the CB in 15 healthy human subjects was evaluated using DWI based tractography, and compared to tract-tracing findings from nonhuman primates. Brain regions of interestwere defined to coincide with the animalmodel. Tractographywas performed using 3 techniques (FSL probabilistic, Camino probabilistic, and Camino deterministic). Differences in connectivity were assessed, and the CB segment with the greatest connectivity was determined.

RESULTS: Each tractography technique successfully reproduced the animal tracing model with amean accuracy of 72%(68-75%, P<.05).Additionally, one region of the CB, the rostral dorsal segment, had significantly greater connectivity to associated brain structures than all other CB segments (P< .05).

CONCLUSION: Noninvasive, in vivo human analysis of the CB, using clinically available DWI for tractography, consistently reproduced the results of an animal tract-tracing model. This suggests that tractography of the CB can be used for clinical applications, which may aid in neurosurgical targeting for psychiatric disorders.

 

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