High spatial resolution nerve-specific DTI protocol outperforms whole-brain DTI protocol for imaging the trigeminal nerve in healthy individuals

Trigeminal Neuralgia: Disease Characterization and Prediction of Response to Surgical Intervention

PURPOSE OF REVIEW

Trigeminal neuralgia (TN) is a highly heterogeneous condition with a wide choice of successful treatment options. However, differences between subtypes are poorly understood and it remains unknown which patients will respond to different treatments. This review aims to summarize the current state of the TN field and explore the problem of predicting surgical outcomes.

RECENT FINDINGS

Attempts have been made to standardize classification, outcome reporting, and treatment guidelines. Identification of risk factors for poor surgical treatment outcomes has led to the development of prognostic scoring systems to predict outcomes and guide management. Advances in imaging techniques including diffusion tensor imaging show promise in better understanding the underlying pathophysiology and predicting surgical outcomes. Progress is hampered by lack of understanding of the pathophysiology in TN and differences between disease subtypes. Further work needs to be done to create accurate prediction tools for widespread use, including use of advanced imaging and computing tools, multicenter collaboration, and prospective validation.

A novel potential measurement indicator with objective and quantitative effect for trigeminal neuralgia: fractional anisotropy in MR-DTI

Objectives

To investigate the effect of diffusivity metrics of magnetic resonance diffusion tensor imaging (MR-DTI) in the assessment of treatment effects.

Methods

MR-DTI examination for trigeminal neuralgia (TN) patients and the diffusivity metrics of the trigeminal ganglion (TG) were analyzed. Before and after the percutaneous stereotactic radiofrequency rhizotomy (PSR) operation, the treatment effect was assessed using pain scores and MR-DTI. The correlation between the diffusivity metrics of cranial nerve five (CNV) and visual analog scale (VAS) pain scores before and after treatment in TN patients was explored.

Results

In PSR patients, the fractional anisotropy (FA) of the affected TG is a significantly lower than that of the unaffected side (p < 0.01). After PSR, the diffusivity metrics on the bilateral TGs are not significantly different (p > 0.05). Following PSR treatment, both of the diffusivity metrics (FA) in the lowest area of the CNV and the VAS scores of TN patients show changes. Furthermore, diffusivity metric (FA) on the lowest area of the CNV preoperative is significantly negatively correlated with the VAS scores (p < 0.05).

Conclusion

MR-DTI is capable of investigating the longitudinal changes of FA before and after radiofrequency treatment, and diffusivity metrics could be an independent reliable efficacy indicator for TN.

Significance

The alteration of the diffusivity on TG may be correlated with the effect of radiofrequency treatment.

A novel indicator to predict the outcome of percutaneous stereotactic radiofrequency rhizotomy for trigeminal neuralgia patients: diffusivity metrics of MR-DTI

Magnetic resonance-diffusion tensor imaging (MR-DTI) has been used in the microvascular decompression and gamma knife radiosurgery in trigeminal neuralgia (TN) patients; however, use of percutaneous stereotactic radiofrequency rhizotomy (PSR) to target an abnormal trigeminal ganglion (ab-TG) is unreported. Fractional anisotropy (FA), mean and radial diffusivity (MD and RD, respectively), and axial diffusivity (AD) of the trigeminal nerve (CNV) were measured in 20 TN patients and 40 healthy control participants immediately post PSR, at 6-months, and at 1 year. Longitudinal alteration of the diffusivity metrics and any correlation with treatment effects, or prognoses, were analyzed. In the TN group, either low FA (value < 0.30) or a decreased range compared to the adjacent FA (dFA) > 17% defined an ab-TG. Two-to-three days post PSR, all 15 patients reported decreased pain scores with increased FA at the ab-TG (P < 0.001), but decreased MD and RD (P < 0.01 each). Treatment remained effective in 10 of 14 patients (71.4%) and 8 of 12 patients (66.7%) at the 6-month and 1-year follow-ups, respectively. In patients with ab-TGs, there was a significant difference in treatment outcomes between patients with low FA values (9 of 10; 90%) and patients with dFA (2 of 5; 40%) (P < 0.05). MR-DTI with diffusivity metrics correlated microstructural CNV abnormalities with PSR outcomes. Of all the diffusivity metrics, FA could be considered a novel objective quantitative indicator of treatment effects and a potential indicator of PSR effectiveness in TN patients.

Vestibular paroxysmia entails vestibular nerve function, microstructure and endolymphatic space changes linked to root-entry zone neurovascular compression

Combining magnetic resonance imaging (MRI) sequences that permit the determination of vestibular nerve angulation (NA = change of nerve caliber or direction), structural nerve integrity via diffusion tensor imaging (DTI), and exclusion of endolymphatic hydrops (ELH) via delayed gadolinium-enhanced MRI of the inner ear (iMRI) could increase the diagnostic accuracy in patients with vestibular paroxysmia (VP). Thirty-six participants were examined, 18 with VP (52.6 ± 18.1 years) and 18 age-matched with normal vestibulocochlear testing (NP 50.3 ± 16.5 years). This study investigated whether (i) NA, (ii) DTI changes, or (iii) ELH occur in VP, and (iv) to what extent said parameters relate. Methods included vestibulocochlear testing and MRI data analyses for neurovascular compression (NVC) and NA verification, DTI and ELS quantification. As a result, (i) NA increased NVC specificity. (ii) DTI structural integrity was reduced on the side affected by VP (p < 0.05). (iii) 61.1% VP showed mild ELH and higher asymmetry indices than NP (p > 0.05). (iv) "Disease duration" and "total number of attacks" correlated with the decreased structural integrity of the affected nerve in DTI (p < 0.001). NVC distance within the nerve's root-entry zone correlated with nerve function (Roh = 0.72, p < 0.001), nerve integrity loss (Roh = - 0.638, p < 0.001), and ELS volume (Roh = - 0.604, p < 0.001) in VP. In conclusion, this study is the first to link eighth cranial nerve function, microstructure, and ELS changes in VP to clinical features and increased vulnerability of NVC in the root-entry zone. Combined MRI with NVC or NA verification, DTI and ELS quantification increased the diagnostic accuracy at group-level but did not suffice to diagnose VP on a single-subject level due to individual variability and lack of diagnostic specificity.

Gamma Knife Radiosurgery for Trigeminal Neuralgia : Review and Update

Accurate diagnosis of trigeminal neuralgia (TN) is the starting point for optimal treatment. Gamma knife radiosurgery (GKRS) is currently regarded as one of the first-line treatment options for medically refractory TN. GKRS is a less invasive treatment with a low risk of complications than other surgical procedures that provides a favorable pain control (BNI I–IIIb) rate of >75% at short-term follow-up. Drawbacks of GKRS include the latency period before pain relief and higher recurrence rate compared with microvascular decompression. Therefore, repeat treatment is necessary if the initial GKRS was effective but followed by recurrence. The concept of dose rate and the biologically effective dose of radiation has been actively studied in radiation oncology and is also applied in GKRS for TN to achieve high safety and efficacy by prescribing the optimal dose. Recent progress in functional imaging, such as diffusion tensor imaging, enables us to understand the pathophysiology of TN and predict the clinical outcome after GKRS. Here, we review TN, GKRS, and recent updates, especially in the concepts of radiation dose, diffusion tensor imaging studies, and repeat treatment in GKRS for TN.