Meckel Cave: An Anatomical Study Using Magnetic Resonance Imaging

Predicting balloon shape in percutaneous microcompression : an observational comparative analysis of Meckel's cave imaging and balloon morphology

Achieving a pear-shaped balloon holds pivotal significance in the context of successful percutaneous microcompression procedures for trigeminal neuralgia. However, inflated balloons may assume various configurations, whether it is inserted into Meckel's cave or not. The absence of an objective evaluation metric has become apparent. To investigate the relationship between the morphology of Meckel's Cave and the balloon used in percutaneous microcompression for trigeminal neuralgia and establish objective criteria for assessing balloon shape in percutaneous microcompression procedures. This retrospective study included 58 consecutive patients with primary trigeminal neuralgia. Data included demographic, clinical outcomes, and morphological features of Meckel's cave and the balloon obtained from MRI and Dyna-CT imaging. MRI of Meckel's cave and Dyna-CT of intraoperative balloon were modeled, and the morphological characteristics and correlation were analyzed. The reconstructed balloon presented a fuller morphology expanding outward and upward on the basis of Meckel's cave. The projected area of balloon was strongly positively correlated with the projected area of Meckel's cave. The Pearson correlation coefficients were 0.812 (P<0.001) for axial view, 0.898 (P<0.001) for sagittal view and 0.813 (P<0.001) for coronal view. Similarity analysis showed that the sagittal projection image of Meckel's cave and that of the balloon had good similarity. This study reveals that the balloon in percutaneous microcompression essentially represents an expanded morphology of Meckel's cave, extending outward and upward. There is a strong positive correlation between the volume and projected area of the balloon and that of Meckel's cave. Notably, the sagittal projection image of Meckel's cave serves as a reliable predictor of the intraoperative balloon shape. This method has a certain generalizability and can help providing objective criteria for judging balloon shape during percutaneous microcompression procedures.

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.

Microanatomical findings with relevance to trigeminal ganglion enhancement on post-contrast T1-weighted magnetic resonance images in dogs

Introduction

Trigeminal ganglion contrast enhancement (TGCE) is reported to be a normal and a common finding on magnetic resonance imaging studies of dogs, cats and humans. The intent of the present study was to describe the anatomical characteristics of the trigeminal ganglion, its surrounding structures, and histological features that are relevant to explain or hypothesize on the reason for TGCE on T1-weighted post-contrast MRI studies of the brain in dogs.

Methods

Eight dog cadavers were dissected to study the anatomy of the trigeminal ganglion. The presence and anatomy of vessels was studied by dissection and by histological techniques. Two trigeminal ganglia were isolated and stained with hematoxylin-eosin (HE). Two other trigeminal ganglia included in the trigeminal canal and trigeminal cavity were decalcified with formic acid/formalin for 12 weeks and stained with HE to study the related vessels. Additionally, a corrosion cast was obtained from a separate canine specimen.

Results

Leptomeninges and a subarachnoid space were identified at the level of the trigeminal nerve roots and the trigeminal ganglion. No subarachnoid space was identified and leptomeninges were no longer present at the level of the three trigeminal nerve branches. Small arterial vessels ran to and supplied the trigeminal ganglion, passing through the dura mater. No venous plexus was visualized at the level of the trigeminal ganglion in the dissections. A complex arterial vascular network was identified within the leptomeningeal covering of the trigeminal ganglion and was best appreciated in the corrosion cast. Histological examination revealed small-to moderate-sized blood vessels located in the epineurium around the ganglion; from there a multitude of arterioles penetrated into the perineurium. Small endoneurial branches and capillaries penetrated the ganglion and the trigeminal nerve branches.

Discussion

Limitations to this study include the limited number of canine specimens included and the lack of electron microscopy to further support current hypotheses included in our discussion. In conclusion, this study provides further support to the theory that TGCE in dogs may be due an incomplete blood-nerve barrier or blood-ganglion barrier at the interface between the central nervous system and the peripheral nervous system.

The Consistency Between the Preoperative 3D-Reconstructed Meckel's Cave and the Intraoperative Balloon Results in Percutaneous Balloon Compression

Objective

To predict the volume and shape of the balloon before PBC by reconstructing the Meckel's cave (MC) and establishing a volumetric measurement model, supporting preoperative preparation and intraoperative decisions.

Methods

The clinical data of 31 patients with good therapeutic effects who underwent PBC are retrospectively collected, including preoperative MRI, the volume of contrast agent injected into the balloon, and intraoperative lateral X-ray images. The MC on the affected side of the 31 patients is reconstructed based on MRI using 3D Slicer, while the volume of the MC is calculated to compare with the volume of contrast agent. The width (W) and length (L) of the model of the MC in lateral view are measured and used to classify the shape of the MC based on W/L. The consistency between the W/L of the model of the MC and the W/L of the intraoperative balloon is evaluated.

Results

For volume, the mean value of the models of the MC (V1) in 31 patients is 399.77±155.13 mm³, while the mean value of the contrast agent injected during PBC (V2) is 539.03±111.93 mm³. The formula obtained by linear regression is V2= 392.1 + 0.3676×V1. Based on the value of W/L, the shape of the MC is classified into thin "pear" in 5 patients (16.13%), standard "pear" in 22 patients (70.97%), and square "pear" in 4 patients (12.90%). There is no significant difference in W/L between the models of the MC and the intraoperative balloons in 31 patients (P=0.221).

Conclusion

In 31 patients with good efficacy, it is verified that the prediction of the MC before PBC by 3D Slicer is consistent with the actual situation of the intraoperative balloon. This method can provide certain basis for preoperative preparation and intraoperative judgment.

Effects of the MR-DTI Characteristics of the Trigeminal Ganglion Target on Radiofrequency Treatment in Patients with Trigeminal Neuralgia: A Retrospective Observational Clinical Study

Background. In the percutaneous treatment of trigeminal neuralgia (TN), the difficulty in accessing the foramen ovale (FO) has been widely recognized. However, the most efficient percutaneous treatment target is the so-called trigeminal ganglion target (TGT). We propose that the TGT in a puncture can be identified by magnetic resonance diffusion tensor imaging (MR-DTI). Objectives. To observe the effect of the characteristics of the TGT as detected by MR-DTI on percutaneous stereotactic radiofrequency rhizotomy (PSR) in TN patients. Methods. In our observational study, we preoperatively performed MR-DTI and/or 3D-CT for 48 TN patients, analyzed the characteristics of the TGT and/or FO, and designed appropriate surgical schemes for producing an accurate PSR trajectory according to these characteristics. The position and size of the TGT aided in adjusting the puncture angle and guiding the approach. Then, we successfully performed a customized PSR guided by the characteristics of the FO or TGT. During the postoperative and follow-up periods, we assessed the effect of treatment with pain scores and MR-DTI findings. Results. The characteristics of the TGT vary from patient to patient. We performed PSR with a single puncture guided by MR-DTI and 3D-CT in 16 patients, and only one patient required three punctures. All three of these punctures reached the FO target, as confirmed by intraoperative C-arm X-ray. We finally reached the TGT successfully after 2 additional attempts, confirming that the probe reached the TGT that accurately covered the pain territory with an electrophysiology test. The characteristics of the TGT were negatively correlated with the number of PSR punctures. Fewer complications occurred for PSRs guided by the TGT than for PSRs guided by the FO. Conclusions. The characteristics of the TGT are correlated with the number of punctures in the PSR. The application of MR-DTI for detecting the size of the TGT is an important step in predicting the difficulty of puncture. The PSR approach can be guided by the TGT and FO for TN patients who present with multiple adverse factors and thus may be beneficial in reducing the number of complications.

The Focus and New Progress of Percutaneous Balloon Compression for the Treatment of Trigeminal Neuralgia

Trigeminal neuralgia is a condition confined to the trigeminal nerve, causing one or more branches of facial nerve pain. Surgical treatment options for trigeminal neuralgia include microvascular decompression(MVD), percutaneous balloon compression (PBC), radiofrequency thermocoagulation(RF), percutaneous retrogasserian glycerol rhizotomy(PRGR), gamma knife, etc. Of these treatments, PBC is increasingly being used by clinicians for trigeminal neuralgia. PBC is a simple surgical operation performed to treat trigeminal neuralgia. Owing to its advantages, PBC is favored by many clinicians. In this study, we aimed to emphasize the need to analyze the shape of the balloon, position, compression time, and pressure, as these factors can affect the efficacy of PBC. The relief of pain by balloon compression is related to the shape of the balloon on X-ray, which is the key to the operation. Owing to continued progress and advances in current imaging technologies, clinicians revealed that the precise positioning of the foramen ovale is no longer an intraoperative problem. Instead, the anatomy of Meckel’s cave and the shape of the balloon must be the focus to achieve the best treatment effect. For clinicians, PBC is simple and is associated with a short operation time. PBC also has other advantages, such as low cost and immediate postoperative pain relief. The recurrence rate of pain post-PBC is low, despite the occurrence of facial numbness post-op. However, this side effect is reversible and does not affect daily life of the patient. In fact, the patient can be discharged 1–2 days after surgery. Overall, PBC can be considered as one of the preferred surgical methods for the treatment of primary trigeminal neuralgia. In this paper, we explain the main points of PBC operation in detail in terms of Meckel’s cave, surgical procedure, complications, discussion of the focus and new progress, etc.