High-resolution 3D-constructive interference in steady-state MR imaging and 3D time-of-flight MR angiography in neurovascular compression: a comparison between 3T and 1.5T

Compressive lesions of the head and neck: Common and uncommon must-know entities

There are many lesions that cause compression of nerves and vessels in the head and neck, and they can often be overlooked in the absence of adequate history or if not suspected by the radiologist. Many of these lesions require a high index of suspicion and optimal positioning for imaging. While a multimodality approach is critical in the evaluation of compressive lesions, an MRI utilizing high-resolution (heavily weighted) T2-weighted sequence is extremely useful as a starting point. In this review, we aim to discuss the radiological features of the common and uncommon compressive lesions of the head and neck which are broadly categorized into vascular, osseous, and miscellaneous etiologies.

Comparing 1.5 T and 3.0 T MR data for 3D visualization of neurovascular relationships in the posterior fossa

BACKGROUND

Neurovascular relationships in the posterior fossa are more frequently investigated due to the increasing availability of 3.0 Tesla MRI. For an assessment with 3D visualization, no systematic analyzes are available so far and the question arises as to whether 3.0 Tesla MRI should be given preference over 1.5 Tesla MRI.

METHODS

In a prospective study, a series of 25 patients each underwent MRI investigations with 3D-CISS and 3D-TOF at 1.5 and 3.0 Tesla. For both field strengths separately, blood vessel information from the TOF data was fused into the CISS data after segmentation and registration. Four visualizations were created for each field strength, with and without optimization before and after fusion, which were evaluated with a rating system and verified with the intraoperative situation.

RESULTS

When only CISS data was used, nerves and vessels were better visualized at 1.5 Tesla. After fusion, flow and pulsation artifacts were reduced in both cases, missing vessel sections were supplemented at 3.0 Tesla and 3D visualization at 1.5 and 3.0 Tesla led to anatomically comparable results. By subsequent manual correction, the remaining artifacts were further eliminated, with the 3D visualization being significantly better at 3.0 Tesla, since the higher field strength led to sharper contours of small vessel and nerve structures.

CONCLUSION

3D visualizations at 1.5 Tesla are sufficiently detailed for planning microvascular decompression and can be used without restriction. Fusion further improves the quality of 3D visualization at 3.0 Tesla and enables an even more accurate delineation of cranial nerves and vessels.

Application of Neuronavigation in Microvascular Decompression: Optimizing Craniotomy and 3D Reconstruction of Neurovascular Compression

OBJECT

Microvascular decompression (MVD) is the best curative treatment for trigeminal neuralgia and hemifacial spasm. We used the neuronavigation to reconstruct the 3D image of cranial nerve and blood vessel to identify the neurovascular compression, and to reconstruct the venous sinus and skull to optimize craniotomy.

PATIENTS AND METHODS

A total of 11 trigeminal neuralgia and 12 hemifacial spasm cases were selected. All patients had preoperative MRI which included 3D Time of Flight (3D-TOF), Magnetic Resonance Venography (MRV) and computer tomography (CT) for navigation. Imaging sequences were fused and reconstructed by navigation system before operation. The 3D-TOF images were used to delineate cranial nerve and vessel. The CT and MRV images were used to mark transverse sinus and the sigmoid sinus for craniotomy. All patients underwent MVD and have the preoperative view compared with intraoperative findings.

RESULTS

Approaching to the cerebellopontine angle right after opening the dura and got no cerebellar retracion or petrosal vein rupture during craniotomy. Ten of 11 trigeminal neuralgia and all 12 hemifacial spasm patients got excellent preoperative 3D reconstruction fusion images, which were also confirmed by intraoperative findings. All 11 trigeminal neuralgia patients and 10 of 12 hemifacial spasm patients were symptom free without any neurological complications just after the surgery. Other 2 hemifacial spasm patients got delayed resolution in 2 months after surgery.

CONCLUSIONS

Through the neuronavigation guided craniotomy and the 3D neurovascular reconstruction, surgeons can better identify the compression of nerve and blood vessel, and reduce complications.

Three-Dimensional Constructive Interference in Steady State (3D CISS) Imaging and Clinical Applications in Brain Pathology

Three-dimensional constructive interference in steady state (3D CISS) is a steady-state gradient-echo sequence in magnetic resonance imaging (MRI) that has been used in an increasing number of applications in the study of brain disease in recent years. Owing to the very high spatial resolution, the strong hyperintensity of the cerebrospinal fluid signal and the high contrast-to-noise ratio, 3D CISS can be employed in a wide range of scenarios, ranging from the traditional study of cranial nerves, the ventricular system, the subarachnoid cisterns and related pathology to more recently discussed applications, such as the fundamental role it can assume in the setting of acute ischemic stroke, vascular malformations, infections and several brain tumors. In this review, after briefly summarizing its fundamental physical principles, we examine in detail the various applications of 3D CISS in brain imaging, providing numerous representative cases, so as to help radiologists improve its use in imaging protocols in daily clinical practice.

Utility of Neuroimaging in the Management of Chronic and Acute Headache

Imaging plays an important role in identifying the cause of the much less common secondary headaches. Such headaches may be caused by a variety of pathologic conditions which can be categorized as intracranial and extracranial. Idiopathic intracranial hypertension imaging findings include "empty sella," orbital changes, and dural venous sinus narrowing. Intracranial hypotension (ICH) is frequently caused by CSF leaks. Imaging findings include loss of the CSF spaces, downward displacement of the brain, as well as dural thickening and enhancement. Severe cases of ICH may result in subdural hematomas. A variety of intracranial and skull base tumors may cause headaches due to dural involvement. Extracranial tumors and lesions that frequently present with headaches include a variety of sinonasal tumors as well as mucoceles. Neurovascular compression disorders causing headaches include trigeminal and glossopharyngeal neuralgia. Imaging findings include displacement and atrophy of the cranial nerve caused by an adjacent arterial or venous structure.

Data fusion and 3D visualization for optimized representation of neurovascular relationships in the posterior fossa

Background

Reliable 3D visualization of neurovascular relationships in the posterior fossa at the surface of the brainstem is still critical due to artifacts of imaging. To assess neurovascular compression syndromes more reliably, a new approach of 3D visualization based on registration and fusion of high-resolution MR data is presented.

Methods

A total of 80 patients received MRI data with 3D-CISS and 3D-TOF at 3.0 Tesla. After registration and subsequent segmentation, the vascular information of the TOF data was fused into the CISS data. Two 3D visualizations were created for each patient, one before and one after fusion, which were verified with the intraoperative situation during microvascular decompression (MVD). The reproduction quality of vessels was evaluated with a rating system.

Results

In all cases, the presented approach compensated for typical limitations in the 3D visualization of neurovascular compression such as the partial or complete suppression of larger vessels, suppression of smaller vessels at the CSF margin, and artifacts from heart pulsation. In more than 95% of the cases of hemifacial spasm and glossopharyngeal neuralgia, accurate assessment of the compression was only possible after registration and fusion. In more than 50% of the cases with trigeminal neuralgia, the presented approach was crucial to finding the actually offending vessel.

Conclusions

3D visualization of fused image data allows for a more complete representation of the vessel-nerve situation. The results from this approach are reproducible and the assessment of neurovascular compression is safer. It is a powerful tool for planning MVD.

Construction of super-rapid brain MRA using oblique transverse acquisition phase contrast angiography with tilted optimized non-saturated excitation pulse

[Background] Magnetic resonance angiography (MRA) is one of the most important sequences to estimate a cerebrovascular disease. We often encounter poor image quality due to slow arterial flow related to aging and motion artifact caused by disturbance of consciousness. We focused on phase contrast angiography (PCA) to overcome these difficulties. PCA can reduce scan time drastically by combining transverse acquisition and partial slab setting covering entire brain arteries. However, transverse acquisition in PCA has a large difference in signal intensity between proximal and distal vessels. Therefore, we apply tilted optimized non-saturated excitation (TONE) to improve image quality. [Purpose] The purpose of this study to investigate the usefulness of TONE for PCA. [Method] We estimated the efficacy of TONE in transverse acquisition PCA using measurement of signal intensity in arteries. We compared image quality among 1 min PCA with/without TONE and time-of flight (TOF)-MRA, by visual. [Result] TONE improved the signal inhomogeneity in entire brain arteries. PCA with TONE (5°-9°) demonstrated the highest image quality. [Conclusion] Oblique transverse acquisition PCA with TONE provides superior image quality compared with TOF with similar scan time. TONE improved image quality by the homogenizing signal intensity of vessels from proximal to distal in oblique transvers acquisition PCA. Our MRA can be performed in about 1 min and provides sufficient quality to estimate brain vessels.

Improving the accuracy of pre-operative evaluation of neurovascular conflict in trigeminal neuralgia using magnetic resonance subtraction

PURPOSE

To investigate the ability of magnetic resonance (MR) subtraction to evaluate neurovascular conflict (NVC) and to compare it with conventional MR protocols.

METHODS

This prospective study included 82 patients with trigeminal neuralgia who underwent microvascular decompression for NVC. All patients had a pre-operative examination using 3T MRI. The MRI protocols used comprised 3D balanced (B)-fast field echo (FFE), 3D steady-state magnetic resonance angiography (MRA), and 3D T1-FFE sequences. MR subtraction images were obtained by subtracting native images from B-FFE and steady-state MRA. NVC evaluation was performed using subtraction images (MR subtraction) and combination images (conventional MR protocols using B-FFE and T1-FFE in combination). Clinical assessment of the degree of compression, the type of compressing vessel, and the location of conflict were undertaken by two independent observers. The two methods were then compared using surgical criteria.

RESULTS

MR subtraction exhibited greater accuracy than the conventional method in terms of the estimated severity of conflict (87.80% vs. 57.32%, p < 0.05), and demonstrated better consistency with surgical findings (k = 0.794 vs. k = 0.365, p < 0.05). For the type of compressing vessel and the location of conflict, both methods were highly accurate and agreed to a similar extent with surgical findings (p = 0.987, compressing vessel; p = 0.665, location of conflict).

CONCLUSION

MR subtraction proved reliable in NVC pre-operative evaluation, with increased accuracy when estimating severity. This result strongly supports the wider use of MR subtraction as the preferred choice in clinical application.

Vertebrobasilar Dolichoectasia as a Rare Cause of Simultaneous Abducens and Vestibulocochlear Nerve Symptoms: A Case Report and Literature Review

Vertebrobasilar dolichoectasia (VBD) can lead to cranial nerve symptoms. However, multiple cranial nerve symptoms associated with VBD in one case remain extremely rare. We here present the case of a 33-year-old male with VBD diagnosed by multimodality imaging, who developed simultaneous abducens and vestibulocochlear nerve symptoms and subsequently improved after blood pressure control treatment. To our knowledge, this is the first report of such a vascular disorder resulting in simultaneous symptoms of the abducens and vestibulocochlear nerves. This study highlights that such a vascular anomaly should be considered when cranial nerve symptom is encountered, especially when multiple cranial nerves involved. Meanwhile, radiological evalurrrrrrrrrrrrrrrrrrration of such neurovascular conflict using three-dimensional constructive interference in steady-state imaging is recommended.

Morphometric analysis of facial and cochlear nerves in normal-hearing ears using 3D-CISS

Purpose

The aim of the current study was to establish a normative data set for the morphometric parameters of the facial nevre (FN) and cochlear nevre (CN) according to age and sex in the adult population, using 3-dimensional constructive interference in steady state (3D-CISS) sequence on magnetic resonance imaging.

Methods

We retrospectively analyzed 157 ears of 102 adults with no hearing impairment, facial palsy or Ménière's disease. The vertical (VD) and horizontal (HD) diameters as well as cross-sectional areas (CSAs) of the FNs and CNs were measured on the parasagittal oblique image created using the axial 3D-CISS sections passing through the internal acoustic canal. We related the measurement results with side, sex and age.

Results

The mean VD, HD and CSA of the FNs were 1.09 ± 0.18 mm, 0.84 ± 0.17 mm, and 0.75 ± 0.27 mm², respectively, whereas those of the CNs were 1.34 ± 0.17 mm, 1 ± 0.15 mm and 1.06 ± 0.3 mm², respectively. There was no statistically significant difference between the morphometric parameters of both the nerves according to side or sex (P > 0.05). However, except for the CSA of the FNs among males, we found a statistically significant decrease in all the morphometric parameters of both the nerves with ageing (P < 0.05).

Conclusion

The normative morphometric data obtained in this study can be beneficial in clinical applications for sensorineural hearing loss, facial palsy and Ménière's disease.

Efficacy of microvascular decompression in patients with trigeminal neuralgia with negative neurovascular relationship shown by magnetic resonance tomography

OBJECTIVE

To explore the surgical efficacy of microvascular decompression(MVD) when the recent magnetic resonance tomography angiography(MRA) is unable to determine the relationship between blood vessels and nerves in patients with trigeminal neuralgia(TN).

MATERIALS AND METHODS

The MRI images of 146 patients with TN who underwent MVD from January 2016 to December 2019 were analyzed retrospectively. The relationship between nerves and vessels was categorized as no contact, suspicious contact, and clear contact. Suspicious contact and clear contact were both defined as positive neurovascular relationship, whereas no contact was defined as negative neurovascular relationship. The efficacy of MVD in positive and negative groups was compared.

RESULTS

1. A total of 146 TN patients underwent MVD. Intraoperative examination revealed that out of 146, 143 patients exhibited contacts, including 110 cases with arterial contact, 22 cases with combined arterial and venous contact, and 11 cases with venous contact. Considering the surgical result as a gold standard, the sensitivity of three-dimensional time leap angiography (3D-TOF-MRA) in assessing vascular compression in TN was 74.0 %; and the sensitivity of three-dimensional steady-state precession rapid imaging sequence (3D-FIESTA) in determining vascular compression was 82.2 %. Out of a total of 17 cases demonstrating negative neurovascular relationship by 3D-TOF-MRA together with 3D-FIESTA, 14 cases were found to have vascular contact during the surgery, and the sensitivity was determined to be 88.4 %. 2.Among the 38 patients with a negative neurovascular relationship demonstrated by 3D-TOF, postoperative efficacy was noted as a cure: 30 cases, improved: 5 cases, no effect: 3 cases. 3D-FIESTA showed 26 cases of negative neurovascular relationship, among them, cured: 20 cases, improved: 3 cases, no effect: 3 cases. A total of 17 patients with negative neurovascular relationships were established by 3D-TOF-MRA together with 3D-FIESTA, and the postoperative effects were found to be cure: 13 cases, improvement: 2 cases, and no effect: 2 cases. There was no statistically significant difference between the negative group and the positive group (x² test; p > 0.05).

CONCLUSION

To conclude, 3D-TOF-MRA, together with 3D-FIESTA, can illustrate the large blood vessels surrounding the trigeminal nerve efficiently, and determine whether it is the offending blood vessel. The interpretation would help reproduce the local anatomical spatial structure of the site before surgery, yet it is impossible to assess the peripheral anatomical relationship of the trigeminal nerve cistern comprehensively and accurately. This hints that a perfect prediction of the surgical effect of MVD is not possible at present. Thus, typical symptoms of TN are the most critical indicators for MVD surgery.

3D-Visualization of Neurovascular Compression at the Ventrolateral Medulla in Patients with Arterial Hypertension

Purpose

Controversy exists on the association of arterial hypertension (HTN) and neurovascular compression (NVC) at the ventrolateral medulla (VLM). No standardized and reproducible technique has been introduced yet for detection of NVC in HTN. This study aimed to generate, analyze and compare different results of exact reproducible anatomical 3D-representations of the VLM in patients with HTN, based on magnetic resonance imaging (MRI).

Methods

A 3T scanner provided MRI (T2-constructive interference in steady state (CISS) high resolution imaging and three-dimensional Time-of-flight (3D-TOF) angiography) from the posterior fossa of 44 patients with clinical treatment-resistant HTN. Image processing consists of segmentation of the CISS data, registration and fusion of the CISS and TOF data and visualization. For each patient two 3D-visualizations (before and after fusion) were obtained. The reproduction quality of the vessels, flow-related signal variability and pulsation artifacts were analyzed and compared, using a ranking score.

Results

Integrating vascular information from TOF into CISS data reduced artifacts in 3D-visualizations of exclusively processed CISS data. The quality of 3D-visualization of the vessels near the brain stem was significantly improved (p = 0.004). The results were reproducible and reliable. The quality of the 3D-presentations of neurovascular relationships at the VLM improved significantly (p < 0.001).

Conclusion

The 3D-visualization of fused image data provides an excellent overview of the relationship between cranial nerves and vessels at the VLM and simplifies the detection of NVC in HTN. It provides a powerful tool for future clinical and scientific research. Although microvascular decompression (MVD) in treatment resistant HTN is not a standard procedure, it can be discussed in selected patients with intractable severe HTN.

Preoperative visualization of neurovascular contact with 3D-FIESTA combined with 3D-TOF MRA to guide microvascular decompression surgery planning

Background:

Neurovascular compression syndromes including trigeminal neuralgia (TN) and hemifacial spasm (HFS) are caused by neurovascular conflicts at the root entry zone of the corresponding cranial nerves in the posterior fossa. Microvascular decompression (MVD) is the best choice for the treatment of TN and HFS. An accurate delineation of the responsible vessel could decrease the rate of possible operative complications such as nerve paresis.

Methods:

In this study, three-dimensional fast imaging employing steady-state acquisition (3D-FIESTA) and three-dimensional time-of-flight magnetic resonance angiography (3D-TOF MRA) were performed on 113 patients with TN or HFS. The imaging data were compared to the intraoperative findings and the accuracy of the data was calculated among the different responsible blood vessels and disease types. The accuracy of the data among different genders, disease durations, disease sides, and disease types was also calculated to identify the target patients for the preoperative diagnostic approach with 3D-FIESTA combined with 3D-TOF MRA.

Results:

The accuracy of detection with the imaging was above 75% in cases with single-vessel compression. Among these, the accuracy of the preoperative imaging result was the highest when the lesions were in the superior cerebellar artery (SCA; 91.1%). In cases of multiple-vessel compression, however, the coincidence between the preoperative and intraoperative results was only 30.0%. In most of the cases of TN, the responsible blood vessels were in the SCA, and the accuracy in the SCA reached 94.9%. In HFS patients, the responsible blood vessels were in the anterior inferior cerebellar artery (AICA) and posterior inferior cerebellar artery (PICA), and the accuracy was 86.8% and 90.0%, respectively. The differences in the accuracy of the data among different genders, disease durations, disease sides, and disease types were not statistically significant.

Conclusion:

This study verified the clinical instructional value of 3D-FIESTA combined with 3D-TOF MRA in MVD, and showed that this preoperative examination is reliable for all genders, disease durations, disease sides, and disease types.

Neuroanatomical Determinants of Secondary Trigeminal Neuralgia: Application of 7T Ultra-High-Field Multimodal Magnetic Resonance Imaging

BACKGROUND

Seven-Tesla (7T) magnetic resonance imaging (MRI) has demonstrated value for evaluating a variety of intracranial diseases. However, its utility in trigeminal neuralgia has received limited attention. The authors of the present study applied ultra-high field multimodal MRI to two representative patients with secondary trigeminal neuralgia due to epidermoid tumors to illustrate the possible clinical and surgical advantages of 7T compared with standard clinical strength imaging. Techniques included co-registration of multiple 7T sequences to optimize the detection of potential concurrent neurovascular and neoplasm-derived compression.

METHODS

7T MRI studies were performed using a whole body scanner. Two- and three-dimensional renderings of potential neurovascular conflict were created by co-registering time-of-flight angiography and T2-weighted turbo spin echo images in MATLAB and GE software. Detailed comparisons of the various field strength images were provided by a collaborating neuroradiologist (B.D.).

RESULTS

7T MRI clearly illustrated minute tumor-adjacent vasculature. In contrast, conventional, low-field imaging did not consistently provide adequate details to distinguish cerebrospinal fluid pulsatility from vessels. The tumor margins, although distinct from the trigeminal nerve fibers at 7T, blended with those of the surrounding structures at 3T. Two- and three-dimensional co-registration of time-of-flight angiography with T2-weighted MRI suggested that delicate, intervening vasculature may have contributed to these illustrative patients' symptomatology.

CONCLUSIONS

7T provided superior visualization of vital landmarks and subtle nerve and vessel features. Co-registration of various advanced 7T modalities may help to resolve complex disease etiologies. Future studies should explore the extent to which this dual etiology might persist across tumor types and utilize diffusion-based techniques to quantify what microstructural differences might exist between patients with trigeminal neuralgia from varying etiologies.

Computational Fluid Dynamics Analysis of the Offending Artery at Sites of Neurovascular Compression in Trigeminal Neuralgia Using Preoperative MRI Data

This study aimed to analyze the hemodynamic features of the offending artery at sites of neurovascular compression (NVC) using computational fluid dynamics (CFD). A total of 23 patients who underwent microvascular decompression (MVD) for primary trigeminal neuralgia (TN) between January 2015 and December 2016 were enrolled in this study. The compressing vessel at the NVC site was identified microsurgically in all cases, and patients were divided into two groups based on the intraoperative findings: (1) the arterial NVC group and (2) the non-arterial NVC control group. A 3D surface model of the structures surrounding the NVC was created using preoperative magnetic resonance imaging (MRI), and CFD analysis was performed for the target artery. In addition to standard parameters, such as the wall shear stress (WSS), flow velocity, and pressure, we calculated the WSS ratio (WSSR) by dividing the WSS at the NVC by the mean WSS of the target. Arterial compression was observed intraoperatively in 13 patients. The mean WSSR of the arterial NVC group was significantly higher than that of the control group (2.36 ± 1.00 vs. 1.18 ± 0.73, P <0.05). There were no significant intergroup differences in the other calculated parameters. High WSSR, which indicates elevated WSS at the sites of NVC, was identified as a unique parameter of arterial compression that may contribute to TN. CFD could be a useful clinical tool in determining the target of MVD under preoperative conditions.

Accuracy of computed tomography-magnetic resonance imaging image fusion using a phantom for skull base surgery

BACKGROUND

To assess the positional accuracy of image fusions of the skull base region using different magnetic resonance imaging (MRI) and computed tomography (CT) image pairs.

METHODS

An image set of 3D fast imaging employing steady-state acquisition-C (FIESTA-C) was used as the base image set. Image fusions were performed using an image set with different fields of view (FOVs): one with different matrix size, one with a different sequence of 3D spoiled gradient recalled acquisition, and one with different modality (CT), using a phantom including multi columnar objects. Position of columns at the center, and 4 and 8 cm from the center were measured. The displacements between the base image set and fused image set were measured. For slices with different z-positions, the displacement of the 8-cm column was assessed. For 20 clinical MRI cases, the distance between the dorsum sellae and the cranial nerves was measured.

RESULTS

No significant differences were found between the different FOVs or image sequences. However, with the different matrix sizes and modalities, significant displacements were observed, although they were all within 0.5 mm. Similar displacements were observed in the slices at different z-positions. All cranial nerves were located within 40 mm of the dorsum sellae.

CONCLUSIONS

The displacements following image fusion were within approximately 0.5 mm, even at 8 cm from the center. This suggests that the region where the cranial nerves are located, within 40 mm of the dorsum sellae, had no risk of positional error following image fusion.

Analysis of morphological measurements of the trigeminal nerve in the linac stereotactic radiosurgery simulation targeting the root entry zone in trigeminal neuralgia

PURPOSE

To describe the anatomical measurements of the trigeminal nerve in patients with trigeminal neuralgia (TN) during Linac (linear accelerator)-based stereotactic radiosurgery (SRS) simulation, targeting the root entry zone (REZ), with a 30% isodose line tangential to the pons, using 4-mm and 6-mm collimators.

METHODS

In this retrospective study, 53 TN patients, who underwent Fiesta sequence scanning prior to any treatment modality, were assessed. Bilateral measurements were obtained from the cisternal segment of the trigeminal nerve, the trigeminal-pontine angle, and the lateral width of the pontine cistern on the Fiesta MRI sequence. Linac-based SRS simulations were estimated with a radiation dosage of 90Gy to 30% isodose line tangential to the pons, with both 4- and 6-mm collimators. Distances from the calculated targets to the pons and the Gasserian ganglion were measured for later analysis. The statistical analysis was performed comparing the affected side against the unaffected side.

RESULTS

Right trigeminal nerve was affected in 36 patients (67.9%), and left one in 17 (32.1%) patients. The mean length of the trigeminal nerve was 9.8mm (range: 4.6-16.8mm) on the affected side, and 10.5mm (range: 5.6-18.4mm) on the unaffected side (p=.02). The mean trigeminal-pontine angle was 12.5° (range: 5.4° to 19.5°) on the affected side, and 10.2° (range: 5.0° to 30.5°) on the unaffected side (p=.01). In the simulations, the distances from the estimated targets to the pons and the Gasserian ganglion were not statistically different between sides. The variation of target-pons and target-ganglion distances was statistically significant on the affected side with the change of collimators (p<.001).

CONCLUSIONS

In this anatomical study, significant differences were identified in the length of the affected trigeminal nerve and trigeminal-pontine angle compared to the unaffected side in TN patients in Fiesta sequences prior to surgery or radiosurgery. Significant variation of the target location was found on the REZ between the 4- and 6-collimators during the Linac-based SRS simulations with the estimated radiation dosage of 90Gy and 30% isodose line tangential to the pons.

Imaging and Surgical Findings in Patients with Hemi-Laryngopharyngeal Spasm and the Potential Role of MRI in the Diagnostic Work-Up

BACKGROUND AND PURPOSE

Hemi-laryngopharyngeal spasm is a recently discovered condition characterized by episodic coughing and unilateral throat contractions that may lead to severe stridor. These symptoms are caused by a vascular compression of the ipsilateral vagus nerve, typically the PICA. Microvascular decompression of the vagus nerve has been demonstrated to be a potential cure for this neurovascular compression syndrome. The main aim of this study was to clarify the role of MR imaging in the diagnostic work-up of this rare condition.

MATERIALS AND METHODS

We describe the imaging and surgical findings of 3 patients from our prospective case series of patients with hemi-laryngopharyngeal spasm from 2015 to 2017. Second, the imaging data of 100 patients (control cohort) with symptoms unrelated to hemi-laryngopharyngeal spasm were reviewed to investigate the rate and degree of neurovascular conflict of the vagus nerve.

RESULTS

All patients with hemi-laryngopharyngeal spasm reported to date have had vascular compression of the vagus nerve due to the PICA. In the control cohort, there was a good interrater agreement in scoring the "contact" and "compression" of the vagus nerve (κ = 0.73. P = < .001). The frequency of contact or compression of the vagus nerve was approximately 50%. The PICA was the most frequent vessel involved in 74%.

CONCLUSIONS

The presence of unilateral neurovascular contact or compression of the vagus nerve does not confirm the diagnosis of hemi-laryngopharyngeal spasm. The MR imaging finding of ipsilateral vascular compression of the vagus nerve is a necessary but not sufficient finding for the diagnosis of hemi-laryngopharyngeal spasm.

MRI Findings and Outcomes in Patients Undergoing Microvascular Decompression for Glossopharyngeal Neuralgia

BACKGROUND AND PURPOSE

Glossopharyngeal neuralgia causes extreme paroxysmal pain in the posterior pharynx, tonsillar region, base of tongue, or deep ear, that is, the distribution of the glossopharyngeal nerve. Some cases of glossopharyngeal neuralgia are associated with neurovascular conflict, usually by the posterior inferior cerebellar artery. Such symptomatic compression occurs only in proximal, centrally myelinated portions of the glossopharyngeal nerve near the brainstem. Microvascular decompression provides effective and durable pain relief for properly selected patients with medically refractory glossopharyngeal neuralgia. The purpose of this study is to describe a tailored MRI evaluation of neurovascular conflict in glossopharyngeal neuralgia to improve candidate selection for microvascular decompression.

METHODS

Our team developed a glossopharyngeal neuralgia imaging and evaluation protocol including a grading system for neurovascular conflict of the glossopharyngeal nerve and applied it to evaluate candidates for microvascular decompression.

RESULTS

Our team grades neurovascular conflict as "contact" (vessel touching nerve without intervening cerebrospinal fluid) versus "deformation" (deviation or distortion of nerve from its normal course by the offending vessel). MRIs of patients with glossopharyngeal neuralgia demonstrate proximal neurovascular conflict. Postoperative MRI demonstrates separation of the glossopharyngeal nerve from the offending vessel.

CONCLUSION

A tailored glossopharyngeal neuralgia imaging evaluation protocol is presented. We believe this approach has helped improve microvascular decompression outcomes and reduce unnecessary procedures at our institution. Further research may elucidate whether clinical and imaging features, including neurovascular conflict severity, predict surgical outcome for glossopharyngeal neuralgia.

A local excitation magnetic resonance imaging method for intracranial unruptured aneurysm at the distal internal carotid artery

It is often difficult to diagnose an intracranial aneurysm at the distal internal carotid artery by conventional magnetic resonance imaging.

PURPOSE

We assessed the effectiveness of the local excitation technique, a new application for magnetic resonance imaging, to clarify the geometric structure of aneurysm and adjacent branches at the distal internal carotid artery.

STUDY DESIGN

Two independent evaluators diagnosed 10 cases of suspected aneurysms at the distal internal carotid artery by T2-weighted magnetic resonance imaging with application of local excitation, adding it to conventional time-of-flight-magnetic resonance angiography.

FINDINGS

We successfully distinguished the aneurysm from infundibular dilatation in five of 10 cases.

CONCLUSION

Our results suggested that addition of local excitation to conventional magnetic resonance angiography was effective to diagnose unruptured aneurysm at the distal internal carotid artery, to clarify the configuration of the prominent lesion or whether the location of the adjacent branch orifice on the parent vessel was symmetric or asymmetric.

Prognostic Impact and Post-operative Evaluation of Volumetric Measurement of the Cerebellopontine Cistern in Trigeminal Neuralgia Using 3 Tesla Magnetic Resonance Imaging

The aim of this study was to evaluate the importance of pre- and post-operative volumetric measurement of the cerebellopontine angle (CPA) using 3 Tesla (3T) magnetic resonance imaging (MRI). Between April 2012 and December 2015, a total of 87 consecutive patients underwent microvascular decompression (MVD) for trigeminal neuralgia (TN), of whom 51 with primary TN caused by arterial compression were enrolled in this study. Bilateral CPA cistern volume was evaluated using 3T MRI before and after surgery; the Cistern Deviation Index was used to represent the degree of deviation of the CPA cistern. The relationships between CPA cistern volume and the etiology of TN were assessed, and post-operative changes in anatomical parameters were examined to determine differences between recurrent and non-recurrent patients with TN. The mean volume of the CPA cistern on the affected side was significantly smaller than the unaffected side (P < 0.001). Five of 51 (10%) patients experienced TN recurrence. The recurrent cases demonstrated significantly lower pre-operative Cistern Deviation Index scores than non-recurrent cases (P = 0.035). On the unaffected side-but not the affected side-post-operative volume reduction was significantly greater in the recurrence group than in the non-recurrence group (P = 0.004). The pre-operative Cistern Deviation Index was a useful parameter to predict the recurrence of TN. In recurrent patients, post-operative inflammatory reaction may extend to not only the operated side but also the healthy side and reduce the volume of the CPA cistern.

Tenth case of bilateral hemifacial spasm treated by microvascular decompression: Review of the pathophysiology

BACKGROUND

Bilateral hemifacial spasm (BHFS) is a rare neurological syndrome whose diagnosis depends on excluding other facial dyskinesias. We present a case of BHFS along with a literature review.

METHODS

A 64-year-old white, hypertense male reported involuntary left hemiface contractions in 2001 (aged 50). In 2007, right hemifacial symptoms appeared, without spasm remission during sleep. Botulinum toxin type A application produced partial temporary improvement. Left microvascular decompression (MVD) was performed in August 2013, followed by right MVD in May 2014, with excellent results. Follow-up in March 2016 showed complete cessation of spasms without medication.

RESULTS

The literature confirms nine BHFS cases bilaterally treated by MVD, a definitive surgical option with minimal complications. Regarding HFS pathophysiology, ectopic firing and ephaptic transmissions originate in the root exit zone (REZ) of the facial nerve, due to neurovascular compression (NVC), orthodromically stimulate facial muscles and antidromically stimulate the facial nerve nucleus; this hyperexcitation continuously stimulates the facial muscles. These activated muscles can trigger somatosensory afferent skin nerve impulses and neuromuscular spindles from the trigeminal nerve, which, after transiting the Gasser ganglion and trigeminal nucleus, reach the somatosensory medial posterior ventral nucleus of the contralateral thalamus as well as the somatosensory cortical area of the face. Once activated, this area can stimulate the motor and supplementary motor areas (extrapyramidal and basal ganglia system), activating the motoneurons of the facial nerve nucleus and peripherally stimulating the facial muscles.

CONCLUSIONS

We believe that bilateral MVD is the best approach in cases of BHFS.

Computed Tomography in the Diagnosis of Classical Trigeminal Neuralgia

OBJECTIVE

This study aims to characterize the pathogenesis of neurovascular conflict in trigeminal neuralgia (TN) with the goal of producing a reliable diagnostic method.

METHODS

Data were obtained during microvascular decompression surgery. The normal relationship between the superior cerebellar artery (SCA) and the trigeminal nerve root also was characterized in postmortem cases. Furthermore, SCA was imaged with high-resolution computed tomography angiography.

RESULTS

Our results indicate that contact between SCA and the trigeminal nerve root is present in both TN and non-TN cases, but in patients with TN, the apex of SCA loop was always at the bottom of the upper edge of the trigeminal root forming the state of neurovascular conflict. High-resolution angiography supported the intraoperative results.

CONCLUSIONS

These findings indicate a clear difference between neurovascular contact and conflict and point to the use of high-resolution computed tomography visualization of the position of SCA loop apex relative to the trigeminal nerve root as a primary diagnostic method.

Clinical utility of optimized three-dimensional T1-, T2-, and T2*-weighted sequences in spinal magnetic resonance imaging

This article reviews the clinical utility of 3D magnetic resonance imaging (MRI) sequences optimized for the evaluation of various intraspinal lesions. First, intraspinal tumors with hypervascular components and arteriovenous malformations (AVM) are clearly shown on contrast-enhanced (CE)-3D T1-weighted gradient-echo (GE) sequences with high spatial resolution. Second, dynamic CE-3D time-resolved magnetic resonance angiography (MRA) shows delineated feeding arteries of intraspinal AVM or arteriovenous fistula (AVF), greatly aiding subsequent digital subtraction angiography (DSA). Third, 3D multiecho T2*-weighted GE sequences are used to visualize intraspinal structures and spinal cord lesions and are sensitive to the magnetic susceptibility of intraspinal hemorrhages. Three-dimensional balanced steady-state free precession (SSFP) and multishot 3D balanced non-SSFP sequences produce contiguous thin images with high signal-to-noise ratio (SNR) in short scanning times. Intraspinal cystic lesions and small nerve-root tumors in subarachnoid space can be viewed using 3D balanced SSFP. Spinal cord myelomalacia and cord compression can be evaluated on fat-suppressed multishot 3D balanced non-SSFP. Finally, a 3D T2-weighted fast spin-echo (FSE) sequence with variable flip angle (FA) refocusing pulse improves through-plane spatial resolution over conventional 2D T2-weighted FSE sequences while matching image contrast.

Trigeminal Neuralgia

Trigeminal neuralgia (TN) is a sudden, severe, brief, stabbing, and recurrent pain within one or more branches of the trigeminal nerve. Type 1 as intermittent and Type 2 as constant pain represent distinct clinical, pathological, and prognostic entities. Although multiple mechanism involving peripheral pathologies at root (compression or traction), and dysfunctions of brain stem, basal ganglion, and cortical pain modulatory mechanisms could have role, neurovascular conflict is the most accepted theory. Diagnosis is essentially clinically; magnetic resonance imaging is useful to rule out secondary causes, detect pathological changes in affected root and neurovascular compression (NVC). Carbamazepine is the drug of choice; oxcarbazepine, baclofen, lamotrigine, phenytoin, and topiramate are also useful. Multidrug regimens and multidisciplinary approaches are useful in selected patients. Microvascular decompression is surgical treatment of choice in TN resistant to medical management. Patients with significant medical comorbidities, without NVC and multiple sclerosis are generally recommended to undergo gamma knife radiosurgery, percutaneous balloon compression, glycerol rhizotomy, and radiofrequency thermocoagulation procedures. Partial sensory root sectioning is indicated in negative vessel explorations during surgery and large intraneural vein. Endoscopic technique can be used alone for vascular decompression or as an adjuvant to microscope. It allows better visualization of vascular conflict and entire root from pons to ganglion including ventral aspect. The effectiveness and completeness of decompression can be assessed and new vascular conflicts that may be missed by microscope can be identified. It requires less brain retraction.

Comparison of brain MRI angiography and brain MRI cisternography in patients with hemifacial spasm

OBJECTIVE

The aim of this study was to compare the ability of brain magnetic resonance imaging angiography and brain magnetic resonance imaging cisternography of showing the neurovascular contiguity of the facial nerve in patients with hemifacial spasm.

METHOD

This study included a total of 35 patients (28 females, 7 males), with an average age of 57.5 ± 13.8 years, who presented to our outpatient clinic of movement disorders. All patients were prospectively applied brain magnetic resonance imaging angiography and brain magnetic resonance imaging cisternography, and the results were evaluated by a radiologist who was blind to study protocol.

RESULTS

The study included 35 patients, of whom 28 (80 %) were female and 7 (20 %) were male. Brain magnetic resonance imaging angiography demonstrated facial nerve compression of vascular origin in 5 (14.3 %) patients presenting with the clinical presentation of hemifacial spasm. Neurovascular compression of facial nerve was shown by brain magnetic resonance imaging cisternography in 13 (37.1 %) patients.

CONCLUSION

No statistically significant difference was found between brain magnetic resonance imaging angiography and brain magnetic resonance imaging cisternography techniques in detecting a compressive interaction causing hemifacial spasm between facial nerve and adjacent vascular structures (p > 0.05).

Novel imaging approaches to cerebrovascular disease

Imaging techniques available to the physician treating neurovascular disease have substantially grown over the past several decades. New techniques as well as advances in imaging modalities continuously develop and provide an extensive array of modalities to diagnose, characterize, and understand neurovascular pathology. Modern noninvasive neurovascular imaging is generally based on computed tomography (CT), magnetic resonance (MR) imaging, or nuclear imaging and includes CT angiography, CT perfusion, xenon-enhanced CT, single-photon emission CT, positron emission tomography, magnetic resonance angiography, MR perfusion, functional magnetic resonance imaging with global and regional blood oxygen level dependent imaging, and magnetic resonance angiography with the use of the noninvasive optional vessel analysis software (River Forest, Ill). In addition to a brief overview of the technique, this review article discusses the clinical indications, advantages, and disadvantages of each of those modalities.

Trigeminal neuralgia caused by brain arteriovenous malformations: A case report and literature review

Few cases of trigeminal neuralgia (TGN) induced by brain arteriovenous malformations (bAVMs) have previously been reported. The present case report described one case of TGN caused by bAVMs in a 32-year-old male patient who suffered from recurrent pain in his right cheek for a period of two years, for whom the seizure frequency and duration of pain increased for 6 months. Magnetic resonance imaging was performed, which demonstrated flow-void signals in the abnormal vessels in the right cerebellopontine angle. Subsequent digital subtraction angiography confirmed the diagnosis of bAVMs, and showed the nidus was fed by the right superior cerebellar and the right anterior inferior cerebellar, and drained into the adjacent venous sinuses on the same side. The patient underwent an interventional embolization treatment. TGN was completely relieved following embolization of the majority of the bAVMs. Pain relief may be associated with blocking of the pulsatile compression of the feeding arteries of the bAVMs, the arterialized draining veins or the malformed niduses following embolization, which is similar to the effects induced by microvascular decompression surgery of the trigeminal nerve. In the present case study and review, the underlying mechanism and treatment strategy of TGN caused by bAVMs were discussed in the context of present case, and a literature review was carried out.

MRI of the Trigeminal Nerve in Patients With Trigeminal Neuralgia Secondary to Vascular Compression

OBJECTIVE

Trigeminal neuralgia is a debilitating facial pain disorder, frequently caused by vascular compression of the trigeminal nerve. Vascular compression that results in trigeminal neuralgia occurs along the cisternal segment of the nerve.

CONCLUSION

Imaging combined with clinical information is critical to correctly identify patients who are candidates for microvascular decompression. The purpose of this article is to review trigeminal nerve anatomy and to provide strategies for radiologists to recognize important MRI findings in patients with trigeminal neuralgia.

Preoperative Three-Dimensional Diagnosis of Neurovascular Relationships at the Root Exit Zones During Microvascular Decompression for Hemifacial Spasm

OBJECTIVE

Hemifacial spasm occurs when a blood vessel compresses against an area near the root exit zone of the facial nerve. Developments in diagnostic neuroimaging have allowed three-dimensional (3D) observation of artery and nerve locations, an effective aid for treatment selection. However, an accurate interpretation of the 3D data remains challenging because imaging representations of complex small vessels are drowned out by noise. We used a noise elimination method to analyze artery and nerve locations and to determine their 3D relationship.

METHODS

Fifteen patients treated for hemifacial spasm were included. Images fused from 3 modalities of magnetic resonance imaging, 3D computed tomography, and angiography were used as source images. Using the images, models of the nerve and candidate vessels were created and shown in 3D to observe how the arteries were compressing the nerve and to identify the portions of the offending vessels that were closest to the nerve. These preoperative results were then compared with operative field observations during surgery. 3D models of the unaffected side were created and evaluated as controls.

RESULTS

We confirmed that these models were accurate reconstructions of the source images as the tubular nerve and artery cross-sections showed good alignment onto magnetic resonance imaging axial slice images. The preoperative diagnoses of the compression sites and offending arteries all matched intraoperative findings.

CONCLUSIONS

An accurate identification of the offending arteries and compression sites was possible, and this method is anticipated to offer effective means of preoperative simulation.

Neurovascular study of the trigeminal nerve at 3 t MRI

This study aimed to show a novel visualization method to investigate neurovascular compression of the trigeminal nerve (TN) using a volume-rendering fusion imaging technique of 3D fast imaging employing steady-state acquisition (3D FIESTA) and coregistered 3D time of flight MR angiography (3D TOF MRA) sequences, which we called "neurovascular study of the trigeminal nerve". We prospectively studied 30 patients with unilateral trigeminal neuralgia (TN) and 50 subjects without symptoms of TN (control group), on a 3 Tesla scanner. All patients were assessed using 3D FIESTA and 3D TOF MRA sequences centered on the pons, as well as a standard brain protocol including axial T1, T2, FLAIR and GRE sequences to exclude other pathologies that could cause TN. Post-contrast T1-weighted sequences were also performed. All cases showing arterial imprinting on the trigeminal nerve (n = 11) were identified on the ipsilateral side of the pain. No significant relationship was found between the presence of an artery in contact with the trigeminal nerve and TN. Eight cases were found showing arterial contact on the ipsilateral side of the pain and five cases of arterial contact on the contralateral side. The fusion imaging technique of 3D FIESTA and 3D TOF MRA sequences, combining the high anatomical detail provided by the 3D FIESTA sequence with the 3D TOF MRA sequence and its capacity to depict arterial structures, results in a tool that enables quick and efficient visualization and assessment of the relationship between the trigeminal nerve and the neighboring vascular structures.

Three-dimensional observation of Virchow-Robin spaces in the basal ganglia and white matter and their relevance to idiopathic normal pressure hydrocephalus

Background

Virchow–Robin spaces (VRS) are brain perivascular spaces containing perforating arteries. Although enlarged VRS are associated with various disorders such as Alzheimer’s disease, cerebrovascular disease, and head trauma, their functional role remains unclear. Using highly fluid-sensitive magnetic resonance imaging (MRI) sequences, fine morphological features of VRS and their relevance to idiopathic normal pressure hydrocephalus (iNPH) were investigated.

Methods

Three-dimensional constructive interference in steady state (3D-CISS) on 3 Tesla MRI was applied to 29 individuals. The morphology and number of VRS in the basal ganglia and white matter were compared between 20 patients with iNPH and nine age-matched controls. The VRS number per hemisphere was classified into three grades: few, moderate, and abundant.

Results

Virchow–Robin spaces in the basal ganglia were curved, irregularly sized and shaped, and communicated with the cerebrospinal fluid in the subarachnoid space; they contained perforating arteries. VRS in the white matter were straight, smooth, homogeneously sized and shaped, and did not penetrate the cortex. Arteries were not seen in VRS of the white matter. White matter VRS were sparse in patients with iNPH. In contrast, basal ganglia VRS positively correlated with age. Postoperatively after shunt surgery, VRS in the white matter were mildly decreased in diameter, but not in number. No significant changes were noted in basal ganglia VRS.

Conclusions

The present study revealed different morphological features of VRS in the basal ganglia and white matter. VRS in the basal ganglia were seen as genuine perivascular spaces; while neither communication with subarachnoid spaces nor arteries were seen in white matter VRS, even by 3D-CISS sequences and high-resolution magnetic resonance angiography on 3T-MRI. White matter VRS were sparse in patients with iNPH and they were mildly decreased in diameter, but did not change in number after surgery. At present, it remains unclear whether the white matter VRS are dilated interstitial fluid spaces or cerebral amyloid angiopathy, or both. Further studies are necessary to elucidate the functional role of VRS in normal subjects and patients with iNPH.

Preoperative Evaluation of Patients with Hemifacial Spasm by Three-dimensional Time-of-Flight (3D-TOF) and Three-dimensional Constructive Interference in Steady State (3D-CISS) Sequence

PURPOSE

The purpose of this study was to investigate and evaluate the accuracy and the preoperative diagnostic value of high-resolution magnetic resonance imaging (MRI) techniques, three-dimensional time-of-flight (3D-TOF) and three-dimensional constructive interference in steady state (3D-CISS) sequence, solely or in combination for the detection of the relationship between the facial nerve and adjacent vessels in patients with hemifacial spasm (HFS).

METHODS

A total of 95 patients with primary HFS were subject to 3D-TOF and 3D-CISS MRI. The MR images were then used to evaluate the anatomical neurovascular relationships, and the results were compared with the surgical findings. We categorized the neurovascular relationship into three types: compression, contact, and neighboring or distant. Compression and/or contacts between root exit zone (REZ) and vessels were defined as positive, whereas neighboring or distant was considered to be negative.

RESULTS

3D-TOF combined with 3D-CISS assessment showed that 94 of 95 patients had artery compression or contact at REZ, whereas the remaining patient had compression at the peripheral branch of the facial nerve but not at REZ. The positive rates and the overall accuracy were 98.95 and 100 %, respectively, for the 3D-TOF combined with 3D-CISS assessment; 92.63 and 93.68 %, respectively, for the 3D-TOF assessment; and 85.26 and 86.32 %, respectively, for the 3D-CISS assessment. The positive rates and overall accuracy for the 3D-TOF combined with 3D-CISS assessment was significantly higher than those for the 3D-TOF or 3D-CISS assessment.

CONCLUSIONS

Combination of 3D-TOF with 3D-CISS imaging well delineates the relationship between the facial nerve and adjacent vessels in terms of increased positive rates and accuracy.

Microvascular decompression for trigeminal neuralgia

The microvascular decompression procedure has proven to be a safe and effective option in the surgical management of neurovascular compression syndromes in general and trigeminal neuralgia in particular. This article aims to serve as an overview of the decision-making process, application of the surgical technique, and clinical outcome pertaining to this procedure.

Value of 3-Dimensional High-Resolution Magnetic Resonance Imaging in Detecting the Offending Vessel in Hemifacial Spasm

BACKGROUND:

High-resolution 3-dimensional (3-D) magnetic resonance imaging (MRI) is widely used to predict the neurovascular anatomy within the cerebellopontine angle.

OBJECTIVE:

To assess the value of 3-D steady-state free precession imaging (SSFP) and time-of-flight magnetic resonance angiography (TOF MRA) in detecting the offending vessels in hemifacial spasm in comparison to intraoperative endoscopic visualization.

METHODS:

42 patients underwent endoscope-assisted microvascular decompression (MVD). All available preoperative 3-D SSFP and TOF MRA images were checked. Intraoperative videos were captured by a high-definition endoscopic camera attached to endoscopes while exploring the area of facial nerve root exit zone (REZ). Evaluation of the 3-D images was performed by 2 independent groups of observers and compared with the operative findings.

RESULTS:

Three-D MRI had an average positive predictive value (PPV) of 89.1% in differentiating between simple and complex compression. Mean accuracy of the images in detection of the offending vessels was 83.3% and 77% according to the first and second groups of observers, respectively. Averaged inter-observer agreement between the 2 groups of observers was substantial, with an averaged Kappa coefficient (K) of 0.56. In the simple compression group, mean accuracy was 97% and 89.4% according to the first and second groups of observers, respectively. Averaged K for agreement was substantial (K = 0.65).

CONCLUSION:

According to endoscopic visualization, 3-D SSFP and TOF MRA images are accurate in detecting the offending vessels in simple compression of the facial nerve, and in predicting presence of a complex compression with variable sensitivity in identifying all offending vessels.