Utility of magnetic resonance cisternography using three-dimensional fast asymmetric spin-echo sequences with multiplanar reconstruction: the evaluation of sites of neurovascular compression of the trigeminal nerve

The practical limits of high-quality magnetic resonance imaging for the diagnosis and classification of trigeminal neuralgia

BACKGROUND

Neurovascular compression (NVC) has been the primary hypothesis for the underlying mechanism of classical trigeminal neuralgia (TN). However, a substantial body of literature has emerged highlighting notable exceptions to this hypothesis. The purpose of this study is to assess the reliability and diagnostic accuracy of high resolution, high contrast MRI-determined neurovascular contact for TN.

METHODS

We performed a retrospective, randomized, and blinded parallel characterization of neurovascular interaction and diagnosis in a population of TN patients and controls using four expert reviewers. Performance statistics were calculated, as well as assessments for generalizability using shuffled bootstraps.

RESULTS

Fair to moderate agreement (ICC: 0.32-0.68) about diagnosis between reviewers was observed using MRIs from 47 TN patients and 47 controls. On average reviewers performed no better than chance when diagnosing participants, with an accuracy of 0.57 (95% CI 0.40, 0.59) per patient.

CONCLUSION

While MRI is useful in determining structural causes in secondary TN, expert reviewers do no better to only slightly better than chance with distinguishing TN with MRI, despite moderate agreement. Further, the causal role of NVC for TN is not clear, limiting the applicability of MRI to diagnose or prognosticate treatment of TN.

The anterior one third of the posterior limb of the internal capsule is also supplied by the anterior choroidal artery

PURPOSE

It is universally recognized that the anterior choroidal artery (AChA) supplies the posterior two-third of the posterior limb of internal capsule (PLIC). On the other hand, the blood supply to the anterior one third of the PLIC has remained undetermined. We posit the anterior one third of the PLIC is also supplied by the AChA referring the previous microsurgical descriptions.

METHODS

Ninety consecutive patients with isolated acute infarction in the PLIC were studied. We classified patients into 4 groups. 1. The anterior type that involved the anterior one-third part of the PLIC. 2. The posterior type that involved the caudal two-third part of the PLIC, 3. The combined type that located in the full length of the PLIC, 4. The dot type that restricted within PLIC up to10mm in diameter.

RESULTS

Patient numbers in groups 1 through 4 were 7 (7.7%), 46 (51.1%), 9 (10.6%) and 28 (31.1%). The anterior type involved the medial part of pallidum (MPP) in 5 patients (71.4%) and none in the lateral thalamus (LT), while the posterior type involved MPP only in 6 patients (13.0%) and LT in 33 patients (71.7%).

CONCLUSION

Corresponding to previous microsurgical descriptions, an occlusion of the proximal branches may cause anterior type infarct and that of the distal branches may cause posterior type infarcts. The anterior one third of the PLIC is also supplied by the branches of the AChA, albeit the low prevalence.

Comparison of iterative model, hybrid iterative, and filtered back projection reconstruction techniques in low-dose brain CT: impact of thin-slice imaging

INTRODUCTION

The purpose of this study was to evaluate the utility of iterative model reconstruction (IMR) in brain CT especially with thin-slice images.

METHODS

This prospective study received institutional review board approval, and prior informed consent to participate was obtained from all patients. We enrolled 34 patients who underwent brain CT and reconstructed axial images with filtered back projection (FBP), hybrid iterative reconstruction (HIR) and IMR with 1 and 5 mm slice thicknesses. The CT number, image noise, contrast, and contrast noise ratio (CNR) between the thalamus and internal capsule, and the rate of increase of image noise in 1 and 5 mm thickness images between the reconstruction methods, were assessed. Two independent radiologists assessed image contrast, image noise, image sharpness, and overall image quality on a 4-point scale.

RESULTS

The CNRs in 1 and 5 mm slice thickness were significantly higher with IMR (1.2 ± 0.6 and 2.2 ± 0.8, respectively) than with FBP (0.4 ± 0.3 and 1.0 ± 0.4, respectively) and HIR (0.5 ± 0.3 and 1.2 ± 0.4, respectively) (p < 0.01). The mean rate of increasing noise from 5 to 1 mm thickness images was significantly lower with IMR (1.7 ± 0.3) than with FBP (2.3 ± 0.3) and HIR (2.3 ± 0.4) (p < 0.01). There were no significant differences in qualitative analysis of unfamiliar image texture between the reconstruction techniques.

CONCLUSION

IMR offers significant noise reduction and higher contrast and CNR in brain CT, especially for thin-slice images, when compared to FBP and HIR.

Can the neurovascular compression volume of the trigeminal nerve on magnetic resonance cisternography predict the success of local anesthetic block after initial treatment by the carbamazepine?

OBJECTIVES

Whether NVC volume on magnetic resonance (MR) cisternography might be related to the success of local anesthetic block by tetracaine (TNB) as an additional treatment after carbamazepine (CBZ) treatments in patients with trigeminal neuralgia (TN) was evaluated.

STUDY DESIGN

Detectable NVC volumes were measured from MR cisternography in 65 patients with TN treated by TNB after CBZ treatments. The correlation between the success of TNB and the NVC volume or the improvement in pain by CBZ was evaluated retrospectively.

RESULTS

A significant difference was found between the improvement in pain by CBZ and the success of TNB, but not between NVC volume on MR cisternography and the success of TNB.

CONCLUSIONS

The present results suggest that the success of CBZ as initial treatment, but not NVC volume on MR cisternography, may be a significant predictor of the success of TNB as additional therapy in patients with TN.

Trigeminal neuralgia: Assessment of neurovascular decompression by 3D fast imaging employing steady-state acquisition and 3D time of flight multiple overlapping thin slab acquisition magnetic resonance imaging

Background:

Trigeminal neuralgia is most commonly caused by vascular compression at the trigeminal nerve (TN) root entry zone. Microvascular decompression (MVD) has been established as a useful treatment. Outcome depends on the correct identification of the compression site and its adequate decompression at surgery. Preoperative identification of neurovascular compression might predict which patients will benefit from MVD. Management of persistent or recurrent trigeminal neuralgia after an MVD is a baffling problem for neurosurgeons. An accurate neuroradiological evaluation of the TN padding following a failed MVD might help identify the underlying cause and plan further treatment.

Case description:

A 68-year-old female presented with a right-sided trigeminal neuralgia (V3) refractory to medical therapy. A high-resolution three-dimensional magnetic resonance imaging (3D MRI) study included fast imaging employing steady-state acquisition (FIESTA) and time of flight multiple overlapping thin slab acquisition (TOF MOTSA) sequences to evaluate the neurovascular anatomy in the cerebellopontine angle. An unambiguous compression of the right TN at the rostral-medial site by the superior cerebellar artery (SCA) was identified. The SCA loop compressing the TN was identical in location and configuration to that predicted in the preoperative study. After the MVD, the patient was relieved from her pain and a postoperative high-resolution 3D MRI study confirmed the appropriate placement of the Teflon implant between the TN and SCA.

Conclusion:

To our knowledge, this is the first report that characterizes the proper TN padding by high-resolution 3D MRI after trigeminal MVD. The present case also emphasizes the importance of performing a 3D MRI in patients with trigeminal neuralgia to anticipate the surgeon's view and predict the outcome after MVD.

Persistent trigeminal artery causing "double" neurovascular conflict

We report the case of a 73-year-old woman who presented with right VI nerve palsy and homolateral atypical trigeminal neuralgia; standard neuroradiological investigation of orbital/retroorbital regions and intracranial arteries excluded the most commonly demonstrable underlying causes while brain magnetic resonance (T1-weighted fat suppression; T2-weighted thin-section) and magnetic resonance angiography disclosed the evidence of "double" neurovascular conflict because of persistent trigeminal artery with aneurysmal dilation. A role of this almost rare vascular condition in causing painful ophthalmoplegia is discussed.