Association between the Putative Meningeal Lymphatics at the Posterior Wall of the Sigmoid Sinus and Delayed Contrast-agent Elimination from the Cerebrospinal Fluid

Comparative study of 3D-T2WI vs. 3D-T2-FLAIR MRI in displaying human meningeal lymphatics vessels

AIM

Various magnetic resonance imaging (MRI) sequences can be utilized to visualize human meningeal lymphatic vessels (MLVs) for investigating the associations between MLVs and central nervous system (CNS) disorders. This study aimed to compare the quality of contrast-enhanced 3D-T2WI and 3D-T2-fluid-attenuated inversion recovery (FLAIR) MRI sequences to display human MLVs.

MATERIALS AND METHODS

Sixty-two patients (27 males, 35 females; mean age 55.8 ± 14.9 years) underwent 3D-T2WI and 3D-T2-FLAIR scan in combination with Gd-DTPA injection to show MLVs.

RESULTS

(1) The positivity rates of the 3D-T2WI sequence were 98.4%, 29.0%, and 46.8%, around the dural sinus, middle meningeal artery, and ethmoid sinus, respectively. The positivity rates of the 3D-T2-FLAIR sequence were 100%, 48.4%, and 66.1%, respectively. The positivity rate was significantly higher with the 3D-T2-FLAIR sequence compared with the 3D-T2WI sequence for the middle meningeal artery and ethmoid sinus regions (p < 0.05). (2) In patients with brain lesions and intracranial space-occupying lesions, the positivity rate was significantly higher with the 3D-T2-FLAIR sequence compared with the 3D-T2WI sequence for the middle meningeal artery and ethmoid sinus regions (p < 0.05). (3) The mean cross-sectional areas of MLVs around the dural sinus, middle meningeal artery, and ethmoid sinus were all higher using the 3D-T2-FLAIR sequence compared with the 3D-T2WI sequence at all three sites (p < 0.01). (4) The signal intensity was significantly higher using the 3D-T2-FLAIR sequence compared with the 3D-T2WI sequence around the dural sinus and ethmoid sinus (p < 0.001).

CONCLUSION

The 3D-T2-FLAIR sequence contrast-enhanced scan showed superior visualization of MLVs compared with the 3D-T2WI sequence.

Diffusion Tensor Image Analysis ALong the Perivascular Space (DTI-ALPS): Revisiting the Meaning and Significance of the Method

More than 5 years have passed since the Diffusion Tensor Image Analysis ALong the Perivascular Space (DTI-ALPS) method was proposed with the intention of evaluating the glymphatic system. This method is handy due to its noninvasiveness, provision of a simple index in a straightforward formula, and the possibility of retrospective analysis. Therefore, the ALPS method was adopted to evaluate the glymphatic system for many disorders in many studies. The purpose of this review is to look back and discuss the ALPS method at this moment.The ALPS-index was found to be an indicator of a number of conditions related to the glymphatic system. Thus, although this was expected in the original report, the results of the ALPS method are often interpreted as uniquely corresponding to the function of the glymphatic system. However, a number of subsequent studies have pointed out the problems on the data interpretation. As they rightly point out, a higher ALPS-index indicates predominant Brownian motion of water molecules in the radial direction at the lateral ventricular body level, no more and no less. Fortunately, the term "ALPS-index" has become common and is now known as a common term by many researchers. Therefore, the ALPS-index should simply be expressed as high or low, and whether it reflects a glymphatic system is better to be discussed carefully. In other words, when a decreased ALPS-index is observed, it should be expressed as "decreased ALPS-index" and not directly as "glymphatic dysfunction". Recently, various methods have been proposed to evaluate the glymphatic system. It has become clear that these methods also do not seem to reflect the entirety of the extremely complex glymphatic system. This means that it would be desirable to use various methods in combination to evaluate the glymphatic system in a comprehensive manner.

Glymphatic-lymphatic coupling: assessment of the evidence from magnetic resonance imaging of humans

The discoveries that cerebrospinal fluid participates in metabolic perivascular exchange with the brain and further drains solutes to meningeal lymphatic vessels have sparked a tremendous interest in translating these seminal findings from animals to humans. A potential two-way coupling between the brain extra-vascular compartment and the peripheral immune system has implications that exceed those concerning neurodegenerative diseases, but also imply that the central nervous system has pushed its immunological borders toward the periphery, where cross-talk mediated by cerebrospinal fluid may play a role in a range of neoplastic and immunological diseases. Due to its non-invasive approach, magnetic resonance imaging has typically been the preferred methodology in attempts to image the glymphatic system and meningeal lymphatics in humans. Even if flourishing, the research field is still in its cradle, and interpretations of imaging findings that topographically associate with reports from animals have yet seemed to downplay the presence of previously described anatomical constituents, particularly in the dura. In this brief review, we illuminate these challenges and assess the evidence for a glymphatic-lymphatic coupling. Finally, we provide a new perspective on how human brain and meningeal clearance function may possibly be measured in future.

Imaging of brain barrier inflammation and brain fluid drainage in human neurological diseases

The intricate relationship between the central nervous system (CNS) and the immune system plays a crucial role in the pathogenesis of various neurological diseases. Understanding the interactions among the immunopathological processes at the brain borders is essential for advancing our knowledge of disease mechanisms and developing novel diagnostic and therapeutic approaches. In this review, we explore the emerging role of neuroimaging in providing valuable insights into brain barrier inflammation and brain fluid drainage in human neurological diseases. Neuroimaging techniques have enabled us not only to visualize and assess brain structures, but also to study the dynamics of the CNS in health and disease in vivo. By analyzing imaging findings, we can gain a deeper understanding of the immunopathology observed at the brain-immune interface barriers, which serve as critical gatekeepers that regulate immune cell trafficking, cytokine release, and clearance of waste products from the brain. This review explores the integration of neuroimaging data with immunopathological findings, providing valuable insights into brain barrier integrity and immune responses in neurological diseases. Such integration may lead to the development of novel diagnostic markers and targeted therapeutic approaches that can benefit patients with neurological disorders.