This study used 2D PCASL, a type of non-enhanced sequence, to detect changes in cerebral perfusion patterns and CBF connectivity changes of MwoA in the interictal phase. As far as the authors are concerned, this study is the first of its kind to utilize ASL-MRI for establishing the CBF connectivity patterns of MwoA patients. Furthermore, among similar studies using perfusion MRI to obtain perfusion maps of migraine during the interictal phase, our case series features the largest sample size. The trigeminal nerve vascular hypothesis, which is one of the most recognized approaches to describe the pathogenic mechanisms of migraine, states that changes in the blood flow within the brain tissue may be mediated by the secretion of certain vasoactive substances, with varying effects between different brain regions [3].
In our study, increased perfusion was detected in the ORBmid.R and MFG.R, which are key areas of the prefrontal lobe. The orbital frontal cortex (OFC) is considered as a key area for sensory integration, self-control and emotional expression[31, 32]. Patients showed corresponding behavioral changes after OFC injury, such as recognition defects of emotional expression[32]. Chen et al. investigated the regional brain volume changes in episodic migraine, and showed that the right orbital frontal lobe had increased volume [33]. Compared with HC, the ALFF score of the orbital cortex in migraine patients was significantly increased during the interictal period[34]. In non-menstrual phase of primary dysmenorrhea, reduced ReHo values were observed in OFC[35]. We speculated that the increased volume, ALFF value and decreased ReHo value of orbital cortex may indicate the adaptation of the central nervous system, which could enhance descending pain modulation. The basis of these adaptations is the increase in local blood flow. Conversely, these adaptations may lead to increased local blood flow affecting the metabolism of the orbital cortex. This hypothesis can also be explained by the correlation between the attack frequency score and the CBF of ORBmid.R area, as established in our research.
Magnetic resonance imaging technology has been extensively featured in research on the connection changes in patients with migraine, such as the anatomical connection of diffusion tensor imaging, the structural connection of structural MRI, and the functional connection of functional MRI. Nonetheless, to our knowledge, no research has yet investigated the CBF connections of migraine. Although both blood oxygen level dependent (BOLD) connections and CBF connections measure the functional correlation among brain regions, their calculation methods are different and the results also have different physiological meanings. BOLD connectivity can be obtained by measuring the time correlation between BOLD signal fluctuations in various brain regions. Meanwhile, the calculation of CBF correlation coefficient among a group of brain regions yields the CBF connectivity. Although multiple BOLD connectivity values (one value per person) can be obtained from a given dataset, only a single such value can be established of CBF connectivity. While BOLD connectivity represents the timely synchronization of neural activity between different brain regions, CBF connectivity indicates the synchronization of perfusion or metabolism between these regions. It is worth noting that the CBF connection is regulated only by regional CBF and has a clearer physiological mechanism than BOLD connections, which are affected by hemodynamic parameters, such as cerebral blood volume and cerebral oxygen metabolic rate. Animal experiments have shown that OFC selectively connects with other prefrontal lobes (dorsolateral prefrontal cortex and medial prefrontal cortex) and the sensory cortex, including smell, taste, somatosensory, auditory and visual processing centers, and the amygdala[36]. In this study, we detected CBF disconnections between ORBmid.R and the regions of right putamen, SFG.L, right caudate, right angular, as well as left calcarine cortex during MwoA interictal periods.
The putamen and caudate are important areas of the basal ganglia. Previous studies have found changes in basal ganglia volume, functional connectivity (FC), and abnormal iron deposition in migraine patients[37, 38]. Our study showed that putamen and caudate CBF connections were abnormal, and it supported the role of basal ganglia in migraine patients.
The angular gyrus, an essential member of the default mode network (DMN), is considered as the connecting hub of global information integration[39]. Studies have shown that the functional connection of the angular gyrus is abnormal in migraine with visual aura[40]. In visual snow patients, there is an enhanced resting state functional connection between the prefrontal lobe and the angular gyrus[41]. Consistently with previous studies, we also identified decreased CBF disconnections between the ORBmid.R and the angular gyrus. These studies showed that the angular gyrus significantly contributes to visual information processing and the sensory cortical network.
Much of the primary visual cortex (BA 17) is hidden from view within the banks of the calcarine sulcus[42]. Significantly increased functional connectivity between the right thalamus and the left calcarine cortex was reported in the study of Wei et al., which also showed a positive correlation between the neural activation of the left calcarine cortex and the visual analogue scale scores[43]. The FC between the cerebellum and the left calcarine cortex also increases in migraine patients[44]. In line with previous findings, we also identified CBF disconnections between ORBmid.R and the left calcarine cotex. Photophobia is a common accompanying symptom in migraine patients, while visual abnormality is the most common aura symptom in migraine patients with aura[5]. The abnormal CBF connectivity of the calcarine cotex and angular gyrus can help us better understand the pathophysiological basis of photophobia in migraine patients. Accordingly, the disconnection between ORBmid.R and these areas may be related to functional defects in optical signal processing in MwoA patients. The CBF of ORBmid.R was positively correlated with the VLSQ-8 score, which may indicate interactions between optical signal processing and the perception regulatory network.
The vermis is located within the spinocerebellum and receives somatic sensory input from the head and proximal body parts via ascending spinal pathways. Cerebellar vermis atrophy in hemiplegic migraine has been previously detected by MRI[45]. Vermis atrophy has also been found in patients with familial hemiplegia migraine (FHM)[46]. Functional MRI also revealed an increase in the apparent diffusion coefficient median values. N-acetyl aspartate (NAA) and glutamate (Glu), was were significantly reduced while myo-inositol (mI) was significantly elevated in the vermis in patients with FHM[47]. In the present study, we identified decreased CBF in the vermis for the first time in paroxysmal migraine. However, the function of the vermis remains unclear, which necessitates further research.
This study has certain limitations. Firstly, only interictal MwoA patients were enrolled, thus we cannot speculate on whether there is a difference between MwoA and MWA patients. Secondly, we only performed a single scan for each patient, thereby the dynamic perfusion changes during different phases of a migraine attack and post-attack were not gauged. Thus, we might repeatedly scan migraine patients at several time points in future studies. Finally, only the regions with statistical differences in CBF between groups were selected as the ROI for CBF connectivity analysis, which may lead to potential loss of data. Therefore, follow-up research will consider the whole brain CBF connection analysis method.