Structural and functional abnormalities of the insular cortex in trigeminal neuralgia: a multimodal magnetic resonance imaging analysis

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Trigeminal neuralgia (TN) is a chronic neuropathic pain disorder characterized by intense, lancinating attacks of facial pain. Increasing evidence suggests that TN is accompanied by abnormalities in brain morphology, white matter microstructure, and function. However, whether these abnormalities are linked or reflect independent etiologies remains unknown. Using multimodal magnetic resonance imaging data of 20 patients with TN and 21 healthy controls, we investigated cortical gyrification abnormalities, their relationships with abnormalities of the underlying white matter microstructure and gray matter morphology, as well as their functional significance in TN. Compared with controls, patients with TN showed significant local gyrification index (LGI) reductions predominantly in the left insular cortex, which were negatively correlated with pain intensity. In this cluster, patients with TN had concurrent cortical thickness reductions but unaltered cortical surface area. Meanwhile, LGI of this cluster was not correlated with overlying cortical thickness or surface area but was positively correlated with the fractional anisotropy of 2 nearby white matter clusters, suggesting that insular LGI reductions may be primarily driven by microstructural abnormalities of the underlying white matter tracts, rather than by abnormalities in cortical thickness and surface area. In addition, patients with TN exhibited increased insula functional connectivity to the left posterior cingulate cortex and thalamus, which was positively correlated with disease duration. These findings provide new evidence for the involvement of insular abnormalities in the pathophysiology of TN.

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