Increased Cortical Thickness Combined With Altered Structural Covariance Networks in Functional Anorectal Pain

Functional anorectal pain (FAP) is a chronic disorder of gut-brain interaction with unclear pathophysiology. While evidence from previous research revealed localized alterations in both brain function and structure in patients with FAP, the large-scale structural network organization in FAP is still unexplored.

We acquired T1-weighted magnetic resonance images from 29 patients with FAP and 19 healthy controls to investigate cortical thickness (CTh) and structural covariance networks (SCNs). Surface-based morphometry was employed to analyze CTh, and SCNs were built based on interregional Pearson correlations, followed by topological characterization using graph theory metrics. Partial correlation analyses were conducted to explore relationships with clinical measures.

Compared to controls, patients with FAP exhibited significantly increased CTh in the left supramarginal gyrus extending to the postcentral gyrus and the left medial orbitofrontal cortex. At the network level, while global network properties remained preserved, nodal analyses uncovered widespread alterations in centrality and efficiency within distributed brain regions, including frontal, temporal, and cingulate areas. Additionally, thicker CTh in the left medial orbitofrontal cortex showed significant positive correlations with anxiety severity, overall pain experience, and subjective pain intensity in the patients group.

These findings reveal a distinct pattern of neuroanatomical changes in FAP, characterized by the coexistence of regional cortical thickening and a reorganized nodal architecture in structural networks. The association between medial orbitofrontal cortex morphology and key clinical symptoms highlights the significant role of affective processing in FAP. Collectively, this study provides the first evidence of system-level neural substrate in FAP, thereby advancing our insight into its neurobiological mechanisms.