Quantitative analysis of collagen architecture in the human uterotubal junction (UTJ) using optical coherence...

Abnormal uterotubal junction (UTJ) structure is implicated in the pathogenesis of endometriosis and infertility; however, this relationship remains poorly characterized. We quantitatively characterized the orientation of collagen fiber bundles in the UTJ using optical coherence tomography (OCT). UTJ tissue from nine individuals undergoing hysterosalpingectomy were collected and longitudinally opened to expose the lumen. Volumetric OCT images were acquired from proximal (uterine), middle, and distal (isthmic) UTJ segments. Images were preprocessed to enhance contrast and continuity of fiber bundles. Local fiber bundle orientation was extracted from Sobel-filtered intensity gradients. Orientation values were binned corresponding to the expected alignment of collagen fiber bundle groups in UTJ smooth muscle: longitudinal (0°-30°), oblique (30°-60°), and circumferential (60°-90°). Proportions were plotted as a function of depth, and depth-dependent trends in alignment were compared across UTJ segments using mixed-effects models. Measurements revealed a prominent inner longitudinal muscle layer which emerged proximally and thinned distally, and an outer muscle layer composed of oblique uterine fiber bundles proximally and a mixed oblique-circumferential contribution distally. These findings provide the first quantitative, depth-resolved analysis of UTJ collagen architecture and establish an analytical framework which can support future studies investigating how UTJ structure relates to function and disease.