Assessing mature and immature collagen in tonsillar tissue using second harmonic generation microscopy

Recurrent tonsillitis (RT) and obstructive sleep apnoea (OSA) are major indications for tonsillectomy, yet their tissue-level pathology remains unclear. Recurrent inflammation in RT may induce collagen remodelling through excess extracellular matrix deposition. Here, we used label-free second harmonic generation (SHG) microscopy to quantify the area fraction of the ratio of forward-to-backward SHG signals in palatine tonsils from RT and OSA patients. The ratio of forward-to-backward SHG signals showed a higher mean area fraction in OSA when compared to RT, agreeing with trends previously found using immunohistochemical staining methods; however, no statistical significance was found. Spatial analysis of epithelial dominant regions and interior regions of tissue show higher forward/backward SHG signal in OSA rather than RT; however, no statistical significance was found in either measurement. These results demonstrate a new method of using SHG microscopy to measure collagen distribution within palatine tonsils of OSA and RT.