Advances in Cellular and Tissue based Imaging Techniques for Sarcoid Granulomas

Sarcoidosis embodies a complex inflammatory disorder spanning multiple systems, with its origin remaining elusive. It manifests as the infiltration of inflammatory cells that coalesce into distinctive non-caseous granulomas within afflicted organs. Unravelling this disease needs the utilization of cellular or tissue-based imaging methods to both visualize and characterize the biochemistry of these sarcoid granulomas. Whilst hematoxylin and eosin stain, standard in routine use alongside cytological stains have found utility in diagnosis within clinical contexts, special stains such as Masson's trichrome, reticulin, methenamine silver, and Ziehl-Neelsen provide additional varied perspectives of sarcoid granuloma imaging. Immunohistochemistry aids in pinpointing specific proteins and gene expressions further characterizing these granulomas. Finally, recent advances in spatial transcriptomics promises to divulge profound insights into their spatial orientation and 3D molecular mapping. This review focuses on a range of pre-existing imaging methods employed for visualizing sarcoid granulomas at the cellular level, while also exploring the potential of the latest cutting-edge approaches like spatial transcriptomics and matrix-assisted laser desorption ionization mass spectrometry imaging, with the overarching goal of shedding light on the trajectory of sarcoidosis research.