Exploring Cellular and Molecular Insights in Chronic Subdural Hematoma Neomembranes

Introduction/Purpose Chronic subdural hematomas (cSDH), atraumatic intracranial hemorrhages, are one of the leading neurosurgical conditions observed in the United States. Notably, cSDH is characteristically encased by a neovascular fibroproliferative granulation tissue layered between the meninges and hematoma—comprising of a dura‐facing outer membrane (OM) and an arachnoid‐facing inner membrane (IM). The purpose of our study is to investigate the role of neomembranes in cSDH pathophysiology, via a robust approach of molecular biology and biochemical techniques to explore the cellular and molecular diversity of neomembranes. Materials and Methods We hypothesize that we will identify key angiogenic and inflammatory regulators across various radiographical stages and clinical features including recurrence status. In a collaborative effort with a molecular biology lab and a neurosurgical team, we collected OMs and IMs from adult patients who received surgical drainage and craniotomy for their cSDH. We processed the samples by formalin fixation and paraffin embedding and analyzed tissue sections by H&E and Masson's trichrome staining, and immunostaining. For our study, we have collected and processed 31 OMs and 11 IMs from 21 males (ages 57‐90 yo), and 10 females (ages 57‐88 yo). Results We have identified a spatial distribution of cells and structures across the OM tissues, stratified by highly vascular regions along the dura‐facing surface, acellular and cellular intermediate layers with smaller vasculature, and highly cell‐dense regions along hematoma‐facing surfaces. Various leukocytes, including eosinophils, neutrophils, and lymphocytes at various stages of maturation, are present throughout the OM tissue. In comparison, IMs lack this overall spatial architecture and are largely avascular. We also observe this granulation tissue is composed of loosely and tightly woven collagen fibers throughout the entirety of the tissue. Further, detailed analysis by immunofluorescence and immunohistochemical staining shows a spatial distribution of proteins in both OMs and IMs. Endothelial cells (CD31+/PECAM), leukocytes (CD45+), hemosiderin‐laden macrophages (CD68+), myofibroblasts and vascular smooth muscle cells (α‐SMA), fibroblasts (vimentin), water channels (AQP1), and epithelial cells (EMA) are present spatially along both OMs and IMs. Conclusion The spatial biology across neomembranes, not yet reported in literature, may play a critical role in cSDH pathophysiology. We aim to identify key cell types, distributions and protein signatures across the tissue with respect to clinical cSDH grading and recurrence status. This study will uncover molecular insights into drivers of cSDH pathophysiology and recurrence, to advance targeted therapeutic intervention and treatment modalities.