Subdural haematomas drain into the extracranial lymphatic system through the meningeal lymphatic vessels

Subdural haematomas (SDHs) are characterized by rapidly or gradually accumulated haematomas between the arachnoid and dura mater. The mechanism of haematoma clearance has not been clearly elucidated until now. The meningeal lymphatic vessel (mLV) drainage pathway is a novel system that takes part in the clearance of waste products in the central nervous system (CNS). This study aimed to explore the roles of the mLV drainage pathway in SDH clearance and its impacting factors. We injected FITC-500D, A488-fibrinogen and autologous blood into the subdural space of mice/rats and found that these substances drained into deep cervical lymph nodes (dCLNs). FITC-500D was also observed in the lymphatic vessels (LYVE+) of the meninges and the dCLNs in mice. The SDH clearance rate in SDH rats that received deep cervical lymph vessel (dCLV) ligation surgery was significantly lower than that in the control group, as evaluated by haemoglobin quantification and MRI scanning. The drainage rate of mLVs was significantly slower after the SDH model was established, and the expression of lymphangiogenesis-related proteins, including LYVE1, FOXC2 and VEGF-C, in meninges was downregulated. In summary, our findings proved that SDH was absorbed through the mLV drainage pathway and that haematomas could inhibit the function of mLVs.