Anatomic evidence shows that lymphatic drainage exists in the pituitary to loop the cerebral lymphatic circulation

Respiratory infections can result in intracranial infections and unknown neurological symptoms. The central nervous system lacks classical meningeal lymphatic (circulation) drainage, and the exact underlying mechanisms of how immune cells from the peripheral lymphatic system enter the central nervous system (CNS) remain unknown. To determine whether the perinasal lymphatic system or lymphatic vessels are involved in cerebral immune defence and play a role in causing CNS infections (especially respiratory tract-related infections), we performed an anatomic study to investigate the drainage differences between the perinasal and intracerebral lymphatic systems by using injection of Evans blue and anatomic surgery, together with immunohistochemistry and immunofluorescence assays. Surprisingly, we found that (1) the pituitary (adenohypophysis) is involved and is rich in lymphatic vessels and (2) perinasal tissue could communicate with central pituitary lymphatic vessels in a specific and unidirectional manner. Taken together, our study may be the first to anatomically demonstrate the existence of novel lymphatic vessel structures in the pituitary, as well as their communication with the perinasal (lymphatic) tissue. Our findings suggest the existence of an ultimate loop for "classical" meningeal lymphatic drainage and are relevant to cerebral infection and immune defence.