Skull base foramina provide a route for the exit of brain lymphatic vessels from the human skull

The brain lymphatic vessels (LV) drain fluids, metabolic waste, and immune cells. The abnormal accumulation of toxic substances causes neurodegenerative, cerebrovascular diseases, and brain tumors. Despite their intracranial importance, the precise extracranial exit routes of brain LVs remain poorly characterized. We evaluated the presence of LVs in the dural samples overlying the foramina/canals (superior orbital fissure, foramen rotundum, foramen ovale, Meckel's cave, internal acoustic meatus, foramen lacerum, jugular foramen, and hypoglossal canal) using immunohistochemistry.

Samples from six human cadavers were stained with Podoplanin, LYVE-1 (LV endothelial markers), and CD31 (vascular endothelial marker).

The LVs were observed in all the dura samples except the internal acoustic meatus. The dura overlying the Meckel's cave had the largest LVs, and the smallest ones were observed in the superior orbital fissure. Further, the dura overlying the jugular foramen had the largest FCs, and the smallest ones were observed in Meckel's cave. The diameters of the LVs may indicate their efficiency in the transfer of lymphatic fluid. Fluid channels of varying diameters were closely localized to the LVs.

Our findings can increase the understanding of how LVs exit the skull and contribute to the neuropathophysiological processes. Knowledge of the lymphatic network is important for identifying metastatic sites of various cancers. Furthermore, special attention should be given during regional surgery to preserve lymphatic drainage.