Fig. 1

LMD imaging and pathology and hypotheses of spread. The leptomeningeal space consists of the pia mater, subarachnoid space, and arachnoid mater (A). Brain MRI with contrast showing leptomeningeal enhancement in supratentorial and infratentorial sulci, consistent with LMD (B). Spine MRI with contrast demonstrating linear enhancement along the cervical and thoracic regions of the spinal cord, consistent with LMD (C). CSF showing large multinucleated tumor cells, consistent with LMD (D). A main hypothesis of leptomeningeal spread is escape of tumor cells into the blood; cells cross the blood-CSF barrier, which is likely the choroid plexus, and enter the CSF, where they have access to seed the leptomeninges (E). Another hypothesis of leptomeningeal spread is contiguous spread from parenchymal metastasis (F). Another hypothesis of leptomeningeal spread is that tumor cells enter the CSF and blood during or after surgical resection of a parenchymal metastasis (G). Images A, E, F, G created in https://BioRender.com. Images B, C, D courtesy of PK