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Definition of Leptomeninges
1. Noun. The two innermost layers of the meninges; cerebrospinal fluid circulates between these innermost layers.
Medical Definition of Leptomeninges
1. The two delicate layers of the meninges, the arachnoid mater and pia mater (vs. The tough pachymeninx or dura mater), considered together; by this concept, the arachnoid and pia are two parts of a single layer, much like the parietal and visceral layers of a serous membrane or bursa; although separated by the subarachnoid space they are connected via the arachnoid trabeculae and become continuous where the nerves and filum terminale exit the subarachnoid space (the cerebrospinal fluid-filled space bounded by the leptomeninges). See: arachnoid, pia mater. Synonym: meninx tenuis, pia-arachnoid, piarachnoid. Origin: Lepto-+ G. Meninx, pl. Meninges, membrane (05 Mar 2000)