abluminal

adjective

ab·​lu·​mi·​nal ˌab-ˈlü-mə-nᵊl 

variants also ablumenal

: forming, involving, or occurring on the outer surface of a body part or device with an internal cavity or channel : not adjacent to the lumen of a tubular organ or part

… the abluminal surface of the stent …

—Ron Waksman, The Lancet

We have observed that the individual extravasated cells extend pseudopodial projections that wrap around the abluminal surface of vessel …

—Ann F. Chambers et al., in Advances in Cancer Research