Vegetations on under surface of cusps are found in:
Vegetations in Libmann sacks endocarditis occur on surfaces of cusps.Both surfaces may be involved but more commonly the undersurface is affected .(ref Robbins 7th/597,89,9/e p558)
Infective endocarditis
Libman sacks endocaditis
SABE
Rheumatic fever
Cardiovascular system