NCIt definition : A sac-like closed membranous structure that may be empty or contain fluid or amorphous
material.;
Alternative definition : CDISC: A sac-like closed pocket of tissue that may be empty or may be filled with
fluid, gas, semisolid, or amorphous material. It typically has an outer epithelial-lined
capsule.; NCI-GLOSS: A sac or capsule in the body. It may be filled with fluid or other material.;