Cystic Corpus Luteum.
Cavitated or hollow corpora lutea are normally functioning corpora lutea with a central space, a lacuna. They are commonly referred to as cystic corpora lutea which is technically correct because they do contain a cavity, an encystment. The term leads to confusion, especially on the part of the layman who expects them to require treatment. Hollow corpora lutea produce as much progesterone as normal solid CL, hence do not require treatment.
Roberts SJ (1973)