<P> This type can form when ovulation doesn't occur, and a follicle doesn't rupture or release its egg but instead grows until it becomes a cyst, or when a mature follicle involutes (collapses on itself). It usually forms during ovulation, and can grow to about 7 cm in diameter . It is thin - walled, lined by one or more layers of granulosa cell, and filled with clear fluid . </P> <P> Ultrasound is the primary tool used to document the follicular cyst . A pelvic exam will also aid in the diagnosis if the cyst is large enough to be seen . A doctor monitors these to make sure they disappear, and looks at treatment options if they do not . </P>

Presence of the theca folliculi indicates that a secondary follice is now producing estrogen