Final answer:
Functional ovarian cysts develop due to abnormal follicle development and ovulation. On ultrasound, they appear as fluid-filled sacs within the ovary.
Step-by-step explanation:
A functional ovarian cyst develops as a result of the normal process of follicle development and ovulation in the ovaries. Normally, follicles develop in the ovaries and release mature eggs during ovulation. However, in the case of functional ovarian cysts, the follicles do not properly release an egg, leading to the formation of cysts.
On ultrasound (U/S), functional ovarian cysts appear as fluid-filled sacs within the ovary. These cysts can vary in size and shape, but they generally have well-defined borders and are distinguishable from other types of ovarian growths.