Functional ovarian cysts
Functional ovarian cysts develop because of a slight alteration in the normal function of the ovary during the menstrual cycle. Functional cysts are often called physiological cysts, because they arise from the normal physiology of the ovary. These cysts occur in women during the reproductive years and are very common. They are either follicular cysts or luteal cysts.
Follicular cysts develop from a normal follicle. In the first half of the menstrual cycle follicles develop within the ovary. These follicles are small cysts filled with fluid in which the eggs are maturing. Usually one follicle becomes dominant and just before ovulation when the egg is released it is over 20 mm in diameter. If the egg is not released properly, the follicle may persist as a follicular cyst which may reach 5 or 6 cm in size. Follicular cysts are usually very thin-walled and simple in appearance and will usually resolve spontaneously within a few weeks.
Luteal cysts develop from a corpus luteum. After ovulation, when the follicle has ruptured to release the mature egg, the follicle becomes the corpus luteum, which may appear as a cyst on ultrasound examination. Often bleeding occurs into the cyst when it is referred to as haemorrhagic. Luteal cysts are often confused as being abnormal, but they will usually resolve spontaneously without treatment within a few weeks.
When endometriosis (Link to more info) affects the ovaries, one or more cysts may form within the ovaries. Old blood within these cysts breaks down to form a thick chocolate-coloured fluid, hence the name, ‘chocolate cysts’. They may persist for many years and tend to get slowly bigger, if left untreated.
These arise from the egg or germ cells within the ovary. Dermoid cysts are common in young women and are completely benign. They are called ‘dermoid’ because they tend to contain many elements from the skin and its accessory tissues. A dermoid cyst is typically filled with a fatty fluid, like sebaceous secretion, and may contain hair and teeth-like structures. This produces a classic appearance on a plain x-ray with what appear to be teeth within the pelvis. Because these tumours (Link to more info) arise from eggs that are able to develop eventually into any tissue, many other tissues may be found including cartilage, glands and nervous tissue. They may occur in both ovaries.
These are the most common ovarian tumours (Link to more info) and arise from surface layer of the ovary called the serosa or epithelium. These cysts can occur at any age and are benign. They are subdivided into serous type that contains a thin fluid and mucinous type which contain a thick gelatinous fluid. They tend to get bigger slowly over time and may become as large as a fully pregnant uterus.
There are many different less common types of ovarian cysts other than those listed above.