Though ovarian cysts are usually a result of hormonal imbalances, pregnancy, endometriosis or pelvic infections, different types of ovarian cysts form differently. For example, 

Functional Cysts: Functional cysts, as the name suggests, are formed as a result of the basic functioning of ovaries. They are of two kinds and are usually benign (non-cancerous) and asymptomatic. 

1. Follicular cysts: Follicular cysts are the most common kind of ovarian cysts. They get formed as a result of ovulation and range from the size of a pea to the size of an orange. 

   Typically, in a woman’s normal reproductive cycle, her ovaries release around five to twenty eggs (oocytes) enveloped in tiny fluid-filled structures called- follicles. Then, every month as one of these eggs matures, the follicle bursts open, luteinises, and the egg funnels towards the fallopian tube to aid conception. But, the problem begins when this egg-producing follicle does not break open and rather, the ovum inside it slowly degenerates and starts disappearing. Here, while the egg ceases to exist, the sack keeps luteinising and swelling with the fluid. When this fluid-filled sack keeps enlarging instead of breaking open, it forms a follicular cyst. 

   These cysts usually remain tiny and dissolve naturally within 2-3 menstrual cycles and bear no symptoms or harm. But sometimes, they can grow exponentially and enlarge up to 8cm or more, causing acute pain, nausea and compromising fertility adversely.  This makes the surgical intervention (cystectomy) an absolute necessity.

2. Corpus Luteum Cysts: Typically, once the follicle releases the matured egg, it starts producing estrogen and progesterone to help fertilisation. Because of its luteum production function, it is then called- a corpus luteum. But, sometimes, due to some abnormal changes in the follicle, while the egg breaks open, the opening end seals close, and the luteum hormone keeps accumulating. This makes the cyst grow abnormally large and forms- corpus luteum cyst. 

   However, these too, are extremely common in women of reproductive ages and typically go away naturally within 2-3 menstrual cycles.  But, in rare cases, when they do not get dissolved naturally, they can grow as large from about 8cm to 12 cm and turn extremely painful. Then, surgical removal remains the only solution.

Pathological Cysts: Pathological cysts, as the name suggests, get formed as a result of certain pathologies or abnormalities in the normal function of ovaries. They are primarily of 3 types and typically go away only through a surgical removal (ovarian cystectomy).

1. Dermoid Cysts: Dermoid cysts, also known as teratomas (monster tumors), are one of the most common types of pathological cysts and are usually present from birth. Their average size runs between 12cm to 40 cm. 

   Typically, in a normal pregnancy, when a woman’s oocyte (primary germ cell) fertilises with sperm and forms a zygote, its cell multiply and form different tissues and organs of the body. However, not all tissues differentiate into separate kinds and some, rather retain their original ability to turn into any human tissue at any point in time. These undifferentiated cells usually head to ovaries in women (in the female fetus) or testes in men (in the male fetus), to eventually develop into egg or sperm in later years.But the problem begins when they stop being passive, and rather, start to mature and enlarge. Now, since they are composed of the primary germ cell, they can grow exponentially (almost an inch every year) and form fat, skin, hair, tooth, bone, eye- in fact, almost every other human tissue in the body, right inside their sac. They also contain a sebaceous fluid in them that is thick, sticky, and foul-smelling. Though just like other ovarian cysts, tiny dermoid cysts do not cause many symptoms and can be treated conservatively, however, their abnormal growth can cause severe pelvic pain, nausea and vomiting. Also, unlike functional cysts, pathological cysts do not shrink/dissolve naturally and almost always require surgical removal (ovarian cystectomy).

2. Endometriomas Cysts: Endometriomas is one of the most common pathological types of cyst that develops as a result of a condition, called- endometriosis.In this condition, the uterine tissues that usually develop inside the uterine walls start to develop outside it, that is- on the outer wall of the uterus, fallopian tubes, ovaries, or precisely, any and everywhere around the uterus. These abnormal growths on the ovaries are then called- endometriomas and are typically composed of blood. Thus, earning its name- ‘chocolate cysts’.

   These cysts, just like others, are harmless when tiny, but dangerously infectious and painful when large. Large endometriomas cysts are almost always treatable only by surgical cyst removal and require immediate medical attention.

3. Cystadenomas: Cystadenomas are liquid or mucous-filled ovarian cysts. 
4. Hemorrhagic ovarian cyst: Hemorrhagic ovarian cyst, as the name suggests, gets formed when an ovarian cyst ruptures and bleeds. This usually forms while an egg-producing follicle struggles to break open and release its eggs.Typically, the outer wall of a follicle is very thin. Sometimes, especially in the corpus luteum, the wall ruptures in the process of ovum expulsion. This causes bleeding and the formation of a haemorrhagic ovarian cyst. This, too, like other cysts, is harmless when tiny but acutely painful when large. But, the difference is, unlike functional cysts, haemorrhagic cysts are extremely stubborn and usually cannot be resolved without surgical removal (cystectomy).