I just came across another article that specifically says losing one ovary "appears to be associated with a significant increase in risk for dementia late in life. This challenges conventional gynecologic thought that the loss of one ovary would not have serious medical consequences....In summary, the removal of either ovary or of the uterus may have far-reaching health consequences. Therefore, the surgical removal of female reproductive organs should be considered carefully."
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3804006/
This information is not new as a number of older studies have the same conclusions but this 2012 published article is a good summary. It is very concerning (as this article states) that the rates of organ removal are still so high. But given that it is so profitable and hysterectomy is still emphasized in resident training (each resident must do 70 hysterectomies), it is no wonder.
There is no doubt that the possibility of ovarian cancer strikes fear. It did for me too but I allowed this fear (mostly instilled by my long-time gynecologist) to overtake my rational thoughts. And it made for a very bad outcome (removal of healthy organs - hysterectomy and oophorectomy - when JUST the cyst should have been removed).
MOST ovarian cysts, even complex ones, are benign. If you do not have a family history or predisposition for ovarian cancer then your LIFETIME risk is VERY LOW (less than 2%). Unfortunately, too many women lose a healthy ovary or ovaries and even healthy uteri when it is totally unnecessary. A measly 2% of hysterectomies and oophorectomies are done for a cancer diagnosis making up to 98% unwarranted.
The uterus, ovaries, and tubes work together and have LIFELONG functions. So the removal of any one sex organ (even one ovary) can induce menopause and wreak havoc on health and well-being. An INTACT woman's ovaries do not shut down at menopause but continue producing hormones into her 80's especially testosterone, some of which the body converts into estrogen as needed.
This article http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2815011/ states:
"Premature menopause and early menopause, whether spontaneous or induced, are associated with long-term health risks which may include premature death, cardiovascular disease, neurologic disease, osteoporosis, psychosexual dysfunction, and mood disorders. Estrogen mitigates some but not all of these consequences."
If this cyst needs to be surgically removed (sometimes they resolve on their own), you may need to seek out a surgeon with good cystectomy (cyst removal) skills if your gynecologist wants to remove the ovary.
The surgical consent forms are typically "open-ended" allowing the surgeon discretion to remove all your sex organs while you are under anesthesia regardless of what was verbally agreed upon by surgeon and patient. So be sure your wishes are clearly stated on the consent form and signed off on by the surgeon.
I hope this helps. And I wish you the best of luck in getting proper (health restoring) treatment!