Oophorectomy
Encyclopedia
Oophorectomy icon is the surgical
removal of an ovary
or ovaries. The surgery is also called ovariectomy, but this term has been traditionally used in basic science research describing the surgical removal of ovaries in laboratory animals. Removal of the ovaries in women is the biological equivalent of castration
in males; however, the term castration is only occasionally used in the medical literature to refer to oophorectomy in humans. In the veterinary sciences, the complete removal of the ovaries, oviducts, uterine horns, and the uterus is called spaying and is a form of sterilization
.
Partial oophorectomy is a term sometimes used to describe a diverse variety of surgeries such as ovarian cyst removal or resection of parts of the ovaries. This kind of surgery is fertility preserving although ovarian failure may be relatively frequent. Most of the long term risks and consequences of oophorectomy are not or only partially present with partial oophorectomy.
In humans, oophorectomy is most often performed due to diseases such as ovarian cysts or cancer
; as prophylaxis to reduce the chances of developing ovarian cancer
or breast cancer
; or in conjunction with removal of the uterus
.
The removal of an ovary together with the fallopian tube
is called salpingo-oophorectomy or unilateral salpingo-oophorectomy (USO). When both ovaries and both Fallopian tubes are removed, the term bilateral salpingo-oophorectomy (BSO) is used. Oophorectomy and salpingo-oophorectomy are not common forms of birth control
in humans; more usual is tubal ligation
, in which the Fallopian tubes are blocked but the ovaries remain intact. In many cases, surgical removal of the ovaries is performed concurrently with a hysterectomy
. The formal medical name for removal of a woman's entire reproductive system (ovaries, Fallopian tubes, uterus) is "Total Abdominal Hysterectomy
with Bilateral Salpingo-Oophorectomy (TAH-BSO); the more casual term for such a surgery is "ovariohysterectomy". The term "hysterectomy
" is often used to refer to removal of any part of the female reproductive system, including just the ovaries; however, the correct definition of "hysterectomy
" is removal of the uterus (from the Greek ὑστέρα hystera "womb" and εκτομία ektomia "a cutting out of") without removal of the ovaries or Fallopian tubes.
), an oophorectomy is generally performed by abdominal laparotomy
or laparoscopy.
(87%). Conversely, unilateral oophorectomy is commonly performed for a medical indication (73%; cyst, endometriosis, benign tumor, inflammation, etc.) and less commonly in conjunction with hysterectomy (61%).
Special indications include several groups of women with substantially increased risk of ovarian cancer, such as high risk BRCA mutation
carriers and women with endometriosis who also suffer from frequent ovarian cysts.
Bilateral oophorectomy has been traditionally done in the belief that the benefit of preventing ovarian cancer would outweigh the risks associated with removal of ovaries. However, it is now clear that prophylactic oophorectomy without a reasonable medical indication decreases long term survival rates substantially and has deleterious long term effects on health and wellbeing.
s.
For women with high risk BRCA1
mutations prophylactic oophorectomy around age 40 reduces the risk of ovarian and breast cancer and provides significant and substantial long-term survival advantage. Earlier intervention does not, on average, provide any additional benefit but increases risks and adverse effects.
For women with high risk BRCA2
mutations, oophorectomy around age 40 has a relatively modest benefit on survival; the positive effect of reduced breast and ovarian cancer risk is nearly balanced by adverse effects. The survival advantage is more substantial when oophorectomy is performed together with prophylactic mastectomy.
by eliminating the menstrual cycle, which will reduce or eliminate the spread of existing endometriosis as well as reducing the pain. Since endometriosis results from an overgrowth of the uterine lining, removal of the ovaries as a treatment for endometriosis is often done in conjunction with a hysterectomy
to further reduce or eliminate recurrence.
Oophorectomy for endometriosis is used only as last-resort often in conjunction with a hysterectomy
, as it has rather severe side effects for women of reproductive age and low success rate.
Oophorectomy at age 40 or later might also be used to prevent ovarian cancer although there is currently no evidence that cancer prevention alone is a sufficiently strong indication to justify the surgery.
Partial oophorectomy—ovarian cyst removal not involving total oophorectomy—is often used to treat milder cases of endometriosis when non-surgical hormonal treatments fail to stop cyst formation. Removal of ovarian cysts through partial oophorectomy is also used to treat extreme pelvic pain from chronic hormonal-related pelvic problems.
A infrequent complication is injuring of the ureter at the level of the suspensory ligament of the ovary
.
The effect is not limited to women who have oophorectomy performed before menopause, an impact on survival is expected even for surgeries performed up to an age of 65 years. Surgery at age 50-54 reduces the probability to survive until age 80 by 8% (from 62% to 54% survival), surgery at age 55-59 by 4%. Most of this effect is due to excess cardiovascular risk and hip fractures.
Removal of ovaries causes hormonal changes and symptoms similar to, but generally more severe than, menopause
. Women who have had an oophorectomy are usually encouraged to take hormone
replacement drugs to prevent other conditions often associated with menopause. Women younger than 45 who have had their ovaries removed face a mortality risk 170% higher than women who have retained their ovaries. Retaining the ovaries when a hysterectomy
is performed is associated with better long term survival. Hormone therapy for women with oophorectomies performed before age 45 improves the long term outcome and all cause mortality rates.
and progesterone
, and lose about half of their ability to produce testosterone, and subsequently enter what is known as "surgical menopause
" (as opposed to normal menopause, which occurs naturally in women as part of the aging process). In natural menopause the ovaries generally continue to produce low levels of hormones, especially androgens long after menopause which may explain why surgical menopause is generally accompanied by a more sudden and severe onset of symptoms than natural menopause, symptoms which may continue until natural age of menopause arrives. These symptoms are commonly addressed through hormone therapy, utilizing various forms of estrogen, testosterone, progesterone or a combination of them.
A potential risk for oophorectomy performed after menopause is not fully elucidated. Reduced levels of testosterone in women is predictive of height loss, which may occur as a result of reduced bone density. In women under the age of 50 who have undergone oophorectomy, hormone replacement therapy
(HRT) is often used to offset the negative effects of sudden hormonal loss (e.g., early-onset osteoporosis) as well as menopausal problems like hot flush
es (also called "hot flashes") that are usually more severe than those experienced by women undergoing natural menopause.
is somewhat controversial due to the known carcinogenic and thrombogenic properties of estrogen
; however, many physicians and patients feel the benefits outweigh the risks in women who may face serious health and quality of life issues as a consequence of early surgical menopause
. The ovarian hormones estrogen, progesterone, and testosterone are involved in the regulation of hundreds of bodily functions; it is believed by some doctors that hormone therapy programs mitigate surgical menopause
side effects such as increased risk of cardiovascular disease, and female sexual dysfunction.
Short-term hormone replacement with estrogen has negligible effect on overall mortality for high-risk BRCA mutation
carriers. Based on computer simulations overall mortality appears to be marginally higher for short term HRT after oophorectomy or marginally lower for short term HRT after oophorectomy in combination with mastectomy. This result can probably be generalized to other women at high risk in whom short term (i.e., one- or two-year) treatment with estrogen for hot flashes, may be acceptable.
Glossary
Surgery
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
removal of an ovary
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
or ovaries. The surgery is also called ovariectomy, but this term has been traditionally used in basic science research describing the surgical removal of ovaries in laboratory animals. Removal of the ovaries in women is the biological equivalent of castration
Castration
Castration is any action, surgical, chemical, or otherwise, by which a male loses the functions of the testicles or a female loses the functions of the ovaries.-Humans:...
in males; however, the term castration is only occasionally used in the medical literature to refer to oophorectomy in humans. In the veterinary sciences, the complete removal of the ovaries, oviducts, uterine horns, and the uterus is called spaying and is a form of sterilization
Sterilization (surgical procedure)
Sterilization refers to any of a number of medical techniques that intentionally leave a person unable to reproduce. It is a method of birth control. For other causes of sterility, see infertility....
.
Partial oophorectomy is a term sometimes used to describe a diverse variety of surgeries such as ovarian cyst removal or resection of parts of the ovaries. This kind of surgery is fertility preserving although ovarian failure may be relatively frequent. Most of the long term risks and consequences of oophorectomy are not or only partially present with partial oophorectomy.
In humans, oophorectomy is most often performed due to diseases such as ovarian cysts or cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
; as prophylaxis to reduce the chances of developing ovarian cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
or breast cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
; or in conjunction with removal of the uterus
Hysterectomy
A hysterectomy is the surgical removal of the uterus, usually performed by a gynecologist. Hysterectomy may be total or partial...
.
The removal of an ovary together with the fallopian tube
Fallopian tube
The Fallopian tubes, also known as oviducts, uterine tubes, and salpinges are two very fine tubes lined with ciliated epithelia, leading from the ovaries of female mammals into the uterus, via the utero-tubal junction...
is called salpingo-oophorectomy or unilateral salpingo-oophorectomy (USO). When both ovaries and both Fallopian tubes are removed, the term bilateral salpingo-oophorectomy (BSO) is used. Oophorectomy and salpingo-oophorectomy are not common forms of birth control
Birth control
Birth control is an umbrella term for several techniques and methods used to prevent fertilization or to interrupt pregnancy at various stages. Birth control techniques and methods include contraception , contragestion and abortion...
in humans; more usual is tubal ligation
Tubal ligation
Tubal ligation or tubectomy is a surgical procedure for sterilization in which a woman's fallopian tubes are clamped and blocked, or severed and sealed, either method of which prevents eggs from reaching the uterus for fertilization...
, in which the Fallopian tubes are blocked but the ovaries remain intact. In many cases, surgical removal of the ovaries is performed concurrently with a hysterectomy
Hysterectomy
A hysterectomy is the surgical removal of the uterus, usually performed by a gynecologist. Hysterectomy may be total or partial...
. The formal medical name for removal of a woman's entire reproductive system (ovaries, Fallopian tubes, uterus) is "Total Abdominal Hysterectomy
Hysterectomy
A hysterectomy is the surgical removal of the uterus, usually performed by a gynecologist. Hysterectomy may be total or partial...
with Bilateral Salpingo-Oophorectomy (TAH-BSO); the more casual term for such a surgery is "ovariohysterectomy". The term "hysterectomy
Hysterectomy
A hysterectomy is the surgical removal of the uterus, usually performed by a gynecologist. Hysterectomy may be total or partial...
" is often used to refer to removal of any part of the female reproductive system, including just the ovaries; however, the correct definition of "hysterectomy
Hysterectomy
A hysterectomy is the surgical removal of the uterus, usually performed by a gynecologist. Hysterectomy may be total or partial...
" is removal of the uterus (from the Greek ὑστέρα hystera "womb" and εκτομία ektomia "a cutting out of") without removal of the ovaries or Fallopian tubes.
Technique
When performed alone (without hysterectomyHysterectomy
A hysterectomy is the surgical removal of the uterus, usually performed by a gynecologist. Hysterectomy may be total or partial...
), an oophorectomy is generally performed by abdominal laparotomy
Laparotomy
A laparotomy is a surgical procedure involving a large incision through the abdominal wall to gain access into the abdominal cavity. It is also known as coeliotomy.- Terminology :...
or laparoscopy.
Statistics
According to the Center for Disease Control, 454,000 women in the United States underwent this type of operation in 2004.Indication
Most bilateral oophorectomies (63%) are performed without any medical indication at the same time as hysterectomyHysterectomy
A hysterectomy is the surgical removal of the uterus, usually performed by a gynecologist. Hysterectomy may be total or partial...
(87%). Conversely, unilateral oophorectomy is commonly performed for a medical indication (73%; cyst, endometriosis, benign tumor, inflammation, etc.) and less commonly in conjunction with hysterectomy (61%).
Special indications include several groups of women with substantially increased risk of ovarian cancer, such as high risk BRCA mutation
BRCA mutation
A BRCA mutation is a mutation in either of the genes BRCA1 and BRCA2. Harmful mutations in these genes produce a hereditary breast-ovarian cancer syndrome in affected families...
carriers and women with endometriosis who also suffer from frequent ovarian cysts.
Bilateral oophorectomy has been traditionally done in the belief that the benefit of preventing ovarian cancer would outweigh the risks associated with removal of ovaries. However, it is now clear that prophylactic oophorectomy without a reasonable medical indication decreases long term survival rates substantially and has deleterious long term effects on health and wellbeing.
Cancer prevention
Oophorectomy can significantly improve survival for women with high risk BRCA mutationBRCA mutation
A BRCA mutation is a mutation in either of the genes BRCA1 and BRCA2. Harmful mutations in these genes produce a hereditary breast-ovarian cancer syndrome in affected families...
s.
For women with high risk BRCA1
BRCA1
BRCA1 is a human caretaker gene that produces a protein called breast cancer type 1 susceptibility protein, responsible for repairing DNA. The first evidence for the existence of the gene was provided by the King laboratory at UC Berkeley in 1990...
mutations prophylactic oophorectomy around age 40 reduces the risk of ovarian and breast cancer and provides significant and substantial long-term survival advantage. Earlier intervention does not, on average, provide any additional benefit but increases risks and adverse effects.
For women with high risk BRCA2
BRCA2
BRCA2 is a protein that in humans is encoded by the BRCA2 gene.BRCA2 orthologs have been identified in most mammals for which complete genome data are available....
mutations, oophorectomy around age 40 has a relatively modest benefit on survival; the positive effect of reduced breast and ovarian cancer risk is nearly balanced by adverse effects. The survival advantage is more substantial when oophorectomy is performed together with prophylactic mastectomy.
Endometriosis
In rare cases, oophorectomy can be used to treat endometriosisEndometriosis
Endometriosis is a gynecological medical condition in which cells from the lining of the uterus appear and flourish outside the uterine cavity, most commonly on the ovaries. The uterine cavity is lined by endometrial cells, which are under the influence of female hormones...
by eliminating the menstrual cycle, which will reduce or eliminate the spread of existing endometriosis as well as reducing the pain. Since endometriosis results from an overgrowth of the uterine lining, removal of the ovaries as a treatment for endometriosis is often done in conjunction with a hysterectomy
Hysterectomy
A hysterectomy is the surgical removal of the uterus, usually performed by a gynecologist. Hysterectomy may be total or partial...
to further reduce or eliminate recurrence.
Oophorectomy for endometriosis is used only as last-resort often in conjunction with a hysterectomy
Hysterectomy
A hysterectomy is the surgical removal of the uterus, usually performed by a gynecologist. Hysterectomy may be total or partial...
, as it has rather severe side effects for women of reproductive age and low success rate.
Oophorectomy at age 40 or later might also be used to prevent ovarian cancer although there is currently no evidence that cancer prevention alone is a sufficiently strong indication to justify the surgery.
Partial oophorectomy—ovarian cyst removal not involving total oophorectomy—is often used to treat milder cases of endometriosis when non-surgical hormonal treatments fail to stop cyst formation. Removal of ovarian cysts through partial oophorectomy is also used to treat extreme pelvic pain from chronic hormonal-related pelvic problems.
Surgical risks
Oophorectomy is a minor surgery and serious complications stemming directly from the surgery are rare. When performed together with hysterectomy it has influence on choice of surgical technique as the combined surgery is much less likely to be performed by vaginal hysterectomy.A infrequent complication is injuring of the ureter at the level of the suspensory ligament of the ovary
Suspensory ligament of the ovary
The suspensory ligament of the ovary, also infundibulopelvic ligament , is a fold of peritoneum that extends out from the ovary to the wall of the pelvis....
.
Long term effects
Oophorectomy has serious long term consequences stemming mostly from the hormonal effects of the surgery and extending well beyond menopause. The reported risks and adverse effects range from premature death, cardiovascular disease, cognitive impairment or dementia, parkinsonism, osteoporosis and bone fractures, decline in psychological wellbeing, and decline in sexual function. Hormone replacement therapy does not always improve the adverse effects.Mortality
Oophorectomy is associated with significantly increased all-cause long-term mortality except when performed for cancer prevention in carriers of high risk BRCA mutations. This is particularly pronounced for women who undergo oophorectomy before age 45.The effect is not limited to women who have oophorectomy performed before menopause, an impact on survival is expected even for surgeries performed up to an age of 65 years. Surgery at age 50-54 reduces the probability to survive until age 80 by 8% (from 62% to 54% survival), surgery at age 55-59 by 4%. Most of this effect is due to excess cardiovascular risk and hip fractures.
Removal of ovaries causes hormonal changes and symptoms similar to, but generally more severe than, menopause
Menopause
Menopause is a term used to describe the permanent cessation of the primary functions of the human ovaries: the ripening and release of ova and the release of hormones that cause both the creation of the uterine lining and the subsequent shedding of the uterine lining...
. Women who have had an oophorectomy are usually encouraged to take hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
replacement drugs to prevent other conditions often associated with menopause. Women younger than 45 who have had their ovaries removed face a mortality risk 170% higher than women who have retained their ovaries. Retaining the ovaries when a hysterectomy
Hysterectomy
A hysterectomy is the surgical removal of the uterus, usually performed by a gynecologist. Hysterectomy may be total or partial...
is performed is associated with better long term survival. Hormone therapy for women with oophorectomies performed before age 45 improves the long term outcome and all cause mortality rates.
Menopausal effects
Women who have had bilateral oophorectomy surgeries lose most of their ability to produce the hormones estrogenEstrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
and progesterone
Progesterone
Progesterone also known as P4 is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy and embryogenesis of humans and other species...
, and lose about half of their ability to produce testosterone, and subsequently enter what is known as "surgical menopause
Menopause
Menopause is a term used to describe the permanent cessation of the primary functions of the human ovaries: the ripening and release of ova and the release of hormones that cause both the creation of the uterine lining and the subsequent shedding of the uterine lining...
" (as opposed to normal menopause, which occurs naturally in women as part of the aging process). In natural menopause the ovaries generally continue to produce low levels of hormones, especially androgens long after menopause which may explain why surgical menopause is generally accompanied by a more sudden and severe onset of symptoms than natural menopause, symptoms which may continue until natural age of menopause arrives. These symptoms are commonly addressed through hormone therapy, utilizing various forms of estrogen, testosterone, progesterone or a combination of them.
Cardiovascular risk
When the ovaries are removed a woman is at a seven times greater risk of cardiovascular disease, but the mechanisms are not precisely known. The hormone production of the ovaries currently cannot be sufficiently mimicked by drug therapy. The ovaries produce hormones a woman needs throughout her entire life, in the quantity they are needed, at the time they are needed in response to and as part of the complex endocrine system.Osteoporosis
Oophorectomy is associated with an increased risk of osteoporosis and bone fractures.A potential risk for oophorectomy performed after menopause is not fully elucidated. Reduced levels of testosterone in women is predictive of height loss, which may occur as a result of reduced bone density. In women under the age of 50 who have undergone oophorectomy, hormone replacement therapy
Hormone replacement therapy (menopause)
Hormone replacement therapy is a system of medical treatment for surgically menopausal, perimenopausal and to a lesser extent postmenopausal women...
(HRT) is often used to offset the negative effects of sudden hormonal loss (e.g., early-onset osteoporosis) as well as menopausal problems like hot flush
Hot flush
Hot flashes are a symptom of the changing hormone levels that are considered to be characteristic of menopause.- Presentation :...
es (also called "hot flashes") that are usually more severe than those experienced by women undergoing natural menopause.
Adverse effect on sexuality
Oophorectomy does substantially impair sexuality. Substantially more women who had both an oophorectomy and a hysterectomy reported libido loss, difficulty with sexual arousal, and vaginal dryness than those who had a less invasive procedure (either hysterectomy alone or an alternative procedure), and hormone replacement therapy was not found to improve these symptoms. In addition, testosterone levels in women are associated with a greater sense of sexual desire, and oophorectomy greatly reduces testosterone levels.Non-hormonal treatments
The side effects of oophorectomy may be alleviated by medicines other than hormonal replacement. Non-hormonal biphosphonates (such as Fosamax and Actonel) increase bone strength and are available as once-a-week pills. Low-dose Selective Serotonin Reuptake Inhibitors (e.g. Paxil, Prozac) alleviate vasomotor menopausal symptoms, i.e. "hot flashes".Hormonal treatments
In general, hormone replacement therapyHormone replacement therapy (menopause)
Hormone replacement therapy is a system of medical treatment for surgically menopausal, perimenopausal and to a lesser extent postmenopausal women...
is somewhat controversial due to the known carcinogenic and thrombogenic properties of estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
; however, many physicians and patients feel the benefits outweigh the risks in women who may face serious health and quality of life issues as a consequence of early surgical menopause
Menopause
Menopause is a term used to describe the permanent cessation of the primary functions of the human ovaries: the ripening and release of ova and the release of hormones that cause both the creation of the uterine lining and the subsequent shedding of the uterine lining...
. The ovarian hormones estrogen, progesterone, and testosterone are involved in the regulation of hundreds of bodily functions; it is believed by some doctors that hormone therapy programs mitigate surgical menopause
Menopause
Menopause is a term used to describe the permanent cessation of the primary functions of the human ovaries: the ripening and release of ova and the release of hormones that cause both the creation of the uterine lining and the subsequent shedding of the uterine lining...
side effects such as increased risk of cardiovascular disease, and female sexual dysfunction.
Short-term hormone replacement with estrogen has negligible effect on overall mortality for high-risk BRCA mutation
BRCA mutation
A BRCA mutation is a mutation in either of the genes BRCA1 and BRCA2. Harmful mutations in these genes produce a hereditary breast-ovarian cancer syndrome in affected families...
carriers. Based on computer simulations overall mortality appears to be marginally higher for short term HRT after oophorectomy or marginally lower for short term HRT after oophorectomy in combination with mastectomy. This result can probably be generalized to other women at high risk in whom short term (i.e., one- or two-year) treatment with estrogen for hot flashes, may be acceptable.
Glossary
See also
- Ovarian Cysts
- Tubal ligationTubal ligationTubal ligation or tubectomy is a surgical procedure for sterilization in which a woman's fallopian tubes are clamped and blocked, or severed and sealed, either method of which prevents eggs from reaching the uterus for fertilization...
- Birth controlBirth controlBirth control is an umbrella term for several techniques and methods used to prevent fertilization or to interrupt pregnancy at various stages. Birth control techniques and methods include contraception , contragestion and abortion...
- HysterectomyHysterectomyA hysterectomy is the surgical removal of the uterus, usually performed by a gynecologist. Hysterectomy may be total or partial...
- Hormone Replacement TherapyHormone replacement therapy (menopause)Hormone replacement therapy is a system of medical treatment for surgically menopausal, perimenopausal and to a lesser extent postmenopausal women...
- CastrationCastrationCastration is any action, surgical, chemical, or otherwise, by which a male loses the functions of the testicles or a female loses the functions of the ovaries.-Humans:...
or orchidectomy - the male equivalent
External links
- Useful list of currently available hormone replacements in the US
- Useful list of currently available hormone replacements in the UK
- A Survivor's Guide to Surgical Menopause: Collected information on managing post-surgical menopause conditions
- Encyclopedia of Surgery Article on Hysterectomy