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Gynaecological Ultrasound Examination
- A gynaecological ultrasound (US) examination is indicated if a gynaecological disease is suspected. Gynaecological US examinations have revolutionized the diagnosis of such diseases. For US examinations during pregnancy, see Ultrasound Scanning during Pregnancy.
- US examinations are safe for both the patient and the fetus.
- To optimize image quality, examinations are normally performed transvaginally so that the probe is as close as possible to the target.
The normal menstrual cycle
- After menstruation, the endometrium is thin (picture 1), and fluid-filled cysts of < 5-6 mm in diameter, i.e. antral follicles (picture 2), can be seen in the ovaries.
- Early in the menstrual cycle oestrogen causes the endometrium to grow and produces the triple-layer structure typical for the proliferative phase, as the mucosal layers in the anterior and posterior endometrial walls grow towards each other in the uterine cavity (picture 3). In the proliferative phase, the endometrium itself appears darker (more hypoechogenic) between the layers than the surrounding myometrium. In a couple of weeks, the endometrium grows to a thickness of approx. 10 mm.
- Ovulation occurs when the dominant follicle is approx. 20-25 mm in diameter (picture 4). The corpus luteum develops from the dominant follicle. Profuse neovascularization is typical for luteal activity and can be observed by Doppler sonography (picture 5).
- In the secretory phase, progesterone makes the endometrium appear lighter (more echogenic) on US compared to the surrounding myometrium but no longer increases the thickness of the endometrium (picture 6). At the same time, the three-layer structure of the endometrium becomes less distinct.
Pregnancy
Normal first trimester, weeks 4-8
- See also Ultrasound Scanning during Pregnancy.
- In the 4th week of pregnancy, no gestational sac (GS) can be seen in the uterus and the decidua resembles that in the secretory phase. As a result of hCG stimulation, the corpus luteum is active and shows profuse vasculature.
- In the 5th week of pregnancy, a GS containing a yolk sac (YS) can be seen in the uterus (picture 7). Towards the end of the 5th week, the fetal pulse rate can be seen next to the YS.
- In the 6th week of pregnancy, the crown-rump length (CRL) of the embryo, 4-8 mm, can be measured, as seen next to the YS (picture 8).
- In the 7th week of pregnancy, the CRL is 9-16 mm. The fourth cerebral ventricle in the fetal head (picture 9), the spine and limb buds (picture 10) are detectable. A thin amnion lining the actual amnion sac (AS) appears around the fetus (picture 11). The fluid-filled space surrounding the AS disappears by the 11th-12th week of pregnancy as the amnion grows into the chorion lining the GS (picture 12). The corpus luteum remains active until week 7 and subsequently gradually atrophies.
- In the 8th week of pregnancy, the CRL is 16-22 mm (picture 13). Head and limb movements can be seen. The YS is still visible outside the amniotic cavity.
Ectopic pregnancy
- Of ectopic pregnancies, 95% occur in a fallopian tube, the other 5% at sites such as the uterine cervix, cornu uteri (picture 16), caesarean scar, ovary or elsewhere in the abdominal cavity Ectopic Pregnancy.
- If a gestational sac containing a live fetus can be seen outside the uterus, the diagnosis of ectopic pregnancy is evident (picture 17), but this is rarely the case.
- In most cases, only an area with varying echo pattern can be seen outside the uterus, close to the ovary, and possibly some fluid in the free abdominal cavity.
- If serum hCG is 1 000-2 000 IU/l and no pregnancy can be seen in the uterus, the patient probably has an ectopic pregnancy.
Ovaries
- Gynaecological US is a basic examination whenever an ovarian tumour is suspected.
- It is not possible to differentiate reliably between benign and malignant tumours.
Malignant ovarian tumours
- Features suggesting malignancy
- Solid cystic structures
- Multilocular structure
- Thick (> 3 mm) septa
- Papillary growth in inner walls
- Ascites in the free abdominal cavity
- See also Gynaecological Cancers.
Benign ovarian tumours
- Occur in 5-10% of asymptomatic women of fertile age and 3-15% of menopausal women
- Anechoic, smooth-walled unilocular ovarian lesions (cysts) of less than 10 cm in diameter are nearly always benign Benign Gynaecological Lesions and Tumours.
- Dominant follicles burst at a diameter of approx. 2.0-2.5 cm. In women of fertile age with disturbed menstrual cycle, anechoic smooth-walled unruptured ovarian follicles, or cysts, with a diameter of > 3 cm may be detected. Hormonal IUDs, for example, occasionally cause cysts by disturbing the normal development of ovarian follicles.
- Cysts do not normally secrete steroids (i.e. they are hormonally inactive). If a cyst is hormonally active, it grows and maintains the endometrium. If a cyst is observed immediately after menstruation, it must be hormonally inactive.
- In association with ovulation, a blood vessel may burst on the ovarian surface, bleeding into the corpus luteum and forming a haemorrhagic corpus luteum. The lesion resolves spontaneously, in contrast to an endometrioma Endometriosis that may resemble a haemorrhagic cyst on US.
- Other common benign ovarian lesions include serous and mucinous cysts, endometriotic cysts (endometrioma) and dermoids (teratoma) originating from germ cells, each of which have their typical features.
- An endometrioma is a clearly defined, round lesion with even echo pattern. There may be several endometriomas side by side in an ovary. There is usually healthy ovarian tissue with antral follicles around the endometrioma (picture 18).
- Mucinous cysts show a snowstorm echo pattern.
- Dermoids are often inhomogeneous, as they may contain fat, hair, cartilage and bone, for example, as well as cysts with clear contents.
- As malignancy of ovarian tumours cannot be definitely excluded by US examination, indications for surgery should be considered individually.
Polycystic ovary (PCO)
- PCOs either contain a minimum of 12 antral follicles (AF) or their volume exceeds 10 ml (picture 19).
- If, in addition, either hyperandrogenism (hirsutism or high testosterone levels) or anovulation is detected, the patient has polycystic ovary syndrome (PCOS) Polycystic Ovary Syndrome (PCOS).
- If the patient has no hyperandrogenism and if she has regular menstrual cycles, ovarian function is normal. In this case, a polycystic (≥ 12 AFs) ovary cannot be considered an abnormal finding.
Differential diagnosis
- Peristalsis in the fluid-filled intestine usually helps to differentiate the intestine from ovarian tumours.
- Large veins in the vicinity of the uterus can usually be differentiated from cysts by rotating the probe; a cyst will remain spherical but a vein will not be well-defined. In addition, blood flow can be detected in a vein by Doppler US.
- Fluid-filled nabothian cysts may sometimes be seen in the muscle layer in the uterine cervix.
Uterus
Cancer of the uterine corpus
- Abnormal bleeding occurs as a symptom (90%).
- In cancer, Gynaecological Cancers the endometrium appears on US as inhomogeneous structure with a mean thickness of 15 mm. As there may be cancer in an endometrium that is < 5 mm thick, endometrial biopsy should be taken in patients with intermenstrual bleeding Pap (Cervical) Smear and Endometrial Biopsy.
Polyp
- A polyp Benign Gynaecological Lesions and Tumours is a protrusion of the endometrium. It may cause intermenstrual bleeding or heavy menstrual bleeding. Polyps are nearly always benign (99%).
- In women of fertile age, diagnosis can best be made by US examination in the proliferative phase before ovulation. If the US examination is performed in the secretory phase (picture 6) or in a postmenopausal woman, accuracy can be improved by injecting fluid through a catheter into the uterus (picture 20).
- An endometrial biopsy should be taken if there is abnormal bloody discharge Pap (Cervical) Smear and Endometrial Biopsy.
Myoma
- Uterine muscle tumours, myomas or fibroids, are benign tumours Benign Gynaecological Lesions and Tumours increasing in frequency with age; approx. 70% of 50-year-old white women have myomas.
- Myomas are divided by location into submucosal, intramural and subserous (picture 21).
- The symptoms include bleeding disorders, a feeling of weight, miscarriages and infertility.
- In US examination, myomas appear inhomogeneous compared to the myometrium, round and the visible parts are quite well defined. The front margins of large myomas, in particular, are often more clearly defined than the back margins because US passes through a myoma poorly (picture 22).
- Submucosal myomas protrude into the uterine cavity (picture 23).
Adenomyosis
- Growth of endometrial glandular and stroma cells into the muscular wall of the uterus Adenomyosis (cf. endometriosis Endometriosis with endometrial-type tissue outside the uterus).
- US examination (picture 24) may reveal
- inhomogeneity of myometrial echo
- disparity of uterine wall thicknesses
- indistinct border between the endometrium and the myometrium or
- cysts in the myometrium.
- Diagnosis can be confirmed by hysterectomy.
IUD
- The position of both copper and hormonal IUDs can be verified by US examination.
- Copper IUDs are more clearly visible than hormone releasing IUDs (Mirena® ). The copper in the body of the IUD gives a clear echo, whereas the levonorgestrel hormone reservoir is very hypoechogenic. Behind the body and arms of a hormone releasing IUD, there is a hypoechogenic shadow sector (picture 25).
Sonohysterography
- In sonohysterography 5-15 ml of saline solution is injected into the uterine cavity through, for example, an insemination catheter. The saline solution provides contrast in the uterine cavity which allows the best visualization of any polyps in the uterine corpus or submucosal myomas protruding into the cavity. A histological sample of the endometrium should be taken before performing sonohysterography.
Fallopian tubes
- Normal fallopian tubes are not visible in ultrasonography.
- If there is liquid in the abdominal cavity around the fallopian tube, the distal end of the fallopian tube with fimbriae may be visible in ultrasonography.
- A fluid-filled fallopian tube (hydrosalpinx) is seen as a clearly defined, tortuous structure (picture 26).
- Acute severe pelvic inflammatory disease (PID) Pelvic Inflammatory Disease (PID) may be associated with an intraovarian collection of pus that is seen as a multilobular, thick-walled tumour containing cloudy liquid. An inflamed fallopian tube may show profuse vasculature.
Salpingosonography
- Tubular patency can be examined by injecting into the uterine cavity either a galactose-based contrast medium or a mixture of saline and air (hysterosalpingo-contrast sonography [HyCoSy] or salpingosonography).