Pelvic and Transvaginal Ultrasound

Pelvic ultrasound images the uterus, endometrium, cervix, ovaries, fallopian tubes (when abnormal), adnexa, bladder and pouch of Douglas. The transabdominal approach uses a 3 to 5 MHz curvilinear probe through a full bladder, which acts as an acoustic window and displaces bowel, and gives an overview of large masses, the uterus and the bladder.

The transvaginal approach uses a 5 to 9 MHz endocavitary probe with an empty bladder, and gives higher resolution images of the uterus, endometrium, ovaries and adnexa because the probe is close to the structures. Transrectal or transperineal approaches are used in virgins or when the vaginal route is not possible.

Colour and power Doppler assess blood flow in the uterus, ovaries and masses, and three dimensional ultrasound displays the uterine cavity and congenital anomalies. Saline infusion sonohysterography and tubal patency tests are extensions. The examination takes 15 to 30 minutes, with no ionising radiation and no known foetal risk.

Pelvic pain, abnormal uterine bleeding, infertility, suspected pregnancy complications and pelvic masses are the commonest gynaecological presentations.

Ultrasound is the first line test for almost all of them. Transvaginal ultrasound:

• Detects ovarian masses with a sensitivity of about 90% and a specificity of 80 to 90%.
• Diagnoses ectopic pregnancy in the context of a positive pregnancy test and an empty uterus.
• Measures the endometrium (a thickness under 4 to 5 mm in postmenopausal bleeding has a negative predictive value of 99% for endometrial cancer).
• Defines fibroids, adenomyosis and congenital anomalies.

Indications. Pelvic pain (acute and chronic), suspected ovarian torsion, pelvic inflammatory disease and tubo ovarian abscess. Abnormal uterine bleeding (heavy, irregular, postmenopausal bleeding). Early pregnancy problems: bleeding, pain, suspected ectopic pregnancy, miscarriage, molar pregnancy. Pelvic mass, palpable or suspected fibroids, ovarian cysts or tumours.

Infertility (uterine anomalies, ovarian follicle monitoring, antral follicle count, polycystic ovaries, hydrosalpinx). Localisation of an intrauterine contraceptive device and its complications. Amenorrhoea and suspected congenital anomalies, delayed or precocious puberty (in girls, transabdominal). Ovarian cancer risk assessment and surveillance.

Post-operative or post-partum complications (retained products, collection). Control of procedures (oocyte retrieval, cyst aspiration, embryo transfer). Not for the first test of suspected bowel perforation, and CT or MR are used when ultrasound is inconclusive.

Contraindications and precautions. No absolute contraindications. The transvaginal route requires consent and a chaperone, and is not used in girls who have not been sexually active (transabdominal or transrectal scanning is used) or when the patient declines; it is used with care in vaginal bleeding, recent pelvic surgery, and vaginal atrophy.

Latex allergy: latex free probe covers. Gel and probe disinfection protect from infection. A full bladder is drunk (500 to 750 mL, 1 hour before) for transabdominal scans, and the bladder is emptied for transvaginal scans. Menstrual cycle timing: the best time for endometrial assessment is the early proliferative phase (days 4 to 10).

Preparation and technique. The patient lies supine with knees bent (for transvaginal) or flat (for transabdominal).

A covered, gel lubricated probe is introduced and angled in the sagittal and coronal planes. It images:

• The uterus (length, width, anteroposterior depth, position, myometrial pattern).
• The endometrium (thickness measured in the sagittal plane, double layer).
• The cervix.
• Each ovary (three dimensions, follicles, masses).
• The adnexa.
• The pouch of Douglas for fluid.
• The bladder.

Pressure with the abdominal hand (bimanual) brings the pelvic organs to the probe, and sliding of organs shows adhesions ("sliding sign"). Doppler is used with the lowest power for pregnant patients. The tender point is sought with the probe.

Normal appearances. Uterus: pear shaped, anteverted or retroverted, length 7 to 9 cm in a reproductive age woman, width 4 to 5 cm, anteroposterior 2 to 3 cm (smaller after menopause, 4 to 6 cm long; larger in parous women), with uniform mid-grey myometrium.

Endometrium: thin echogenic line in the menstrual phase (1 to 3 mm), 5 to 7 mm in the early proliferative phase, a trilaminar "triple line" pattern of 8 to 12 mm before ovulation, and a bright, thick 8 to 16 mm in the secretory phase. Postmenopausal endometrium: under 4 to 5 mm. Cervix: 3 cm long with a central canal, and Nabothian cysts as incidental cysts.

Ovaries: almond shaped, volume under 10 mL in premenopausal women (about 3 x 2 x 2 cm). They contain follicles of 2 to 9 mm in number (up to 12 in each ovary), a dominant follicle of up to 20 to 25 mm before ovulation, and a corpus luteum after ovulation. Postmenopausal ovaries are small (under 2 mL) and without follicles. Fallopian tubes are not usually seen.

A small amount of free fluid in the pouch of Douglas is normal around ovulation and menstruation.

Interpretation.

• Fibroids (leiomyomas): well defined, round, hypoechoic masses with shadowing at the edges, and whorled pattern, classified as submucosal (distorting the cavity), intramural or subserosal; sizes, number and positions are described, with degeneration shown by cystic areas or calcification.
• Adenomyosis: globular, asymmetrically enlarged uterus with heterogeneous myometrium, myometrial cysts, linear striations ("venetian blind" shadowing), and an ill defined junctional zone.
• Endometrial lesions: thickened endometrium (over 4 to 5 mm after menopause, abnormal if over 16 mm before menopause with bleeding).
• Polyps: focal echogenic mass with a feeding vessel on Doppler ("pedicle artery sign").
• Hyperplasia and carcinoma: irregular, thick endometrium, increased vascularity, myometrial invasion.
• Retained products of conception: echogenic mass in the cavity with vascularity.
• Functional ovarian cysts (follicular and corpus luteum): simple thin walled anechoic cysts under 5 cm, resolving in 1 to 2 cycles; haemorrhagic cyst has a reticular "fishnet" pattern.
• Endometrioma: "ground glass" low level echoes, no vascularity in the contents.
• Dermoid cyst: echogenic nodule, "tip of the iceberg" sign, hair lines and calcifications.
• Cystadenoma: unilocular or multilocular with thin septa.
• Malignancy: solid components, thick irregular septa over 3 mm, papillary projections, high vascularity, ascites; the pattern is classified by validated rules to separate benign and malignant.
• Polycystic ovaries: 20 or more follicles of 2 to 9 mm in each ovary or volume over 10 mL, with a central stroma that is echogenic (in the context of oligo ovulation and hyperandrogenism).
• Pelvic inflammatory disease: thickened, fluid filled tubes (hydrosalpinx, "cogwheel" sign, "beads on a string" sign), tubo ovarian complex or abscess (complex adnexal mass with debris and fluid), free pelvic fluid, tenderness on probe pressure, and increased tubal vascularity.
• Ovarian torsion: enlarged ovary (over 4 cm, volume over 20 mL) with peripheral follicles ("string of pearls"), a twisted pedicle with the "whirlpool" sign, free fluid, and reduced or absent Doppler flow (but normal flow does not exclude torsion).
• Ectopic pregnancy: an empty uterus with positive pregnancy test and an adnexal mass (the "tubal ring" sign, a ring of echogenic tissue separate from the ovary), free fluid or haemoperitoneum in the pouch of Douglas, and a pseudogestational sac in the uterus.
• Congenital anomalies: septate uterus (a fundal indentation of under 1 cm with a septum), bicornuate (fundal cleft over 1 cm), didelphys, unicornuate, and arcuate, best seen on three dimensional ultrasound in the secretory phase.
• Intrauterine device: the echogenic stem and arms in the cavity (T-shaped) at the fundus, with malposition if low, rotated, embedded or perforating.
• Other: cervical masses, Nabothian cysts, Gartner duct cysts, hydrosalpinx, peritoneal inclusion cysts, bladder lesions, and endometriosis (deep nodules, adhesions with a "kissing ovaries" sign and loss of sliding).

Critical values and findings needing immediate action.

• Ectopic pregnancy with haemoperitoneum or haemodynamic instability: resuscitation and emergency surgery; a stable ectopic pregnancy is managed with methotrexate or laparoscopy.
• Ovarian torsion (enlarged oedematous ovary with pain and nausea): urgent laparoscopy to detorse, even if Doppler flow is present.
• Tubo ovarian abscess or ruptured abscess: intravenous antibiotics, drainage, and surgical review.
• Ruptured or bleeding ovarian cyst with haemoperitoneum: surgical review.
• Malignant features in an ovarian mass: urgent MR or CT staging, tumour markers (CA 125) and gynaecological oncology referral.
• Postmenopausal bleeding with a thick endometrium: urgent hysteroscopy and biopsy.
• Retained products with heavy bleeding or sepsis: evacuation and antibiotics.
• Molar pregnancy ("snowstorm" or "bunch of grapes" appearance): gynaecological referral and human chorionic gonadotrophin follow up.
• Perforated intrauterine device: surgical removal.

Limitations and artefacts.

• Transabdominal scanning has poor resolution for small ovarian lesions and endometrial detail; a full bladder can distort the uterus and compress the ovaries. Transvaginal scanning has a limited field of view and misses high or large masses (over 8 to 10 cm) or masses outside the pelvis; the two approaches are combined.
• Obesity, scars, fibroids, bowel gas and a retroverted uterus limit views; the fundus may not be reached by the transvaginal probe in an enlarged uterus.
• Normal ovaries may not be seen (in 10 to 15% of postmenopausal women with transabdominal scan); the endometrium cannot be measured reliably in the presence of fibroids, a device or blood in the cavity.
• Ultrasound cannot always separate benign from malignant ovarian masses (indeterminate masses need MR); endometrioma and haemorrhagic cyst, a dermoid and bowel, and a pedunculated fibroid and a solid ovarian mass may be confused; Doppler is not specific for malignancy.
• Normal Doppler flow does not exclude torsion, and torsion can be intermittent.
• A thin endometrium does not exclude endometrial cancer in some cases (type 2 cancers), and biopsy is needed if bleeding persists.
• Early pregnancy: a gestational sac may be missed before 5 weeks, and a pseudosac mimics an early pregnancy.
• A beta human chorionic gonadotrophin level of 1500 to 3000 IU in each litre is the "discriminatory zone" at which an intrauterine sac should be seen.
• Diagnosis of failed pregnancy requires strict criteria (crown rump length 7 mm or more without heartbeat, or mean sac diameter 25 mm or more without embryo) to avoid error.
• Cervical, vaginal and uterine measurements vary with phase and parity.
• Infection control: probe covers and high level disinfection are essential.

Special groups.

• Girls and adolescents: transabdominal scanning only, for precocious puberty, delayed puberty, ovarian cysts and torsion.
• Postmenopausal women: endometrial thickness and ovarian masses (ovarian cancer risk).
• Pregnant women: first trimester dating and viability, and complications (ectopic, miscarriage, molar pregnancy).
• Women with infertility: ovarian reserve (antral follicle count) and follicle tracking.
• Women with a device (intrauterine contraceptive): location and complications.
• Women with pelvic pain: ultrasound with tender point mapping and sliding sign shows endometriosis and adhesions.
• Regions: pelvic inflammatory disease, genital tuberculosis, ectopic pregnancy, uterine fibroids, cervical cancer with hydronephrosis, and late presentation of ovarian tumours are common; transabdominal ultrasound is often the only available imaging.

Follow up tests.

• MR of the pelvis for indeterminate adnexal masses, fibroids, adenomyosis, congenital anomalies and staging.
• CT of the abdomen and pelvis for staging of malignancy.
• Saline infusion sonohysterography.
• Hysteroscopy and endometrial biopsy.
• Hysterosalpingography or tubal patency test for infertility.
• Laparoscopy for torsion, endometriosis and ectopic pregnancy.
• Serum beta human chorionic gonadotrophin (serial).
• CA 125 and other tumour markers.
• Full blood count and pregnancy test.
• Endocrine tests for polycystic ovary syndrome (luteinising hormone, follicle stimulating hormone, testosterone, prolactin, thyroid function).
• Vaginal swabs for infection and cervical cytology.
• Referral to gynaecology, gynaecological oncology or fertility services.