Female reproductive tract
Female reproductive tract on imaging
Ultrasound and MRI show the uterus, cervix, tubes and ovaries in great detail, and their appearance changes with age, the menstrual cycle and pregnancy. CPSP asks about the zonal anatomy of the uterus, the cyclical endometrium, normal measurements, Müllerian anomalies, ectopic pregnancy sites and the signatures of common adnexal masses.
Uterus: position and age changes
- Normally anteverted (cervix tilted forward on the vagina) and anteflexed (body bent forward on the cervix). A retroverted uterus usually rises and corrects by about 14 weeks of pregnancy; if trapped under the sacral promontory it causes urinary retention.
| Age | Ultrasound appearance |
|---|---|
| Newborn | Relatively large, body equal to cervix, thin bright endometrium (maternal and placental oestrogen) |
| Prepubertal | Small tubular uterus, cervix about twice the body, no endometrial stripe |
| Reproductive | Body about twice the cervix (oestrogen at puberty) |
| Postmenopausal | Small; endometrium thin |
- The fundus becomes palpable above the symphysis at about 12 weeks. The isthmus forms the lower uterine segment in late pregnancy.
MRI zonal anatomy (T2-weighted)
- Three layers: bright endometrium, dark junctional zone (inner myometrium, densely packed smooth muscle with low water content), intermediate outer myometrium.
- Adenomyosis: junctional zone 12 mm or more, globally enlarged uterus.
- Leiomyoma: well-defined, dark on T2; submucosal ones bulge into the cavity on saline sonohysterography; a pedunculated subserosal fibroid shows bridging vessels from the uterus with normal ovaries seen separately; old fibroids give popcorn calcification on plain films.
- Endometrial carcinoma: under half myometrial depth is stage IA, half or more is IB.
- Cervix: the fibrous stroma forms a dark ring on T2. Tumour of intermediate signal breaking through this ring into the fat beside the supravaginal cervix means parametrial invasion.
Endometrium through the cycle
| Phase | Appearance |
|---|---|
| Menstrual | Thin, bright line |
| Late proliferative | Trilaminar ("triple line"): bright outer lines, dark functional layer, bright central line; about 10 mm |
| Secretory | Thick, uniformly echogenic, brighter than myometrium (glandular secretion and stromal oedema) |
- Postmenopausal bleeding: a double-layer thickness of 4 mm or less makes cancer unlikely.
- Polyp: oval echogenic lesion in the cavity with a feeding vessel, endometrial–myometrial interface intact.
- A copper IUD gives a bright line followed by evenly spaced echoes (reverberation).
- Short cervix in mid-pregnancy: under 25 mm on transvaginal scan.
Ovaries and tubes
- Ovary lies in the ovarian fossa: external iliac vessels above, ureter and internal iliac vessels behind, obturator nerve laterally (pain to medial thigh). Vessels run in the infundibulopelvic (suspensory) ligament and reach the hilum through the mesovarium on the posterior leaf of the broad ligament. In young children the small pelvis keeps the ovaries high.
- Ovarian vessels cross in front of the ureter on psoas; the left ovarian vein drains to the left renal vein at a right angle (pelvic congestion). Ovarian lymph runs with these vessels to para-aortic nodes at L1–L2.
- Polycystic ovary: volume 10 mL or more (or many small peripheral follicles) without a dominant follicle. The postmenopausal ovary shrinks to about 1.5–2 cm; a palpable one is abnormal.
- A little clear fluid in the pouch of Douglas at mid-cycle is normal (ovulation).
| Lesion | Imaging signature |
|---|---|
| Haemorrhagic cyst | Lace-like internal strands, retracting clot |
| Endometrioma | Bright on T1 and fat-saturated T1, dark shading on T2 (old blood from repeated bleeds) |
| Dermoid (mature teratoma) | Fat (about −100 HU), fat–fluid level, tooth-like calcification; risk of torsion |
| Torsion | Enlarged oedematous ovary, follicles pushed to the periphery; venous and lymphatic outflow blocked first |
| Mucinous cystadenoma | Huge multilocular cyst, loculi of different signal |
| Dysgerminoma | Young girl, solid lobulated mass, T2-dark enhancing fibrovascular septa |
| Hydrosalpinx | Folded tubular anechoic structure separate from the ovary, incomplete septa |
- Tube: interstitial part (in the myometrium), isthmus (narrow; site for sterilisation clips), ampulla (fertilisation and commonest ectopic), infundibulum with fimbriae. Hysterosalpingography shows tubal patency.
Early pregnancy and ectopic sites
- Double decidual sac: decidua capsularis and parietalis around an intrauterine sac; a secondary yolk sac appears at about 5½ weeks. Normal implantation: posterior wall of the body.
| Site | Imaging and behaviour |
|---|---|
| Ampulla | Commonest |
| Isthmus | Ruptures earliest (about 6 weeks) |
| Interstitial | Sac high and eccentric with thin myometrium; myometrium lets it grow, so rupture is late and torrential |
| Cervical | Sac below the internal os, ballooned cervix; cervical stroma cannot contract to stop bleeding |
Müllerian anomalies
| Anomaly | Defect and imaging |
|---|---|
| Agenesis | No uterus, normal ovaries (not Müllerian) |
| Unicornuate | One duct fails; ipsilateral renal agenesis common (Müllerian duct needs the mesonephric duct) |
| Didelphys | No fusion: two uteri, two cervices, longitudinal vaginal septum |
| Bicornuate | Partial fusion: fundal cleft, two cavities, one cervix |
| Septate | Failed septum resorption: smooth outer fundus, recurrent miscarriage |
- Transverse vaginal septum: cyclical pain, haematocolpos above a blind vagina with normal hymen. Gartner duct cyst in the anterolateral vaginal wall is mesonephric.
Supports and the vagina
- Level I (apex): cardinal (transverse cervical) and uterosacral ligaments; the cardinal ligament is the main support and carries the uterine vessels. Level II: paracolpium to the arcus tendineus fasciae pelvis (lateral sulci), pubocervical and rectovaginal fascia. Level III: perineal body and perineal membrane. The broad ligament gives almost no support.
- Round ligament runs from the cornu through the inguinal canal to the labium majus, carrying cornual lymph to superficial inguinal nodes.
- Vagina: about 8 cm, axis upwards and backwards; posterior fornix deepest, behind it the pouch of Douglas; middle third lies on the rectal ampulla; the urethra is fused to the lower anterior wall; the ureter lies near the lateral fornix.
- Lymph: cervix and upper vagina to iliac and obturator nodes; lower vagina and vulva to superficial inguinal nodes.
Remember Junctional zone 12 mm or more means adenomyosis; triple line means late proliferative endometrium.
Exam trap In Müllerian agenesis the ovaries are normal, because ovaries do not come from the Müllerian ducts.
Exam trap A septate uterus has a smooth outer fundus; a bicornuate uterus has a fundal cleft.
Test yourself on this topic
5 of the 158 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
A 31-year-old woman collapses at 12 weeks' gestation with a large haemoperitoneum. At laparotomy, the pregnancy has ruptured through the wall of the right uterine cornu, lateral to the attachment of the round ligament, where the tube passes through the myometrium. Where was this pregnancy implanted?
Answer: Interstitial part of the tube
The interstitial part of the tube runs through the myometrium of the uterine cornu, lateral to the round ligament attachment. Because the surrounding muscle can stretch, a pregnancy here often grows to 12–16 weeks before rupturing, later than other tubal ectopics. Rupture then bleeds torrentially because the uterine and ovarian arteries anastomose in this region. The ampulla is the commonest site, and isthmic pregnancies rupture early because the isthmus is narrow and thick-walled.
Interstitial ectopic
- Tube within the myometrium of the cornu
- Lateral to the round ligament
- Presents late, bleeds heavily
- Uterine + ovarian arterial anastomosis
Remember A late, torrential ectopic rupture points to the interstitial tube.
Exam trap An angular pregnancy, inside the cavity at the cornu, lies medial to the round ligament and is not an ectopic.
Why the other options are wrong
- Ampulla of the tube Commonest site, but it lies free beside the uterus, not within the cornual wall.
- Lower uterine segment scar Scar pregnancies sit anteriorly in the lower segment at the caesarean scar.
- Right ovary An ovarian ectopic lies within the ovary.
- Isthmus of the tube The narrow isthmus lies outside the uterine wall and usually ruptures early.
A 16-year-old girl has sudden severe left pelvic pain and vomiting. At laparoscopy her left ovary is twisted twice on its pedicle; it is swollen, congested and dusky, but its colour returns after untwisting. Which vascular event occurs first in this condition?
Answer: Venous and lymphatic outflow obstruction
In torsion, the thin-walled veins and lymphatics in the twisted pedicle are compressed first, while the thicker-walled arteries still let blood in. The ovary therefore becomes congested, oedematous and enlarged. Only later does rising pressure cut off arterial inflow, leading to haemorrhagic infarction. Because the ovary also receives blood through the uterine artery anastomosis, a dusky ovary often recovers after detorsion, so it is untwisted and conserved rather than removed.
Ovarian torsion
- Veins and lymphatics compressed first
- Congested, oedematous ovary
- Arterial block comes later
- Detorsion often saves the ovary
Remember Swollen, dusky, twisted ovary: untwist before you remove.
Exam trap Preserved arterial flow is common in early torsion and should not delay surgery.
Why the other options are wrong
- Complete occlusion of the ovarian artery A late event; flow is often still present early on.
- Embolism from the uterine artery Not a cause of ovarian torsion.
- Thrombosis of the left renal vein Affects left gonadal drainage but does not cause acute torsion.
- Spasm of the internal iliac artery Not the mechanism of ovarian swelling in torsion.
A woman with a regular 28-day cycle has an endometrial biopsy. It shows long, slightly tortuous glands lined by pseudostratified columnar cells with many mitoses, in an oedematous stroma. There are no subnuclear vacuoles and no secretions in the gland lumens. Which phase of the cycle does this represent?
Answer: Late proliferative phase
Under oestrogen, the functional layer regrows from the basalis during the proliferative phase. Early on the glands are short, narrow and straight; by the late proliferative phase they are long and slightly tortuous, with pseudostratified nuclei, abundant mitoses and stromal oedema. The first sign of ovulation, about 36–48 hours later, is subnuclear glycogen vacuoles (early secretory phase); these then move above the nucleus and the secretions pass into the lumen. The late secretory phase shows saw-toothed glands and predecidual stroma, and the menstrual phase shows breakdown with blood and stromal collapse.
Endometrial dating
- Proliferative: straight to tortuous glands, mitoses
- Late proliferative: pseudostratified, stromal oedema
- Early secretory: subnuclear vacuoles (ovulation)
- Late secretory: saw-tooth glands, predecidua
Remember No vacuoles yet means ovulation has not happened.
Exam trap Mitoses alone do not rule out the earliest secretory days; the key sign of ovulation is subnuclear vacuolation.
Why the other options are wrong
- Early secretory phase Would show subnuclear glycogen vacuoles, the first sign of ovulation.
- Menstrual phase Would show fragmented, collapsing stroma with blood and neutrophils.
- Late secretory phase Would show saw-toothed glands with secretions and predecidual stroma.
- Early proliferative phase Glands are short, narrow and straight, and the endometrium is thin.
A 5-day-old girl has a little blood-stained vaginal discharge and slightly swollen breasts. She is feeding well and examination is otherwise normal. Which hormonal influence explains these findings?
Answer: Maternal and placental oestrogen
During pregnancy, high levels of placental and maternal oestrogen cross to the fetus and stimulate the uterus, endometrium and breast tissue. After birth these hormones are suddenly withdrawn, so some girls have a small withdrawal bleed in the first week, and breast buds (sometimes with a little milk) are common in both sexes. The changes settle over a few weeks without treatment. Androgens do not stimulate the endometrium, and neonatal FSH does not cause these changes.
Newborn hormonal effects
- Maternal oestrogen crosses placenta
- Withdrawal after birth: small vaginal bleed
- Breast buds, in both sexes
- Settles over weeks
Remember A newborn's bleed and breast buds are borrowed oestrogen.
Exam trap A small vaginal bleed in a newborn girl is usually oestrogen withdrawal, not trauma or disease.
Why the other options are wrong
- Fetal adrenal androgens Androgens do not make the endometrium grow or bleed.
- Neonatal pituitary FSH surge Mini-puberty affects the ovaries, but these newborn changes are from maternal oestrogen.
- Congenital adrenal hyperplasia Causes virilisation of the external genitalia, not bleeding and breast buds.
- Obstructing vaginal septum Would cause a bulging, fluid-filled vagina (hydrometrocolpos), not bleeding.
A 48-year-old woman has a huge, smooth abdominal mass. At laparotomy it is a 22 cm unilateral multilocular ovarian cyst with thin septa, filled with thick, sticky, gelatinous fluid. The loculi are lined by a single layer of tall columnar cells with basal nuclei and no atypia. What is the diagnosis?
Answer: Mucinous cystadenoma
Mucinous cystadenomas are often very large, unilateral, multilocular tumours filled with sticky, gelatinous mucin. Their loculi are lined by a single layer of tall columnar mucin-secreting cells with basal nuclei, resembling endocervical or intestinal epithelium. Without stratification, atypia or stromal invasion they are benign. Serous cystadenomas are more often unilocular with thin, clear fluid and a ciliated tubal-type lining, and fibromas are solid.
Mucinous cystadenoma
- Very large, unilateral
- Multilocular, sticky mucin
- Tall columnar mucin cells
- Check the appendix if pseudomyxoma
Remember Huge, many-chambered and sticky: mucinous.
Exam trap Pseudomyxoma peritonei with an ovarian mucinous tumour usually comes from the appendix, so the appendix must be checked.
Why the other options are wrong
- Serous cystadenoma Clear watery fluid and a ciliated, tubal-type lining.
- Endometrioma Thick dark brown fluid with endometrial glands and stroma.
- Dysgerminoma A solid tumour of sheets of clear cells in young women.
- Ovarian fibroma A solid tumour of spindle fibroblasts.
Where this sits in the CPSP syllabus
- Diagnostic Radiology, Paper 2: Pelvis, Female reproductive tract on imaging