Clinical overview
Ultrasound is the single most powerful first-line tool a gynaecologist has for deciding whether a pelvic mass is benign or possibly malignant. Most adnexal masses are benign — functional cysts, dermoids, endometriomas, hydrosalpinges — and the harm of treating them all as cancer is real: unnecessary surgery, loss of fertility, referral of low-risk women into oncology systems that should be reserved for those who need them. Conversely, missing the features of an early ovarian or endometrial malignancy delays the one intervention — complete surgical staging by a gynaecological oncologist — that most changes survival. The registrar's task is therefore not "is this cancer?" in binary terms but "what is the probability of malignancy, and what does that probability tell me to do next?" That is fundamentally an interpretive skill: reading the grey-scale and Doppler morphology of a lesion, placing it into a structured risk model, and translating the result into a triage decision.
This is a high-order objective. You are expected not just to list ultrasound features but to interpret them — to know which features carry weight, how they combine into validated rules and scores (IOTA Simple Rules, the ADNEX model, O-RADS), and how the answer changes with menopausal status, tumour markers and the patient in front of you. In South Africa the stakes are sharpened by epidemiology and access: cervical and breast cancers dominate, but ovarian cancer presents late, theatre and oncology capacity are concentrated at tertiary centres, and a high HIV prevalence raises the background rate of pelvic infection and tubo-ovarian masses that mimic malignancy. A correct ultrasound interpretation at district or regional level is what gets the right woman onto the right referral pathway. This chapter assumes the probe skills and safety covered in ultrasound-knobology-doppler-safety and the general scanning craft of obstetric-ultrasound.
Core knowledge
Figure F12.1 — Adnexal mass, morphology first: the IOTA language of reassuring B-features vs malignant M-features (and benign patterns that de-escalate) — read the shape and colour score, then estimate the risk.
What "possible malignancy" looks like on ultrasound
The morphological language of adnexal-mass ultrasound was standardised by the International Ovarian Tumour Analysis (IOTA) group, and that vocabulary is now the lingua franca of the field. Two sets of descriptors anchor interpretation — features that reassure (B-features, "benign") and features that worry (M-features, "malignant").
B-features (suggest benign):
- Unilocular cyst
- Presence of solid components where the largest solid component is small (classically <7 mm in its largest diameter)
- Acoustic shadows
- Smooth multilocular tumour with a largest diameter <100 mm
- No detectable blood flow on colour Doppler (IOTA colour score 1)
M-features (suggest malignancy):
- Irregular solid tumour
- Ascites
- At least four papillary projections (papillations are solid projections into a cyst cavity ≥3 mm high)
- Irregular multilocular-solid tumour with a largest diameter ≥100 mm
- Very strong intra-tumoral blood flow (IOTA colour score 4)
The deep teaching point is why these features matter. Malignant tissue is disorganised: it grows as irregular solid nodules rather than smooth walls, it recruits a chaotic neovasculature (hence intense, centrally-located Doppler flow), it sheds fluid into the peritoneum (ascites), and it throws up papillary excrescences. Benign lesions are orderly — thin smooth walls, avascular or peripherally-vascular, often with tissue-specific signatures (the hyperechoic Rokitansky nodule and "dermoid mesh" of a mature teratoma, the homogeneous low-level "ground-glass" echoes of an endometrioma, the incomplete septa and "beads-on-a-string" of a hydrosalpinx). Recognising a specific benign pattern is as important as spotting malignancy, because it lets you confidently de-escalate.
Colour Doppler and its limits
IOTA grades vascularity on a four-point colour score: 1 = no flow, 2 = minimal, 3 = moderate, 4 = very strong. Increasing flow, especially abundant central flow within a solid component, raises suspicion. Historically clinicians chased spectral indices — a low resistance index or pulsatility index was said to indicate the low-impedance tumour vessels of malignancy — but these proved poorly reproducible and are no longer relied upon in the validated models. Interpret Doppler as part of the morphological gestalt, not as a stand-alone test, and remember that inflammatory and physiological tissue (corpus luteum, tubo-ovarian abscess) can be intensely vascular and mislead you. Apply ALARA throughout, particularly any time the patient could be pregnant (see ultrasound-knobology-doppler-safety).
Structured risk models — turning features into probability
Listing features is LOTS; combining them into a defensible probability is the HOTS skill. Several validated systems do this:
- IOTA Simple Rules. Apply the five B- and five M-features above. If one or more M-features and no B-features → classify malignant. If one or more B-features and no M-features → classify benign. If both or neither apply, the rules are inconclusive and the mass should be assessed by an expert examiner or a more detailed model. The Simple Rules are applicable to roughly three-quarters of masses and perform well in those, with reported sensitivity and specificity broadly in the high-80s to low-90s percent in IOTA cohorts — but treat exact figures as study-dependent rather than fixed.
- IOTA ADNEX model. A multinomial logistic-regression model that estimates not just benign-versus-malignant but the probability across five outcomes: benign, borderline, stage I invasive, stage II–IV invasive, and metastatic. It uses simple inputs — age, serum CA-125, maximal lesion diameter, proportion solid, number of locules, number of papillary projections, acoustic shadows and ascites — and is the most useful single tool for nuanced triage because it discriminates the kind of malignancy, which matters for referral and surgical planning.
- O-RADS (Ovarian-Adnexal Reporting and Data System). A reporting lexicon and risk-stratification scheme (categories 0–5) that maps morphology to a malignancy-risk band and an associated management recommendation, analogous to BI-RADS in breast imaging. It standardises the report and the recommendation, which is valuable for communication between the scanning gynaecologist, radiology and the oncology MDT.
The unifying message: a structured model beats unaided "eyeballing" for everyone except the most experienced subjective assessor, and even they benefit from documenting against a recognised system.
Menopausal status changes everything
The pre-test probability of malignancy in a postmenopausal woman with an adnexal mass is far higher than in a premenopausal woman, and the same morphology must be read in that light. This is why the older Risk of Malignancy Index (RMI) explicitly multiplies an ultrasound score by a menopausal score by the CA-125 level: RMI = U × M × CA-125. The ultrasound score (U) counts features — multilocular cyst, solid areas, bilaterality, ascites, intra-abdominal metastases — scoring 0, 1 or 3. The menopausal score (M) is typically 1 for premenopausal and 3 for postmenopausal. An RMI above a defined cut-off (commonly 200 or 250 in different protocols) triages a woman to a gynaecological-oncology centre. RMI is simpler and more conservative than IOTA models and remains embedded in many referral guidelines, including the structure NICE recommends.
Endometrial and other non-ovarian signs
"Possible malignancy" is not only ovarian. In a postmenopausal woman with bleeding, endometrial thickness measured on a sagittal transvaginal image is the key sign: a thin, homogeneous endometrium makes endometrial cancer very unlikely, while a thickened endometrium (a widely-used threshold is >4 mm in a postmenopausal bleeder, with some guidelines using ≤3 mm to reassure) mandates histological assessment. Morphological worry-signs include a heterogeneous or irregular endometrium, loss of the endometrial–myometrial interface (suggesting myometrial invasion), increased vascularity with a dominant feeding vessel, and intracavity fluid with solid components. The IETA (International Endometrial Tumor Analysis) group standardised this endometrial vocabulary just as IOTA did for ovaries. Beware: in asymptomatic postmenopausal women, and in women on tamoxifen (which produces a falsely thickened, cystic-appearing endometrium), thickness thresholds perform poorly and should not by themselves trigger intervention. This connects directly to endometrial-carcinoma.
Assessment
Optimise the examination first
Interpretation is only as good as the image. Use transvaginal scanning as the primary route for adnexal and endometrial assessment — its resolution far exceeds transabdominal — and add transabdominal scanning for large masses that extend beyond the pelvis, to detect ascites and omental disease, and when the vaginal route is impossible. Apply the systematic IOTA approach to every mass: measure it in three planes, describe it as unilocular, unilocular-solid, multilocular, multilocular-solid or solid; count locules and papillary projections; measure the largest solid component; assess wall and septal regularity; apply the colour score; and look explicitly for ascites and peritoneal deposits.
A structured interpretive sequence
- Confirm the origin. Is the mass ovarian, tubal, uterine or extra-genital (bowel, bladder, peritoneal)? The "sliding-organ" sign, the ovarian-crescent sign and following the vascular pedicle help localise it.
- Recognise specific benign patterns. Mature teratoma (Rokitansky nodule, fat–fluid level, acoustic shadowing), endometrioma (homogeneous ground-glass echoes), simple unilocular cyst, hydrosalpinx, peritoneal pseudocyst, and a corpus luteum (a thick-walled, intensely peripherally-vascular "ring of fire" that resolves on rescan). Naming a benign pattern lets you stop here.
- Apply IOTA Simple Rules. Classify benign, malignant or inconclusive.
- For inconclusive or worrying masses, run the ADNEX model and/or assign O-RADS, and calculate an RMI integrating menopausal status and CA-125.
- Look beyond the mass for ascites, omental "caking", liver-surface deposits and lymphadenopathy — signs of established malignancy that change staging and urgency.
Tumour markers and adjuncts
CA-125 is the workhorse, feeding both RMI and ADNEX, but it is neither sensitive in early disease nor specific — it rises in endometriosis, pelvic inflammatory disease, fibroids, pregnancy and even benign ascites. In premenopausal women particularly, a raised CA-125 must be interpreted with caution. In a young woman with a solid ovarian mass, consider germ-cell and sex-cord markers (AFP, β-hCG, LDH, inhibin) because the differential shifts toward germ-cell and stromal tumours. CA 19-9 and CEA help when a mucinous or metastatic (e.g. Krukenberg) tumour is suspected. Cross-sectional imaging (CT chest/abdomen/pelvis, or MRI for problem-solving an indeterminate adnexal mass) and ultimately histology complete the work-up — but the ultrasound interpretation is what sets that machinery in motion.
The South African context
Triage interpretation is inseparable from where the woman is being scanned. A district hospital with basic ultrasound should apply the Simple Rules / RMI logic and refer suspicious or inconclusive masses to a regional or tertiary unit, rather than attempting definitive surgery on a possible cancer — incomplete surgery by a non-oncologist worsens outcomes and is a recognised pitfall. Gynaecological-oncology surgical capacity in South Africa is concentrated at tertiary academic centres, so the referral threshold and the quality of the referral report (state the morphology, the score, the CA-125, the menopausal status) genuinely determine care. The high local burden of pelvic infection and tubo-ovarian abscess — amplified by HIV — means inflammatory masses frequently masquerade as malignancy; a careful history, inflammatory markers and a short-interval rescan after treatment often clarify this without surgery. Adnexal masses discovered in pregnancy are a distinct problem addressed in adnexal-mass-in-pregnancy, where physiological corpora lutea and decidualised endometriomas can mimic worrying features.
Management
Ultrasound interpretation feeds directly into one of four pathways:
- Confident benign pattern, asymptomatic (e.g. simple cyst, classic dermoid, endometrioma): conservative management with interval surveillance is appropriate; many simple cysts resolve. Document the benign descriptors that justify not operating.
- Likely benign but symptomatic or growing: elective gynaecological surgery, ideally minimal-access, by a general gynaecologist — with a clear plan if intra-operative findings prove unexpectedly suspicious (avoid spillage, send for frozen section, do not attempt piecemeal removal).
- Inconclusive: escalate to expert subjective assessment, the ADNEX model, MRI problem-solving, and an MDT discussion. Do not default to either watchful neglect or aggressive surgery.
- Suspicious / high-risk (high RMI, malignant on Simple Rules/ADNEX, O-RADS 4–5): refer to gynaecological oncology for staging laparotomy or appropriately planned surgery, with cross-sectional imaging and markers obtained first. Pre-operative rupture of a malignant cyst upstages disease and must be avoided.
For a postmenopausal woman with bleeding and a thickened or abnormal endometrium, the management line is histology — outpatient endometrial biopsy or hysteroscopy with directed sampling — never reassurance on imaging alone, because no ultrasound appearance excludes cancer in a symptomatic bleeder with certainty.
Emergency drill — ovarian torsion of a mass. Not every urgent adnexal problem is cancer. A woman with sudden severe unilateral pelvic pain, an enlarged oedematous ovary, abnormal or absent intra-ovarian Doppler flow and a "whirlpool" of the twisted pedicle has ovarian torsion until proven otherwise. This is a surgical emergency: resuscitate, give analgesia and antiemetics, keep her nil-by-mouth, obtain urgent senior gynaecology review and proceed to emergency laparoscopy/laparotomy to detorse and salvage the ovary — do not wait for tumour markers or an MDT. Normal Doppler flow does NOT exclude torsion (dual blood supply and intermittent torsion can preserve flow), so the decision is clinical. A large vascular mass that has bled or ruptured causing haemodynamic instability is likewise a resuscitate-and-operate emergency, not an outpatient referral.
Red flags / pitfalls
- Treating Doppler indices as decisive. RI/PI are unreliable; weight grey-scale morphology and use the IOTA colour score, not spectral cut-offs.
- Reading morphology without menopausal status. The same image means very different things before and after menopause — always integrate it (this is the heart of RMI).
- Over-trusting CA-125, especially in premenopausal women where endometriosis, PID and fibroids inflate it; and under-recognising that a normal CA-125 does not exclude early or mucinous/non-epithelial cancer.
- Forcing an answer when the Simple Rules are inconclusive. "Inconclusive" is a valid result that mandates escalation, not a coin-toss.
- Operating on a possible cancer as a generalist, with risk of cyst rupture, spillage and incomplete staging. Refer suspicious masses to gynaecological oncology before surgery.
- Mistaking inflammatory or physiological masses for cancer — tubo-ovarian abscess (common with the SA HIV/PID burden), corpus luteum "ring of fire", decidualised endometrioma in pregnancy. A short-interval rescan or treatment-then-rescan often resolves the doubt without theatre.
- Applying endometrial thickness thresholds to the wrong patient — they are validated for postmenopausal bleeders, not asymptomatic women, and are unreliable on tamoxifen.
- Reassuring a symptomatic postmenopausal bleeder on imaging alone. Bleeding plus an abnormal endometrium means tissue diagnosis, full stop.
Evidence anchors
- IOTA group descriptors, Simple Rules and the ADNEX model — the standardised terminology and validated risk models for adnexal-mass ultrasound; IETA terminology for the endometrium. (Standard teaching in the field; treat quoted sensitivity/specificity figures as cohort-dependent.)
- O-RADS — the Ovarian-Adnexal Reporting and Data System lexicon and risk categories (0–5) for standardised reporting and management triage, referenced for adnexal-mass ultrasound in
docs/VERIFIED-SOURCES.mdalongside IOTA. - NICE CG122 — Ovarian Cancer: Recognition and Initial Management and NICE NG12 — Suspected Cancer: Recognition and Referral for thresholds and pathways that incorporate ultrasound, CA-125 and the Risk of Malignancy Index.
- RCOG GTG 62 — Suspected Ovarian Masses in Premenopausal Women and RCOG GTG 34 — Ovarian Cysts in Postmenopausal Women for ultrasound-led assessment and RMI-based triage by menopausal status.
- ACOG Practice Bulletin 174 — Evaluation and Management of Adnexal Masses for tumour-marker use and surgical triage.
- ISUOG ultrasound safety (ALARA; thermal/mechanical indices) governing Doppler use, especially where pregnancy is possible.
- SA NDoH National Integrated Maternal and Perinatal Care Guideline (NDoH, 2024) and the South African EML — Hospital Level frame the level-of-care and referral logic; gynaecological-oncology surgical capacity in South Africa is concentrated at tertiary centres, making accurate district/regional ultrasound triage decisive. (Level-of-care and capacity points are standard SA service-delivery facts, not specific line-items.)