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 and 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 and 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.