First and second year — the floor first, then every step
The first and usually the best study — transvaginal, with a lexicon and a low-flow Doppler colour score.
Orient first
Transvaginal ultrasound outperforms every other modality for characterising an adnexal mass because of its resolution at short range.
The ovarian CRESCENT sign — a rim of preserved ovarian tissue at the edge of the mass — supports a benign process and helps establish origin.
Classic appearances are diagnostic: a dermoid shows a hyperechoic nodule with shadowing, dot-dash lines and a fat-fluid level; an endometrioma shows homogeneous LOW-LEVEL internal echoes (ground glass) with no internal vascularity; a haemorrhagic cyst shows a reticular fishnet pattern with a retracting clot that is avascular.
The COLOUR SCORE (1 to 4, from no flow to very strong flow) is part of the lexicon and requires low-flow settings to be meaningful.
Acquire the study
Transabdominal first with a full bladder for the overview and any mass too large for the transvaginal field, then transvaginal with an empty bladder for detail.
Set colour Doppler for LOW flow — low scale, low wall filter, gain just below noise — before assigning any colour score.
Assess mobility with gentle probe pressure to test origin and for adhesions.
The manoeuvre
Identify both ovaries separately and state whether the mass arises from one of them.
Measure in three planes and calculate volume where relevant.
Classify contents: anechoic, low-level echoes, ground glass, reticular, or solid.
Describe the wall and septations, measuring septal thickness.
Look for PAPILLARY PROJECTIONS and measure any solid component.
Apply low-flow colour Doppler and assign the colour score.
Look for free fluid, peritoneal nodularity and omental thickening.
Assign a category from a named system with its version.
What confirms it
A vascularised SOLID component, thick irregular septations or papillary projections, with ascites or peritoneal disease, indicates malignancy.
What licenses you to exclude it
⚠️ No imaging study excludes ovarian malignancy. Risk stratification produces a probability and a pathway, and a low-risk category still carries a follow-up interval that belongs in the report.
A simple cyst below the size threshold for the patient's menopausal status is the one appearance that genuinely needs nothing further.
The classic misread
Assigning a colour score on a machine set for arterial flow.
Calling a haemorrhagic cyst solid — the retracting clot is avascular, which is the test.
Not identifying the ipsilateral ovary and therefore not establishing origin.
Reference values
Each value carries the caveat that keeps it from being misused. Normal limits and diagnostic criteria are kept apart on purpose: a disease cut-off read as a normal range is the more dangerous mistake.
Normal limits
Ovaries · ovarian volumeup to 10 mL premenopausal
Postmenopausal ovaries are much smaller; applying the premenopausal figure hides pathology.
USG
Ovaries · Ovarian volume after the menopauseup to about 8 mL
The pre-menopausal limit is registered separately; applying it after the menopause under-calls. A post-menopausal ovary that is readily visible and enlarged deserves comment.
USG
Diagnostic criteria
Adnexal lesion · O-RADS 0–5 (name US versus MRI)
0 incomplete. 1 physiologic (US: a simple cyst up to 3 cm in a premenopausal woman). 2 almost certainly benign (US: simple cysts up to 10 cm). 3 low risk. 4 intermediate. 5 high risk. Category follows the lexicon (wall, septa, solid tissue, flow), not size alone — name US versus MRI and the current table
Category assignment follows the lexicon (wall, septations, solid components, vascularity), not size alone — read the current table rather than reciting it, and name which O-RADS system (US or MRI) was applied. Menopausal status changes the category boundaries. Versioned criterion — verify against the current edition before clinical use.
B-features (benign): unilocular; solid component <7 mm; acoustic shadows; smooth multilocular <100 mm; no blood flow (colour score 1). M-features (malignant): irregular solid; ascites; ≥4 papillary projections; irregular multilocular-solid ≥100 mm; very strong flow (colour score 4). Any M → malignant; only B → benign; both or neither → inconclusive (then ADNEX or O-RADS MRI). Sits alongside, and does not replace, O-RADS
Name WHICH system was applied. An inconclusive Simple-Rules result is a recognised output, not a failure — that is when the model or MRI (O-RADS MRI) is for. Versioned criterion — verify against the current edition before clinical use.
USG
Ovaries · Polycystic ovarian morphology
follicle number per ovary and ovarian volume thresholds are CRITERION- and TRANSDUCER-dependent
Transvaginal where acceptable, counting follicles 2–9 mm throughout the whole ovary.
⚠️ NO FIGURE IS QUOTED HERE ON PURPOSE. The follicle-number threshold has been revised upward as transducer resolution improved, and quoting a superseded number would be worse than quoting none. State which criteria and which revision you applied. PCOS is a clinical–biochemical–radiological diagnosis; morphology alone does not make it.
USG
See it on real cases
Direct links to Radiopaedia — the reference article and worked cases with their images. Each opens on Radiopaedia.