On ultrasound, which feature is MOST suggestive of malignancy in an adnexal cystic lesion?

• A Thick irregular septations with papillary projections and internal vascularity on Doppler ✓
• B Thin-walled unilocular cyst without internal echoes
• C Mobile internal echoes (layering debris) with posterior acoustic shadowing
• D Bilateral cysts with bilateral simple septae

Explanation

The IOTA criteria for malignant ovarian lesions on ultrasound (M-features) include irregular solid components, ascites, at least four papillary structures, irregular multilocular-solid tumor, and high vascularity. Thick irregular septa with papillary projections and internal vascularity (low resistance Doppler flow) are classic malignant features. A thin-walled unilocular cyst is IOTA B-feature (benign). Mobile debris with shadowing suggests dermoid cyst (benign). Simple bilateral cysts are more likely physiological or benign.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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