On pelvic MRI, which feature BEST distinguishes a focal adenomyoma from a uterine fibroid?
- A Ill-defined margins merging with the myometrium, without a pseudocapsule ✓
- B Well-defined margins with a surrounding rim of dilated vessels
- C Homogeneous high signal intensity on T2-weighted images
- D Presence of calcification on T1-weighted images
Correct answer: A. Ill-defined margins merging with the myometrium, without a pseudocapsule
Explanation
An adenomyoma is composed of ectopic glands and smooth muscle that blend imperceptibly with adjacent myometrium, so it appears as a poorly marginated lesion without a pseudocapsule, often containing small bright T2 foci representing glandular islands. B fibroid, by contrast, is sharply circumscribed by a compressed pseudocapsule surrounded by a rim of enlarged feeding vessels. Homogeneous high T2 signal suggests fluid content rather than either lesion, and calcification is a degenerative change typical of old fibroids.
Reference: Berek and Novak's Gynecology, 16th ed.
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