On pelvic MRI, a well-defined myometrial mass shows high signal intensity on T2-weighted images with a surrounding low signal intensity rim. The junctional zone elsewhere is normal. What does this rim represent, and what is the diagnosis?

• A Dilated lymphatics, lymphangioma
• B Pseudocapsule of oedema, adenomyoma
• C Compressed adjacent myometrium, leiomyoma ✓
• D Fibrous capsule, leiomyosarcoma

Explanation

C T2-hyperintense myometrial mass with a low signal intensity rim represents a leiomyoma, where the rim corresponds to compressed adjacent myometrium and dilated vessels, veins and lymphatics forming a pseudocapsule. This intact rim allows sharp demarcation from normal myometrium. An adenomyoma lacks this distinct border because it blends with the hypertrophied junctional zone, and leiomyosarcoma shows irregular margins with necrosis rather than a smooth uniform rim.

Reference: Berek and Novak's Gynecology, 16th ed.

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Written and medically reviewed by the StethoPrep medical team.