Determining Uterine Origin of a Pelvic Mass on MRI

A practical radiology review of Determining Uterine Origin of a Pelvic Mass on MRI, focused on imaging findings, differential diagnosis, reporting points, and high-yield teaching pearls.

The central question

When a large pelvic mass distorts normal anatomy, the first task is to establish the organ of origin. MRI is particularly useful because it demonstrates the continuity of the mass with uterine tissue and its vascular attachments.

Claw sign

The claw sign is present when normal myometrium wraps around the margin of a mass, producing acute angles at the interface. This supports a uterine origin, especially for an exophytic leiomyoma.

Bridging-vessel sign

Flow voids or enhancing vessels extending from the uterus into the mass provide additional evidence of uterine origin. Multiplanar T2-weighted and post-contrast images are helpful for tracing these vessels.

Reporting points

• Uterine attachment site and stalk, when visible
• Relationship to the endometrium and junctional zone
• Signal characteristics, diffusion, and enhancement
• Degeneration, hemorrhage, necrosis, or suspicious solid tissue
• Relationship to ovaries, ureters, bowel, bladder, and pelvic sidewall
• Features that argue against uterine origin

Practical search sequence

Identify both ovaries independently before assigning an adnexal origin. In three planes, follow the interface between the mass and uterus for a myometrial claw, a stalk, or bridging vessels. Review T1-weighted images for blood or fat, T2-weighted images for tissue architecture, diffusion-weighted images with the ADC map, and post-contrast images for viable enhancing tissue. A negative claw or bridging-vessel sign does not exclude uterine origin when the lesion is very large, degenerated, or broadly attached.