Adenomyosis is diagnosed on MRI by a junctional zone (JZ) thickness >12 mm. The junctional zone represents the innermost layer of the myometrium (subendometrial myometrium). Which MRI finding most reliably distinguishes diffuse adenomyosis from leiomyoma on T2-weighted imaging?

• A Leiomyoma: high T2 signal centrally; adenomyosis: uniform T1 hyperintense signal throughout
• B Leiomyoma: well-defined T2 low-signal mass with pseudocapsule; adenomyosis: poorly defined T2 hypointense thickening of junctional zone ≥12 mm without distinct margin ✓
• C Leiomyoma: multiple cystic foci on T2; adenomyosis: single dominant T2 hypointense mass
• D Both appear identical on T2-weighted MRI; gadolinium enhancement is required for differentiation

Explanation

On T2-weighted MRI, leiomyoma appears as a well-defined, rounded, low-signal intensity mass (dark on T2) with a surrounding pseudocapsule of compressed myometrium — the sharp margin and discrete mass-like appearance are characteristic. Adenomyosis appears as diffuse or focal thickening of the junctional zone (JZ ≥12 mm is diagnostic; JZ ≥8 mm is equivocal) with poorly defined borders, T2 hypointensity due to smooth muscle hypertrophy, and often interspersed small T2 hyperintense foci (ectopic endometrial glands). The lack of a pseudocapsule and the ill-defined infiltrative pattern distinguish adenomyosis from fibroid.

Reference: Shaw's Textbook of Gynaecology, 17th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.