On MRI, the junctional zone (JZ) thickness is the most reliable parameter for diagnosing adenomyosis. What maximum JZ thickness on MRI is considered diagnostic of adenomyosis?

• A ≥5 mm
• B ≥8 mm
• C ≥18 mm
• D ≥12 mm ✓

Explanation

The junctional zone on MRI T2-weighted images represents the inner myometrium. A maximum JZ thickness ≥12 mm is the most widely validated threshold for diagnosing adenomyosis on MRI, with sensitivity and specificity exceeding 85% when combined with other features (focal low-signal islands in myometrium, myometrial cysts). A JZ of 8–12 mm is equivocal. Values ≥12 mm are highly specific; some guidelines use ≥10 mm as the cutoff but ≥12 mm remains the most validated threshold.

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

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