On MRI of the female pelvis, 'junctional zone' thickness >12 mm is the MRI criterion for diagnosing which condition?

• A Submucosal fibroid
• B Adenomyosis ✓
• C Endometrial carcinoma
• D Leiomyosarcoma

Explanation

The junctional zone (JZ) is the inner myometrium seen as a band of low T2 signal on MRI, representing compact smooth muscle. An MRI criterion of JZ thickness >12 mm (or JZ max/myometrium ratio >40%) is diagnostic of adenomyosis, reflecting diffuse infiltration of endometrial glands and stroma into the myometrium causing muscular hypertrophy. JZ 8–12 mm is equivocal. JZ <8 mm effectively excludes adenomyosis. Submucosal fibroids are discrete low-T2 masses that distort the endometrial cavity. Endometrial carcinoma disrupts the JZ but is measured by endometrial stripe thickness.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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