The JUNCTIONAL ZONE is the measurement that carries the diagnosis, and it is a T2 finding.
Orient first
- The uterus has three layers on T2: a bright endometrium, a dark JUNCTIONAL ZONE (inner myometrium), and intermediate outer myometrium. Almost every diagnosis here is a statement about the junctional zone.
- ADENOMYOSIS is junctional-zone thickening — commonly quoted as abnormal above 12 mm, indeterminate 8–12 mm — with tiny T2-bright myometrial cysts and sometimes T1-bright foci of haemorrhage.
- A FIBROID is a well-defined, low-T2 mass with a pseudocapsule that DISPLACES the junctional zone; adenomyosis is ill-defined and expands it. That distinction decides between myomectomy and hysterectomy or medical therapy.
- The junctional zone varies with the cycle and is unreliable in the immediate post-partum period and on hormonal therapy — say what the timing was.
- Fibroid LOCATION drives management more than size: submucosal (and its degree of intracavitary extension), intramural, subserosal or pedunculated.
Acquire the study
- High-resolution T2 in three orthogonal planes, aligned to the LONG AXIS of the uterus — an off-axis plane makes the junctional zone unmeasurable.
- T1 with and without fat suppression to identify haemorrhagic foci and to separate a dermoid.
- Dynamic post-gadolinium where degeneration, sarcoma or fertility-sparing intervention is in question.
- Confirm which sequence you are on before judging any signal — see the MRI sequence primer.
- Note cycle day and hormonal status; both change the junctional zone.
The manoeuvre
- Measure the JUNCTIONAL ZONE at its thickest point on a true long-axis T2 image, and state where you measured.
- Assess for tiny T2-hyperintense myometrial cysts and for T1-bright haemorrhagic foci.
- State whether junctional-zone change is diffuse or focal, and whether it is anterior or posterior.
- For each significant fibroid: location (submucosal, intramural, subserosal, pedunculated), size, and T2 signal.
- For a submucosal fibroid, state the PROPORTION protruding into the cavity, which decides hysteroscopic resectability.
- Assess for degeneration: high T2 signal, absent enhancement, or T1-bright red degeneration.
- Assess the endometrium, the cavity, and both ovaries.
- Look for deep infiltrating endometriosis at the torus, uterosacral ligaments and rectovaginal septum if pain is the indication.
What confirms it
- Junctional-zone thickening beyond the threshold WITH myometrial cysts is characteristic of adenomyosis.
- A well-defined low-T2 mass with a pseudocapsule displacing rather than expanding the junctional zone is a fibroid.
What licenses you to exclude it
- A normal-thickness junctional zone on a well-aligned, correctly-timed study makes adenomyosis unlikely.
- ⚠️ An off-axis or badly-timed study cannot exclude it. State the limitation rather than reporting a normal uterus.
- MRI cannot reliably exclude leiomyosarcoma. Rapid growth, irregular margins, restricted diffusion and necrosis raise concern, but the report should say that tissue is the arbiter.
The classic misread
- Measuring the junctional zone on an off-axis plane.
- Calling focal adenomyosis a fibroid — the pseudocapsule and displaced junctional zone are the discriminators.
- Not stating intracavitary extension for a submucosal fibroid.