The inner layer of the myometrium is known as the ______ zone.

• A. Junctional
• B. Subendometrial
• C. Stratum Basalis
• D. Outer Myometrium

Answer: (A)

The inner portion of the myometrium is the junctional zone. This is the thin band of muscle directly surrounding the endometrium, forming a distinct layer that separates the endometrium from the bulk of the myometrium. On ultrasound it often appears as a relatively uniform, hypoechoic stripe between the endometrium and the outer myometrium. This zone is the region that can remodel during the menstrual cycle and in early pregnancy, and thickening or irregularities of it are clinically relevant for conditions like adenomyosis. The other terms don’t describe this specific inner muscular layer: the subendometrial area refers to tissue just beneath the endometrium but is not the inner myometrium itself; the stratum basalis is a layer of the endometrium, not the myometrium; and the outer myometrium is the outer muscular layer, not the inner, junctional zone.