Histological analysis of the uterine junctional zone as seen by transvaginal ultrasound

This study aimed to investigate the histology of the subendometrial halo, the junctional zone between the endometrium and myometrium.

Thirteen ex vivo uteri removed for treatment of menorrhagia were studied. In each case, the subendometrial halo, as seen by transvaginal ultrasound, was marked using a Nottingham breast location biopsy needle. A standard histological examination was performed. Full thickness blocks of the anterior uterine wall were taken and standard serial 5-micron tissue sections were prepared from each block. Subsequent morphometric analysis followed staining with Feulgen reagent, using a CAS 200D quantitative image analysis system. Additionally, anti-CD31, an antibody stain for vascular endothelium, was used.

The histological examination showed the subendometrial halo to consist of apparently normal myometrium. Morphometric analysis demonstrated a greater total nuclear area in the subendometrial halo than the outer myometrium, but no difference in individual nuclear size between the two zones. CD31 stained a greater total area in the inner myometrium.

These results suggest that the subendometrial halo is a distinct compartment of the myometrium comprising tightly packed muscle cells with an increased vascularity. Such architecture would increase the density of this tissue layer, altering its acoustic impedance, and account for its echopenic appearance on ultrasound.