Since the junctional zone myometrium started to be investigated by MR imaging, every abnormality observed has been described as indicative of the presence of endometrium in the outer myometrium or adenomyosis sensu stricto

This condition is expressed mainly by a pathological thickening or abnormality of the subendometrial myometrium (myo- metrial halo or junctional zone).

Proliferation and hyperplasia in the junctional zone may precede the outgrowth of endometrial cells. Leyendecker et al. speculated that disruption of the specific uterine micro- environment in the basal endometrium may explain the structural and functional abnormalities of the junctional zone, such as hyperperistalsis, dysperistalsis, and inordinate smooth muscle proliferation associated with endometriosis and adenomyosis.

There is growing evidence that a pre-pregnancy disorder of the myometrial junctional zone  is at the  basis of defective deep placentation which, in turn, is associated with major reproductive and obstetrical complications.

Today, the investigation of reproductive outcomes in young women with junctional zone abnormalities and/or adenomyosis has become possible—thanks to MR imaging and ultrasonography; using these techniques, an improved and clinically useful correlation with histology-based diagno- sis for adenomyosis has been accomplished, thanks also to the analysis of the myometrial junctional zone. The importance of myometrial junctional zone research in reproductive medicine is frequently underestimated: indeed, the inner myometrium is the critical zone for the adequate transformation of spiral arteries supplying maternal blood to intervillous spaces of the placenta and a defective transformation of myometrial spiral arteries in the placental bed has been associated with major obstetrical syndromes.

The disappearance of the distinct myometrial zonal anatomy very early during pregnancy on MR imaging has also been observed in a unique case report by Turnbull et al.

This may correspond to the early decidualization process of the myometrial spiral arteries in the placental bed well before the zone is colonized by intravascular and interstitial trophoblast .

A junctional zone thickness increase was significantly correlated with implantation failure at IVF: implantation failure rate was 95.8% for patients with an average junctional zone greater than 7 mm and a maximal junctional zone greater than 10 mm, versus 37.5% in other patient groups (p<0.0001), independently from cause of infertility or patients’ age. The authors concluded that a pelvic MR scan showing a thickened uterine junctional zone has a negative predictive factor for embryo implantation after IVF.