The finding of endometrial metaplasia is rare with only a few published cases, being perhaps most common type bone metaplasia. Smooth muscle metaplasia is included within endometrial mesenchymal metaplasia, and although rare, is probably the most common mesenchymal metaplasia. Probably in most cases go unnoticed classified as diffuse fibroids.

It seems that there is presence of endometrial cells with multipotential capacity to differentiate into endometrial stromal as well as smooth muscle fibers. In fact, it is not uncommon to find small pockets of smooth muscle within the endometrial stroma, sometimes being classified as endometrial foci leiomyomas.

The pathology of our case suggests of multiple formations with myomatous appearance, with diameters ranging from 0.3 to 1 cm that occupies a total volume of 3.5 cc. Countless microscopically smooth muscle proliferation without atypia is seen swirling in transition with endometrial stroma and the diagnosis of stromal nodular metaplasia with leiomyoma differentiation is established.

There appears to be similarities between the cases of endometrial leiomyoma and endometrial smooth muscle metaplasia that could be considered as the same entity and is the pathology and the existence of smooth muscle proliferation in endometrial stromal transition, that gives the key aspects for the diagnosis smooth muscle metaplasia.

This is a very rare condition with only a few well-documented cases. To our knowledge this is the first hysteroscopic image of this condition. We have found another similar picture, but it was a subendometrial leiomyomata.