Pregnancy associated endometriosis with pronounced stromal myxoid change

A case of endometriosis presenting as a mass in the groin of a pregnant woman is described. The mass increased in size during the pregnancy and the radiological features were suspicious of malignancy. Histological examination showed atrophic glands set in an abundant stroma. This was not typical of normal endometrial stroma but had a pronounced myxoid appearance with areas of decidualization. The atypical site of the endometriosis together with the unusual stromal changes resulted in diagnostic confusion. Although stromal decidualization is well recognized in endometriosis in pregnancy, pronounced myxoid change appears unusual. The myxoid change in this case may be a degenerative phenomenon related to pregnancy.