Cutaneous decidualized endometriosis in a nonpregnant female: a potential pseudomalignancy

Endometriosis is a disease process characterized by ectopic endometrial tissue. Involvement most commonly occurs in the lower pelvis, outside the uterine cavity, but can occur elsewhere, including the skin. Cutaneous endometriosis is a rare manifestation of this disease, with decidualization occurring in a very small minority of cases, almost always seen in pregnant females. Cutaneous involvement of endometriosis may present a diagnostic problem for the pathologist, particularly in the event of decidualization. Decidualization may mimic a malignancy and as a result may result in unnecessary diagnostic studies for the patient. We present a case of a nonpregnant patient with decidualized cutaneous endometriosis, discuss the histopathologic and immunohistochemical features of this entity, and review the pertinent literature on this subject. To our knowledge, this is the second reported case of cutaneous decidualized endometriosis in a nonpregnant female.