Morphological variations of scar-related and spontaneous endometriosis of the skin and superficial soft tissue: A study of 71 cases with emphasis on atypical features and types of müllerian differentiations

Abstract

Seventy-one cases of scar-related and spontaneous endometriosis of the skin and superficial soft tissue were studied, with a focus on atypical features and types of müllerian differentiation. All patients were women, whose ages ranged from 22 to 65 years (median, 32 years). Histological, immunohistochemical, and electronmicroscopic studies were performed. Clinical information was ascertained via a questionnaire solicited by the referring physicians. All types of metaplastic changes of müllerian epithelium were found, including tubal (61%), oxyphilic (15%), hobnail (10%), mucinous (4%), and papillary syncytial (3%) metaplasia. Atypical features included reactive atypia (23%) and atypical mitoses in glandular epithelium (6%). Stromal changes included smooth muscle metaplasia (31%), decidualization (<1%), stromal endometriosis (<1%), and elastosis (<1%). Other features recognized included lipoblast-like cells (15%), some with intranuclear inclusions; atypical/degenerative myocytes (10%); spiral arteries (4%); and perineurial invasion (<1%). CD56 staining identified large granular lymphocytes in 15 of 20 studied specimens. Ultrastructurally, these cells showed cytoplasmic granules, some with a delimiting membrane. This study utilizes tissue specimens that mainly were received as consultations; therefore some inherent selection bias exists. Specimens were randomly selected for CD56 immunostaining, leading also to potential sampling error. All types of müllerian metaplasia can be encountered in cutaneous endometriosis. In addition, so-called atypical features described in endometriosis affecting other anatomic sites may be seen in the skin. Some features may represent a diagnostic pitfall.