Histology of Endometriosis

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Histological appearance of endometriosis refers to what it looks like under the microscope. This is done when a biopsy or removed tissue (excised tissue) is sent to the pathologist for confirmation.

Overall histological appearance:

“At least two of the following three microscopic features: Endometrial type glands, Endometrial type stroma, Evidence of chronic hemorrhage (hemosiderin laden macrophages)

  • Glandular epithelium commonly has metaplastic changes (tubal, mucinous, squamous, hobnail)
  • Atypical endometriosis: epithelial lining of the glands may show enlargement with abundant eosinophilic cytoplasm, cellular stratification and hyperchromatic nuclei; can be reactive but also has malignant potential and is considered the precursor lesion for endometriosis associated carcinomas (clear cell or endometrioid) (Histopathology 1997;30:249, Case Rep Oncol 2013;6:480)
  • Burnt out endometriosis: this term has been proposed for changes suggestive of endometriosis, namely central necrosis with surrounding fibrosis and pseudoxanthoma cells but lacking confirmatory features as listed above
  • Liesegang rings: acellular ring-like structures seen in areas of chronic inflammation”

Smooth muscle fibers in deep infiltrating endometriosis (DIE):

“Deep infiltrating endometriosis (deeper than 5 mm under the peritoneum) often takes the form of a nodular lesion (or `adenomyotic nodule’) consisting of smooth muscles and fibrosis with active glands and scanty stroma. Thus, among endometriotic lesions, a certain distinction is drawn between musculo-glandular lesions and glandular lesions composed of endometrial-like epithelium surrounded by a cell-producing (cytogenous) stroma. The aim of this study was to detect by immunohistochemistry, with a monoclonal antibody against muscle-specific actin, the presence of smooth muscles in 54 endometriotic lesions originating from four different pelvic locations (peritoneum, ovary, rectovaginal septum and uterosacral ligaments) and to quantify the smooth muscle content. Smooth muscles were frequent components of endometriotic lesions in pelvic locations. In addition, smooth muscles were significantly (P < 0.001) more abundant in endometriotic lesions than in their respective unaffected sites. This finding supports, at least partially, the occurrence of a metaplastic phenomenon in the pathogenesis of endometriotic lesions. The definition of distinct endometriotic entities based on the difference in the tissue composition of the lesions (endometriotic nodules versus adenomyotic nodules) is inconsistent with the very frequent presence of smooth muscle cells in endometriosis irrespective of its localization.”