Pathology

The most common sites of endometriosis, in decreasing order of frequency, are the ovaries, anterior and posterior cul-de-sac, posterior broad ligaments, uterosacral ligaments, uterus, fallopian tubes, sigmoid colon, appendix, and round ligaments. Other sites less commonly involved include the vagina, cervix, and rectovaginal septum. These latter lesions usually result from extension and invasion of posterior cul-de-sac implants. Uncommon locations include the inguinal canal, abdominal or perineal scars, ureters, urinary bladder, umbilicus, kidney, lung, liver, diaphragm, vertebrae, and extremities.

Macroscopic Appearance Endometriotic implants have a variety of appearances. Superficial lesions on the ovarian or peritoneal surface are commonly reddish maculae or nodules similar in consistency to normal endometrium. These implants vary from 1 millimeter to several centimeters in size. Collection of hemosiderin results in yellow-brown or black discoloration (“powder-brown” lesions). Nonpigmented disease appears as whitish opacified peritoneum, translucent blebs, or pinkish polyploid implants. Scarring with retraction of adjacent peritoneum and peritoneal pockets may occur. Endometriosis also may appear as a deeply infiltrative disease.

Tumorlike masses form from invasion, and diffuse fibrosis usually develops in the posterior cul-de-sac, pelvic sidewall, or posterior broad ligament and ovary and may extend deep into the retroperitoneal space, occasionally constricting the ureter. Lesions in the cul-de-sac may invade the rectovaginal septum. The rectosigmoid and small bowel may become adherent to these areas. Endometriotic foci on the ovarian surface may develop a fibrous enclosure and manifest cyst formation as a result of accumulation of fluid and blood. These endometriotic cysts (endometriomas) vary from several millimeters to over 10 centimeters in size. Bleeding with menses gives the cyst a dark red or bluish hemorrhagic color. The degradation of blood pigment over time results in thick, tarry contents, hence the term chocolate cysts.

Occasionally, the content changes to a yellow straw color or clear fluid. Filmy or dense fibroid adhesions from these cysts to the pelvic sidewall and fallopian tubes are common and may obscure visualization of the cyst.

Microscopic Appearance Endometriosis is histomorphologically similar to eutopic endometrium. The four major components of endometriotic implants are endometrial glands, endometrial stroma, fibrosis, and hemorrhage. The relative amount of each component is highly variable and dependent, in part, on the age and location of the lesions. Identifying the endometrial elements in individual implants requires an adequate tissue specimen, proper orientation, and often serial sections of the specimen. The endometrial glands in ectopic implants lack uniform size and shape. The glands may show normal cyclic change with mitotic figures and pseudostratification in response to estrogen, or vacuoles and intraluminal secretion in response to progesterone. The response to endogenous and exogenous hormones is inconsistent. This may imply differences in steroid hormone receptor content and function or a loss of the normal gland-stromal interaction. When glands are responsive, the epithelium becomes attenuated, and hemorrhage ensues at the time of menstruation. The stromal cell morphologies of ectopic and eutopic endometrium are similar. Small arterioles, similar to the spiral arterioles of normal endometrium, usually are present in implants. Interstitial hemorrhage with accumulation of blood products and hemosiderin-laden macrophages is a frequent finding. Fibrosis may occur in older endometriotic implants. This is very common in the lining of endometriomas, where the only histologic finding may be fibroblast proliferation and hemosiderin pigment deposition.

Classification of endometriosis appropriate to the localization:

1. Genital endometriosis (external (intraperitoneal and extraperitoneal) and internal).

2. Extragenital endometriosis.

Internal genital endometriosis – process that develops inside muscle tunic of uterus (internal endometriosis of corpus uteri or adenomyosis), isthmus, cervical canal (endocervix) and of interstitial part of uterine tube.

External genital endometriosis – endometriosis of other parts of uterine tube, ovaries, sacrouterine ligaments and broad ligaments of uterus, of peritoneum of rectouterine (Douglas') pouch.

Extragenital endometriosis – bladder endometriosis, intestinal endometriosis, endometriosis of postoperative laparotomy wound, endometriosis of kidney, of lungs, of conjunctiva and endometriosis with other sites.

Commonly combination of different forms of genital endometriosis or of genital endometriosis and other diseases of genitals (hysteromyoma, inflammatory processes and others) take place.

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