**7. The theory of the secondary Mullerian system**

Lauchlan (1972) first used this term to describe the propensity of the peritoneum which covers the ovary and the lower peritoneal cavity to Mullerian differentiation. The mesothelial covering and the sub-mesothelial stroma of peritoneum exhibit a full spectrum

Pathological Aspects of Endometriosis 105

common site (36%) the fallopian tubes, uterus and cul-de-sac account for 6-14% of biopsies, and the uterosacral ligaments account only for 2% of specimens examined. On a clinical basis, 5-12% of women present extrapelvic endometriosis and in descending order in the sigmoid, the appendix, and omentum, on operative scars and in inguinal region. Rarely endometriosis is observed in distant sites such as lungs, brain, bones and skin (Jenkins et al,

Endometriosis during pregnancy presents a variable behavior among different patients and a variable behavior in the same patient during different pregnancies. The endometriotic lesions usually shrink and an amelioration of the symptoms is observed. In early pregnancy the lesions may enlarge and bleed. The endometriotic stromal decidual transformation during pregnancy may cause softening and rupture of the lesion causing acute abdomen

In patients with extensive abdominal endometriosis, a sero-sanguinous ascites may occur and in one third of these patients a right pleural effusion may be observed. In these cases, there is also present an ovarian lesion caused by endometriosis, and the whole clinical picture is consistent with malignancy. The exact mechanism of the development of ascites and the pleural effusion is not clear, and as the most probable cause is considered the

The location and the age of the endometriotic lesion and the patients' age affect the morphological appearance of endometriosis and may lead to diagnostic difficulties. Gross appearance of endometriotic lesions is affected by their age and this is reflected by the various colors they present. Red color characterizes early lesions and yellow-red color reflect the breakdown of blood products. These lesions eventually progress into old or advanced lesions presenting black color. Hemosiderin is indicated by a yellowish color and occasionally white lesions may be observed indicating the presence of fibrosis. It is possible that the same patient presents endometriotic foci in various stages of development. The size of the lesions varies as well. In early stages blister-like blebs are observed measuring 0.2-0.3 cms in diameter, corresponding to the early red lesion observed mainly in adolescents .As the lesions age, they may enlarge up to 1 cms in diameter and are pigmented , bluish-red, black and eventually white and puckered because of fibrosis. Endometriotic foci are frequently associated with adhesions. The older the patient the more fibrotic the endometriotic lesion is and eventually it atrophies with obliteration of its components Endometriotic lesions become grossly cystic only in the ovaries reaching a diameter up to 15 cms. Ovarian endometriotic cysts present a fibrous wall of various thickness and are filled by chocolate-like contend. The interior surface may be smooth or shaggy. Rarely, endometriosis obtains the form of polypoid masses projecting from serosal surfaces and is

**11. The effect of pregnancy on endometriosis** 

**12. Eendometriosis may cause a Meigs-like syndrome** 

**13. Gross features of endometriosis** 

referred as polypoid endometriosis.

stimulation of the mesothelial layer by the endometriosis to produce ascites.

1986).

and hemoperitoneum.

of Mullerian differentiation from benign to malignant .Many lesions of secondary Mullerian system are described, which are benign, such as endosapingiosis, endocervicosis, of low grade of malignancy, serous and mucinous and malignant ,described as extraovarian peritoneal serous and mucinous carcinomas. The sub-mesothelial stroma gives rise to peritoneal leiomyomatosis and may undergo decidual reaction .Amongst the lesions of secondary Mullerian system are also classed lesions of the retroperitoneal lymph node such as Mullerian inclusions, leiomyomatosis and decidual reaction. Endometriosis is considered as the main lesion of the secondary Mullerian system (Clement & Young, 2008) It has been postulated that the peritoneum of the lower abdominal cavity retains the ability to differentiate to Mullerian tissues due to the proximity to the coelomic epithelium from which the primary Mullerian system is derived. Lauchlan (1994) proposes that the development of peritoneal Mullerian lesions may be secondary to the proximity of pelvic peritoneum to tubal fibria, and the exposure of the peritoneal surfaces to external agents , such as talk, that stimulate the peritoneal Mullerian differentiation.
