Endometrioma

Endometriosis is the presence of functional endometrial tissue outside the uterine cavity and the myometrium. It is an important cause of infertility and pelvic pain in women older than 25 years. Endometriomas are relatively common and can mimic other adnexal masses, and ultrasonography is often the first choice of imaging.
The typical findings of endometriosis are endometriotic implants, endometriomas, and adhesions. Implants may measure from a few millimeters to a few centimeters and may be superficial or deep. Endometriotic cysts (endometriomas) usually occur within the ovaries and result from repeated cyclic hemorrhage. More than 90% of endometriomas are pseudocysts formed by invagination of the ovarian cortex, which is sealed off by adhesions. Endometriomas may completely replace normal ovarian tissue. Cyst walls are usually thick and fibrotic and frequently have dense fibrous adhesions and areas of discoloration. Cyst content generally is composed of thick, dark, degenerate blood products, and this appearance has been called "chocolate cyst." (1).
Ultrasound is often the initial screening test for endometrioma and for follow-up of known endometrioma (2). The sonographic features of endometriomas are varied and range from anechoic cysts to cysts with diffuse low-level echoes to solid-appearing masses. Fluid-fluid or debris-fluid levels can also be seen. One of the more commonly occurring appearances of endometrioma is that of an adnexal mass with diffuse low-level echoes. This appearance is seen in 95% of endometriomas.(3). The "classic" endometrioma has been described as a homogeneous hypoechoic focal lesion within the ovary with diffuse low-level internal echoes. Absence of acoustic streaming may also support the diagnosis of endometriomas.