Disease classification
Our classification system identifies 2 types of endometriomas on the basis of their etiologies and characteristics. Type I, which arise from endometrial tissue implanted on the ovarian surface, are also called true endometriomas. Invagination of cortex and subsequent hemorrhage from endometrial tissue result in cyst formation. Endometrial tissue (endometrial stroma and glands) is histologically present in all type I endometriomas.1,4,9 These endometriomas usually are small (<5 cm in diameter) and have a densely adherent fibrous capsule.4 Often, there is no clear plane between cyst wall and ovarian stroma.3
Type II endometriomas arise from functional cysts involved in or invaded by cortical or pelvic side-wall endometrial implants or by type I endometriomas. Type II endometriomas are subclassified by the extent of endometrial implant involvement in the cyst wall. Type IIA endometriomas are hemorrhagic cysts with less than 10% of endometrial tissue within the cyst wall. Similar to the functional cysts from which they originate, type IIA endometriomas have a cyst wall that is separated easily from ovarian tissue during surgery.4,7,9 Although type II endometriomas tend to be larger than their type I counterparts, in some cases they are identified at an early stage of 2 to 5 cm. Endometriomas larger than 5 cm are almost always type II.4
Type IIB and IIC endometriomas have endometrial implants and fibrosis within their cyst walls, with progressively more endometrial invasion in type IIC endometriomas (>50%) than in type IIB (10% to 50%). Consequently, type IIB cysts are relatively easy to dissect from ovarian tissue, except adjacent to an endometriotic area where the cyst densely adheres to the ovarian stroma. In type IIC, endometrial tissue more extensively penetrates the capsule, making dissection of diseased tissue from the ovarian stroma more difficult; in fact, separating type IIC cyst wall from ovarian stroma can be as challenging as excising a type I endometrioma.7 In most cases, a type IIC cyst is attached by adhesions and fibrosis to the pelvic side wall or uterus and ruptures during mobilization (TABLE).
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Imaging the endometrioma and mature cystic teratoma
Presentation and diagnosis
Almost all patients with an endometrioma concurrently have peritoneal endometriosis, which is characterized by dysmenorrhea, dyspareunia, chronic pelvic pain, infertility, and, in some cases, gastrointestinal or genitourinary dysfunction.1 Pelvic examination may reveal an adnexal mass that is an endometrioma, or an endometrioma may appear on imaging obtained in a pelvic pain or infertility work-up. Given its 73% sensitivity, 94% specificity, safety, and low cost, transvaginal ultrasonography is the preferred imaging modality for endometrioma.3 The characteristic ultrasonographic appearance is that of a round, homogeneous, fluid-filled mass with low-level echoes.1 Magnetic resonance imaging is appropriate when a more sensitive imaging modality is indicated, as for a patient with risk factors for malignancy.3,10–12