Three‐dimensional ultrasonographic characteristics of endometriomata

Abstract

Endometriosis is a common condition, affecting somewhere between 5% and 60% of women of reproductive age and approximately 2 million women in the UK. The exact prevalence is difficult to ascertain and varies according to diagnostic criteria used and the populations studied, varying from 2 to 50% in women without symptoms, 40 to 60% in women with dysmenorrhea, and 20 to 30% in women with subfertility1,2. The etiology is unknown, but the disease is characterized by the objective demonstration of endometrial-like tissue outside the uterus. The condition is seen predominantly in women of reproductive age, and it occurs in all ethnic and social groups. Whilst extrapelvic disease can occur, endometriosis typically affects the pelvic organs and peritoneum. Disease severity is assessed semi-quantitatively at laparoscopy or laparotomy and is scored according to the American Society for Reproductive Medicine3, but is a poor predictor of the patient’s symptoms in many cases. The extent of the disease varies considerably; it may involve small areas of the peritoneum alone, or be associated with significant fibrosis, adhesions and nodular infiltration, in different individuals with the same symptoms1. The ovary may be involved only superficially or can contain a cyst lined with endometrial-like tissue known as an ‘endometrioma’. Endometriotic cysts have always been a controversial entity. There is no consensus as to the pathological processes which define their development or to their management in terms of the timing, type and effects of surgery. Opinion is divided as to whether these cysts arise from progressive invagination of endometriotic deposits on the ovarian cortex4,5, from metaplasia of epithelial inclusions in the ovary5,6 or because of secondary involvement of functional ovarian cysts in the endometriotic process7. The invagination theory is accepted by most, but there is no agreement as to whether the endometrial cells are superficial ovarian implants of endometriosis or they are derived through metaplastic transformation of normal ovarian cortical tissue. The invagination theory is supported by histological studies, which consistently show that these cysts are pseudocysts, with no real plane of cleavage between the endometrialtype stroma and the ovarian cortex, containing an obliterated, mostly endometrial-gland, lining8. The walls of an endometrioma are initially thin, but subsequently become fibrotic and thickened, and can give the cyst an irregular external border. Endometriomata are typically small, with 81% measuring between 30 and 59 mm in diameter9, although they can reach 15–20 cm in diameter. Is an isolated endometrioma a different disease from peritoneal endometriosis? Many women are found to have an endometrioma without evidence of peritoneal disease, and the pathophysiological mechanisms that determine how the disease is expressed remain unclear. Women with peritoneal endometriosis are thought to have reduced fertility, and surgical treatment may improve fecundity in those with minimal to mild disease10. Just how endometriosis affects fertility is unknown, but any effect probably relates to anatomical distortion and immobilization of the pelvic organs through adhesion formation and organ infiltration and/or a change in the peritoneal environment to one that is less favorable for fertilization and embryo implantation. The effect of an isolated endometrioma on fertility is less clear, and there is no definitive evidence that fertility is impaired. However, surgical intervention is often recommended when an endometrioma measures more than 3–4 cm in diameter11 and so, unsurprisingly, endometriomata represent the most frequently reported histological subtype following operative laparoscopy for the excision of ovarian cysts12. Preoperative detection of endometriomata is therefore important, and ultrasound is the investigative tool of choice in most cases. Conventional two-dimensional ultrasound has an established role in the detection of adnexal masses and in their differentiation through pattern recognition of characteristic morphological patterns13. Most studies use transvaginal rather than transabdominal ultrasound, as this approach allows a closer approximation of the probe to the ovary and the use of higher frequencies, which provide better resolution. However, transvaginal