This study was reviewed and approved by the Human Ethics Committee of the University of Teikyo (trial registration number: 18-233). The medical records of 151 female patients with unilateral endometrioma, including 58 right-sided and 93 left-sided cases, from June 1, 2014, to December 31, 2019, were reviewed retrospectively. We defined the former cases as the right-sided endometrioma group (REG, n = 58) and the latter cases as the left-sided endometrioma group (LEG, n = 93). In this study, we did not include patients with recurrent endometriosis. As shown in Figure 1, of the 302 patients who underwent laparoscopic surgery for new onset endometrioma detected during outpatient examinations, 151 were excluded for the following reasons: 95 patients were excluded because they were diagnosed with bilateral endometrioma, and 56 patients were excluded for other reasons, including no cystic lesion detected during surgery (n = 23); other main ovarian cystic diseases, such as mature cystic teratoma (n = 8); ruptured endometrioma (n = 4); and prior abdominal surgery (n = 21). Since the last factor (prior abdominal surgery) was excluded after excluding other factors, this number may be an underestimation (n = 21). Among the 151 remaining cases, we performed 123 laparoscopic cystectomies, including 9 cases performed simultaneously with laparoscopic myomectomies; 9 cases with laparoscopic hysterectomies; 23 laparoscopic salpingo-oophorectomies, including 3 cases performed simultaneously with laparoscopic hysterectomies; and 5 laparoscopic-assisted cystectomies, including 3 cases performed simultaneously with laparoscopic-assisted myomectomies. The following data were collected: 1) size of the ovarian endometrioma before and during surgery; 2) ASRM score (points) ; 3) patient’s age at the time of the operation; 4) presence of adhesions predicted before the operation; 5) history of assisted reproductive technology (ART); 6) presence of complicated adenomyomas, uterine fibroids or other ovarian tumours; and 7) serum carbohydrate antigen 125 (CA125) level (U/ml). Magnetic resonance imaging (MRI) was performed in almost all cases (148/151 cases) to assess the size of the endometrioma. MRI was also used for predicting adhesions, especially in the Douglas pouch. In this study, ART included both in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). In these 151 cases, 28 patients used hormone drugs, including oral contraceptives, gonadotropin-releasing hormone agonists and others. However, conflicting results have been reported in terms of the effect of using hormone drugs prior to surgery on ASRM scores , so this factor was not considered in the present study.
Classification of endometrial lesions
To compare the tendency of endometrial lesion spread between patients with right or left ovarian endometrioma, we divided the endometrial lesion cases based on the location of the endometrioma. Briefly, the so-called ASRM score chart was divided into four parts. First, we calculated the total ASRM score for the uterine adnexa on the same side as the ovarian endometrioma and excluded the score for the endometrioma itself, as shown in Figure 2-A. Second, a similar calculation was performed for the uterine adnexa on the opposite side of the ovarian endometrioma (Figure 2-B). The remaining endometrial lesions were divided into peritoneal (Figure 2-C) or Douglas pouch endometrial lesions (Figure 2-C). In summary, we classified the ASRM scores into the following four categories: 1) “same endometrial lesions (SELs)”, including Ovary-ENDOMETRIOSIS-Superficial, Ovary-ADHESIONS and Tube-ADHESIONS on the same side as the main ovarian endometrioma; 2) “opposite endometrial lesions (OELs)”, including Ovary-ENDOMETRIOSIS-Superficial, Ovary-ADHESIONS and Tube-ADHESIONS on the opposite side of the main ovarian endometrioma; 3) “peritoneal endometrial lesions (PELs)”, including Peritoneum-ENDOMETRIOSIS; and 4) “Douglas pouch endometrial lesions (DELs)”, including POSTERIOR CULDESAC OBLITERATION. For illustration purposes, this classification is shown in Figure 2 for REG. The SEL (Figure 2-A), OEL (Figure 2-B), PEL (Figure 2-C) and DEL (Figure 2-C) scores are the total scores in each cell, as indicated by an italicized letter and thick-bordered box. In the patients with left ovarian endometrioma, the SEL and OEL scores were reversed. In this analysis, the theoretical maximum values of SEL, OEL, PEL and DEL were 36, 36, 10 and 40 points, respectively. We not only compared each average value of SEL, OEL, PEL and DEL between REG and LEG patients but also counted each number of patients with these four lesions in both REG and LEG patients.
The primary outcomes included the difference in the ASRM scores detected during laparoscopic surgery between the patients with right- and left-sided endometriomas. This difference was compared using Student’s t-test in Microsoft Excel 2016 (Microsoft, DC, USA). To assess the influence of the following 8 factors on the ASRM score, we performed a multivariate logistic regression analysis: 1) “right-sided endometrioma”; 2) “predicted adhesion”, which was defined as the detection of the possible presence of adhesion in a patient by a pelvic examination or MRI; 3) “ART history”, which was defined as patients who underwent ART; 4) “adenomyoma”, which was defined as the current presence of adenomyoma based on clinical images; 5) “uterine fibroid”, which was defined as the current presence of a uterine fibroid based on clinical images; 6) “other ovarian tumour”, which was defined as the current presence of an ovarian tumour other than endometrioma based on clinical images; 7) “positive marker”, which was defined as serum CA125 levels of 35 U/ml or higher; and 8) “large endometrioma”, which was defined as a tumour size of 50 mm or larger (described in Table 1). All statistical analyses were performed using JMP version 12 for Windows (SAS Institute, Inc., Tokyo, Japan). The data are presented as the means ± standard deviations. A p-value less than 0.05 was considered statistically significant.