Lateral distribution of nonendometriotic benign ovarian cysts
Correspondence: Dr P. Vercellini, Clinica Ostetrica e Ginecologica ‘Luigi Mangiagalli’, Università di Milan, Via Commenda, 12–20122 Milano, Italy.
To investigate the left- and right-sided distribution of nonendometriotic benign ovarian cysts, data were collected on 406 women undergoing first-line surgery for tumours with various histotypes. Considering the unilateral cysts, the observed proportion of left lesions was 65/129 (50.4%) in the serous, 38/79 (48.1%) in the mucinous, 59/134 (44.0%) in the dermoid, 11/21 (52.4%) in the parovarian, and 3/7 (42.9%) in the miscellaneous cysts group, without significant differences from the expected 50%. This contrasts with the finding of a significantly more frequent development of endometriomas on the left ovary, and suggests that the pathogenesis of endometriotic and nonendometriotic cysts is different.
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The proportion of left ovarian endometriotic cysts is significantly higher than the expected 50%1. This seems against the coelomic epithelium metaplasia or embryonic cell rest theories 2 because they would not explain a major asymmetry in the frequency distribution of left- and right-sided lesions. Thus the menstrual reflux theory seems more likely, as the chance of gonadal implantation of the regurgitated endome-trial cells may be influenced by the anatomical differences of the left and right hemipelvis1. However, little is known about the lateral distribution of nonendometriotic benign ovarian cysts. An asymmetry of ovarian endometriomas, but not of cysts with other histotypes, would strengthen the evidence supporting a different origin. Given this background, we investigated the left- and right-sided distribution of nonendometriotic benign ovarian cysts in a large series of women operated in the same time period considered in our previous study1. According to our hypothesis, cysts arising from coelomic mesothelium (serous and mucinous cysts), germinal tissue (dermoid cysts), and remnants of the mesonephric ducts (parovarian cysts) should be distributed equally on both sides.
Clinical records were retrieved of consecutive women with nonendometriotic benign ovarian cysts undergoing first-line conservative or definitive surgery between January 1990 and December 1997 at the First Department of Obstetrics and Gynaecology of the University of Milan. Women with genital malformations and those who had undergone previous abdominal surgery, except appendectomy, were excluded. Indications and age at surgery, height, weight, parity, and side and size of the ovarian cyst were recorded. When two or more cysts were present in the same gonad, only the one with the largest diameter was considered. The pathologist classified cysts as follows:
- 1Serous: uni-or multilocular cystic or papillary tumours filled with clear watery fluid or thin mucoid material and lined with a single layer of flattened to cuboid, or pseudostratified, tubal-type epithelium;
- 2Mucinous: uni- or multilocular cystic tumours containing thick mucinous material and lined with a single layer of uniform tall columnar cells;
- 3Dermoid, tumours with a smooth, grayish white glistening surface, a cavity filled with fatty material and hair, a typical embryonic nodule and usually lined by skin with dermal appendages;
- 4Parovarian: smooth or lobulated tumours originating in the mesovarium, containing clear fluid, and lined by relatively uniform cuboid epithelial cells3.
The frequency of left- and right-sided ovarian cysts was analysed with the %2 test to compare observed and expected events. The 95% confidence interval of the proportion of left cysts was computed using the normal approximation.
In the study period 406 women underwent first-line surgical treatment for nonendometriotic benign ovarian cysts (Table 1). The vast majority were self-referred for various conditions to a tertiary care academic centre specialising in endoscopic and conservative surgery. Mature cystic teratoma was the most frequent diagnosis (n= 154, 37.9%), followed by serous (n= 139, 34.2%) and mucinous cyst (n= 82, 20.2%). As expected, women with dermoid cysts were younger and more frequently nulliparous than those with serous ones, and the mean largest lesion diameter was found in the subgroup with mucinous tumours (Table 1). In women with unilateral cysts, the observed proportion of left-sided lesions was 65/129 in the serous (50.4%, 95% CI 41.5 to 59.3); 38/79 in the mucinous (48.1%, 95% CI 36.7 to 59.6), 59/134 in the dermoid (44.0%, 95% CI 35.5 to 52.9), 11/21 in the parovarian (52.4%, 95% CI 29.8 to 74.3), and 3/7 in the miscellaneous histotypes cyst group (42.9%, 95% CI 9.9 to 81.6). None of the observed proportions was significantly different from the expected 50%. The dermoid cysts seemed to develop more frequently in the right ovary, although not significantly so (χ21, 1.91, P= 0.167). Pooling of all the unilateral cysts confirmed a similar distribution between the two gonads (176 left-sided and 194 right-sided lesions, χ21, 0.88, P= 0.349). Fifteen patients with ovarian fibroids (five on the left gonad, nine on the right one, and one on both) were not included in the analysis.
Table 1. Clinical characteristics, indication for surgery, and lateral distribution of ovarian cysts in the 406 women studied. Values are given as mean(SD) or n [%].
|Age (years)||44.8 (15.7)||40.1 (12.9)||35.5 (12.6)||35.8 (13.3)||42.2 (14.2)|
|Nulliparous||57 [41.0]||30 [36.6]||90 [58.5]||8 [34.8]||3 [37.5]|
|Body mass index (kg/m2)||23.0 (4.7)||22.3 (4.2)||22.1 (3.5)||24.4 (2.9)||21.9 (3.9)|
|Cyst diameter (cm)||5.8 (2.8)||7.3 (5.9)||6.0 (3.1)||4.3 (3.6)||3.8 (1.8)|
|Indication for surgery|| || || || || |
| Infertility||8 [5.8]||5 [6.1]||10 [6.5]||2 [8.7]||1 [12.5]|
| Pelvic pain||45 [32.4]||28 [34.1]||69 [44.8]||5 [21.7]||2 [25.0]|
| Adnexal mass||47 [33.8]||29 [35.4]||44 [28.6]||11 [47.8]||4 [50.0]|
| Mixed||39 [28.0]||20 [24.4]||31 [20.1]||5 [21.7]||1 [12.5]|
|Left-sided cyst||65 [46.8]||38 [46.3]||59 [38.3]||11 [47.8]||3 [37.5]|
|Right-sided cyst||64 [46.0]||41 [50.0]||75 [48.7]||10 [43.5]||4 [50.0]|
|Bilateral cysts||10 [7.2]||3 [3.7]||20 [13.0]||2 [8.7]||1 [12.5]|
In this large series of consecutive women undergoing surgery for benign ovarian cysts, no significant difference was observed in the proportion of left- and right-sided lesions in any of the study groups. This is at odds with the finding of a significantly more frequent development of endometriomas on the left ovary1.
Information was abstracted from clinical records by three experienced research fellows, and the time period considered is the same as that of our previous study of endometriotic ovarian cysts1. No case was excluded with the exception of those specified in the research protocol and all the diagnoses were based on the pathological report. The surgeons who recorded the clinical data and the pathologist who performed the histological examination were unaware of the hypothesis of the study.
Serous and mucinous cysts develop from metaplasia of the surface epithelium and subjacent stroma of the ovary, mature cystic teratomas or dermoid cysts derive from primitive germ cells of the embryonic gonad, and parovarian cysts are classified among tumours of probable wolf-fian origin3. The observed symmetric lesion distribution between the two gonads suggests that the pathogenesis of cysts with the histotypes considered is different from that of ovarian endometriomas. In our view, when the lesion has an intrinsic ovarian origin, its lateral distribution is symmetric as expected, whereas when the cause is extrinsic (e.g. refluxed and implanted endometrial cells4,5), the lesion distribution is influenced by anatomical factors6, and the difference between the left and right hemipelvis (namely, the presence of the sigmoid) may determine an asymmetry ‘in favour’ of the left gonad.