It has been reported that 40% - 50% of childhood ovarian masses are nonneopalastic, and the majority of ovarian neoplasms in children arise from germ cells [1,2]. A small proportion of ovarian tumors in children (approximately 15% - 20%) is derived from the ovarian epithelium. Such epithelial ovarian tumors are commonly found in adults, but these tumors, including serous and mucinous types, are extremely rare in premenarchal girls [3-5]. Each mucinous ovarian tumor can be further characterized as benign, malignant, or of low malignant potential, with this latter group recognized as borderline tumors [6]. We present herein the case of a mucinous borderline ovarian cystadenoma in a 12-year-old premenarchal girl, and reviewed the cases of mucinous ovarian tumors in premenarchal girls reported in the medical literature.

A 12-year-old premenarchal girl noticed lower abdominal distention about 1 year prior to presentation. She sometimes experienced abdominal pain and constipation, but disregarded those symptoms as not severe enough to prevent the activities of daily life. She consulted a nearby clinic after increasing abdominal distention was detected by her family. She was referred to our hospital after identification of the abdominal tumor by that clinic. Abdominal contrast-enhanced computed tomography (CT) showed a large multilocular tumor with clear boundaries spreading throughout the entire abdominal cavity from the right upper quadrant to the pelvic cavity (Figure 1). The maximum diameter of each cyst was around 15 cm. Cyst contents were homogenous and cyst walls were not enhanced. The tumor compressed the whole bowel and uterus to the left. On magnetic resonance imaging (MRI) lesions showed high intensity on T1-weighted imaging and low intensity on T2-weighted imaging (Figure 2). Carbohydrate antigen 125 (CA125) level was 45.5 IU/l, showing a slight elevation, but the other tumor markers were with normal ranges.

The patient underwent laparotomy with a small lower abdominal incision, as preoperative findings suggested poor malignant potential of the tumor. The tumor was brought out little by little with aspiration of the fluid contents from inside the tumor, which amounted to 4280 ml of serous yellow fluid. Prevention of fluid spillage was then taken into consideration. The tumor was found to originate from the left ovary, independent of surrounding organs and with no adhesion to the small intestine or colon. The patient underwent left oophorectomy

because the right ovary and bilateral adnexa appeared normal. The tumor measured 26 × 18 cm and weighed 5860 g (Figure 3). Intraoperative frozen section of cystic wall showed mucinous cystadenoma. Microscopic examination after the operation showed multilocular lesions with a papillary structure displaying multiple layers

of columnar mucus-producing epithelium. Histological diagnosis was mucinous ovarian cystadenoma with borderline malignancy, as cell dysplasia suggestive of carcinoma was not present and no stromal invasion was identified (Figure 4).

Postoperative course was uneventful. Serum CA125 level normalized within 3 months and menarche occurred 5 months later. No evidence of recurrence has been seen as of 2 years postoperatively.

Mucinous ovarian tumor is rare in children, with only 16 cases in premenarchal girls reported to date [3-5,7-15]. These cases are summarized in Table 1. In all cases, age was more than 10 years and signs and symptoms were vague and non-specific. Abdominal pain presented in cases with torsion, but many of the remaining cases only displayed abdominal distension, as in our case. Many patients presented with large tumors, with some as much as 6 - 7 kg. The extent of tumor enlargement seems attributable to the mildness of the associated abdominal symptoms.

Histological findings included cystadenoma in 9 cases, cystadenocarcinoma in 2 cases, and borderline malignnancy such as in the present patient in 5 cases. Borderline ovarian tumor (BOT), which comprises about 10% - 15% of all epithelial ovarian malignancies, is characterized pathologically by features of malignant tumors, including cellular proliferation, stratification of the epithelial lining of the papillae, nuclear atypia, and mitotic activity, but without destructive stromal invasion [6]. Those findings were identified in our case, so BOT was diagnosed. In this review of premenarchal mucinous ovarian tumors, all BOT cases were stage I and all patients with BOT or adenoma were alive without recurrence as of final follow-up.

CA125 has been widely used as a marker of ovarian tumors. In the cases we reviewed, CA125 levels were increased in three of four BOT cases measured, but only two of nine cases adenoma cases. Serum CA125 levels in BOT cases, including the present case, tended to be high compared to levels in adenoma cases. CA125 level at initial diagnosis is reportedly associated with prognosis in adult BOT cases [16]. Conversely, CA125 shows a high false-positive rate and poor sensitivity and specificity for epithelial ovarian malignancies, so the real utility of CA125 as a marker of ovarian tumors is unclear [5,17]. If the preoperative CA125 level is high as in our case, this value seems useful for identifying recurrent or residual disease [8,15].

Guidelines for surgical treatment of BOT resemble those for ovarian cancer, and include total hysterectomy, bilateral salpingo-oophorectomy and staging procedures in women who do not wish to become pregnant in the future. However, fertility is an important issue for premenarchal children. The role of fertility-sparing surgery has been discussed in adult cases, as the prognosis of BOT is excellent and the lesion tends to arise during the child-bearing years. Some reports have compared the fertility-sparing surgery with radical surgery [16,18]. In those studies, the recurrence rate was somewhat higher in the fertility-sparing group than in the radical surgery group. In the fertility-sparing surgery group, the most common pattern of recurrence was isolated recurrence in the remaining ovaries. In these women, recurrence appears amenable to successful salvege with repeated surgery. Cystectomy may have a greater chance of preserveing fertility, but is associated with higher recurrence rates than those seen after oophorectomy. Salpingo-oophorectomy has thus been recommended as fertility-sparing surgery [3,15,16,18]. In our case, oophorectomy was performed with a small incision because intraoperative frozen-section histopathological examination indicated mucinous cystadenoma and the contralateral ovary was intact. In this review of premenarchal BOT, all cases underwent salpingo-oophorectomy or oophoretomy, and were alive without recurrence as of the last follow-up. Salpingo-oophorectomy or oophoretomy for premenarchal BOT appears appropriate when the operative findings reveal localized unilateral disease.