The ovary in prepubertal girls is active with a low rate of maturation and involution of follicles [25] driven by intermittent release of pituitary gonadotrophins [26]. By ultrasound approximately 2% of girls under the age of 8 years will have small cysts, which may be bilateral. True precocious puberty with elevated levels of gonadotrophins may be the cause of multiple small cysts. However, cysts with a diameter over 1 cm may be hormonally active and associated with pseudoprecocious puberty [15]. In girls aged 2–5 years old, precocious puberty may be the presentation of the McCune–Albright Syndrome, with café-au-lait spots and polyostotic fibrous dysplasia occurring at a later age [25, 27].

With puberty the ovaries increase in size and multiple small cysts are common. The ultrasound appearance is often described as multicystic if the ovaries contain more than six follicles of greater than 4 mm diameter. These cysts result from the ovarian response to pulsatile gonadotrophin secretion [28]. A multicystic ovary should not be confused with a polycystic ovary, which is defined by the ultrasound appearance of 12 or more follicles measuring 2–9 mm in diameter. This can occur in 20% of healthy women but is also associated with the polycystic ovary syndrome [29]. This syndrome of ovarian dysfunction is managed medically by gynaecologists and endocrinologists without the need for surgical intervention.

The risk of malignancy in a prepubertal ovarian cyst is very low but cysts which persist and those with solid elements on imaging should be investigated and surgical excision considered (see the discussion of ovarian neoplasms later in the chapter).

Although most ovarian cysts are asymptomatic, pain can be triggered by torsion [30] or haemorrhage. Girls with signs of precocious puberty or uterine bleeding should undergo endocrine investigations and ovarian scanning. Tumour markers, serum α-fetoprotein (α-FP) and β-human chorionic gonadotrophin (β-HCG) should be measured and the ultrasound scan repeated after an interval of a few weeks. Most ovarian cysts in this age group will resolve spontaneously [31] but persistent, hormonally active, or symptomatic cysts should be excised by an ovarian sparing cystectomy preferably performed laparoscopically.

Follicular cysts are common in adolescents. They are fluid-filled simple cysts, usually 2–3 cm in diameter that arise in the first half of the menstrual cycle. They and resolve in the second half of the cycle. However, if ovulation does not occur, they can grow to a very large volume. Corpus luteal cysts develop in the second half of the menstrual cycle and secrete progesterone. They can grow up to 6 cm in diameter before rupturing.

In addition to physiologic follicular and corpus luteum cysts the differential diagnosis of an ovarian cyst in an adolescent includes neoplasms, ectopic pregnancy, endometriosis, tubal anomalies, and the sequelae of sexually transmitted infections [25].

Histology of excised tissue will confirm the diagnosis. For functional cysts, fenestration has a low recurrence rate with the best chance of preserving ovarian tissue [3]. Cystectomy is required if a neoplastic cyst is suspected. Very large cysts and those with elevated tumour markers can be managed with open surgery through a Pfannenstiel incision. Ovarian preserving resections are the initial procedure of choice because malignant tumours are rare in cystic disease of the ovaries.

The interest in ovarian tumours is related to their great variety rather than their incidence, which is only approximately 2–3 girls per 100,000 population annually [18, 41]. A tertiary paediatric surgical centre may only see a few patients a year with ovarian tumours, three-quarters of which are benign. Malignant ovarian tumours represent only 1% of childhood cancer [42]. However, there is a larger variety of tumours arising from the ovary than from any other organ (Table 24.1). Tumours arise from the three embryological cell lines found in the ovary, with germ cell tumours being the most common, accounting for 75% of ovarian neoplasms, followed by sex cord–stromal tumours, 15%, and finally, epithelial tumours, which usually present in adolescents, making up around 10% [43–45]. The very rare variants of germ cell tumours and metastatic tumours occurring in the ovary will not be discussed. The aetiology of these tumours is largely unknown, although gonadoblastomas, are associated with chromosome anomalies and the WT1 mutation of Frasier syndrome [46, 47].

Thecomas occur rarely in the second decade, with some producing oestrogens and presenting with precocious puberty [48] and others containing androgen-producing lutein cells leading to virilisation [49]. These tumours may be calcified.

Fibromas are rare in childhood and can grow to a large size and be associated with ascites and pleural effusions (Meigs Syndrome). Fibromas have also been described in children with the basal cell nevus syndrome [50].

Gonadoblastomas contain mixed germ cell and sex cord–stromal cell elements and are frequently bilateral. They most often occur in phenotypically female patients with 46 XY or an XY mosaic karyotype [50]. Although benign, they arise in dysgenetic gonads and are associated with malignant ovarian germ cell tumours. Frasier syndrome is the association of nephropathy and gonadoblastoma in a phenotypic female with XY chromosomes and is associated with the WT1 gene [46].

Mature cystic teratomas (MCTs), also known as ovarian dermoid cysts, are the most frequently occurring ovarian tumours accounting for approximately 40% of all ovarian neoplasms in children. The cells are mostly diploid and arise in primordial germ cells which have entered meiosis [42]. All three germ layers may be present, with ectodermal elements predominating including teeth and hair (Fig. 24.3a and b). In children, these are benign tumours containing both solid tissue and cystic areas, with 10% occurring bilaterally. Late recurrent malignant germ cell tumours have been described in young adult women with a previously excised mature cystic teratoma [51].

Immature teratomas are less common than MCTs and contain immature neuroectodermal elements. A careful histological search has to be made within these tumours for yolk sac elements, which are potentially malignant.

Gliomatosis peritonei are nodules of glial tissue sited on the peritoneum or omentum and have been described in patients with immature ovarian teratomas. Studies suggest that these are metaplastic cells arising from peritoneal stem cells and not seeded from the ovarian tumour [52].

Dysgerminomas represent 11% of paediatric ovarian tumours, making them the most common malignant ovarian tumour in children. They are analogous to testicular seminomas. They are solid tumours and are bilateral in up to 15% of patients [53]. Microscopically they consist of epithelioid cells and mature lymphocytes. In addition, multinucleated cells and syncytiotrophoblastic giant cells may be present and produce β-HCG [54]. Dysgerminomas are found in mixed germ cell tumours and can arise with gonadoblastomas in dysgenetic gonads. Dysgerminomas usually present as localised stage 1 disease [55] but metastases can be found in pelvic and retroperitoneal lymph nodes, with rare haematogenous spread to the liver, lungs and bone. Serum lactic dehydrogenase is a useful tumour marker for many of these tumours [56].

Yolk sac tumours or endodermal sinus tumours are the second most common malignant ovarian tumour in children, most often arising in post-menarchal teenage girls but also rarely occurring in younger girls [57]. These solid tumours contain undifferentiated embryonic cells which produce α-fetoprotein [58]. These are aggressive tumours which spread locally in the peritoneal cavity, via the lymphatics to retroperitoneal and pelvic lymph nodes, and via the bloodstream to the liver, lungs and brain [59].

Mixed germ cell tumours make up one-third of malignant germ cell tumours and contain more than one neoplastic germ cell element, mostly dysgerminomas, yolk sac tumours, immature teratomas, and the rarer germ cell malignancies. Malignant germ cell tumours may be aneuploid and may exhibit the isochromosome 12p [60, 61]. They can produce α-fetoprotein or β-HCG [57].

Juvenile granulosa cell tumours are the most common of the stromal sex cord tumours and account for up to 10% of ovarian malignant tumours in children and adolescents [62]. They have cystic and solid elements and secrete oestrogens [63]. Mixed granulosa and thecal cell tumours also occur [64]. They are hormonally active and usually present at an early stage before spread has occurred outside the ovary. Adults with the Peutz–Jeghers Syndrome have an increased risk of developing sex cord–stromal tumours [65].

Sertoli–Leydig tumours or arrhenoblastomas are rare malignant tumours of the ovary with the majority presenting before the age of 20 years [66] and most will produce androgens [49]. Production of α-fetoprotein has also been reported [67]. They have cystic and solid elements and are usually localised to the ovary at presentation.

Epithelial cell tumours are much less common in children and adolescents compared to adults and are classified into serous and mucinous subtypes. The majority are benign or borderline with low malignant potential [68]. Borderline epithelial tumours have varying nuclear atypia but lack stromal invasion and are more common in adolescents [45, 69]. Malignant adenocarcinomas are very rare in adolescents and children [57, 70, 71]. Borderline tumours spread locally in the pelvis and have a high incidence of bilaterality. Malignant epithelial tumours spread in the peritoneal cavity to retroperitoneal and pelvic lymph nodes and via the bloodstream to liver and lungs.

Lymphomas are rare ovarian tumours in Europe and America but are the most commonly described ovarian tumour in West African children [72].