Teaching Case

A 16-year-old girl presented with abdominal pain and menstrual irregularities. The physical examination was unremarkable. The complete blood count and blood biochemical test were in normal limits. The tumour markers including CA 125, beta-hCG, AFP, CEA and CA 19-9 were normal.

Pelvic ultrasound (US) depicted a well-defined, heterogeneous solid mass with central necrotic areas in the right adnexa (Figure 1). The diameter of the mass was measured up to 9 cm and a small amount of ascites accompanied. Doppler US showed hypervascularity at the periphery of the lesion with rare internal vascularity (Figure 2).

Since the US features were indeterminate, pelvic MRI was performed for characterization of the adnexal mass. On T2-weighted images, the mass was solid with central hyperintensity (Figure 3). No haemorrhagic signal was obtained in the tumour. There was heterogeneous diffusion restriction. The mass demonstrated intense contrast enhancement at the periphery (Figure 4).

The patient underwent left oophorectomy with excision of the tumour. The pathological exam showed a solid nodular 10 cm ovarian mass with a tan to yellow solid cut surface. Histopathological findings confirmed sclerosing stromal tumour of the ovary.

Sclerosing stromal tumour (SST) of the ovary is a rare benign neoplasm that accounts for 2% to 6% of ovarian sex cord-stromal tumours. They are classified under the pure stromal tumour group according to WHO.

Approximately 80% of the patients are younger than 30 years including paediatric patients and young adults, which is less than patients with either thecomas or fibromas [1].

Patients may present with symptoms related to pelvic mass such as pelvic pain or menstrual irregularities [1]. Evidence of hormone production is rarely documented. Ca125 levels often stay within normal limits and massive ascites or Meigs syndrome is not frequent.

SSTs are almost always unilateral tumours and range from 1.5 cm to 21 cm in largest diameters.  They are solid tumours with well-defined borders and occasionally a large central cystic cavity may be seen. Histologically, the tumour has a pseudolobular appearance due to alternations of cellular nodules with hypocellular oedematous to markedly collagenized areas [2, 3]. The tumour vasculature is characteristic, with numerous thin-walled vessels resembling those seen in hemangiopericytoma [2].

On ultrasound images, SST is seen as a unilateral solid mass with some cystic areas in the centre or a multilocular cystic mass [4]. Colour Doppler images demonstrate increased vascularity particularly in the periphery of the lesion and between cysts. CT features are nonspecific and overlap with those of malignant ovarian tumours.

On T2-weighted images (T2WI), pseudolobular appearance with low intensity nodules in the high signal intensity stroma may be seen (lake-island sign) [5]. A thin rim of low signal intensity around the lesion accompanies the compressed ovarian stroma [6]. The central cystic areas are hyperintense on T2WI. Diffusion weighted imaging may show low SI on high b values due to its benign stromal nature [6]. Dynamic contrast-enhanced imaging may show early/fast and marked peripheral enhancement with centripetal progression and comb- or wheel-like enhancement which is characteristic for the diagnosis [5, 6].

Differential diagnosis includes a wide spectrum of ovarian tumours in the paediatrics and young adults including other sex cord-stromal tumours and malignant epithelial ovarian tumours as well as krukenberg tumours [1].

As these tumours are typically benign, tumour excision or simple oophorectomy, is the preferred treatment option.

In summary, SST is a rare benign sex cord-stromal tumour of young females. On MRI, lake-island sign on T2WI, progressive centripetal/early/fast continual and comb- or wheel-like enhancement are characteristic imaging features that reflect the microscopic pattern of the tumour.

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