Teaching Case

A 23-year-old woman presented with pelvic discomfort without bowel or genitourinary complaints. Physical examination was normal. Laboratory findings were normal except for a slightly elevated serum lactic dehydrogenase.

Transvaginal ultrasound showed a solid lobulated 8cm right adnexal mass with irregular internal echogenicity and prominent flow signal within some hypoechoic septa.
MRI confirmed a multilobulated solid mass with a small cystic component arising from the right ovary. The mass was hyperintense relative to muscle on T2-weighted images, isointense relative to muscle on T1-weighted images and was separated by enhancing septa into individual lobules.
No other pelvic findings were demonstrated. The patient underwent surgery.

Ovarian dysgerminoma (OG) is a malignant subtype of germ cells tumours (GCT), which arise from the primitive germ cell of the embryonic gonad and account for 20-25% of all ovarian neoplasms (95% of them being benign mature cystic teratoma and 5% being malignant). [1].

Dysgerminoma is the most common ovarian malignant GCT, accounting for 1-2% of primary ovarian neoplasms. Other non-dysgerminoma malignant GCT include immature teratomas, endodermal sinus tumours and mixed GCT, with embryonal carcinomas, polyembriomas and choriocarcinomas being even less common [2].

OG is considered the ovarian counterpart of the testicle seminoma [3] and, although it can occur at any age, 90% affect women in the second and third decade (10-20% of them diagnosed during pregnancy) [4].

Bilaterally is seen in 10-17% of the cases [5].

The risk of dysgerminoma increases in 46XY patients with complete gonadal dysgenesis [6].

Histologically OG is typically solid and well-encapsulated and composed of well-defined nests of uniform polygonal cells with abundant granular eosinophilic or clear cytoplasm and distinct cell membranes (similar to primordial germ cells) separated by fibrous strands and infiltrated by lymphocytes (mostly T cells) [1]. Areas of haemorrhage, coagulative necrosis and cystic changes may be seen.

OG in its pure form is not associated with hormone secretion [7]. Alkaline phosphatase and particularly serum lactic dehydrogenase (95% of the cases) are usually nonspecifically elevated [8]. In rare cases (3-5%) hCG can be slightly elevated due to the presence of multinucleated syncytiotrophoblasts [8].

These tumours tend to present with subacute pelvic pain. Acute pain secondary to torsion or rupture is uncommon(9).

Imaging techniques reflect the histological characteristics of the tumour: a multilobulated well-defined solid mass divided by with fibrovascular septa that markedly enhance after contrast administration and with few cystic, necrotic or haemorrhagic components.

Sonography typically shows solid masses with varying echotexture and prominent flow signal within the fibrovascular septa.

On T1-weighted images, OG is hypointense related to muscle and septa are difficult to appreciate. On T2-weighted images, OG is isointense or slightly hyperintense related to muscle and septa are typically hypointense or hyperintense in cases of associated oedematous changes.

Computed tomography can show calcifications in a speckled pattern [10].

Although very uncommon, OG can also present as multicystic masses with irregular septa and papillary projections, mimicking epithelial ovarian neoplasms [1].

65-75% of the cases are diagnosed when the disease is limited to one ovary (Stage IA) and the five-year survival rate is 90-95% [11]. Treatment is focused on fertility-sparing surgery. Recurrence of Stage IA occurs in 10-15% of cases, typically within the first two years after diagnosis and responds to chemotherapy [5,12].

Written informed patient consent for publication has been obtained.