Ovarian torsion due to ovarian hyperstimulation syndrome

A 28-year-old, otherwise fit and well female, who had her IVF cycle with egg retrieved 3 days ago, presented to the ED with nausea and vomiting and acute right-sided abdominal pain that progressively got worse. There was marked tenderness in the right iliac fossa.

A CT abdomen pelvis with contrast that shows a right ovary is massively enlarged, measuring 9.8 x 8 x 12.5 cm, demonstrating multiple large peripherally arranged follicles cysts with a large area of central stroma giving a “string of pearl appearance” (Figures 1, 2 and 3).

The left ovary is also bulky, measuring 7.1 x 5 x 4.4 cm, demonstrating multiple large follicles that are randomly arranged with only minor stroma seen between the follicles representing a hyper-stimulated ovary (Figures 3 and 4). There is also mild free fluid in the pelvis.

Ovarian hyperstimulation syndrome (OHSS) is one of the complications of assisted reproductive technology where the ovaries enlarge as a response to controlled ovarian hyperstimulation, causing a shift of fluid from intravascular space to third space [1,2]. Most cases of ovarian hyperstimulation are mild, with symptoms like abdominal pain and bloating due to an increase in ovarian size [3]. But there are severe cases resulting in complications like hypovolemia, oliguria, thromboembolic events, and sometimes, like the present case, ovarian torsion [3].

The presentation of OHSS and that of a complicated OHSS with ovarian torsion could be similar. Both can present as a pregnant female with acute abdomen. Symptoms like abdominal pain, bloating, nausea, and vomiting are seen in both cases. Physical examination could have features of abdominal distension and tenderness [4,5]. Hence, imaging findings aid greatly in distinguishing between the two. Ultrasound is used for imaging both OHSS and ovarian torsion. But in some cases, a CT abdomen is also used, which is discussed here.

The features of OHSS in CT are like that of ultrasound with symmetrical enlarged ovaries with enlarged cysts of varying sizes and features of fluid in third spaces like ascites and pleural effusion [6]. A torsed ovary can be identified as an asymmetrically enlarged ovary with a string of pearl appearance due to the follicles being pushed to the peripheries by stromal oedema or haemorrhage. They may be found in unusual locations, i.e., anterior or posterior to the uterus, and could have increased attenuation, indicating haemorrhage [7]. The whirlpool sign showing a thickened vascular pedicle of the torsed ovary may also be seen [8].

In the present case, both ovaries are enlarged with large follicles, but the right ovary is asymmetrically more enlarged in the medial position posterior to the uterus, and the follicles are arranged peripherally compared to the less enlarged left ovary with enlarged cysts that are randomly arranged.

Most cases of OHSS are self-limiting and can be managed conservatively [3], while ovarian torsion is a surgical emergency requiring emergency laparotomy and detorsion. Hence imaging plays a crucial role in management. In this case, the patient underwent emergency laparotomy, which found the right ovary torsed eight times around its pedicle, which was later detorsed.

To summarise, ovarian torsion is one of the rare complications of OHSS. But, because ovarian torsion is a surgical emergency, identification of torsion in the setting of an OHSS is crucial.

Written informed patient consent for publication has been obtained.