Teaching Case

A 66-year-old woman presented to the emergency department with severe abdominal pain and distention, as well as nausea and vomiting. The patient underwent computed tomography (CT) and was admitted to the ward for pain management. During hospitalization magnetic resonance imaging (MRI) was performed.

CT shows a cystic mass originating in the right ovary, measuring 205 x 180 x 140 mm, in a midline position. The wall of the cystic mass presents a density of 50 HU on unenhanced CT and does not enhance after intravenous contrast administration. Furthermore, the right fallopian tube appears to be thickened and the uterus deviates to the right side. A small volume of intraperitoneal free fluid is visible in the pelvis.

MRI confirms the presence of a large right ovarian unilocular cystic mass without evident solid components. There is associated thickening and twisting of the fallopian tube and of the ovarian vascular pedicle, best seen in post-contrast images, giving the appearance of a whirlpool sign. The uterus deviates towards the right side and a small volume of hemoperitoneum is noted in the pelvis.

Ovarian torsion is a surgical emergency triggered by twisting of the ovarian vascular pedicle, leading to blood flow compromise and haemorrhagic infarction [1]. Torsion can occur in normal ovaries, however, in many cases, there is an associated adnexal mass, especially when the mass size is greater than 5 cm [2]. The risk of torsion is higher in benign masses, as malignancies are less mobile, owing to the invasion of adjacent tissues [2].

The classic clinical presentation is of nonspecific acute lower abdominal pain. Laboratory tests, when used, are not helpful. Imaging is needed to establish the diagnosis and to exclude more common causes of acute abdominal pain, such as acute appendicitis, acute diverticulitis and renal colic, among others [3].

In an emergency setting, pelvic ultrasound (US) is usually the first-line examination. Findings of torsion in US include heterogeneous ovarian enlargement (greater than 5 cm), with or without an underlying mass, and abnormal flow on Doppler. However, normal Doppler findings are present in 45-61% of torsion cases [4]. Colour Doppler is also useful in depicting the “whirlpool sign”, which is the characteristic appearance of the vessels in the twisted pedicle, variably reported as seen in 13-88% of cases [5,6].

As in US, CT and MRI show an asymmetric ovarian enlargement and a twisted pedicle. In the absence of a mass, an enlarged oedematous ovary with peripherally displaced follicles can sometimes be identified [7]. CT and MRI can better depict subacute ovarian hematoma and abnormal ovarian enhancement [7]. Subacute blood is expected to have a high density on pre-contrast CT (50-100 HU) and a high signal on pre-contrast T1-weighted images with fat saturation [8]. Ascites or hemoperitoneum, deviation of the uterus to the side of the torsion, fat stranding adjacent to the ovary, and fallopian tube thickening with engorged vessels on the side of the twist are other features of ovarian torsion that can also be depicted on CT and MRI [7,8].

The most common ovarian masses associated with ovarian torsion are follicular or corpus luteal cysts (17%), mature teratomas (17%), cystadenomas (13%), fibromas, and Brenner tumours (3%) [8]. Ovarian torsion can also be a rare presentation of a malignant tumour.

In this case, the ovarian torsion was probably triggered by an underlying large serous cystadenoma, a benign tumour with a peak incidence between the 4th to 5th decades of life, usually presenting as a unilocular thin-walled adnexal cyst on imaging [9].