Spectrum of magnetic resonance imaging findings in ovarian torsion

Introduction

Ovarian torsion is the twisting of the ovary on its vascular pedicle resulting in vascular compromise [1]. Timely identification of ovarian torsion is important because ovarian salvage is possible by surgical untwisting. Infarction and haemorrhagic necrosis occur if no surgical intervention is made. It is also essential to diagnose an infarcted ovary because an untreated infarcted ovary may lead to thrombophlebitis, infection, peritonitis, and sepsis [2].
Ovarian torsion classically presents as lower abdominal or pelvic pain in young females. Ultrasound (US) shows an enlarged ovary with peripherally displaced follicles. Colour Doppler may show absent colour flow [1]. Diagnosis of ovarian torsion is challenging in patients who have atypical clinical or US findings [3]. Magnetic resonance imaging (MRI) can act as the problem solver in complex cases. It not only helps in diagnosis of ovarian torsion but may also assist in identifying infarcted ovaries secondary to torsion.
There are limited published data available on the MRI features of ovarian torsion. The objective of our study was to demonstrate the common MRI imaging features of ovarian torsion to help radiologists make a reliable diagnosis when the clinical and US findings are unclear.

Material and methods

This study was approved by the departmental ethical committee. We retrospectively reviewed the clinical and MRI features in 10 females with surgically proven ovarian torsion. All these patients had inconclusive clinical, US or computed tomography (CT) findings, and MRI had been done to confirm the diagnosis of ovarian torsion.
MR imaging had been performed using a 1.5-Tesla MRI (Magnetom Aera, Siemens). T1-weighted images (repetition time msec/echo time msec 400-600/11-19), T2-weighted images (repetition time msec/echo time msec 3000-3200/80-90), T2-weighted fat saturated (FS) images, T1-weighted FS images, and T1-weighted FS images after intravenous injection of 0.1 mmol/kg of gadopentetate dimeglumine (Magnevist, Schering, Berlin, Germany) were acquired. Other imaging parameters were as follows: field of view 18-26 cm; matrix size 192 × 256; section thickness 4 mm, and intersection gap 2-4 mm. Retrospective evaluation of the common MRI signs of ovarian torsion was done based on a literature search [4-8]. These included ovarian enlargement with or without associated lesion, twisted ovarian pedicle, ovarian haemorrhage, abnormal ovarian enhancement, and ipsilateral deviation of the uterus (Figures 1-10).

Results

The age of the patients ranged from 12 to 28 years. Nine of these patients presented with the clinical history of intermittent pelvic pain, with symptoms ranging from 15 days to five months. One patient complained of the absence of onset of menarche and was later diagnosed with Mayer-Rokitansky-Kuster-Hauser (MRKH) syndrome. In all patients, the initial evaluation had been done with US. Ovarian enlargement or complex adnexal masses were reported on the left side in three patients and on the right side in seven patients. Two patients had also undergone CT because a neoplastic aetiology was suspected on the US (Figures 4, 5).
However, a confident diagnosis of ovarian torsion could not be made on US or CT. MRI was done to characterise these masses and confirm the diagnosis. Patients underwent laparoscopic surgery after the diagnosis of ovarian torsion was confirmed. Unilateral salpingo-oophorectomy was performed for nine patients because their ovaries were found to be non-viable intraoperatively. One patient underwent detorsion of the ovary and is stable on follow-up.

Ovarian enlargement with or without associated lesion

All patients showed an enlarged ovary, with sizes ranging from 5 to 18 cm. Infarcted ovaries with necrosis were seen in two patients. These ovaries were observed as large complex masses with cystic components (Figures 4, 5) [6]. Peripherally lying follicles could be identified in nine cases (Figures 1-7, 9, 10). Two of the affected ovaries showed paraovarian cysts, measuring 4.5 and 3.5 cm in the largest diameter (Figures 2, 9).
These paraovarian cysts were simple cysts without any solid component. One of the enlarged ovaries showed MRI signal characteristic of fat (T1, T2 hyperintense signal, which was suppressed on FS images) within it (Figure 10). This lesion was reported as dermoid on MRI and was confirmed on histopathology post-surgery.
One patient showed torsion of the right ovary, ectopic left ovary, and absence of uterus on MRI (Figure 6). These features were suggestive of MRKH syndrome.

Twisted ovarian pedicle

‘Twisted ovarian pedicle’ sign was seen in seven patients. The fallopian tube or vascular channels were seen in helical configuration on MRI (Figures 2, 4, 6, 8-10) [2,4]. Beaking of the margin of an enlarged ovary due to the twisted pedicle was also seen (Figure 1) [7,8]. Postcontrast MRI sequences were useful to better demonstrate the twisted ovarian pedicle in some cases (Figures 1, 9).

Ovarian haemorrhage

The majority of the cases (eight) showed areas of subacute haemorrhage (T1, T2 hyperintensity, non-suppression on FS sequences) within the ovarian stroma. This signal was seen predominantly in the periphery of the enlarged ovary in six cases (Figures 1, 4, 6, 8-10); while in two cases, a large part of the ovarian stroma (central as well as peripheral) showed the MRI signal of subacute haemorrhage (Figures 3, 5). Haemorrhage was also noted within the twisted pedicle in two cases (Figures 8, 10). Haemorrhagic pedicle was associated with haemorrhage in the ovarian stroma. All patients showing ovarian haemorrhage on MRI were found to have infarcted ovaries intraoperatively. Out of two patients in whom MRI did not show ovarian haemorrhage, one was found to have a viable ovary, and detorsion was done for the same (Figure 2).

Abnormal ovarian enhancement

Non-enhancement of ovarian stroma was seen in six patients. All these patients had non-viable ovaries intraoperatively. Two cases showed a smooth or irregular peripheral enhancing wall of ovaries (Figures 1, 10). Mild ovarian stromal enhancement was seen in two cases (Figures 2, 7).

Ipsilateral deviation of the uterus

Seven patients showed ipsilateral deviation of the uterus (Figures 1, 4, 7). Two patients showed contralateral deviation of the uterus due to the mass effect of the enlarged ovary (Figures 5, 9). In one patient, there was no uterus (Figure 6).

Other findings

A small amount of free fluid in the pelvis was seen in four patients (Figure 6). None of the patients showed haemoperitoneum.

Discussion

Ovarian enlargement with or without associated lesion

Ovarian enlargement, although non-specific, is the most common finding in patients with ovarian torsion [4,5]. Enlarged ovary with peripherally displaced follicles and central afollicular stroma is a more specific sign of ovarian torsion. Massive ovarian oedema refers to tumour-like marked enlargement of the ovary secondary to intermittent torsion, which leads to extensive stromal oedema without infarction. It shows enhancement of stroma on MRI as opposed to infarction. Untreated ovarian torsion may lead to infarction with necrosis, which appears as an enlarged adnexal mass with cystic components on MRI and shows absent enhancement on postcontrast sequences [6].
Lesions that may be seen in association with ovarian torsion include follicular cysts, haemorrhagic cysts, corpus luteal cysts, paraovarian cysts, and benign and malignant neoplasms. Dermoids are the most common neoplasms identified in ovaries with torsion [3]. They can be identified by their fat content, which is seen as hyperintense signal on T1 and T2 sequences and suppressed on FS images.
Enlarged ovary may also be seen in ovarian hyperstimulation syndrome, but clinical history, bilaterality, and the presence of extravascular fluid collections will help to diagnose this condition. However, torsion can also occur in hyperstimulated ovaries, which can be identified if they show asymmetrical enlargement, abnormal enhancement, haemorrhage, and twisted ovarian pedicle.
One of the cases of ovarian torsion reported by us was in a patient with absent uterus, diagnosed as MRKH syndrome. The association of ovarian torsion with MRKH syndrome has been reported previously, and the absence of supporting structures of ovary, primarily the utero-ovarian ligament, has been postulated to be the cause [9].

Twisted ovarian pedicle

The twisted ovarian pedicle is a pathognomonic sign of ovarian torsion [4]. It is formed due to the twisting of the broad ligament containing the thickened fallopian tube and vascular channels [2]. Fallopian tube or broad ligament comprising vascular channels are seen in helical configuration on MRI [2,4]. It is essential to evaluate the images in all three planes to identify the twisted ovarian pedicle. Postcontrast MRI sequences are also useful in demonstrating the twisted ovarian pedicle. Isolated fallopian tube torsion without ovarian torsion can also show thick and twisted pedicle. However, the ipsilateral normal ovary will be seen along with it. Isolated fallopian tube torsion also requires surgical intervention.

Ovarian haemorrhage

Ovarian haemorrhage is highly associated with ovarian torsion with infarction [10-14]. MRI is a sensitive imaging modality for identifying haemorrhage. Subacute haemorrhage is seen as a hyperintense signal on both T1 and T2 sequences, not suppressed on FS images. Haemorrhage may be seen in the periphery of the enlarged ovary or involving the central ovarian stroma. Haemorrhage within the twisted pedicle or haemoperitoneum in the pelvis may also be seen secondary to haemorrhagic infarction of the ovary [10].
Other differential diagnoses of haemorrhagic ovarian lesions include corpus luteal cysts, haemorrhagic primary ovarian tumours or metastasis. However, lack of enhancement and the presence of twisted ovarian pedicle can help to differentiate ovarian torsion from these entities [4,14].

Abnormal enhancement of ovarian stroma

Normal enhancement may be seen in the early stage of ovarian torsion or intermittent torsion. However, infarcted ovaries will show heterogeneous, minimal to absent enhancement [8,15]. They may show only peripheral enhancement. The presence of enhancement does not rule out torsion; however, absent enhancement in an enlarged ovary usually indicates infarction [4,10].

Ipsilateral deviation of the uterus

Ipsilateral deviated uterus seen in association with an enlarged ovary may be a useful feature for recognising ovarian torsion in some cases [5,10,14]. Shortening of the ipsilateral supporting structures has been postulated as the cause. However, it is not a sensitive sign of ovarian torsion. Sometimes, the contralateral deviation may also be seen due to the mass effect of the enlarged ovary.

Other findings

Chiou et al. [5] showed the presence of ascites on MRI in 50% of cases of ovarian torsion. However, it is not a sensitive or specific sign of ovarian torsion. Ascites may also be seen in association with malignant or benign adnexal tumours.
The limitations of our study include mainly its retrospective nature. Second, the small number of patients included in the study. Third, the utility of MRI in differentiating viable versus non-viable ovaries post torsion could not be evaluated. This evaluation could not be done because the majority of our cases were of non-viable (infarcted) ovaries due to the fact that our institute is a tertiary care hospital with many cases being referrals from other hospitals for complicated or undiagnosed cases. However, irrespective of ovarian viability, any ovarian torsion has to be surgically treated (detorsion or oophorectomy) [16].

Conclusions

MRI features of ovarian torsion include ovarian enlargement with or without associated lesion, twisted ovarian pedicle, ovarian haemorrhage, abnormal ovarian enhancement, and ipsilateral deviation of the uterus.
Knowledge of these imaging features will enable the radiologist to recognise ovarian torsion and differentiate it reliably from other benign or malignant ovarian masses even if the clinical and ultrasound signs are inconclusive.

Conflict of interest

The authors report no conflict of interest.

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