**2. Role of pelvic ultrasound in ovarian cancer screening**

Ultrasound has been used as a screening tool to detect early malignant lesions in the ovary and fallopian tube. Features such as presence of septa, papillary projections and solid areas are used to distinguish possible malignant lesions from benign ones. The use of colour flow Doppler to detect altered blood flow as a result of neo-vascularisation has also been explored in diagnosing ovarian neoplasms.

Transvaginal ultrasonography (TVS) has long been considered a useful modality for estimating morphological factors of carcinogenesis. Non-invasiveness and ease of implementation are amongst its benefits for screening, and women generally find TVS an acceptable modality for detection [4]. Factors often used for the assessment of ovarian masses include morphology and volume analysis, but more advanced methods such as Doppler and neuronal network analyses are being investigated for their efficacy.

There are many challenges to overcome in the utilisation of TVS as a screening modality. Variation in operator competence is one such challenge. The United Kingdom Collaborative Trial for Ovarian Cancer Screening (UKCTOCS) trial overcame this challenge by providing standardised training regimes to all sonographers. Although this could be a viable solution, there will always be variation in competence based on operator experience. For example, more experienced sonographers may be better at detecting borderline cysts than less experienced sonographers. The lack of standardised terms to describe ovarian sonographic features is another issue. The International Ovarian Tumour Analysis (IOTA) Group have created a set of recommendations to address this by setting definitions for morphological features such as 'septum, solid, smooth, irregular', and so on. [5].

Patient acceptability of screening modality is also an essential factor to consider. In a recent study, 72.7% of women (n = 651) reported no discomfort during TVS, 23.3% of women reported some pain or discomfort and 3.5% documented moderate to severe pain during the TVS procedure. Increasing pain was attributed to history of hysterectomy and a prolonged scanning time. Interestingly, those who experienced pain were noted less likely to return for a subsequent scan 1 year later [4].

Visualisation of the ovary is a further quality assurance factor to overcome in ovarian cancer screening. Decreasing follicular activity and ovarian shrinkage in postmenopausal women makes visualisation problematic. In a study involving TVS of 43,867 women (median age 60.6 years), factors affecting visualisation of ovaries in postmenopausal women included previous hysterectomy, unilateral oophorectomy, tubal ligation, increasing age and obesity. Interestingly, factors that increased visualisation of the ovaries included a history of infertility and increasing age at menopause [6].

One of the biggest challenges in ovarian screening lies in differentiating between benign and malignant macroscopic changes. Ovarian morphology varies greatly from patient to patient, and thus benign lesions can give rise to false positive results, leading to unnecessary interventions. Unilocular cysts and those with simple septations are often benign and self-resolving. Features increasing the risk of malignancy include identification of neo-angiogenesis, multiple loculations, presence of papillary structures and solid foci [7–9]. False positives can be reduced with serial ultrasonography [10] as many ovarian lesions resolve without intervention. Benign lesions such as cysts and non-malignant solid lesions are also prevalent in the older population. In a study involving histological and ultrasound characterisation of ovarian cysts from autopsy material from 52 postmenopausal women who had died from causes other than gynaecological cancers, 56% were found to have histologically benign ovarian masses. This evidence suggests that many women will have benign lesions and so ultrasound testing could potentiate unnecessary over-investigating and surgical interventions [11]. The malignant potential of inclusion cysts are yet to be determined, however, it has been proven that TVS is a valid system for detecting malignancy after initial assessment at 1 year. In a study assessing the malignant potential of inclusion cysts, of the 1234 patients carrying ovarian inclusion cysts and 22,914 patients with normal ovaries, 432 women were diagnosed with ovarian cancer, respectively. Overall, the study showed the wider potential of application of TVS as a screening modality [12].

A well-defined criteria or reliable method of quantification needs to be introduced in order to differentiate between benign and malignant cysts. The University of Kentucky has developed a morphological index (MI) score looking at ovarian volume and macroscopic features. In their study, malignancy correlated to an increase in MI score with serial imaging, whereas benign tumours correlated to a decreased or stable MI score [13]. There is scope, therefore, for more accurate quantification of malignant potential, using risk predictors and TVS-led assessment.

New strategies to aid in accurate detection of malignant tumours include neuronal networks and pattern recognition models [14]. These developments are still in their infancy; however, a multicentre study demonstrated that borderline tumours, struma ovarii, papillary cystadenofibromas and myomas proved most difficult to reliably differentiate using ultrasound even with logistic regression models [15].

Magnetic resonance imaging (MRI) is a further imaging modality to consider for screening, due to its detailed visualisation of the pelvis. As an option for screening, however, implications of cost, duration of test, contra-indications for the wider population including placement of metal work, all pose great hurdles to acceptability.
