Regional Study Into the Performance and Cost-effectiveness of Simple Ultrasound-based Rules Compared to the Currently Used Risk of Malignancy Index in the Diagnosis of Ovarian Cancer

Estimating whether an adnexal mass is malignant or not is essential in the preoperative management of adnexal masses. Recognizing cancer means treatment is not delayed and appropriate staging or debulking surgery can be carried out after referral to specialized surgical centers. Vice versa, benign lesions may be managed conservatively or with minimal invasive surgery in non-centre hospitals. This will limit morbidity and will avoid unnecessary costs: laparoscopic surgery offers lower estimated blood loss, shorter hospital stay, and fewer postoperative complications with an improved quality of life and faster return to normal functioning.

There are several methods to distinguish benign from malignant adnexal masses. The commonly used method in clinical practice is the Risk of Malignancy Index (RMI). The RMI is an easy to use scoring system recommended by many national guidelines concerning the management of ovarian masses, including the national guideline in the Netherlands. The RMI combines ultrasound variables, menopausal status and serum CA125 into a score used to predict the risk of ovarian cancer before surgery. However, the reported sensitivity and specificity of RMI at a cut-off value of 200 are relatively low; 75-80% and 85-90%, respectively.

Another method called 'simple ultrasound-based rules' (simple rules), uses different morphological ultrasound features of adnexal masses (without including menopausal status or serum CA125 measurement). It includes five simple ultrasound-based rules to predict malignancy (M-rules) and five rules to predict a benign tumor (B-rules). If both or none of the M- and B-rules are met (20% of the patients) the test is inconclusive. Recent reports show that simple rules might be superior to the RMI. In adnexal masses for which the simple ultrasound rules yield an inconclusive result, subjective assessment of Gray-scale and color Doppler ultrasound images by an experienced ultrasound examiner can be used as a second stage test to achieve an optimal diagnostic performance. Subjective assessment by an expert sonographer is superior to any scoring system or mathematical model when classifying adnexal masses as benign or malignant. However, it is not feasible and efficient that every patient would undergo an expert ultrasonography. Therefore, this method is better used as a second stage test.

Another option is to use Diffusion Weighted - Magnetic Resonance Imaging (DW-MRI) as a second stage test, when the simple rules yield an inconclusive result. The use of MRI - when interpret by specialized radiologists- also seems to be superior to RMI in the preoperative identification of adnexal masses.

The Risk of Malignancy Index (RMI) is the current standard in differentiating benign from malignant adnexal masses. The simple ultrasound-based rules as a first stage triage test followed by either subjective assessment by an experienced ultrasound examiner or DW-MRI in case the simple rules are inconclusive, is the test of comparison. Both the RMI and the simple rules will be performed in the regional hospitals and MUMC+ by general gynaecologists during the same ultrasound scan. Only when the simple rules are inconclusive the patient will be referred to the MUMC+ for a second stage test. From previous publications it can be deducted that this will be in approximately 20% of patients. Approximately 80% of patients will not need any additional second stage test.