Quality assessment:
A modified set of questions was used to assess the internal and external validity of the studies. Internal validity was assessed based on study design (prospective/ retrospective/ randomised), recruitment of population (consecutive/randomised/other) and ascertainment of reported outcomes (USS diagnosis or clinical, Surgical Confirmation).  External validity was assessed by reviewing the representativeness of the population. All items were classified as being of high or low risk for bias. A study found to be of high risk for bias in more than two categories for internal validity was classified as ”high risk” for internal validity. The single item (population representativeness) classifies each study as being of high or low risk for external validity.