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.