Unclassifiable Pelvic masses

Which extrauterine pelvic masses are difficult to correctly classify as benign or malignant on the basis of ultrasound findings and is there a way of making a correct diagnosis? By-Valentin L et al

"Papillary projections, >10 locules in a cyst without solid components, low-level echogenicity of cyst fluid, and moderate vascularization as assessed subjectively at color Doppler examination are found to be ultrasound variables associated with unclassifiable mass. Borderline malignant tumors proved to be most difficult to assess.Papillary cystadeno(fibro)mas, myomas and cases of struma ovarii were also more common among the unclassifiable masses.Borderline tumors cause great diagnostic difficulties, but so do papillary cystadeno(fibro)mas, struma ovarii and some myomas. "

Reference-Ultrasound Obstet Gynecol 2006 Mar 9; [Epub ahead of print]