 Introduction/Background A variety of benign and malignant processes may present clinically as a soft tissue mass. The behavior of a mass, whether nonaggressive, indeterminant, or aggressive, can often be discerned based on history and physical examination. However, when a benign clinical diagnosis cannot be confidently provided, further characterization of a soft tissue mass with imaging is warranted [1]. Urgent imaging requests should be sought for masses that are >5 cm in diameter, deep in location, or have shown rapid growth [2]. Modern imaging techniques allow for a detailed analysis of the morphology of a soft tissue mass as well as further insight into its biologic activity, which informs the interpreter on diagnosis and appropriate next steps in management [3,4]. The purpose of this document is to identify the most appropriate imaging study(ies) to order for the assessment of a soft tissue mass based on the most frequently encountered clinical scenarios in medical practice. The rationale for the level of appropriateness granted to each study option is also described in accordance with the current literature and the consensus opinion of the members of the ACR Appropriateness Criteria Expert Panel on Musculoskeletal Imaging. This document does not address follow-up recommendations for patients with previously diagnosed masses or the appropriate approach or techniques for the imaging-guided biopsy of known masses. The former is covered by a separate ACR Appropriateness Criteria document [4], whereas the latter requires direct communication with the clinician or orthopedic oncologist supervising and coordinating patient care. OR aMayo Clinic Florida, Jacksonville, Florida. bPanel Chair, Mayo Clinic, Jacksonville, Florida. cPanel Vice-Chair, Wake Forest University School of Medicine, Winston Salem, North Carolina. dJohns Hopkins University School of Medicine, Baltimore, Maryland. eMallinckrodt Institute of Radiology Washington University School of Medicine, Saint Louis, Missouri.
Soft Tissue Masses.  Introduction/Background A variety of benign and malignant processes may present clinically as a soft tissue mass. The behavior of a mass, whether nonaggressive, indeterminant, or aggressive, can often be discerned based on history and physical examination. However, when a benign clinical diagnosis cannot be confidently provided, further characterization of a soft tissue mass with imaging is warranted [1]. Urgent imaging requests should be sought for masses that are >5 cm in diameter, deep in location, or have shown rapid growth [2]. Modern imaging techniques allow for a detailed analysis of the morphology of a soft tissue mass as well as further insight into its biologic activity, which informs the interpreter on diagnosis and appropriate next steps in management [3,4]. The purpose of this document is to identify the most appropriate imaging study(ies) to order for the assessment of a soft tissue mass based on the most frequently encountered clinical scenarios in medical practice. The rationale for the level of appropriateness granted to each study option is also described in accordance with the current literature and the consensus opinion of the members of the ACR Appropriateness Criteria Expert Panel on Musculoskeletal Imaging. This document does not address follow-up recommendations for patients with previously diagnosed masses or the appropriate approach or techniques for the imaging-guided biopsy of known masses. The former is covered by a separate ACR Appropriateness Criteria document [4], whereas the latter requires direct communication with the clinician or orthopedic oncologist supervising and coordinating patient care. OR aMayo Clinic Florida, Jacksonville, Florida. bPanel Chair, Mayo Clinic, Jacksonville, Florida. cPanel Vice-Chair, Wake Forest University School of Medicine, Winston Salem, North Carolina. dJohns Hopkins University School of Medicine, Baltimore, Maryland. eMallinckrodt Institute of Radiology Washington University School of Medicine, Saint Louis, Missouri.