Mass with Indistinct Margins

Masses described as having indistinct margins lack a clear demarcation of a portion or the entire margin from the surrounding tissues. The indistinctness of the margin raises the possibility of infiltration; therefore, this descriptor implies suspicion for malignancy. “Indistinct” differs from “obscured.” A mass with obscured margins insinuates that the surrounding tissues masks or covers the presence of the lesion. This chapter, appearing in the section on asymmetry, mass, and distortion, reviews the key imaging and clinical features, imaging protocols and pitfalls, differential diagnoses, and management recommendations for masses with indistinct margins. Topics discussed include differentiation of the mass with indistinct margins from an obscured mass and focal asymmetry, and how the presence of adjacent features can increase the suspicion of the mass with indistinct margins.