Clinical Presentation

A 40-year-old man presents with an enlarging mass in the left thigh.

(A,B) Magnetic resonance (MR) images through the left thigh show a large, solid mass (M) infiltrating the quadriceps musculature. Heterogeneous T2 signal increase is present, with solid enhancement and surrounding muscle edema (e). A low-signal capsule (arrows) encircles the mass.

Differential Diagnosis