Figure 18a.

Large popliteal (Baker) cyst in a 66-year-old woman. (a) Long-axis gray-scale US image in the region of a palpable mass at the posterior aspect of the knee shows a large anechoic popliteal cyst (arrows). (b) Color elastogram of the same region shows low shear-wave velocities (white arrows) (mean, 2.8 m/sec) in the region of synovial proliferation at the periphery of the popliteal cyst, with a signal void centrally (black arrow) because the shear waves do not propagate though the fluid. SWE data were collected using an Acuson S3000 US scanner with an L9–4-MHz linear transducer.