The "Halo Appearance" of Shear Wave Elastography in the Setting of Fat Necrosis: A Potentially Useful Sonographic Discriminator.

Objective: To describe the morphologic sonographic appearances and frequency of the "halo sign" in the setting of fat necrosis on shear wave elastography (SWE).

Methods: Patients with clinically suspected fat necrosis were prospectively scanned using SWE in addition to standard gray-scale and Doppler images. Cases were qualitatively grouped into one of three sonographic appearances: focal hypoechoic lesion with increased internal tissue stiffness ("focal stiffness"), focal hypoechoic lesion with isoechoic or hyperechoic periphery demonstrating increased tissue stiffness relative to the central hypoechoic lesion ("halo stiffness"), heterogeneously echogenic lesion with diffusely increased stiffness ("heterogeneous stiffness").

Results: Exactly 19 patients met inclusion criteria (female n = 14; male n = 5). Shear wave velocities were recorded and retrospectively evaluated. The mean clinical follow-up was 11.4 months (range 3.0-25.5). Lesions demonstrated higher average tissue stiffness than background tissue (overall mass shear wave velocity 3.26 m/s, background 1.42 m/s, P < .001; lesion Young's modulus 40.85 kPa vs background 7.22 kPa, P < .001). The halo sign was identified in 10/19 (55%) patients.

Conclusion: The halo sign is a potentially useful sign in the setting of fat necrosis seen in the majority of clinically suspected cases.