Long-standing Morel-Lavallée lesion of the thigh simulating a neoplasm

We report on the case of a 56-year-old man in whom a Morel-Lavallée lesion developed in the thigh. Ultrasound revealed a well-defined thick-walled cystic mass between the hypodermis and fascial planes that in some areas constituted hyperechoic papillar extensions in its wall. Magnetic resonance T1-weighted images showed that the mass was well circumscribed and mildly inhomogeneous and had a high signal intensity. On T2-weighted images, the mass had mixed signal intensity and a fluid–fluid level. We also discuss both the difficulty in making a differential diagnosis for and the treatment of this lesion.